Modeling of leading edge vortex burst

Abstract

The burst of leading edge vortex (LEV) is investigated by a modified quasi-cylindrical approximation (MQCA) for the sub-core of the vortex. By assembling LEV with the MQCA and evaluating the total pressure drop along the sub-core of LEV, a model for predicting the location of LEV burst is proposed. The present model demonstrates a close consistency with the experimental results. The study shows that the location of burst can be affected by the axial flow within the sub-core and the inlet diameter of the sub-core near the apex, angle of attack, leading-edge sweep angle and Reynolds Number. INTRODUCTION The location of leading edge vortex (LEV) burst will largely affect the aerodynamic load acting on the wing with high sweep angle. This burst location has been taken as an internal state parameter in some modern aerodynamic models, with which to successfully represent the global aerodynamic characteristics of air vehicle when LEV burst involved. The prediction of the vortex burst location becomes an important factor in aerodynamic load estimation, especially for the maneuvering case with LEV burst over wing surface at high angle of attack. . Many significant approaches have been done to understand this complicated flow and disclosing the mechanisms of LEV burst. Based on analogizing a filament pipe in the sub-core as a modified quasi-cylindrical * Copyright © 2001 The American Institute of Aeronautics and Astronautics Inc. All rights reserved. 1 Ph. D cadidate Senior Research Officer, Associate Fellow AIAA 1 American Institute of Aeronautics and Astronautics approach, a simple concept is proposed in this paper for investigation of the vortex burst. LEV burst is assumed as following stages within a very short time interval i.e. 1, flow acceleration by vortex inducement, 2, flow deceleration and related blockage by viscous friction, 3, total pressure recovery and, finally, the burs. The criterion of LEV burst used here is by evaluating the total pressure drop along the filament pipe in the sub-core. As an example, vortex burst on a 65 degree delta wing is estimated with this concept. LEV SUB-CORE FLOW MODEL Leading-edge vortex develops from leading edge boundary-layer separation and then rolls up to upper surface of the wing. Its structure is sustained by a continuous vorticity feeding along the leading edge and concentrate into a steady vortex structure until burst take place. Pressure and axial velocity in LEV A simplified longitudinal section of the LEV is shown in Fig. 1. In most cases, the vortical structure is in a form of swirling flow having a nearly cylindrical shape. The sub-core can be approximately assumed as an axis-symmetric flow along the vortex centerline. Under cylindrical coordinate system, the vortex flow could be represented by the following equations with axial velocity Vx(r), tangential velocity V^f r ) and radial velocity Vr( r ) components: (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.