Hey,

sorry, i dont have any experince in calculating the “right” wall distance for a turbulence modell.

I would like to ask, if the results could be correct.

Initital values:

rh = L = 0,12\:m \\
U = 1,025\:m/s \\
\rho = 999,1\:kg/m³\\
\mu = 0,00114\:kg/m\cdot s \\
y+ = 30

Reynoldsnumber:

Re =(\rho \cdot U \cdot L) / \mu = ( 999,1 \cdot 1,025 \cdot 0,12)/0,00114 = 104.324

Cf:

Cf = (2\cdot \log_{10}(Re)-0,65)^{-2,3} = 0,0058

tau wall:

\tau_{wall}= (1/2) \cdot C_{f} * \rho \cdot U^{2} = (1/2) * 0,0058 \cdot 999,1 \cdot 1,025^{2} = 3,043 kg/(m\cdots^{2})

Ufric

U_{fric} = \sqrt{\tau_{wall} / \rho} = \sqrt{ 3,043 / 999,1 } = 0,0552

y:

y= (y+ \cdot \mu) /( U_{fric} \cdot \rho) = (30 * 0,00114)/(0,00552 \cdot 999,1) = 0,00062\:m\\
1st\:Cellheight\: 2\cdot y = 0,00124\:m

So the first cell has to be 1,24 mm height, would you say ok, that could be, or did it feel way to small ?

I’d like to settle this before I create the mesh and consume many core hours in simulations .

Best regards

Kai