Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/14445
標題: 紊流場中二維矩柱表面風壓之特性及數值驗證
A study on the characteristics of surface pressures of rectangular cylinders in uniform turbulent flow and numerical verification
作者: 陳荻閎
Chen, Ti-Hung
關鍵字: 2D rectangular cylinders;二維矩柱;wind tunnel test;surface pressure;computational fluid dynamics;風洞實驗;表面風壓;計算流力
出版社: 土木工程學系
摘要: 
摘要
本研究以深寬比(D/B)0.6、1.0、2.5及4.0四組二維矩柱模型在三種不同的流場條件下進行一系列的氣動力實驗,以探討其受風行為、表面風壓及其尖峰事件機率的分佈情形等特性。同時搭配數值計算,相互驗證正確性與精準度。
研究結果顯示,在風力係數方面,不同的流況下阻力係數均隨深寬比增加而降低。在小攻角情況下,風力係數則隨深寬比的改變而有不同的變化趨勢。紊流強度的增加在較小深寬比的模型(D/B=0.6、1.0)側風面及背風面風壓係數變化較大,對深寬比大的模型則較小,而在小攻角改變之情況下則反之。
在風壓機率分佈方面,本研究首先利用K-S檢定探討風壓訊號與常態、對數常態機率型式的符合情形,結果顯示,在零攻角條件下,除低深寬比矩柱(D/B=0.6、1.0)之側風面及背風面則較不符合,其餘大多會符合常態與對數常態的機率型式。深寬比1.0、4.0的模型實驗中,以風攻角改變促使原側風面逐漸轉為迎風面,顯示風壓機率分佈漸趨於符合此兩種機率分佈型式。同時,紊流強度的增加亦促使風壓訊號更趨向於常態與對數常態的機率型式。
本研究亦探討風壓尖峰因子小於-2的獨立尖峰事件,在不同深寬比的情形下,其側風面及背風面發生獨立尖峰事件機率的分佈變化皆隨著紊流強度增加而漸趨一致,且其值會有下降的趨勢。在小攻角的改變下,當側風面轉向迎風面時,發生獨立事件的機率也會降低,而在背風面則會有升高情形。在深寬比為1.0的風壓尖峰因子小於-2之獨立尖峰事件平均作用型態上,除其迎風面受紊流強度影響外,小攻角的改變對其平均作用型態值的大小與形狀沒有太大的影響。表面風壓獨立尖峰事件發生機率型式上,在不同流況、不同深寬比與不同風攻角下,大多僅符合TYPE I之機率分佈型式。
在數值方面,本研究數值模式對柱體在小風攻角變化的情況下,其對於風力係數等計算會有較好的結果。在風攻角大於10度時,數值結果與實驗所得之值有明顯的差距。此外對於高紊流強度流場條件下的模擬,其結果也與實驗值有一段差距,仍有待加強。
關鍵字:二維矩柱、風洞實驗、表面風壓、計算流力

Abstract
A series of aerodynamic experiments on 2D rectangular cylinders with variant depth-to-width ratio (D/B) were conducted to investigate the aerodynamic characteristics, included surface pressures coefficients, probability distribution type and independent peak events. The numerical computation procedures, with LES schemes, were also adopted to verify the results of aerodynamic experiments.
The results shown, the drag coefficients will be decreased as the depth-to-width ratio is increased, and the trends will be changed with small variant angle of approaching flow. The pressure coefficients of side face and rear face of cylinders with small depth-to-width ratio were affected by the turbulence intensity of approaching flow, but the affection will be inversed in the flow field with small angle of approaching flow.
The K-S test method was adopted to identify the distribution type of probability of wind pressures. The results have shown the PDF will close to normal-type and log-normal type for most cases but the pressure signals at side face and rear face with small depth-to-width ratio. The surface pressures of cylinders, depth-to-width equal to 1.0 and 4.0, were also measured with small angle of approaching flow. The result shown, the PDF of side face pressures will close to normal and log-normal type. The increasing of turbulent intensity will promote the type of PDF of surface pressures closer to normal and log-normal type.
The probability distribution of independent peak events at side face and rear face of cylinders will be more uniform as the turbulent intensity increased, but the values will be slightly decreased. With small angle of wind and the side face change slightly into the front face, the probability of independent peak events will be decreased but in the same time will be increased at the rear face. For the ensemble average of peak events, only the front face will be affected by the change of turbulent intensity. The PDF of independent peak events were found to be identical to the type I distribution type.
The numerical simulation results were quite similar to the result of aerodynamic experiments in the condition of small angle of approaching flow. For the cases of angle larger than 10 degree and high turbulence intensity, there were lots of differences between the simulated results and experiments results.
Keyword: 2D rectangular cylinders, wind tunnel test, surface pressures, computational fluid dynamics
URI: http://hdl.handle.net/11455/14445
Appears in Collections:土木工程學系所

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