Control of 3D turbulent boundary layer separation caused by a wing-body junction

In three-dimensional flows, boundary layer separation leads to the formation of vortical structures formed by the rolling up of the viscous flow sheet previously confined in a thin layer attached to the wall. Several characteristics of the vortex flow development have negative effects; for example, it may be responsible for unsteadiness or generating unwanted vibration or noise. There are several ways to alter the properties of the vortex or to eliminate it as an organized structure. The objective of this paper is to present two different vortex control approaches. The first solution involves a modification of the pressure field induced by the obstacle by altering its geometry with a strake. The second solution, which can be called active control, consists of suction through an aperture located near the separation line. In this study, we have considered the incompressible three-dimensional boundary layer separation induced by an obstacle mounted perpendicular to a flat plate. The tests were conducted in the F2 subsonic wind tunnel of the ONERA Fauga-Mauzac center. The test section has a cross sectional area of 1.8 x 1.4 m(2) and the upstream velocity of the flow was 50 m/s. The surface flow properties have been characterized by using a viscous coating which allows the visualization of the skin friction line patterns. The essential part of the study has been devoted to Laser Doppler Velocimetry (LDV measurements. The plane of symmetric flow ahead of the leading edge has been qualified by using 3D laser velocimetry in the forward scatter mode. Results show that the geometrical extent of the separation region is reduced and the primary separation line is much closer to the model's leading edge when considering the configuration with a strake. Using an active control system, with suction through a hole located in the plane of symmetry in front of the obstacle's leading edge, the vortex size is reduced and its location displaced towards the origin of the obstacle. (C) 1998 Published by Elsevier Science Inc. All rights reserved.