使用了紊流模型 Enhanced RNG，还需将壁面网格细化吗？

The Enhanced Two-Equation Models
The k-ε models are primarily valid for turbulent core flows (that is, the flow in the regions somewhat far from walls).  Consideration therefore needs to be given as to how to make these models suitable for wall-bounded flows.

Turbulent flows are significantly affected by the presence of walls.  Obviously, the mean velocity field is affected through the no-slip condition that has to be satisfied at the wall.  However, the turbulence is also changed by the presence of the wall in non-trivial ways.  Very close to the wall, viscous damping reduces the tangential velocity fluctuations, while kinematic blocking reduces the normal fluctuations.  Toward the outer part of the near-wall region, however, the turbulence is rapidly augmented by the production of turbulence kinetic energy due to the large gradients in mean velocity.

The near-wall modeling significantly impacts the fidelity of numerical solutions, inasmuch as walls are the main source of mean vorticity and turbulence.  It is in the near-wall region where the solution variables have large gradients and where the momentum and other scalar transports are the greatest.  Therefore, accurate representation of the flow in the near-wall region determines successful predictions of wall-bounded turbulent flows.

Numerous experiments have shown that the near-wall region can be largely subdivided into three layers.  In the innermost layer, called the " viscous sublayer " , the flow is almost laminar, and the (molecular) viscosity plays a dominant role in momentum and heat or mass transfer.  In the outer layer, called the fully-turbulent layer, turbulence plays a major role.  Finally, there is an interim region between the viscous sublayer and the fully turbulent layer where the effects of molecular viscosity and turbulence are equally important.

To more accurately resolve the flow near the wall, the enhanced two-equation models combine three k-ε models (standard, RNG and realizable) with enhanced wall treatment.


Enhanced Wall Treatment
Enhanced wall treatment is a near-wall modeling method that combines a two-layer model with enhanced wall functions.

In the two-layer model, the viscosity-affected near-wall region is completely resolved all the way to the viscous sublayer.
The two-layer approach is an integral part of the enhanced wall treatment and is used to specify both ε and the turbulent viscosity in the near-wall cells. In this approach, the whole domain is subdivided into a viscosity-affected region and a fully-turbulent region. The demarcation of the two regions is determined by a wall-distance-based, turbulent Reynolds number.

If the near-wall mesh is fine enough to be able to resolve the laminar sublayer (y+≈typically ), then the enhanced wall treatment will be identical to the traditional two-layer zonal model. However, the restriction that the near-wall mesh must be sufficiently fine everywhere might impose too large a computational requirement. Ideally, then, one would like to have a near-wall formulation that can be used with coarse meshes (usually referred to as wall-function meshes) as well as fine meshes (low-Reynolds-number meshes). In addition, excessive error should not be incurred for intermediate meshes that are too fine for the near-wall cell centroid to lie in the fully turbulent region, but also too coarse to properly resolve the sublayer.

To achieve the goal of having a near-wall modeling approach that will possess the accuracy of the standard two-layer approach for fine near-wall meshes and will not significantly reduce accuracy for wall-function meshes, ANSYS Icepak combines the two-layer model with enhanced wall functions to result in the enhanced wall treatment.
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使用了紊流模型 Enhanced RNG，还需将壁面网格细化吗？
壁面网格划分尺寸要多少，Enhanced RNG 才会发挥作用？

简单点的方法一般是算个稳态流场看看Y+分布，超过30的话就加密网格，反复测试直到小于30。这个湍流模型其实在传热计算中不是很实用，如果网格比较细的话还是K-w SST实用性好点.