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?

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

-------------------------------------分割,填坑-------------------------------------------------

let"s non-dimensionaliz ar{u} and x, and y by following method:

u^{+}=ar{u}  /u*

x^{+}=xu*/
u

y^{+}=yu*/
u

where ar{u} 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 ar{u} 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*.

u*=left( frac{	au _{0}  }{
ho } 
ight) ^{0.5}

where 	au _{0} is the actual wall shear stress of your case, is the apparent shear stress at y=0.

	au _{0} =
ho 
u frac{partial ar{u} }{partial y}

now you have everything you need to calculate u^{+} V.S y^{+}

however, if you do not have simulated or measured 	au _{0} , you can calculate it from friction factor.

	au _{0} =f*
ho U^{2}

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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