| 摘要: | 本文主要探討方柱體在剪力流場作用下, 所產生之流場特性。實驗以紗網所產生的兩種 剪力流場,其剪力參數.beta.=(D/Uc)*(dU/dy)各別為 0.008和0.020,其中D為柱體寬度,Uc為剪力流中心速 度,dU/dy為y方向之速度梯度,加上均勻流等三種逼進流場進行風洞模擬實驗。試驗係利用模型 表面軸向排列之壓力孔,及設置於模型後側之 兩根熱膜探針(hot-film)分別量測方柱體所受之 風壓及風速,並計算各點的風壓頻譜,速度頻譜, 及壓力交頻譜等探討在剪力流場下柱體軸向的 流場現象。結果顯示,剪力流場的速度梯度會 造成渦散頻率在軸向上呈現階梯狀格元(cell)的 現象,隨著剪力參數的增加格元的現象亦愈明 顯。軸向上壓力相關性亦隨著剪力參數的增加而降低。
Experiments with square cylinder displaced in a plane uniform and two uniformly sheared free streams, has been investigated experimentally. The free stream shear parameters [ .beta.=(D/Uc)* (dU/dy) ] were 0.020 and 0.008. Pressure coefficient, pressure spectrum, cospectrum and velocity spectrum, cospectrum along the spanwise of the model were measured and compared. The results showed that the field of shear flow velocity gradient is a important factor of spanwise variation of vortex shedding and local pressure coefficient. |
