A primer on direct numerical simulation of turbulence - methods, procedures and guidelines

Direct Numerical Simulation (DNS) is the branch of CFD devoted to high-fidelity solution ofturbulent flows. DNS differs from conventional CFD in that the turbulence is explicitly resolved,rather than modelled by a Reynolds-averaged Navier-Stokes (RANS) closure. It differs fromlarge-eddy simulation (LES) in that all scales, including the very smallest ones, are captured,removing the need for a subgrid-scale model. DNS can thus be viewed as a numericalexperiment producing a series of non-empirical solutions, from first principles, for a virtualturbulent flow (see Figure 1). Its great strength is the ability to provide complete knowledge,unaffected by approximations, at all points within the flow, at all times within the simulationperiod. DNS is therefore ideal for addressing basic research questions regarding turbulencephysics and modelling. This ability, however, comes at a high price, which prevents DNS frombeing used as a general-purpose design tool.The defining characteristics of DNS stem from the distinctive characteristics of turbulence.Because turbulence is inherently unsteady and three-dimensional, DNS requires timedependentcalculations within a three-dimensional domain.? These two features are sharedwith LES (and therefore LES/RANS hybrid strategies such as detached eddy simulation(DES)). The unique feature of DNS is associated with the manner in which turbulence isaffected by viscosity. This is responsible for the two chief drawbacks of DNS – its extremecomputational cost, and severe limitation on the maximum Reynolds number that can beconsidered