Non-iterative method in CCM+
 

Dear all,


I am a new user of CCM+ and I have used Fluent for quite sometime.



My work is related to swirling flows for which I am using LES closure with WALE Subgrid Scale model. My CCM+ settings include a constant density flow, Implicit unsteady with time step size of 0.1ms (this resulted in convective Courant number of less than 5) and 2nd-order temporal discretization, High-Accuracy Temporal Discretization Option with Optimized 2nd-order (5), MinMod limiter method, MUSCL 3rd-order/CD Convection in Segregated flow, Maximum Inner Iterations were 5 (default) and this has resulted in residuals to fall below 0.001 except axial velocity, that did not go below 0.01. No Synthetic Turbulence Specification in the initial conditions were considered. For Relaxation Scheme,Gauss-Seidel approach has been used. Regarding the mesh, I have tried both uniform trimmer mesh (without prism layers over the walls) as well as block structured mesh generated in ICEM CFD.



With these settings, I am unable to extract the correct RMSE values (calculated from Variance of the flow variables). In the regions where the velocity fluctuations are very large (experimentally), the solver elucidates significantly damped fluctuation levels; at some locations, instead of a shoot up, I can see a dip! Did I do something wrong with the solver settings? Inlet is velocity inlet, outlet is pressure outlet (zero gauge pressure), and rest all walls with no-slip condition.


Secondly, in Fluent (using LES), I have used non-iterative scheme with fractional time step, and this has reduced the wall-clock time per time step calculation. Unfortunately, I could not find any such setting in CCM+. I have also searched in the user guide as well as Siemens support portal but could not find any. Are there non-iterative options for incompressible turbulent flows in CCM+ similar to fractional time step option?



Any reference on this would also help me a lot.