COMPUTATIONAL STUDY OF VISCOUS EFFECTS ON LOBED MIXER FLOW FEATURES AND PERFORMANCE

This article describes a computational study of viscous effects on lob ed mixer flowfields. The computations, which were carried out using a compressible, three dimensional, unstructured-mesh Navier-Stokes solve r, were aimed at assessing the impacts on mixer performance of inlet b oundary-layer thickness and boundary-layer separation within the lobe. The geometries analyzed represent a class of lobed mixer configuratio ns used in turbofan engines. Parameters investigated included lobe pen etration angles From 22 to 45 deg, stream-to stream velocity ratios fr om 0.5 to 1.0, and two inlet boundary-layer displacement thicknesses. The results show quantitatively the increasing influence of viscous ef fects as lobe penetration angle is increased. It is shown that the sim ple estimate of shed circulation given by Skebe et al. (Experimental I nvestigation of Three-Dimensional Forced Mixer Lobe Flow Field, AIAA P aper 88-3785, July, 1988) can be extended even to situations in which the flow is separated, provided an effective mixer exit angle and heig ht are defined. An examination of different loss sources is also carri ed out to illustrate the relative contributions of mixing loss and of boundary layer viscous effects in cases of practical interest.