WInd resource assessment in urban areas for sustainable development

WInd resource assessment in urban areas for sustainable development

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  Building Simulation Conference -2015 WIND ASSESSMENT IN URBAN AREA WITH CFD TOOLS APPLICATION TO NATURAL VENTILATION POTENTIAL AND OUTDOOR PEDESTRIAN COMFORT Stéphane Sanquer, Guillaume Caniot, Sachin Bandhare Meteodyn, FRANCE
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  CONTEXTE AND OBJECTIVES Froman urban designer point of view, the knowledge of the urban climatology and especially the wind flow around buildings is crucial in many applications such as: • Air quality and thermal behaviour inside buildings since heat exchange depends on Air change rate; • Wind energy production from small wind turbines ; • Wind pedestrian comfort in outdoor spaces and in opened indoor spaces exposed to wind. CFD tools dedicated to calculating wind flow inside built environment give advantages to understand and interpret the wind in any urban area. Wind mappings become useful to urban designers to optimize the master plan: position and orientation of buildings (Jansen et al. 2013, Fadl and Karadelis 2013, Szücz 2013) IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015
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  CONTEXTE AND OBJECTIVES Theaim of this work is to present a methodology that allows the quick assessment of urban master plan without carrying out complex long computations. • The natural ventilation potential based on pressure coefficients mappings Air Flow inside the building depends on external condition. • Wind Mappings/Pressure on the wall are the key parameters to optimize the master plan. Cp DataBase useful for simple building shape otherwise not accurate for complex with neighboring buildings IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015
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  CONTEXTE AND OBJECTIVES Thehuman comfort index is based on wind speeds exceedance statistics Quick computations for urban designer : Which model ? Validation cases to show the performances of the CFD tool (UrbaWind) Applications to explain the approach and their practical advantages IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015
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  NUMERICAL APPROACH (UrbaWind) IBPSABuilding Simulation Conference , Hyderabad, India, Dec. 7-9, 2015 RANS equations : Turbulence Equation k-L :   0''                                 iji i j j i jij ij Fuu x u x u xx P x uu                                        j j i j j i Tk ik T i i x u x u x u P x k ku x Tt Lk 2/1   TL k C 2/3   𝐿 𝑇 = 𝜅 𝐷 𝑊 𝐶𝐿 Turbulence viscosity : Dissipation rate Turbulence Length Scale 09.001.0  CDepends on thermal stability (Yamada and Arritt) 𝐶𝐿 ? Two parameters to tune : 𝐶𝐿 𝑎𝑛𝑑 𝐶𝜇
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  VALIDATION : flowseparation around buildings IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015 Turbulence model Reference XR/b XR_TOP/b k-e (Standard) Tominaga el al. 2.7 No separation k-e (Modified) Tominaga el al. 3 to 3.2 0.52 to 0.58 Differential stress model Mochida et al. 4.2 >1 LES Tominaga el al. 1 to 2.1 0.50 to 0.62 k-l (CL=0.20, Cmu=0.09) UrbaWind 1.7 0.25 k-l (CL=0.15, Cmu=0.09) UrbaWind 2.5 0.60 k-l (CL=0.10, Cmu=0.09) UrbaWind 2.5 0.70 k-l (CL=0.15, Cmu=0.01) UrbaWind 1.5 0.60 k-l (CL=0.10, Cmu=0.01) UrbaWind 2 0.70 Experiment Meng and Hibi 1.42 0.52 Dimensions : 20 x 20 x 40 mb CFD : Tominaga et al., 2008 Experiments : Meng & Hibi, 1996
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  VALIDATION : pressureon building walls IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015 Pressure coefficient on buildings : -1.5 -1.0 -0.5 0.0 0.5 1.0 0 1 2 3 CFD (UrbaWind) 0 3 2 1 Cp Wind tunnel and full scale results range Mean results Experimental values from the Silsoe 6m Cube (Richards et al., 2007)
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  VALIDATION : pressureon buildings IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015 Sensibility of geometry of the building and wind direction Cp=0 Cp=0.5 Cp=0.6 Cp=0.6 Impact of geometry Impactofwinddirection
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  VALIDATION : pressureon buildings IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015 -1.5 -1.0 -0.5 0.0 0.5 1.0 0 1 2 3 0°-Detached 45°-Detached 0°- Urban 45° - Urban 0 3 2 1 Cp 0° 45° CFD (DCp) 0° 45° Detached 1.0 0.7 Urban 0.1 0.2 Tables (DCp) 0° 45° Urban 0.45 0.35 Influence of complex urban environment DCp over estimated using table. WINDa UCpAQ 
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  VALIDATION : windspeed in urban area IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015 Nigata experiments : Yoshie et al. 77 points at h=2m =Cv(CFD)-Cv(exp) Mean error = 0.04 Standard deviation=0.14 50% ||<0.1 RANS underestimates the wind speed in the wake compared to experiment made with thermistor anemometers High value of  are in low speed area or closed to flow separation zone => small change of position leads to important speed variation.
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  Application : Naturalventilation potential IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015 Threshold on Cp : example of warm tropical climate WIND BD a WINDa UCp V A ACH UCpAQ   0 1 2 3 4 5 6 7 8 9 10 0 10 20 30 40 50 T(indoor)-T(outdoor)(C) ACH (1/h) Roof without insulation Roof insulation Roof and NE wall insulation Indoor Thermal comfort Givoni diagram : Thermal dynamic simulation in an office at La Réunion Island during the summer (Garde R., 2006)
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  Application : Naturalventilation potential IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015 H H H H H M L L L L H H H HM Threshold on Cp : example of warm tropical climate Guidelines for Natural ventilation potential in tropical warm climate (Gandemer et al.) Level of natural ventilation efficiency DCp range ACH too low DCp < 0.2 ACH enough 0.2 ≤ DCp < 0.4 ACH good 0.4≤ DCp < 0.6 ACH very good 0.6≤ DCp WINDa UCpAQ  UrbaWind UrbaWind
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  Application : Naturalventilation potential IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015 Level of natural ventilation efficiency DCp range ACH too low DCp < 0.2 ACH enough 0.2 ≤ DCp < 0.4 ACH good 0.4≤ DCp < 0.6 ACH very good 0.6≤ DCp Threshold on Cp : example of warm tropical climate Réunion Island (Indian Ocean) French Guiana (South America)
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  Application : Pedestriancomfort IBPSA Building Simulation Conference , Hyderabad, India, Dec. 7-9, 2015 Pedetrian Wind comfort assessment on Seguin Island in Paris UrbaWind Green : suitable for stationary position Yellow : unconfortable Frequency of exceeding the comfort threshold
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  Conclusions IBPSA Building SimulationConference , Hyderabad, India, Dec. 7-9, 2015 • Numerical methodology to assess the wind pedestrian comfort and the natural ventilation in any complexe urban area • Purposes : To develop an Automatic, Quick and Accurate CFD Tools (UrbaWind) to urban designers • Turbulence modeling : k-l to urban flows => reproduce the flow separation • Validation with experimental data • Wind and pressure field used to assess the comfort and the natural ventilation potential