GENERATION OF TURBULENT INFLOW DATA FOR SPATIALLY-DEVELOPING BOUNDARY-LAYER SIMULATIONS

A method for generating three-dimensional, time-dependent turbulent in flow data for simulations of complex spatially developing boundary lay ers is described, The approach is to extract instantaneous planes of v elocity data from an auxiliary simulation of a zero pressure gradient boundary layer. The auxiliary simulation is also spatially developing, but generates its own inflow conditions through a sequence of operati ons where the velocity field at a downstream station is rescaled and r e-introduced at the inlet, This procedure is essentially a variant of the Spalart method, optimized so that an existing inflow-outflow code can be converted to an inflow-generation device through the addition o f one simple subroutine. The proposed method is shown to produce a rea listic turbulent boundary layer which yields statistics that are in go od agreement with both experimental data and results from direct simul ations, The method is used to provide inflow conditions for a large ed dy simulation (LES) of a spatially evolving boundary layer spanning a momentum thickness Reynolds number interval of 1530-2150. The results from the LES calculation are compared with those from other simulation s that make use of more approximate inflow conditions, When compared w ith the approximate inflow generation techniques, the proposed method is shown to be highly accurate, with little or no adjustment of the so lution near the inlet boundary. In contrast, the other methods surveye d produce a transient near the inlet that persists several boundary la yer thicknesses downstream,Lack of a transient when using the proposed method is significant since the adverse effects of inflow errors are typically minimized through a costly upstream elongation of the mesh. Extension of the method for non-zero pressure gradients is also discus sed. (C) 1998 Academic Press.