Numerical Simulation of Flow over an Open Cavity with Self-Sustained Oscillation Mode Switching

Takashi Yoshida,Takashi Watanabe

doi:10.4236/ojfd.2016.64027

Abstract

Numerical simulations are used to investigate the self-sustained oscillating flows past an open cavity. The two-dimensional incompressible Navier-Stokes equations are solved directly by using the finite difference method for cavities with an upstream laminar boundary layer. A series of simulations are performed for a variety of cavity length-to-depth ratio. The results show the switching among some flow modes including non-oscillation mode, shear layer mode and wake mode. The variation of the Strouhal number is in favorable agreement with available experimental data. The results of flow fields in the cavity reveal the relationship between the cavity shear layer oscillation modes and recirculating vortices in the cavity.

Highlights

Flows over open cavities occur in a wide variety of aerospace and engineering applications, for example, the landing systems of aircrafts, sunroofs and windows of automobiles, and spaces between bullet train cars
As will be discussed in sec. 3.2 about the difference between the mode III and the wake mode predicted in the present study, the shear layer in the mode III oscillats on the multiple recirculating vortices in the cavity, while the flow in the wake mode has a vortex that expands to nearly entire cavity and sheds from the cavity in a long time period
Though the shear layer is disturbed by the ejection and the flow pattern is different from those in mode II and mode III, the shape of the shear layer is consistent with the dye visualization result of Figure 7 of Gharib and Roshko [5]

Summary

Introduction

Flows over open cavities occur in a wide variety of aerospace and engineering applications, for example, the landing systems of aircrafts, sunroofs and windows of automobiles, and spaces between bullet train cars. Cavity flow is of interest, because the presence of cavity causes selfsustained oscillations of the separated shear layer by a complex feedback mechanism, despite its geometrical simplicity. Rockwell and Naudascher [1] classified the flowinduced cavity oscillations and the feedback mechanism into fluid-dynamic and fluidresonant. Incompressible flows such as low-Mach number air flows, low-speed water flows over an open cavity are classified as fluid-dynamic oscillations.

Methods

Results

Conclusion