CONSTRUCTION OF INLET CONDITIONS FOR LES OF TURBULENT CHANNEL FLOW.

Implementation of boundary conditions for LES is a serious problem. Whilst a great deal of efiort has been expended investigating wall boundary conditions, much less has been done on the equally problematic issue of inlet boundaries. On a mechanistic level this involves creating a time-varying inlet velocity with mathematical properies that ensure that it is compatible with the Navier-Stokes equations : on a physical level the inlet ∞ow should behave like a turbulent ∞ow. In this paper we concentrate on the simplest possible problem of turbulent channel ∞ow between two inflnite planes. Three difierent inlet conditions are tested : i. a Fourier synthesis technique, ii. a precomputed library technique and iii. a mapping technique to create an inlet section to the computational domain. Downstream of the inlet, proflles of the various moments of velocity are compared, and the structure of the turbulent ∞ow throughout the computational domain is analysed. Technique iii. is the most straightforward to use, but technique i. provides the possibility of tailoring the inlet turbulence conditions.