Is there a way to specify surface roughness while using the SST model? Is it possible to use scalable wall functions with these turbulence models?
Wall roughness is a hidden beta feature for omega_based turbulence. To activate this, a manual CCL edit of the Fluid Models section and each wall boundary is required. First, activate the CFX 11.0 beta Features under Edit à Options_ CFX-Pre (see attached). Then, set SST up the default way and write out the .def file. Finally, extract the ccl from the .def file using the cfx5cmds executable and modify the ccl as shown below to activate scalable wall functions (if desired) and wall roughness height. (For instructions on the use of cfx5cmds, type "cfx5cmds `help" in a CFX Commandline window (in Windows) or at the command prompt (Linux/Unix).) Below are CCL examples using automatic and scalable wall functions respectively. Automatic wall treatment This is the default. In order to specify the automatic near wall treatment explicitly, the Option ` parameter in `TURBULENT WALL FUNCTIONS` (under the FLUID MODELS section ` see attached) must be set to `Rough Wall Omega Automatic`. In the following, an example is given for a heated wall with automatic wall treatment: BOUNDARY : Bottom Boundary Type =WALL Location = RCT B BOUNDARY CONDITIONS : WALL INFLUENCE ON FLOW : Option = No Slip TURBULENT WALL FUNCTIONS: Option = Rough Wall Omega Automatic END END WALL ROUGHNESS: Option = Rough Wall Roughness Height = 0.0005 [m] END # WALL ROUGHNESS HEAT TRANSFER: Option = Fixed Temperature Fixed Temperature = 8.E1 [K] TURBULENT WALL FUNCTIONS: Option = Rough Wall Omega Automatic END END # HEAT TRANSFER END Scalable wall functions In order to specify the scalable wall functions, the Option ` parameter in `TURBULENT WALL FUNCTIONS` must be set to `Rough Wall Omega Scalable`. The example shows the parameters for a heated wall with scalable wall functions. The default value of the lower - limit (Minimum Yplus) is 2.5 and can be changed via the ccl: BOUNDARY : Bottom Boundary Type = WALL Location = RCT B BOUNDARY CONDITIONS : WALL INFLUENCE ON FLOW : Option = No Slip TURBULENT WALL FUNCTIONS : Option = Rough Wall Omega Scalable Rough Wall Minimum Yplus = 2.5 END END WALL ROUGHNESS:Option = Rough Wall Roughness Height = 0.0005 [m] END # WALL ROUGHNESS HEAT TRANSFER: Option = Fixed Temperature Fixed Temperature = 8.E1 [K] TURBULENT WALL FUNCTIONS : Option = Rough Wall Omega Scalable END END # HEAT TRANSFER END In addition, an expert parameter must be set to use the max-function for the computation of the effective diffusion coefficients. EXPERT PARAMETERS : effective viscosity type = 2 END |
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