Statistics of the Navier-Stokes-alpha-beta regularization model for fluid turbulence

We explore one-point and two-point statistics of the Navier-Stokes-alpha-beta regularization model at moderate Reynolds number in homogeneous isotropic turbulence. The results are compared to the limit cases of the Navier-Stokes-alpha model and the Navier-Stokes-alpha-beta model without subgrid-scale stress, as well as with high resolution direct numerical simulation. After reviewing spectra of different energy norms of the Navier-Stokes-alpha-beta model, the Navier-Stokes-alpha model, and Navier-Stokes-alpha-beta model without subrid-scale stress, we present probability density functions and normalized probability density functions of the filtered and unfiltered velocity increments along with longitudinal velocity structure functions of the regularization models and direct numerical simulation results. We highlight differences in the statistical properties of the unfiltered and filtered velocity fields entering the governing equations of the Navier-Stokes-alpha and Navier-Stokes-alpha-beta models and discuss the usability of both velocity fields for realistic flow predictions. The influence of the modified viscous term in the Navier-Stokes-alpha-beta model is studied through comparison to the case where the underlying subgrid-scale stress tensor is neglected. The filtered velocity field is found to have physically more viable probability density functions and structure functions for the approximation of direct numerical simulation results, whereas the unfiltered velocity field is found to have flatness factors close to direct numerical simulation results.