Engine Inflow Boundary Conditions for Specification of Mass Flow

Abstract

Two engine inflow boundary conditions with direct specification of the integral quantities massflow and WAT respectively are formulated and implemented in the DLR Tau-code. For the formulation a summary of characteristic theory for the Euler equations is given, followed by the application of this theory to the derivation of several permeable boundary conditions with various flow quantities specified on the inflow surface. It is noted that the specification of a single integral quantity on the inflow face is insufficient to prescribe the flow there fully, and a remedy is proposed whereby the massflow distribution over the inflow boundary is obtained from the boundary near points. It is shown that this method is more efficient than specification of massflow by iteration on the inflow pressure, and has also less user-defined parameters. Similar results for the WAT boundary condition are given. Finally the relevant parameter settings as implemented in Tau are described, and best-practice guidelines are given on the use of the new boundary conditions.