A secondary flow approach to the inlet vortex flow field

Abstract

A theoretical study is presented of the fluid mechanics of the inlet vortex (or ground vortex) phenomenon. The vorticity field associated with the vortex is investigated using a secondary flow approach. In this approach the flow is assumed to be composed of an irrotational primary flow and a weak shear flow, with the vortex filaments associated with the latter being regarded as convected by the former. The potential flow field induced by the inlet-ground plane combination is computed using the panel method developed by · Hess, Mack and Stockman. Using the analysis, material lines (which coincide with vortex lines) can be tracked between a far upstream location, where this vorticity can be taken as known, and the engine face location. The deformation of the material lines thus shows directly the generation and amplification of the streamwise component of vorticity, which is responsible for the velocity distortion at the compressor face. Two representative flow configurations are considered, one with headwind only and one with the flow at forty-five degrees to the inlet axis of symmetry. Although the results so far yield only qualitative information, they appear to provide some insight into one mechanism associated with the inlet vortex formation.