Temporal resolution

A wide range of time scales puts turbulent flows into the category of stiff systems for time advancement. Such stiff systems are often handled using implicit time advancement algorithms in CFD which allow use of large timesteps. Unfortunately, the requirement of time accuracy over a wide range of scales does not permit very large timesteps in DNS. Use of large timesteps implies that the small scales can have large errors, which can corrupt the solution. A common practice in incompressible DNS of wall-bounded flows is to use implicit time advancement for the viscous terms and explicit time advancement for the convective terms. For DNS of turbulent channel flow using implicit timestepping, studies by Choi & Moin [1] showed that very large timesteps cause the turbulence to decay to a laminar state.