|摘要: ||本文係以風洞模型試驗,設法分離紊流 強度與長度尺度,藉以探討各參數對於方柱模 型所受風力之影響。實驗參數的範圍為紊流強 度:T.I.=3%-18%,無因次長度尺度比 L/sub u//D=0.9-4.4。本文實驗在不同流 場條件與模型尺寸組合條件下量測方柱體所到 的平均阻力係數C/sub d/,擾動性阻力係數 C/sub d/',擾動性昇力係數C/sub 1/',順風向 風力頻譜,氣動力阻抗函數(Aerodynamic admittance function)及橫風向風力頻譜。由 實驗結果得知,平均阻力係數隨紊流強度增加 而遞減,擾動性阻力係數隨紊流強度增強而加 大。擾動性昇力係數隨長度尺度之增加而遞減 。並以紊流強度與長度尺度為基本變數,根據 實驗結果建立氣動力阻抗函數及橫風向風力頻 譜之經驗公式,其預測能力較平常用之經驗式 為佳。|
This research project studied the turbulence effects on the aforementioned wind load characteristics on a 2D square cylinder through wind tunnel model tests. The range of controlled parameters were: turbulence intensity T.I.=3%-18%, length scale ratio L/sub x//D=0.9-4.4. Total of 27 flow conditions were studied in order to identify the individual effect of each turbulence characteristics on wind force coefficients and force spectra. Experimental results indicated that the mean drag coefficient. Cd, decreased with the increase of turbulence intensity. The fluctuating drag coefficient, Cd', increased with enhancement of turbulence intensity while insensitive to the variation of length scale ratio. The r.m.s lift coefficient, C/sub 1/', stayed invariant to the change of turbulence intensity but exhibited a significant trend of decrease with the increase of length scale ratio. Besides force coefficients, aerodynamic admittance functions and crosswind force spectra were obtaained . In this paper, both turbulence intensity and length scale were used as the basic parameter to derive the empirical model of alongwind admittance function and the crosswind force spectra. The present empirical models exhibited ability to predict wind force spectra to a satisfactory accuracy at various flow conditions.