Numerical Simulation Of The Unsteady Cavity Flow Features

In recent years, Compressible cavity flow has numerous applications in aerospace engineering, for example, aircraft weapon bays and wheel wells. In addition, it involveds many complex problems, including unsteady flow, vortex dynamics and acoustics-vortex interation, ect, which can have adverse effects on the aircraft performance and stability.Therefore, it is important to study the cavity flow in both fluid dynamics points and engineering points of view.In this paper, the steady N-S equations are solved numerically employing Spalat-Allmaras One-Equation turbulence model: spatial discretization is performed with cell-centered finite volume method and the five-stage Runge-Kutta explicit scheme is used for time marching. The unsteady N-S solver is achieved by using the dual time-stepping approach, and then the DES method based on Spalat-Allmaras model is sdudied. Both the Spalat-Allmaras and the DES model are used to simulate the cavity flow, and the computed results from the DES model agree better with experimental data.Based on the unsteady N-S solver, the present work is mainly focused on the following aspects: First, numerical simulations of two and three dimensional cavity flows are performed in the paper. The pressure histories, the pressure distributions and the streamlines on the center plane, demonstrate that the spanwise flow seems to simplify the streamwise vortex structure inside the cavity and therefore attenuates the pressure fluctuation. However, the pressure evolution is more irregular and unpredictable due to the contribution of the spanwise circulation of the fluid. Second, the Mach number effects on cavity flow characteristics are studied.The results show that the variety of Mach numbers can cause the change of the cavity flow field type; cavities of certain length-to-depth ratio will tend to open type with the increase of the Mach numbers. Third, twin, closely spaced cavities are studied to understand the physics of the interaction mechanisms between them. The important results emerged from this study: when twin cavities are placed in close proximity they exhibit coupled resonant instability modes that can be distinct from those produced by each cavity resonating by itself,'coupling'is a phenomenon that occurs when both cavities exhibit instabilities that have the same frequency of oscillation. Finally, the Aerodynamic characteristics of the DLR-F6 aircraft with a cavity is revealed,numerical simulations show that the cavity makes the lift decrease ,the drag increase and, moreover, the flow field becomes more complex .