自然通風在建築物設計上是相當重要的課題之一，而窗戶的配置及風向對於風壓通風有著相當重要的影響。本研究採用計算流體動力學模式研究開口的配置對於室外風壓及通風量的影響，並利用積分法及通風模式計算通風量。主要探討的參數為風向角及開口的位置。結果顯示除了兩個開口放置在迎風面，其他的窗口配置會隨著風向角增大導致通風量變小。當窗口的配置導致剪力通風時，通風效果變差，在計算通風量時會有明顯的誤差。另一方面，三個窗口分別配置於建築三面外牆上的流況，利用積分法計算得之通風量遵守質量守恆定律與通風模式預測之值。本研究繪製之壓力分佈圖及速度分佈圖可幫助瞭解空氣在建築物室內室外之流動狀況。

This study used a three-dimensional Large Eddy Simulation (LES) model to investigate the influences of wind-driven ventilation of a cubic building with multiple openings. Five different configurations of openings are considered with three different wind directions. The ventilation rate Q through the building openings was calculated by two different methods. The first method is to integrate the predicted time-averaged velocities normal to the openings, another method is to substitute the predicted pressure coefficients Cp1 and Cp2 at the openings into a ventilation model. The results indicate that, the ventilation rates predicted by two different methods agree with each other when the openings were on different walls, but have large discrepancy when the openings were on the same wall. For buildings with three openings on three different external walls, the ventilation rates computed by the integration method satisfied the law of mass conservation, and agreed with the values predicted by the ventilation model. The simulated pressure distribution and velocity vectors around and inside the building can help us to understand the ventilation process.

[1] Allard F. Natural ventilation in buildings: a design handbook, James and James Ltd., London, England; 1998.
[2] Aynsley R. Estimating summer wind driven natural ventilation potential for indoor thermal comfort. J Wind Eng Ind Aerodyn 1999; 83:515-525.
[3] Linden PF. The fluid mechanics of natural ventilation. Annual Review of Fluid Mechanics 1999; 31:201-238.
[4] Etheridge D. Natural ventilation of buildings: Theory and measurement and design. John Wiley and Sons, Chichester, England, 2012.
[5] Awbi HB. Ventilation of Buildings. 2nd ed. Taylor and Francis, London, England, 2003.
[6] Etheridge D, Sandberg M. Building ventilation: Theory and Measurement. John Wiley and Sons, Chichester, England, 1996.
[7] Chu CR, Chiu YH, Chen YJ, Wang YW, Chou CP. Turbulence effects on the discharge coefficient and mean flow rate of wind-driven cross ventilation. Build Environ 2009; 44:2064-2072.
[8] Karava P, Stathopoulos T, Athienitis AK. Airflow assessment in cross-ventilated buildings with operable façade elements. Build Environ 2011; 46(1):266-279.
[9] Johnson MH, Zhai Z, Krarti M. Performance evaluation of network airflow models for natural ventilation. HVAC&R Research 2012; 18(3):349-365.
[10] Hu CH, Ohba M, Yoshie R. CFD modelling of unsteady cross ventilation flows using LES. J Wind Eng Ind Aerodyn 2008; 96 (10-11): 1692-1706.
[11] Chu, CR, Chen RH, Chen JW. A laboratory experiment of shear-induced ventilation. Energy and Buildings 2011; 43(10), 2631-2637.
[12] Evola G, Popov V. Computational analysis of wind driven natural ventilation in buildings. Energy Build 2006; 38: 491-501.
[13] Kato S, Murakami S, Mochida A, Akabashi S, Tominaga Y. Velocity-pressure field of cross-ventilation with open windows analyzed by wind tunnel and numerical simulation. J Wind Eng Ind Aerodyn 1992; 41-44: 2575-2586.
[14] Jiang Y, Chen Q. Effect of fluctuating wind direction on cross natural ventilation in buildings from large eddy simulation. Build Environ 2002; 37(4):379-386.
[15] Ramponi R, Blocken B. CFD simulation of cross-ventilation flow for different isolated building configurations: validation with wind tunnel measurements and analysis of physical and numerical diffusion effects. J Wind Eng Ind Aerodyn 2012; 104-106: 408-418.
[16] Tominaga Y, Mochida A, Yoshie R, Kataoka H, Nozu T, Masaru Y, Shirasawa T. AIJ guidelines for practical applications of CFD to pedestrian wind environment around buildings. J Wind Eng Ind Aerodyn 2008; 96:1749-1761.
[17] Ramponi R, Blocken B. CFD simulation of cross-ventilation for a generic isolated building: Impact of computational parameters. Build Environ 2012; 53:34-48.
[18] Chu CR, Chiang BF. Wind-driven cross ventilation with internal obstacles. Energy Build 2013; 67:201-209.
[19] Germano M, Piomelli U, Moin P, Cabot WH. A dynamic subgrid scale eddy viscosity model. Physics of Fluids A 1991; 3(7):1760-1765.
[20] Smagorinsky J. General circulation experiments with the primitive equations. I. The basic experiment. Monthly Weather Review 1963; 91(3):99-164.
[21] Chen Q. Ventilation performance prediction for buildings: A method overview and recent applications. Build Environ 2009; 44:848-858.
[22] Launder BE, Spalding DB. The numerical computation of turbulent flows. Computer Methods in Applied Mechanics and Engineering 1974; 3(2):269-289.
[23] Blocken B, Stathopoulos T, Carmeliet J. CFD simulation of the atmospheric boundary layer: wall function problem. Atmospheric Environment 2007; 41:238-252.
[24] Irtaza H, Beale RG, Godley MHR, Jameel A. Comparison of wind pressure measurements on Silsoe experimental building from full-scale observation, wind-tunnel experiments and various CFD techniques. International Journal of Engineering, Science and Technology 2013; 5(1):28-41.
[25] Feustel HE. COMIS-an international multizone air-flow and contaminant transport model. Energy Build 1999; 30:3-18.