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How to correctly use CFD as a tool for ventilation design?

Qingyan (Yan) Chen

Principal Director of Air Transportation Center of Excellence (CoE) for Airliner Cabin Environment Research (ACER)

Professor of Mechanical EngineeringPurdue University

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Outline

BackgroundVerification of CFD modelValidation of CFD resultsReporting of CFD resultsConclusions

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Background: CFD for physical phenomena of ventilation

CFD is used to quantitatively predict thermal-fluid physical phenomena of ventilation

Simultaneous heat flows (e.g., heat conduction through the building enclosure, heat gains from heated objects indoors, and solar radiation through the building fenestration)Phase changes (e.g., condensation and evaporation of water contents)Chemical reactions (e.g., combustion in case of a fire)Mechanical movements (e.g., fans and occupant movement)

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Background: Procedure of CFD simulations

CFD modeling of ventilation and corresponding phases

Conceptual model

CFDmodel

Engineer’sspecific problemModel

qualificationModel validation

Model verification

AnalysisProgramming

Simulation

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Background: Example of ventilation design

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Verification

Identify the relevant physical phenomena for ventilation analyses Provides a set of instructions on how to assess whether a particular CFD code has the capability to account for those physical phenomena

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Verification: What to be verified?

Basic flow featuresTurbulence modelsAuxiliary heat transfer and flow modelsNumerical methodsAssessing the CFD applications

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Verification: Example

g

x

y

TwTw

Tfl 24mm

18mm

L=1.04m

L

Tw

Tin, Uin

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Verification: Example

Verification of the CFD model for mean temperature and turbulence kinetic energy with the experimental data

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Validation

Provide a set of instructions on how one can demonstrate the coupled ability of a user and a CFD code to accurately conduct representative indoor environmental simulations with which there are experimental data available

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Validation: What to be validated?

Basic flow and heat transfer (convection, diffusion, conduction, and/or radiation) Turbulence models Auxiliary heat transfer and flow modelsNumerical methodsAssessing CFD predictions

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Validation: Differences between validation and verification

Identification of flow features Modeling of complex physical conditions (approximation and simplifications)Ability to achieve converged and good results

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Validation: Example

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Validation: Example

Qualitative comparison of airflow pattern of smoke visualizationwith CFD results

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Validation: Example

Quantitative comparison of computed U, T, C, and Tu (lines) with experimental data (symbols)

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Reporting of CFD results

Experimental design CFD models and auxiliary heat transfer and flow modelsBoundary conditions Numerical methodsComparison of the CFD results with the dataDrawing conclusions

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Conclusions

Verification – Use simple (2D) cases with same basic flow features as the case to be studied. The simple case should have excellent data quality Validation - Represent complete flow, heat transfer, and mass transfer features as the case to be studied. Partial validation is acceptable.Reporting - Contain experimental design, models, numeric, assessment, and conclusions. Do not have to be in a uniform format.