Turbulent channel flow - Githubissues

PR to incorporate the channel_flow flow case and the features associated with it.

Using dealii's subdivided_hyper_cube to generate a wall-clustered mesh based on a stretching function
Added functionality for setting and updating model variables from within the FlowSolver environment using a FlowSolverCase object

Additional contributions:

store_vol_flux_nodes flag in dg.cpp is corrected to check if the PDE physics has nonzero physical source term; setter function added in DGBaseState
store_surf_flux_nodes flag in dg.cpp is corrected to check if parameter all_boundaries_are_periodic is true (default value for all_boundaries_are_periodic is false meaning that store_surf_flux_nodes will true by default); setter function added in DGBaseState
removed unused parameter use_classical_FR
post_get_needed_update_flags in PhysicsModel is corrected
adding post-processor to NavierStokes for outputting viscous flow quantities to the vtk files
adding parameter flag output_face_results_vtk as false by default to suppress the output of surface_solution vtk files
setting enable_higher_order_vtk_output as true by default
deprecating output_solution_files_at_velocity_field_output_times, can now output the solution vtk files at specific fixed times
improved the time step update location in FlowSolver and its usage for outputting files
improvements to restart file output
added the shear-improved Smagorinsky SGS model
added the high-pass filtered (DG-VMS) SGS model
closes the issue with enforcing the solution gradient at the boundary; issue #240

dougshidong / PHiLiP