The goal is to determine the required near wall mesh spacing,
, in terms of Reynolds number, running length, and a target value. A < 200 is acceptable if you are using the automatic wall treatment, if not, continue to read
the advice below. After running a solution, the value of
(in particular, the value given by the solver variable , representing the value for the first node from the wall) should agree with:
model means using a fine mesh and one of the
models (which include the SST model). The
models do accept coarser meshes, due to the automatic near-wall treatment for
these models. with characteristic velocity and length of the plate .
The correlation for the wall shear stress coefficient, , is given by: where is the distance along the plate from the leading edge.
The definition of for this estimate is:
目的是由雷诺数、行程长度及”
with being the mesh spacing between the wall and the first node away from the wall. Using the definition
can be eliminated in
can be eliminated using
Further simplification can be made by assuming that:
where is some fraction.
Assuming that , then, except for very small
This equation allows us to set the target value at a given location and obtain the mesh spacing, for nodes in the boundary layer.
湍流模型计算准确。

最低层数如下
where N is the number of nodes in the boundary layer in the direction normal to the wall.
下面为计算边界层厚度公式推导：
The boundary layer thickness can then be computed from the correlation:
to be:
The boundary layer for a blunt body does not start with zero thickness at the stagnation point for . It is, therefore, safe to assume that is some fraction of , say 25%. With this assumption, you get:
位置开始，因此，安全起见设Red
You would, therefore, select a point, say the fifteenth off the surface (for a low-Re model, or。