Effect of Aspect Ratio on the Three-Dimensional Global Instability Analysis of Incompressible Open Cavity Flows F. Meseguer-Garrido * , J. de Vicente, E. Valero and V. Theofilis † School of Aeronautics, Universidad Polit´ ecnica de Madrid, Pza. Cardenal Cisneros 3, E-28040 Madrid, Spain Abstract The stability analysis of open cavity flows is a problem of great interest in the aeronautical industry. This type of flow can appear, for example, in landing gears or auxiliary power unit configurations. Open cavity flows is very sensitive to any change in the configuration, either physical (incoming boundary layer, Reynolds or Mach numbers) or geometrical (length to depth and length to width ratio). In this work, we have focused on the effect of geometry and of the Reynolds number on the stability properties of a three- dimensional spanwise periodic cavity flow in the incompressible limit. To that end, BiGlobal analysis is used to investigate the instabilities in this configuration. The basic flow is obtained by the numerical integration of the Navier-Stokes equations with laminar boundary layers imposed upstream. The 3D perturbation, assumed to be periodic in the spanwise direction, is obtained as the solution of the global eigenvalue problem. A parametric study has been performed, analyzing the stability of the flow under variation of the Reynolds number, the L/D ratio of the cavity, and the spanwise wavenumber β. For consistency, multidomain high order numerical schemes have been used in all the computations, either basic flow or eigenvalue problems. The results allow to define the neutral curves in the range of L/D = 1 to L/D = 3. A scaling relating the frequency of the eigenmodes and the length to depth ratio is provided, based on the analysis results. Nomenclature L Length of the cavity. D Depth of the cavity. L z Periodicity length on the spanwise direction. β Spanwise wavenumber. ω Complex eigenvalue in the temporal analysis. Re Reynolds number. Unless otherwise noted, based on the depth of the cavity. St Dimensionless frequency of the eigenmode. σ Amplification/damping rate of the disturbance. δ 0 Incoming boundary layer thickness. δ 1 Boundary layer thickness at the upstream corner of the cavity. ¯ q basic flow component ˆ q perturbation component * Correspondence to: fernando.meseguer@upm.es † Research Professor, Associate Fellow AIAA 1 of 17 American Institute of Aeronautics and Astronautics 6th AIAA Theoretical Fluid Mechanics Conference 27 - 30 June 2011, Honolulu, Hawaii AIAA 2011-3605 Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.