本文以直徑7.3公尺之高風量低速大吊扇為分析對象，探討其在高度10公尺之大截面積的封閉環境下，以60rpm運轉之流場與性能特性，並在知名商用CFD模擬軟體Fluent之架構進行相關之數值模擬及流場可視化；首先針對單一吊扇運作的流場進行分析，選定扇葉安裝角、吊扇與天花板距離、及環境尺寸作為變數，並依熱舒適度理論將有效風速定為0.5m/s，觀察其入出口流量以及有效空氣速度範圍覆蓋率(ASRC)，藉以判斷吊扇在不同環境中運轉之效能和其適用性。系統化參數分析之模擬結果顯示，扇葉安裝角17度之吊扇能產生最大出口流量，且必需安置於距離天花板至少1.5公尺處，即可確保吊扇入口進風之順暢；同時得知邊長40公尺之正方形環境為此吊扇之最大適用空間，在此環境下能有最佳之出口流量及ASRC表現。接著，以上述單一吊扇之最佳配置方案為依據，進行兩個吊扇相距不同距離之模擬分析，結果顯示在兩吊扇距離為8~10個半徑時，彼此之出風不會干擾且可維持個別出風流量，甚至產生些許強化性能之效果，使吊扇出口流量增加9%；為了檢驗這些結論在更大環境之適用性，本研究將四個吊扇以陣列安置並選定最佳的吊扇距離10個半徑，CFD計算得出吊扇的平均出口流量及ASRC值，成功地驗證所得之結論可用於更大的空間。另外，為擴大研究成果之適用性，在此對吊扇運作相關之參數藉π理論進行無因次分析，以取得重要參數的無因次之函數關係式，並藉模擬結果以求得對應之多項式和係數，獲得包括出口流量及ASRC這兩個吊扇性能重要參數，二者與吊扇天花板距離、環境尺寸、和兩吊扇間距之無因次公式，如此使用者經由上述公式的協助，即可輕易地達成吊扇安裝效能最佳化的規劃。

Recently, HVLS (high volume low speed) ceiling fan, also called as helicopter fan, has become a popular product to incorporate with the air-conditioning system inside the large-size building. Besides the energy-saving advantage, helicopter fan can offer a spreader velocity distribution with the thermal-comfort air speed. Clearly, the appropriate arrangement on fan installation and its ASRC (air speed range coverage) are important to maximize the thermal-comfort effect, and become the topic of this study. At first, this numerical investigation performs the flow field simulation on the helicopter fan with five 3.65m-in-radius blades operating at 60 rpm in a space with square floor and 10-m height. Also, blade setting angle, installing distance from the ceiling, and space size are covered in the parametric study, which is executed within the framework of CFD tool (Ansys Fluent). The result indicates that the optimum combination consisting of the 17-degree setting angle and installing at 1.5m from the ceiling can provide the best ASRC value based on the 0.5m/s air velocity, which is determined with the aids of weather condition in Taipei, Taiwan and thermal comfort tool developed by center for the built environment of University of California at Berkeley.
Next, this proper installation setting is utilized to the two-fan operation space, in which floor area varies with the change on distance between two HVLS fans. Thereafter, the best fan distance is identified by the numerical evaluation on the corresponding discharge and ASRC for different fan distances. It is found that fans separated by 8~10 radius not only can avoid the discharge flow interference, but also results in a slight enhancement on the discharge volume (9%) and the ASRC. Furthermore, these optimized parameter settings are checked on the 4-fan installing case by the CFD simulation. Finally, the dimensional analysis is applied to obtain the function forms among several dimensionless groups for the convenient use of the above best settings. It follows that dimensionless flow coefficient and ASRC ratio can be expressed as functions of Reynolds number, nondimensional distances from the ceiling, and distance between fans. Also, these functions are approximately expressed in polynomial form, in which coefficients are decided easily by fitting with previous CFD outcomes. In summary, this numerical work performs parametric study to attain the proper installation setting for several helicopter fans operating within a huge closed space. Also, the dimensionless forms of discharge flowrate and ASRC are expressed in the ready-to-use equations, which offer the proper installation plan for different fan sizes and various spaces.

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