Planar laser sheet visualization of oblique shock wave/vortex interaction

Abstract

Planar laser sheet visualizations of the flowfield generated by the interaction of a streamwise wing tip vortex and a strong oblique shock front at several distances downstream of a shock generating wedge were performed in a Mach 2.49 flow. The experimental scheme involved positioning a two-dimensional wedge surface downstream of a vortex generator wing section so that the wing-tip vortex interacts with the planar oblique shock front. The results of the investigation revealed an expansion of the vortex core in crossing a strong oblique shock front. The maximum vortex core diameter was seen to occur at a distance of 12.7 mm downstream of the wedge leading edge while at distances further downstream, the vortex core diameter remained approximately constant. The vortical structure was observed to persist along the entire chord of the shock generating wedge but was seen to diffuse with distances downstream of the wedge leading edge. Measurements of the vortex position relative to the wedge surface indicated that immediately downstream of the portion of a bulged-forward shock wave, the vortex axis was parallel to the direction of the freestream flow. On the other hand, the vortex was observed to travel parallel to the wedge surface at distances downstream of the wedge mid-chord position. The conical structure which forms as a result of vortex distortion was found to be sensitive to downstream disturbances in a manner similar to the incompressible vortex breakdown. INTRODUCTION A problem of considerable importance in the study of external and internal aerodynamics is the interaction between coneen&ated streamwise vortiees-and shock Copyright O 1996 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. * Associate Professor, Department of Mechanical, Aerospace and Manufacturing Engineering, Member AIAA. ** Graduate Research Fellow, Department of Mechanical, Aerospace and Manufacturing Engineering, Currently NRC Fellow, NASA Langley Research Center Hampton Virginia, Student Member AIAA. fronts, hi practice, such encounters may involve interaction of vortices generated by forward sections of a supersonic aircraft or missile with shock waves formed over aft components of the vehicle, or shock waves present in the air intake system, leading to performance deterioration of the vehicle. In internal flows, shock wave/vortex interaction leading to vortex breakdown has been suggested to be a potential candidate for fuel-air mixing enhancement in the combustor of a supersonic combustion ramjet (scramjet). Despite the practical importance of the shock wave/vortex interaction problem, relatively few experimental and numerical studies of the problem have been attempted. Previous studies of the shock wave/vortex interaction problem have included interaction of streamwise vortices with both normal and oblique shock Moreover, these investigations have been carried out primarily in an attempt to develop vortex breakdown criteria based on vortex strength and shock wave intensity. In summary, the results of previous shock wave/vortex interaction studies have indicated a significant dependence of the problem on the shock wave strength, vortex intensity and the Mach number distribution of the incoming vortex. Of particular interest to the present investigation is the interaction of supersonic wing-tip vortices exhibiting a wake like axial Mach number distribution with otherwise planar and oblique shock fronts. Previous studies' have indicated formation of a subsonic conical structure surrounded by a conical shock wave for both oblique and shock waves alike. The length scale associated with the size of the subsonic region has been found to be on the order of subsonic flow-downstreanrof~ the original shock for the shock interaction, and the approaching vortex core diameter for the oblique shock interactions. In addition, flow visualization by means of spark shadowgraphs during the oblique