The realizable two-layer k - [epsilon] model used in this study combines realizable k - [epsilon] model with two-layer wall modelling approach, which allows the k - [epsilon] model to be applied in the viscous sublayer .
The low-Re approach for wall modeling used in this study resolves the viscous sublayer by applying damping functions to the model coefficients.
The control over the entire surfaces to force viscous sublayer
resolution was computationally expensive and judged unnecessary.
For the high Prandtl numbers, the grid resolution which captures the viscous sublayer can be inadequate and insufficient for the thermal conduction region.
It is well known that the viscous sublayer (0 [less than or equal to] [y.
However, with the roughness reduced on the inner wall, the small convex parts are all completely submerged in the viscous sublayer and the gas pipeline becomes "hydraulic smooth pipe" That means even though the coating surface is smoothed further, the wall friction is difficult to further reduce.
In order to improve the drag-reducing effect further, the triangle groove is designed as s=135 urn, h=100 um (s-width of the groove, h- height of the groove), where the tips of grooves stick out of the viscous sublayer, and the good drag reduction effect can also be received.
The boundary layers that cover airfoil are divided into viscous sublayer
, buffer layer and log-low region (MA, 20009).
While wall roughness hardly affects the pressure drop in laminar flow, its influence in the turbulent case is quite considerable if the mean protrusion height k is greater than the thickness of the viscous sublayer
Near the wall, wall functions are used when the mesh is too coarse to resolve the viscous sublayer
In the simple models in common engineering use, the effect of viscosity is confined to a thin viscous sublayer
near the pipe wall.
In turbulent flow near a straight wall there must be a viscous sublayer
, the [y.