Detailing the effects of geometry approximation and grid simplification on the capability of a CFD model to address the benchmark test case for flow around a computer simulated person

This paper details the use of a simplified CFD model to predict the flow patterns around a computer simulated person in a displacement ventilated room. The use of CFD is a valuable tool for indoor airflow analysis and the level of complexity of the model being investigated is often critical to the accuracy of predictions. The closer the computational geometry is to the real geometry of interest, the more accurate the corresponding results are expected to be. High complexity meshes enable elaborated geometries to be resolved. The drawback is, however, their increased computational cost. The Fire Dynamics Simulator (FDS) model (Version 5) enabled to investigate the effects of geometry and computational grid simplification on the accuracy of numerical predictions. The FDS model is based on a three-dimensional Cartesian coordinate system and all solid obstructions are forced to conform to the underlying numerical grid which is a potential limitation when dealing with complex geometries such as those of a human body. Nevertheless, the developed computational model was based exclusively on a three-dimensional rectangular geometry. At the same time, in order to limit the total number of grid cells, a relatively coarser grid than those used for similar simulations was adopted in the investigation. The developed model was then assessed in terms of its capability of reproducing benchmark temperature and air velocity distributions. The extent to which numerical results depend on different simulation settings was detailed and different boundary conditions are discussed in order to provide some guidance on the parameters that resulted to affect the accuracy of the predicted results. The comparison between numerical results and measurements showed that a simplified CFD model can be used to capture the airflow characteristics of the investigated scenario with predictions showing a favourable agreement with experimental data at least in the qualitative features of the flow (the detailed investigation of the local airflow field near the occupant can not be probably conducted apart from considering the real human geometry). Significant influence of simulator geometry and of boundary conditions was found.

[1]  George Hadjisophocleous,et al.  Guidelines for the use of CFD simulations for fire and smoke modeling , 2005 .

[2]  J. Fröhlich,et al.  Investigation of wall-function approximations and subgrid-scale models in large eddy simulation of separated flow in a channel with streamwise periodic constrictions , 2003 .

[3]  Zhecho Dimitrov Bolashikov,et al.  Advanced Methods for Air Distribution in Occupied Spaces for Reduced Risk from Air-Borne Diseases and Improved Air Quality , 2010 .

[4]  Arsen Krikor Melikov,et al.  Impact of personal factors and furniture arrangement on the thermal plume above a human body , 2007 .

[5]  Zhao Zhang,et al.  Evaluation of Various Turbulence Models in Predicting Airflow and 1 Turbulence in Enclosed Environments by CFD : Part-1 : 2 Summary of Prevalent Turbulence Models 3 4 , 2007 .

[6]  J. Floyd,et al.  Computational fluid dynamics modelling of fire , 2012 .

[7]  Xinlei Wang,et al.  Numerical study of air movement in a slot-ventilated enclosure , 2007 .

[8]  Gary S. Settles,et al.  A Computational and Experimental Investigation of the Human Thermal Plume , 2005 .

[9]  Mingsheng Liu,et al.  Correlation between minimum airflow and discharge air temperature , 2010 .

[10]  Mohammad H. Hosni,et al.  Comparison of Large Eddy Simulation Predictions with Particle Image Velocimetry Data for the Airflow in a Generic Cabin Model , 2006 .

[11]  Kevin B. McGrattan,et al.  Evaluation of a Fast, Simplified Computational Fluid Dynamics Model for Solving Room Airflow Problems | NIST , 2001 .

[12]  Patrick Hearn.  Editorial: Will There Be a Fuel Cell in Your Future HVAC Application? , 2006 .

[13]  Jianlei Niu,et al.  CFD Study of the Thermal Environment around a Human Body: A Review , 2005 .

[14]  Refrigerating.  ASHRAE handbook of fundamentals , 1967 .

[15]  Jelena Srebric,et al.  CFD boundary conditions for contaminant dispersion, heat transfer and airflow simulations around human occupants in indoor environments , 2008 .

[16]  Glenn P. Forney,et al.  Fire Dynamics Simulator (Version 2) -- Technical Reference Guide | NIST , 2001 .

[17]  Steven J. Emmerich,et al.  Application of a large eddy simulation model to study room airflow , 1998 .

[18]  Steven J. Emmerich,et al.  Use of computational fluid dynamics to analyze indoor air quality issues , 1997 .

[19]  P. Everitt,et al.  Modelling the effect of an occupant on displacement ventilation with computational fluid dynamics , 2008 .

[20]  E. Arens,et al.  Convective and radiative heat transfer coefficients for individual human body segments , 1997, International journal of biometeorology.

[21]  T. Doherty,et al.  Indoor Environmental Quality ( IEQ ) Title Evaluation of the physiological bases of thermal comfort models , 2006 .

[22]  Henrik Brohus,et al.  CFD Models of Persons Evaluated by Full-Scale Wind Channel Experiments , 1996 .

[23]  Jean-Michel Most,et al.  Large-eddy-simulation of buoyancy-driven fire propagation behind a pyrolysis zone along a vertical wall , 2002 .

[24]  Malcolm J. Cook,et al.  A NEW SIMULATION SYSTEM TO PREDICT HUMAN-ENVIRONMENT THERMAL INTERACTIONS IN NATURALLY VENTILATED BUILDINGS , 2007 .

[25]  Qingyan Chen,et al.  Natural Ventilation in Buildings: Measurement in a Wind Tunnel and Numerical Simulation with Large Eddy Simulation , 2003 .

[26]  Kevin B. McGrattan,et al.  Fire dynamics simulator (ver-sion 3) technical reference guide , 2001 .

[27]  Zhao Zhang,et al.  State-of-the-art methods for studying air distributions in commercial airliner cabins , 2011, Building and Environment.

[28]  C. Farnham,et al.  Study of mist-cooling for semi-enclosed spaces in Osaka, Japan , 2011 .

[29]  Henrik Brohus,et al.  Personal Exposure to Contaminant Sources in Ventilated Rooms , 1997 .

[30]  Kevin B. McGrattan,et al.  CFD Fire Simulation Using Mixture Fraction Combustion and Finite Volume Radiative Heat Transfer , 2003 .

[31]  Kevin B. McGrattan,et al.  Fire Dynamics Simulator (Version 5): User's Guide , 2007 .

[32]  Dominique Marchio,et al.  Numerical simulation of single-sided ventilation using RANS and LES and comparison with full-scale experiments , 2012 .

[33]  Jianbo Jiang.  Experimental and Numerical Study of Air Flows in a Full Scale Room , 2009 .

[34]  Charles Fleischmann,et al.  Experimental Verification Of The Fire Dynamics Simulator Hydrodynamic Model , 2003 .