A robust method for generating inflow conditions for direct simulations of spatially-developing turbulent boundary layers

A method for generating inflow conditions for direct numerical simulations (DNS) of spatially-developing turbulent boundary layers is presented. The method is a modification of that of Lund et al. [J. Comput. Phys. 140 (1998) 233]. The approach of Lund et al. is based on having an auxiliary simulation (Code-A) in a three-dimensional domain similar to that of the main simulation (Code-B). The instantaneous velocity field on a selected plane in Code-A is used as the instantaneous inflow conditions for Code-B. The inflow conditions for Code-A are generated through a sequence of operations in which the velocity field at a downstream station is rescaled and re-introduced at the inlet plane. Our present method modifies the operations in Code-A by introducing a set of additional steps preceding the rescaling process. This set involves imposing at the inlet plane an appropriate spectrum E(k) for the turbulence kinetic energy (TKE) and a condition for insuring that the statistical correlation 〈u1′u3′〉 between the streamwise and vertical velocity fluctuations retain a non-vanishing magnitude. This modification is essential for sustaining the production rate of TKE near the wall throughout the domain. Our DNS results obtained with the new modification are in excellent agreement with the experimental data of DeGraaff and Eaton [J. Fluid Mech. 422 (2000) 319] for Reθ=1430.