Building Physics
Analyse how air moves through and around buildings using Computational Fluid Dynamics (CFD), delivering detailed numerical airflow simulation to understand ventilation behaviour, pressure distribution and air movement before construction begins.
For architects, engineers, developers and project teams investigating natural ventilation, wind flow, smoke movement, façade performance, HVAC airflow, external aerodynamics and complex air movement within proposed developments. CFD modelling supports informed design decisions where airflow performance cannot be reliably assessed using simplified calculations alone.
Discuss CFD Modelling RequirementsIn Brief
Computational Fluid Dynamics (CFD) is a numerical simulation method used to predict and visualise how air moves through and around buildings under defined environmental and operating conditions. By solving the governing equations of fluid flow, CFD provides detailed airflow simulation before a building is constructed.
A CFD model can evaluate airflow velocity, direction, pressure distribution, turbulence, ventilation pathways, recirculation zones and local temperature behaviour. It helps project teams understand how building geometry, façade design, surrounding structures, internal layouts and mechanical ventilation systems influence air movement throughout a proposed development.
CFD is particularly valuable where airflow behaviour is too complex for simplified engineering calculations. It provides detailed insight into specific design scenarios, but it does not independently assess occupant thermal comfort, predict annual building energy performance or demonstrate NCC compliance. Instead, CFD complements broader building performance assessments by providing a detailed understanding of airflow physics.
Airflow velocity, pressure distribution, turbulence, ventilation effectiveness, recirculation zones, stagnant air, wind flow, smoke movement and local temperature behaviour.
CFD is used where complex building geometry, natural ventilation, HVAC systems, façade design or surrounding developments create airflow conditions that require detailed numerical analysis.
It allows project teams to compare design options, visualise invisible airflow and optimise ventilation strategies before construction, reducing uncertainty and supporting more informed design decisions.
Knowledge Navigation
Follow this guide to understand what Computational Fluid Dynamics (CFD) is, where it is used, how airflow simulation works and what information is typically required to produce reliable modelling outcomes.
Foundation
Learn how CFD uses numerical simulation to predict airflow, pressure distribution, turbulence and ventilation behaviour within and around buildings.
Applications
Discover how CFD supports natural ventilation, wind engineering, smoke movement, façade design, HVAC optimisation and complex airflow assessment.
Assessment Process
Understand the typical modelling workflow, from geometry preparation and boundary conditions through to simulation, validation and interpretation of results.
Project Preparation
Review the drawings, BIM models, ventilation data, surrounding context and design assumptions typically needed to develop an accurate CFD model.
CFD Process
Computational Fluid Dynamics (CFD) uses numerical simulation to predict how air behaves within a digitally modelled environment. Rather than relying on simplified engineering calculations, CFD divides the model into thousands or millions of small computational cells and solves the governing equations of fluid flow across the entire space. This allows airflow behaviour to be analysed with a high level of spatial detail before construction begins.
The process begins with preparing an accurate three dimensional representation of the proposed building or external environment. Rooms, façades, openings, ventilation systems, surrounding buildings and landscape features are incorporated where relevant. Boundary conditions are then assigned, including wind conditions, airflow rates, opening positions, temperatures or mechanical ventilation inputs that define the simulation scenario.
Once the model is solved, CFD produces detailed visual outputs including airflow vectors, velocity contours, pressure distribution, streamlines and sectional views. These results help engineers and design teams understand how air moves throughout a building, identify recirculation zones, stagnant air, areas of elevated air speed and other airflow characteristics that may influence design decisions.
The results always represent the specific geometry, boundary conditions and operating assumptions selected for the simulation. CFD therefore provides a detailed prediction of defined airflow scenarios rather than a guarantee of real world performance under every possible operating condition. Where occupant comfort or regulatory compliance is being assessed, CFD is often used alongside broader building performance assessments rather than as a standalone evaluation method.
Geometry
The simulation begins with an accurate representation of the building, surrounding context, openings, façades, ventilation systems and other features that influence airflow.
Boundary Conditions
Wind conditions, airflow rates, temperatures, opening positions and operating assumptions establish the scenario that will be analysed.
Simulation Results
Velocity fields, airflow vectors, pressure contours and streamlines reveal how air behaves throughout the model and where design refinements may improve performance.
Airflow Analysis
Computational Fluid Dynamics (CFD) provides detailed numerical analysis of airflow within and around buildings. Instead of producing a single average value, CFD predicts how airflow behaves throughout a three dimensional space, allowing engineers and designers to understand how velocity, pressure, turbulence and ventilation patterns vary across different locations and operating conditions.
The variables included depend on the engineering question being investigated. A CFD model may evaluate airflow behaviour, pressure gradients, ventilation effectiveness, wind driven movement, heat transport or the influence of geometry, façades and mechanical systems on overall airflow performance.
Velocity Fields
Velocity fields identify areas of low airflow, accelerated air speeds, ventilation effectiveness and regions where airflow may not perform as intended.
Flow Paths
Vectors, streamlines and flow visualisations show how air enters, circulates through and exits internal spaces or external environments.
Pressure Distribution
Pressure contours explain how wind, openings, façades and mechanical systems influence airflow between spaces and around buildings.
Turbulence
CFD predicts turbulent airflow, recirculation zones and unstable flow behaviour that may influence ventilation performance around façades, corners and openings.
Heat Transport
Where heat transfer is included, CFD can demonstrate how moving air transports heat through the model. Assessing occupant comfort generally requires Thermal Comfort Modelling alongside CFD.
Scenario Comparison
Alternative façade designs, opening positions, ventilation strategies, wind conditions and operating scenarios can be compared using consistent modelling assumptions.
Every CFD study should begin with a clearly defined engineering objective. Establishing the design question early allows the computational mesh, boundary conditions, model refinement and reporting outputs to be aligned with the decisions the project team needs to make, resulting in more reliable and meaningful simulation outcomes.
Internal Airflow Simulation
Internal Computational Fluid Dynamics (CFD) modelling predicts how air moves through enclosed spaces under defined operating conditions. It provides detailed airflow simulation that helps visualise how air enters, circulates and exits individual rooms or interconnected spaces before a building is constructed.
Rather than relying solely on ventilation rates, CFD reveals how building geometry, internal partitions, ceiling heights, openings, façades and mechanical supply or extract systems influence actual airflow behaviour. Spaces receiving identical airflow volumes may perform very differently because of diffuser locations, pressure differences or internal obstructions.
This detailed spatial analysis allows project teams to identify airflow pathways, recirculation zones, stagnant areas, high velocity jets and ventilation short circuiting before construction. Where the primary objective is to evaluate occupant comfort rather than airflow behaviour, additional Thermal Comfort Modelling is typically undertaken alongside CFD.
Flow Paths
CFD illustrates how air travels between inlets, outlets, openings and adjoining spaces, revealing where airflow follows or departs from the intended path.
Ventilation Effectiveness
The simulation shows whether fresh air reaches the intended occupied zones or becomes concentrated in limited parts of the space.
Flow Behaviour
CFD identifies recirculation zones, turbulent airflow, stagnant regions, high velocity jets and short circuiting that simplified engineering calculations may not reveal.
CFD is an engineering analysis tool rather than a ventilation design method. It helps validate and optimise proposed ventilation strategies by demonstrating how air behaves under defined conditions, but it does not replace mechanical design, equipment selection or regulatory compliance undertaken by the project's mechanical engineer.
External Airflow Simulation
External Computational Fluid Dynamics (CFD) modelling predicts how wind and airflow interact with buildings and the surrounding environment. By simulating airflow around façades, roofs, courtyards, streets and adjacent developments, CFD helps project teams understand how building geometry influences local airflow, pressure distribution and ventilation behaviour before construction begins.
Airflow around a building is affected by its height, orientation, massing, façade articulation and relationship to nearby structures. Roof forms, setbacks, narrow passages, podiums and changes in ground level can accelerate, shelter or redirect airflow, creating complex wind patterns that are difficult to interpret from drawings or simplified engineering calculations alone.
CFD allows these interactions to be visualised using airflow vectors, pressure contours and velocity fields. This supports investigations into façade pressures, airflow around ventilation openings, natural ventilation strategies, courtyard performance and the interaction between external wind conditions and building design.
Building Geometry
CFD demonstrates how massing, building height, roof geometry, façade articulation and orientation influence wind flow and local airflow behaviour.
Pressure Distribution
Pressure contours reveal where positive and negative façade pressures develop and how they may influence ventilation openings or external airflow pathways.
Surrounding Context
Adjacent developments, vegetation, terrain and topography can significantly alter incoming wind conditions before airflow reaches the proposed building.
Every external CFD study should begin with a clearly defined engineering objective. This may involve understanding façade pressures, natural ventilation performance, courtyard airflow or wind behaviour around a proposed building. Where the primary objective is to evaluate wind conditions experienced by pedestrians, a dedicated Pedestrian Wind Assessment may be more appropriate, as these studies typically apply different assessment criteria, weather datasets and comfort standards.
CFD Applications
Computational Fluid Dynamics (CFD) is widely used to evaluate how proposed ventilation strategies perform before construction. Whether airflow is generated through natural ventilation, mechanical systems or a combination of both, CFD provides detailed airflow simulation that helps engineers understand how air actually moves throughout a building.
Rather than designing the ventilation system itself, CFD evaluates how the proposed design performs under defined operating conditions. This allows project teams to compare alternative layouts, opening arrangements, airflow rates and operating scenarios while identifying airflow patterns that simplified engineering calculations may not reveal.
Every simulation should begin with a clearly defined engineering objective. CFD is most valuable when it answers a specific airflow question, such as whether fresh air reaches occupied zones, how external wind influences natural ventilation or how mechanical supply and extract systems interact within complex spaces.
Natural Ventilation
CFD can simulate airflow through windows, louvres, atriums, roof vents and other natural openings to demonstrate how wind pressure and buoyancy influence airflow throughout a proposed building. Where natural ventilation forms part of a broader low energy strategy, it is often considered alongside Passive House design principles.
Typical investigations include:
Mechanical Ventilation
CFD evaluates how supplied air moves through occupied spaces using airflow rates and diffuser layouts provided by the mechanical engineer. The analysis visualises how air distributes throughout the building rather than designing the mechanical system itself.
Typical investigations include:
Buildings combining operable openings with mechanical systems can be analysed under multiple operating scenarios. CFD enables direct comparison between natural, mechanical and mixed mode strategies, helping project teams understand how airflow behaviour changes as building operation and external conditions vary.
CFD is an airflow simulation tool. It does not independently determine ventilation rates, size mechanical equipment or replace mechanical engineering design documentation. Instead, it provides detailed engineering evidence that supports informed ventilation design decisions.
Simulation Outputs
A Computational Fluid Dynamics (CFD) simulation generates detailed engineering data that describes how air behaves throughout the modelled domain. Rather than producing a single result, CFD calculates airflow conditions at thousands or millions of computational cells, allowing engineers to visualise airflow patterns, velocity fields, pressure distribution and other performance variables across the entire model.
The most appropriate outputs depend on the engineering question being investigated. An internal airflow study may focus on ventilation effectiveness and airflow pathways, while an external simulation may prioritise façade pressures, wind flow around buildings or airflow through courtyards and external spaces.
Selecting the required outputs before modelling begins ensures that the simulation, reporting views and quantitative results directly support the design decisions the project team needs to make.
Velocity Fields
Colour contours illustrate how air velocity varies throughout the model, identifying stagnant regions, accelerated airflow and local air jets.
Vectors and Streamlines
Flow vectors and streamlines reveal the direction of airflow, recirculation patterns and the interaction between openings, occupied spaces and ventilation systems.
Pressure Contours
Pressure plots demonstrate where positive and negative pressure regions develop, helping explain airflow through façades, openings and connected spaces.
Section Views
Horizontal and vertical slices through the model reveal how airflow changes between occupied zones, upper levels and complex internal geometries.
Quantitative Results
Engineers can extract numerical values at nominated points, lines, surfaces or volumes to compare airflow velocity, pressure and other calculated variables throughout the model.
Scenario Comparison
Multiple simulations prepared using consistent assumptions allow engineers to compare alternative building geometries, ventilation layouts, operating conditions and design options.
CFD graphics are visual representations of numerical calculations rather than conclusions in themselves. Velocity contours, pressure plots and streamlines must always be interpreted in the context of the modelling assumptions, boundary conditions, engineering objectives and applicable project performance criteria.
A high quality CFD report explains the modelling methodology, assumptions, simulation outputs and engineering interpretation, enabling project teams to understand how the results influence design decisions rather than simply viewing airflow graphics in isolation.
Project Suitability
Computational Fluid Dynamics modelling is most useful when a project needs to understand how airflow varies across a space, around a building or between connected areas. It provides greater spatial detail than an average ventilation rate or simplified calculation by showing where air accelerates, circulates, stagnates or follows an unintended pathway.
A CFD study may be appropriate where complex geometry, ventilation openings, mechanical inputs or surrounding structures create airflow behaviour that cannot be assessed confidently from drawings alone. It can also support projects where alternative layouts, façade arrangements or operating scenarios need to be compared using consistently defined assumptions.
The decision to undertake CFD should begin with a clearly defined engineering or design question. A focused model that tests a specific airflow assumption is generally more valuable than a broad simulation without agreed outputs, performance criteria or a clear decision it is intended to inform.
Complex Geometry
Atriums, tall spaces, interconnected rooms, courtyards, setbacks and irregular building forms can create three dimensional airflow patterns that simplified methods may not represent adequately.
Local Air Movement
Detailed airflow simulation may be valuable where local velocity, high speed jets, recirculation, short circuiting or stagnant zones matter more than an overall airflow value.
Ventilation Pathways
CFD can test whether naturally or mechanically driven air enters, reaches and leaves the intended parts of a building under the nominated operating conditions.
External Interaction
Nearby buildings, terrain, roof forms, façades and opening locations can alter wind pressure and airflow before external conditions reach the proposed development.
Design Comparison
Alternative openings, diffuser positions, ventilation strategies, building geometries or operating modes can be compared using consistent boundary conditions and reporting outputs.
Design Risk
Modelling may be justified where an important design decision depends on airflow behaving in a particular way and that performance has not yet been demonstrated.
CFD may not provide meaningful additional value where the airflow question can be resolved reliably through established engineering calculations, manufacturer data, standard design guidance or information already available from the relevant project specialists.
An initial project review can consider the proposed geometry, ventilation strategy, available design inputs, level of risk and required outcome. This helps determine whether detailed spatial modelling is appropriate, which scenarios should be assessed and what information the CFD study should produce.
Simulation Workflow
Every Computational Fluid Dynamics (CFD) study begins with a clearly defined engineering question. Rather than attempting to reproduce every detail of a building, the simulation is developed to investigate a specific airflow problem, allowing engineers to evaluate how air behaves under carefully defined operating conditions.
The proposed building or external environment is converted into a three dimensional computational domain and divided into thousands or millions of computational cells. Using governing fluid flow equations, the CFD solver calculates airflow velocity, pressure, turbulence and other selected variables throughout the model.
Boundary conditions representing wind, ventilation systems, openings and operating scenarios are then applied. After the simulation converges, the results are reviewed and interpreted against the original engineering objective to determine whether the proposed design performs as intended.
Step 01
The project team establishes the airflow question, performance objective or design decision that the CFD study will investigate.
Step 02
Relevant geometry, façades, openings, ventilation components, surrounding buildings and other features are simplified into a model suitable for numerical analysis.
Step 03
Wind conditions, airflow rates, inlet and outlet properties, operating scenarios and other modelling assumptions are defined before the simulation begins.
Step 04
The computational domain is divided into a mesh of cells, with additional refinement applied where complex geometry or airflow gradients require greater numerical accuracy.
Step 05
The CFD solver calculates airflow throughout the mesh while convergence and solution stability are reviewed to confirm the results are suitable for engineering interpretation.
Step 06
Velocity fields, pressure contours, streamlines and quantitative outputs are interpreted against the engineering objective and documented with the modelling assumptions, limitations and key findings.
CFD modelling is rarely completed in a single simulation. Initial results often identify opportunities to refine the computational mesh, adjust boundary conditions or investigate additional operating scenarios. This iterative approach improves confidence that the simulation accurately represents the engineering question being investigated.
Where multiple design options are compared, every scenario should be prepared using consistent modelling assumptions, mesh quality and reporting methods. This ensures that differences between the results reflect genuine design performance rather than changes in the simulation methodology.
Project Inputs
The information required for a Computational Fluid Dynamics (CFD) study depends on the engineering question, the airflow scenario being investigated and the level of detail needed in the results. Accurate project information allows the simulation to represent the proposed design and produce engineering outputs that can support informed decision making.
Not every part of a building needs to be included within the computational model. Instead, the model should contain the geometry, openings, ventilation systems, surrounding context and operating conditions that materially influence the airflow behaviour being assessed. This focused approach improves simulation efficiency while maintaining engineering accuracy.
Before modelling begins, the project team should also define the scenarios to be analysed and the outputs required. Establishing these objectives early helps ensure that the simulation directly addresses the design decision the CFD study is intended to support.
Project Geometry
Architectural plans, elevations, sections and coordinated three dimensional models define the spaces, façades, roofs and external areas included within the computational domain.
Openings and Internal Features
Windows, doors, louvres, vents, partitions, screens, large equipment and other significant features may need to be included where they influence airflow pathways or pressure distribution.
Ventilation Design Information
Where ventilation performance is being assessed, the simulation may require supply and extract locations, airflow rates, diffuser information, opening configurations and relevant operating modes supplied by the design team.
External Conditions
Surrounding buildings, terrain, site orientation, wind conditions and other environmental information may be required where external airflow or façade pressure forms part of the engineering assessment.
Operating Scenarios
Opening positions, equipment operation, airflow schedules, temperatures and other scenario assumptions should be defined where they influence airflow behaviour during the simulation.
Required Outputs
Required velocity fields, pressure contours, streamlines, sectional views, quantitative data, comparison scenarios and reporting criteria should be agreed before modelling begins.
Reliable CFD simulations depend on reliable project information. While engineering assumptions can be made where information is incomplete, those assumptions influence how confidently the results can be interpreted and should be documented within the final report.
CFD modelling can also support projects during early design stages using preliminary information. As the design develops, the simulation may be refined to reflect changes in geometry, ventilation systems, operating conditions or surrounding context, ensuring the engineering assessment remains aligned with the evolving project.
Model Definition
Boundary conditions define how air enters, leaves and interacts with a Computational Fluid Dynamics model. They convert the selected design, environmental conditions and operating strategy into the numerical inputs used by the simulation.
Depending on the modelling objective, these inputs may include wind speed and direction, airflow rates, inlet profiles, outlet conditions, opening positions, temperatures and system operation. Each assumption should be appropriate to the question being investigated and supported by the best project information available at the time.
A CFD result represents the specific scenario defined within the model rather than every possible future condition. Clearly documenting the selected boundary conditions is therefore essential for understanding what the simulation demonstrates, where its conclusions apply and how confidently the results can inform design decisions.
External Conditions
External airflow studies may require nominated wind speeds, directions, turbulence characteristics and vertical wind profiles that reflect the site, surrounding terrain and modelling objective.
Ventilation Inputs
Mechanical airflow rates, inlet velocities, diffuser directions, supply temperatures and outlet conditions should be based on coordinated information provided by the relevant design team.
Opening Configuration
Windows, doors, louvres, vents and other openings may be represented as open, closed or partially open according to the operating condition being tested.
Temperature Inputs
Air, surface, equipment or supply temperatures may be included where temperature differences influence buoyancy, stack effect or the local distribution of airflow.
Computational Domain
The selected rooms, external areas, surrounding buildings, terrain and major obstructions should provide sufficient domain extent to represent the airflow influences relevant to the study.
Operating Scenario
System operation, opening states, occupancy assumptions and environmental conditions should be combined into a clearly described scenario for each CFD simulation.
Where confirmed project information is unavailable, reasonable assumptions may be required to allow the CFD study to proceed. These assumptions should be identified during scoping, coordinated with the relevant project specialists where possible and recorded clearly in the final report.
Where an uncertain input could materially affect the airflow response, sensitivity testing may be undertaken using additional scenarios. Comparing these scenarios can help distinguish findings that remain consistent from conclusions that depend strongly on a particular boundary condition or modelling assumption.
Design Testing
Computational Fluid Dynamics (CFD) can compare alternative design scenarios where a project team needs to understand how a proposed change may influence airflow behaviour. Each option is modelled using consistent assumptions so that differences in velocity, direction, pressure distribution and airflow pathways can be assessed on a comparable basis.
Scenario testing may examine changes to opening sizes, façade configurations, internal layouts, ventilation arrangements, operating modes or building form. The objective is not to simulate every possible future condition, but to isolate the airflow effect of a selected design variable and determine whether the change improves or weakens the intended performance.
CFD comparison is most valuable when the design question, assessment locations, boundary conditions and reporting outputs are agreed before modelling begins. This ensures that each scenario is assessed using the same methodology and that the results remain connected to a clear architectural or engineering decision.
Opening Configuration
Alternative windows, louvres, vents or doors can be tested to determine how opening area, location and operating state influence airflow pathways, pressure relationships and ventilation effectiveness.
Ventilation Arrangement
Different inlet, outlet, diffuser or grille positions can be compared to identify changes in air distribution, recirculation, stagnant regions and ventilation short circuiting under defined airflow rates.
Internal Geometry
Changes to room layouts, partitions, screens, furniture zones or major equipment can be compared where they may redirect, restrict or divide airflow within the modelled space.
Built Form
Alternative building forms, roof profiles, setbacks, façade elements or courtyard configurations can be examined where they influence external airflow, pressure distribution or air movement towards openings.
A reliable comparison changes the design variable being investigated while keeping the relevant geometry, boundary conditions, mesh approach and reporting methodology consistent. If wind conditions, airflow rates, opening states or computational extent change at the same time, it may be difficult to identify what caused the difference in the simulation results.
CFD provides evidence about how the selected options perform within the defined scenarios. It does not select the final design in isolation. The preferred response should be determined by the wider project team with consideration of architectural intent, mechanical requirements, construction constraints, operation and other project objectives.
Modelling Boundaries
Computational Fluid Dynamics (CFD) and thermal comfort modelling may both examine indoor building conditions, but they are used to answer different project questions. CFD focuses on the detailed spatial behaviour of airflow, while thermal comfort modelling evaluates the environmental conditions experienced by occupants over time.
A CFD simulation can show where air travels, how quickly it moves, how pressure differences influence that movement and where local recirculation or stagnant zones develop. Thermal comfort modelling considers whether the combined effects of temperature, radiant conditions, air movement, humidity, solar gains and occupancy are likely to support acceptable comfort within the occupied space.
The two methods can complement each other where a project requires both broader comfort assessment and detailed investigation of local airflow. However, CFD does not automatically demonstrate occupant comfort and thermal comfort modelling does not provide the same level of three dimensional airflow detail.
Airflow Behaviour
CFD examines how air moves within or around a defined three dimensional computational model under selected environmental and operating conditions.
It primarily investigates:
Occupant Conditions
Thermal comfort modelling examines how indoor environmental conditions may be experienced by occupants and how those conditions vary across relevant seasons, hours and operating periods.
It primarily investigates:
A broader thermal comfort assessment may identify that local airflow requires closer examination within a particular atrium, room, occupied zone or naturally ventilated area. CFD can then provide detailed spatial information about air velocity, distribution, recirculation or temperature transport within that selected area.
Conversely, CFD may explain how air moves without establishing whether the complete combination of temperature, radiant effects, humidity, air speed and occupant assumptions produces acceptable comfort. The appropriate assessment depends on whether the primary project question concerns airflow behaviour, occupant experience or both.
Modelling Boundaries
Computational Fluid Dynamics (CFD), building energy modelling and compliance modelling may all use digital representations of the same building, yet each assessment answers a different engineering question. CFD investigates how air behaves within a defined three dimensional space, while energy and compliance assessments evaluate whole building performance against operational or regulatory objectives.
CFD produces detailed spatial information about airflow velocity, pressure distribution, ventilation pathways and local air movement. Energy and compliance modelling examines broader building behaviour, including heating and cooling demand, annual energy performance and compliance with the National Construction Code or other applicable assessment pathways.
Because these modelling approaches answer different questions, they are often complementary rather than interchangeable. CFD does not replace energy modelling, Section J assessments or JV3 modelling, just as compliance modelling does not provide the detailed airflow analysis available from CFD.
Local Airflow Behaviour
CFD provides detailed spatial analysis of airflow within or around selected parts of a building under defined environmental and operating conditions.
It typically investigates:
Whole Building Performance
Energy and compliance modelling evaluates the overall performance of a building against energy efficiency objectives, operational performance targets or regulatory compliance requirements.
It typically investigates:
An energy, environmental or compliance assessment may identify a specific airflow question that requires more detailed investigation than whole building modelling can provide. CFD can then supply engineering evidence about ventilation pathways, local air distribution, façade pressures or airflow behaviour to support the wider design process.
CFD results should be interpreted alongside other building performance assessments rather than in isolation. While CFD can improve understanding of airflow related design decisions, it does not independently demonstrate National Construction Code compliance, replace Section J or JV3 assessments or predict annual building energy consumption.
Result Interpretation
Computational Fluid Dynamics (CFD) is a predictive engineering method. It estimates how air may behave within a defined geometry and set of boundary conditions rather than measuring every condition that will occur after a building is constructed, commissioned and occupied.
The reliability and usefulness of the results depend on the quality of the project information, the suitability of the computational domain and mesh, the selected physical models and the extent to which the simulated scenarios represent the design question. Changes to geometry, ventilation operation, opening positions, heat inputs or external conditions may produce a different airflow response.
CFD results should therefore be interpreted as technical evidence for clearly defined scenarios. They are most valuable when the modelling scope, assumptions, convergence criteria, limitations and intended use are documented alongside the reported velocity fields, pressure contours, vectors and streamlines.
Defined Scenarios
Each simulation represents the nominated wind direction, airflow rate, opening state, system operation, temperature inputs and other boundary conditions established for that scenario.
Input Quality
Preliminary, incomplete or uncertain project information may require engineering assumptions. The significance of those assumptions should be considered when confidence in the findings is evaluated.
Model Resolution
The geometry and computational mesh require sufficient resolution around openings, obstructions, occupied zones and other areas that materially influence the airflow behaviour being investigated.
Design Changes
Changes to building form, internal layouts, openings, ventilation rates or surrounding context may affect whether earlier CFD results remain representative of the proposed design.
Variable Conditions
Wind, occupancy, door and window use, equipment loads and ventilation system operation may vary after construction and cannot usually be represented by a single steady state simulation.
Professional Interpretation
Contours, vectors and streamlines should be interpreted against the modelling objective, quantitative results, relevant criteria and the assumptions documented for the CFD study.
Where actual operational performance needs to be confirmed, post construction testing, system commissioning, air balancing or site measurements may still be required. These activities assess the completed building and installed systems rather than the proposed conditions represented within the computational model.
CFD can help project teams investigate potential airflow behaviour before construction, compare design options and identify areas requiring closer attention. Its conclusions should remain proportionate to the modelling scope, the certainty of the inputs and the range of scenarios analysed.
Project Planning
The time and cost of Computational Fluid Dynamics modelling depend on the engineering question, the extent of the computational domain, the complexity of the geometry and the number of scenarios required. A focused study of one defined airflow issue will generally require a different level of effort from a broader investigation involving multiple spaces, wind directions, operating modes or design alternatives.
A CFD study may involve reviewing project information, simplifying or rebuilding geometry, defining boundary conditions, generating the computational mesh, running the solver, checking convergence, refining the model and interpreting the results. The effort required at each stage depends on the quality of the supplied information and the level of technical detail needed to answer the project question.
The modelling scope should therefore be structured around the decisions the project team needs to make. Defining the model extent, scenarios, evaluation criteria and reporting outputs early can reduce unnecessary simulation work and provide a clearer basis for programme and fee review.
Model Extent
A single room, interconnected interior, complete building exterior or surrounding precinct will require different levels of geometry preparation, domain setup, mesh generation and computational effort.
Geometry Complexity
Irregular forms, narrow openings, detailed façades, internal obstructions, plant equipment and surrounding structures may increase geometry preparation, quality checking and mesh requirements.
Number of Scenarios
Alternative wind directions, opening configurations, ventilation rates, operating modes or design options may each require a separate simulation, review and comparative analysis.
Mesh and Solver Requirements
Narrow openings, local air jets, complex flow separation and detailed assessment locations may require finer mesh resolution, additional solver iterations and longer computational run times.
Available Project Information
Coordinated drawings, usable three dimensional geometry and confirmed ventilation or operating information can reduce uncertainty, assumptions and additional preparation before modelling begins.
Reporting Requirements
The number of contour plots, sectional views, streamlines, extracted values, comparison tables, design observations and reporting stages will influence the overall scope of the CFD assessment.
A reliable quotation usually requires enough information to identify the modelled area, the primary airflow question, the boundary conditions, the scenarios to be tested and the required deliverables. Where these items are still developing, the engagement may be divided into an initial technical review followed by a confirmed modelling scope.
Design revisions made after geometry preparation, meshing or simulation may require parts of the model to be updated and rerun. Confirming key geometry, ventilation inputs and operating assumptions before detailed modelling begins can help reduce avoidable rework and programme delays.
Project Coordination
Computational Fluid Dynamics (CFD) modelling is most effective when the airflow question, project geometry, operating assumptions and required outputs are coordinated with the relevant design consultants before the computational model is developed.
Architectural form, internal layouts, ventilation inputs, opening configurations, thermal inputs and surrounding buildings may each influence the predicted airflow response. Because these elements are often controlled by different disciplines, the CFD model should be based on coordinated project information rather than assumptions developed in isolation.
The CFD consultant translates the agreed design information into a computational domain, applies the selected boundary conditions and interprets the resulting velocity fields, pressure contours and airflow patterns. Responsibility for architectural design, mechanical system design, operation, fire engineering and regulatory compliance remains with the appropriately appointed project specialists.
Architectural Team
The architectural team provides coordinated information about the building form, internal arrangement, façades, doors, windows, louvres, courtyards and relevant design options that define the geometry of the CFD model.
Mechanical Team
Where mechanical ventilation is represented, the mechanical engineer may provide supply and extract airflow rates, diffuser or grille locations, discharge characteristics, equipment heat loads and operating modes for each simulation scenario.
CFD Modelling Team
The CFD modeller defines the computational domain, simplifies geometry where appropriate, applies the agreed boundary conditions, generates the computational mesh, operates the CFD solver and interprets the resulting airflow behaviour.
Wider Project Team
The wider project team reviews the CFD findings against architectural intent, mechanical requirements, constructability, operation, safety and approval obligations before determining whether design refinement is required.
CFD generally provides the greatest design value when the principal geometry, airflow objective and operating scenarios are sufficiently developed to support a credible model, while there is still an opportunity to refine openings, layouts, façades or ventilation arrangements.
Starting before key inputs are available may result in extensive assumptions or repeated model reconstruction as the design develops. Starting after major design decisions have been fixed may limit the practical value of the findings and reduce the options available to address identified airflow issues.
An early CFD scope review can identify the appropriate modelling stage, confirm which consultants need to provide inputs and establish the design decisions, comparison scenarios and reporting outputs that the study is intended to support.
Engineering Workflow
A Computational Fluid Dynamics study is more than running simulation software. The engineering value comes from defining the correct question, selecting appropriate modelling assumptions, preparing a robust computational model and interpreting the results within the context of the project.
Although every project differs, most building related CFD studies follow a structured workflow that progressively develops the computational model before the engineering findings are reviewed with the design team.
Step 01
The first stage establishes exactly what the CFD study needs to investigate. This may involve natural ventilation, mechanical air distribution, external wind behaviour, façade pressures, local airflow conditions or comparison of alternative design options.
Step 02
Architectural drawings, three dimensional geometry, surrounding buildings, ventilation information and operating assumptions are reviewed to determine whether sufficient information is available to develop the computational model.
Step 03
The computational domain is established, geometry is prepared where required and the agreed boundary conditions, airflow inputs and physical assumptions are applied before numerical simulation begins.
Step 04
The geometry is divided into thousands or millions of computational cells. Areas requiring greater engineering resolution, such as narrow openings or local air jets, may use a finer mesh than less critical regions.
Step 05
The CFD solver calculates airflow behaviour throughout the computational domain. Multiple scenarios may be simulated to compare different wind directions, ventilation arrangements, operating modes or design alternatives.
Step 06
Velocity contours, pressure distributions, streamlines, vectors and other engineering outputs are interpreted in relation to the original project question. The final report documents the modelling assumptions, simulation results, limitations and engineering observations that support design decision making.
The accuracy and usefulness of a CFD study depend on much more than the software used to generate the simulation. Clear engineering objectives, appropriate boundary conditions, coordinated project information, suitable mesh resolution and informed engineering interpretation all contribute to producing results that can meaningfully support design decisions.
A well defined workflow also makes it easier for architects, mechanical engineers and project managers to understand how the modelling has been developed, what assumptions have been adopted and how the reported findings should be interpreted within the wider design process.
Engineering Quality
The reliability of a Computational Fluid Dynamics study depends on far more than producing attractive airflow images. Confidence in the results comes from appropriate engineering judgement throughout the modelling process, including geometry preparation, boundary condition selection, computational mesh development, numerical solution behaviour and technical interpretation.
While every CFD project has different technical requirements, experienced engineers typically review several aspects of the model before interpreting the simulation results and preparing engineering recommendations.
Geometry Review
The computational model should appropriately represent the parts of the building and surrounding environment that influence the airflow being investigated. Simplification may be appropriate where it does not materially affect the engineering objective.
Boundary Conditions
Wind conditions, ventilation rates, pressure boundaries, temperatures and operating assumptions should reflect the agreed project scope. Unrealistic inputs will produce unrealistic simulation outcomes regardless of software quality.
Computational Mesh
The computational mesh should provide sufficient resolution in critical regions such as openings, occupied zones, air jets and areas where significant velocity gradients are expected, while remaining computationally practical.
Numerical Behaviour
The CFD solver should demonstrate acceptable numerical behaviour before engineering conclusions are drawn. Depending on the study, engineers may review convergence behaviour, residual trends and other numerical indicators relevant to the selected simulation approach.
Engineering Interpretation
Velocity contours, streamlines, pressure fields and extracted values should be interpreted alongside the project objectives rather than viewed as isolated graphics. Engineering judgement remains essential when assessing the significance of predicted airflow behaviour.
Scenario Comparison
When comparing multiple design options, consistent modelling assumptions help ensure that differences in the reported results are caused by the design changes rather than unnecessary variation in the computational model.
Modern CFD software is a powerful engineering tool, but the quality of a simulation ultimately depends on the decisions made throughout the modelling process. Appropriate project information, suitable modelling assumptions, numerical review and experienced engineering interpretation are all fundamental to producing results that can support informed design decisions.
For this reason, CFD results should always be considered together with the documented modelling assumptions, boundary conditions and scope of the engineering assessment. Understanding how the model was developed is just as important as understanding the airflow patterns that it predicts.
Engineering Decisions
A Computational Fluid Dynamics study should begin with a clearly defined engineering question rather than a request to simply "run a CFD model". The purpose of the simulation is to provide evidence that supports specific design decisions by predicting how air is expected to behave under the selected conditions.
The questions below illustrate the types of engineering investigations that CFD can support during design development, coordination and technical review.
CFD can identify the expected airflow pathways through rooms, corridors, atriums, voids and other interconnected spaces under the selected operating conditions.
The simulation can identify locations where airflow is expected to slow, recirculate or become less effective, allowing alternative design options to be investigated.
CFD can compare different opening sizes, locations and operating arrangements to understand how these changes may influence natural ventilation pathways and local air movement.
Where mechanical ventilation forms part of the project, CFD can help visualise how supplied air is distributed throughout the space using the operating information provided by the mechanical engineer.
External CFD can investigate how neighbouring buildings, topography, podiums and façade geometry influence local wind conditions, pressure distribution and airflow around the proposed development.
One of the greatest strengths of CFD is comparing alternative design scenarios using a consistent engineering methodology, helping the project team understand how proposed changes influence predicted airflow behaviour.
The quality of a CFD assessment is closely linked to how clearly the engineering objective has been defined. Rather than attempting to answer every possible airflow question, an effective study focuses on the decisions that need to be made, the scenarios that should be compared and the information required by the project team.
By establishing these objectives before modelling begins, the computational domain, boundary conditions, simulation scenarios and reporting outputs can all be aligned with the project's engineering requirements, resulting in findings that are more relevant, efficient and easier to apply during design development.
Frequently Asked Questions
Computational Fluid Dynamics, or CFD, is a numerical engineering method used to predict how air or another fluid may move through or around a defined three dimensional space.
A CFD model uses a computational mesh and solver to calculate variables such as air velocity, direction, pressure and distribution for the geometry, boundary conditions and physical assumptions represented in the simulation.
CFD may be used where building geometry, openings, ventilation systems or surrounding structures create airflow behaviour that cannot be understood adequately through simplified calculations alone. It is commonly applied to investigate natural ventilation, mechanical air distribution, atriums, large internal spaces, façade pressures, external airflow and specific areas of recirculation or poor air movement.
CFD can analyse air velocity, airflow direction, pressure distribution, ventilation pathways, recirculation, stagnant zones, short circuiting, façade pressure and external flow around buildings. It may also model the transport of heat, smoke or contaminants where these variables form part of the defined engineering question.
No. CFD may not be necessary where the airflow question can be resolved reliably through established engineering calculations, manufacturer data, design guidance or information provided by the relevant project consultants. It is most valuable where airflow is strongly affected by three dimensional geometry or where local conditions need to be compared in greater detail.
CFD examines detailed airflow behaviour within or around a defined computational domain. It provides spatial information about velocity, direction, pressure and air distribution for selected scenarios.
Energy modelling evaluates broader building performance over time, including heating and cooling demand, annual energy consumption, envelope performance and regulated building services. The methods may support the same project, but they do not replace one another.
CFD focuses on how air moves, including local velocity, direction, pressure, recirculation and distribution. Thermal comfort modelling evaluates how the combined indoor environment may be experienced by occupants over relevant periods.
Thermal comfort assessment may consider air temperature, radiant temperature, humidity, air speed, clothing and activity assumptions. CFD may provide more detailed air velocity or temperature distribution where required, but it does not automatically demonstrate occupant comfort.
Yes. CFD can model airflow through windows, louvres, roof vents, atriums, courtyards and other openings under defined wind, pressure and temperature conditions. It can help determine how opening size, position, orientation and operating state influence airflow pathways and local air movement.
Yes. CFD can examine how supplied air moves through a space, how effectively it reaches occupied zones and extract points and where recirculation, stagnant regions, draught risk, short circuiting or uneven distribution may occur. The model normally uses airflow rates, diffuser characteristics and operating information provided by the mechanical design team.
No. CFD can test the airflow produced by a proposed ventilation arrangement, but it does not independently determine statutory ventilation rates, size ductwork, select equipment, prepare complete mechanical documentation or certify the installed system. Those responsibilities remain with the appointed mechanical engineer and other relevant specialists.
Yes. External CFD can examine how building height, orientation, massing, setbacks, façades and surrounding structures influence local airflow, turbulence and pressure distribution.
A formal pedestrian wind comfort or wind safety assessment may require multiple wind directions, local weather data, defined comfort criteria and specialist interpretation beyond a general external airflow study.
Yes. CFD can compare alternative opening arrangements, façade configurations, internal layouts, ventilation strategies or building forms. Meaningful comparison requires the relevant boundary conditions, model extent, mesh approach and reporting locations to remain consistent while the selected design variable is changed.
Typical inputs may include coordinated plans, elevations, sections, usable three dimensional geometry, opening details, façade information, surrounding context, ventilation rates, diffuser or grille data, operating assumptions and the scenarios or assessment locations that need to be reported. The exact requirements depend on whether the study concerns internal airflow, external airflow or both.
CFD is generally most useful when the principal geometry, airflow question and operating assumptions are sufficiently developed to support a credible simulation, but there is still an opportunity to adjust openings, layouts, ventilation arrangements or building form. An early scope review can help identify the appropriate modelling stage.
The programme depends on the model extent, geometry complexity, number of scenarios, mesh resolution, solver requirements, quality of the supplied information and reporting scope. A focused study of one airflow issue will usually require less time than a project involving multiple spaces, wind directions, operating modes or design comparisons.
CFD cost is influenced by the size of the computational domain, geometry preparation, number of scenarios, mesh and solver requirements, required outputs and the level of engineering interpretation. Coordinated drawings, confirmed operating assumptions and a clearly defined modelling question generally provide a more reliable basis for quotation.
Outputs may include velocity contours, pressure contours, vectors, streamlines, sectional plots, extracted values and comparisons between simulation scenarios. A technical report should also document the computational domain, boundary conditions, assumptions, modelling methodology, limitations and engineering interpretation of the results.
No. CFD predicts airflow behaviour for the geometry, boundary conditions, physical models and assumptions represented in the simulation.
Actual conditions may vary as wind, occupancy, opening use, system operation and the completed building change over time. CFD results should therefore be interpreted as engineering evidence for defined scenarios rather than a guarantee of every future operating condition.
No. CFD can help predict airflow before construction or investigate potential design issues, but post construction testing, air balancing, commissioning or site measurement may still be required where the actual performance of the completed building and installed systems needs to be confirmed.
Not by itself. CFD may provide supporting airflow information for a wider building performance investigation, but it does not replace a Section J assessment, JV3 model or the documentation required to demonstrate compliance with the applicable National Construction Code pathway.
The required project participants depend on the question being investigated. Architectural teams may provide geometry and opening information, mechanical engineers may provide ventilation inputs and operating modes and the CFD consultant defines and interprets the simulation. The wider project team then reviews the findings against design, construction, operational and approval requirements.
Related Knowledge
Computational Fluid Dynamics focuses on detailed airflow behaviour within and around buildings. Related assessment services examine occupant comfort, daylight availability and the wider environmental and planning questions that may influence design development.
Occupant Conditions
Assess how indoor environmental conditions may be experienced by occupants across different spaces, operating periods and seasonal conditions. Thermal comfort modelling considers a broader range of comfort variables than airflow analysis alone.
Explore Thermal Comfort Modelling →
Natural Light
Evaluate the availability, distribution and consistency of natural light within proposed buildings. Daylight modelling answers visual and illumination questions rather than airflow or pressure questions.
Explore Daylight Modelling →
Knowledge Gateway
Explore Certified Energy’s wider family of building physics, environmental modelling, solar access, shadow, visibility and spatial analysis services for Australian design and planning projects.
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Project Review
Send the available plans, sections, three dimensional geometry, opening information, ventilation inputs and the specific airflow issue the project team needs to investigate.
Certified Energy can undertake an initial technical review to determine whether Computational Fluid Dynamics is an appropriate engineering method for the project. This review can help distinguish a clearly defined CFD question from matters better resolved through mechanical design, thermal comfort assessment, energy modelling or conventional engineering calculations.
Where CFD is suitable, the modelling scope can be structured around the required computational domain, simulation scenarios, boundary conditions, project inputs, comparison criteria and reporting outputs. Defining these items before geometry preparation and meshing provides a clearer basis for quotation, programme planning and engineering decision making.
Last reviewed: July 2026. This page is maintained by Certified Energy as part of its Commercial Performance Knowledge Hub.
