看文獻,湍流無因次距離y+,u+之類的數據圖,這些數據是怎麼計算得來的?
01-07
剛接觸數值模擬,不太明白,例如y+的計算公式知道,可是公式裡面的每個量怎麼得到。希望推廣談談相關經驗,不知前輩們可否傳授,不勝感激!
http://geolab.larc.nasa.gov/APPS/YPlus/看看這個網址,右鍵看Javascript源碼。
源碼里唯一沒有說清楚的是表面摩擦力Cf哪裡來的,
再看看這個http://www.cfd-online.com/Wiki/Skin_friction_coefficient,Cf其實是根據某些實驗數據擬合的函數關係。這些計算都是先於流場計算的,用來計算第一層網格大約多厚。占坑
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let"s non-dimensionaliz and x, and y by following method:
where is the mean velocity in x direction you measured in boundary layer(BL), u* is the friction velocity and v is kinematic viscosity. I believe you have x, y and in hand (you measured it or calculated it). kinematic viscosity can be found in a look up table. thus, the only remain problem is u*.
where is the actual wall shear stress of your case, is the apparent shear stress at y=0.now you have everything you need to calculate V.Showever, if you do not have simulated or measured , you can calculate it from friction factor.
f can be found in some experience equation and Moody chart Moody chart.數值求解得到流場參數,根據流場參數就可以算出來了。
有相關網站輸入一些必要的值,直接得到自己算也太傷了!
這個問題讓我想到了另一個問題。我使用Star-CCM+做數值模擬。一直以為y+ u+是先計算流場和shear stress 然後求解的。但是看了說明和help,老感覺是先求速度場然後擬合u+然後求shear stress。好奇怪
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