The formulas used are give in CFD-Wiki here.The Schlichting skin-friction formula, as desribed here (equation 21.16 footnote in Schlichting), is used to estimate the local skin-friction for a turbulent boundary layer on a smooth flat plate.

2018年5月1日 · There can never be a last word in regard to the axioms of any physical theory. All we can ask of them is that they lead to conclusions in agreement with observation. Sooner or later more refined observations will find the weak point in any set of physical axioms. Nature is far too complicated to be completely described in a few equations. - J.L. Synge (1938) …

Y+ Wall Distance Estimation; A y+ wall distance estimation script provided by CFD Online. Uses the free-stream velocity and gas-data to estimate the wall distance needed to obtain a desired y+ value at a certain boundary layer length. This is one of those wonderful little tools that saves you from learning a formula! Viscous Grid Spacing Calculator

Y+ Estimation Estimates the wall distance needed to obtain a desired Y+ value. Turbulence Properties, Conversions & Boundary Estimations Use the tools here to convert and estimate turbulent properties at boundaries.

2020年2月28日 · \(y+\) is the dimensionless wall distance that is helpful in determining the thickness of the first cell away from the wall boundary for the given flow parameters. Equation (1) from the forum article above states: $$ y+ = y \frac{u_t}{\nu} $$ where, \(u_t\) is the friction velocity \(y\) is the absolute distance from the wall

When meshing it is often useful to be able to estimate the wall-distance needed to obtain a certain Y+ value. To estimate this you can do the following: 1. Compute the Re number: 2. Estimate the skin friction using one of the formulas given here, for example, using the Schlichting skin-friction correlation: 3. Compute the Wall shear stress: 4.

2005年10月23日 · The distance is usually measured in the dimensionless wall units, y+ (≡ ρuτy/µ), or y*. Note that y+ and y* have comparable values when the first cell is placed in the log-layer but are different by C_µ^(1/4), i.e. ≈ 0.5. «

2015年1月8日 · Ideally, you should have a y+ smaller than 1 on all your surface. But there is no need to go to 1e-3 ! Be careful, the size of your first cell must correspond to your turbulence model. For example a RAS k-omega SST requires a y+ smaller than 1 but a k-epsilon standard requires a y+ between 30 and 60.

2013年1月17日 · If the y+ of the first cell is 5, the extent of the next cells can only be equal or larger than 5 for a mesh with a reasonable expansion ratio. While the velocity is a linear function in the region of y+<5, it becomes nonlinear beyond this point and may not be resolved adequately with cells larger than y+=5.

2020年7月28日 · For your desired Y+ of 150 and using wall functions, you have done this correctly. Now you just have to achieve this Y+ and verify it. For this i HIGHLY suggest you download the Y+ histogram and ORSI program created by Dale, it is amazing. Here is the link for this information. Y+ Histogram program. Instrucitons for Y+ Histogram and ORSI use