Selected Eddy Simulation (SES): A non-DNS approach with Navier-Stokes dynamics at all scales*

Direct Numerical Simulations (DNS) resolve all dynamically relevant modes of turbulent flows and have, thus, become indispensable to fundamental turbulence research despite its high computational cost at high Reynolds numbers. To reach realistic conditions, though, one still needs less expensive (and less accurate) methods like Large Eddy Simulation that resolves only the large scales and models the small scales. This presents a challenge in flows where small-scale physics is dominant, like reacting species.  

We present a novel method, named Selected Eddy Simulation (SES), that resolves a subset of modes across the entire spectrum and models the complementary set. Our investigation is in the selection and modeling of unresolved modes which can generally be tailored to particular problems. We compare results from SES of isotropic turbulence at different Reynolds numbers to DNS and show that we can obtain the entire spectrum and a number of important statistics with high degree of accuracy with as low as 10% of modes. Effects of modeling methods, and the fraction and distribution of unresolved modes, and their variation with Reynolds number are discussed.