Yiyang Sun

Width and sidewall effects on high speed cavity flows

The present work examines the influence of cavity width, sidewall boundary conditions, free stream Mach numbers, and Reynolds numbers on open rectangular cavity flows. Threedimensional direct numerical simulations and large eddy simulations are performed for open-cavity flows with length-to-depth ratio L/D = 6, width-to-depth ratio W/D = 1 and 2 for Reynolds number of ReD = 500 and 10 . To numerically examine the effects of sidewall on the flows, we consider (1) two-dimensional cavities with spanwise periodicity and (2) finite-span cavities with no-slip adiabatic walls. Furthermore, the analyses are conducted for subsonic (M∞ = 0.6) and supersonic (M∞ = 1.4) speeds to reveal compressibility effect on the base flow. Companion experiments are carried out for sidewall-to-sidewall and finitespan cavities in the subsonic and supersonic wind tunnels at similar operating conditions but with ReD ∼ 10. We find that at low ReD, widening the cavity can decrease the velocity fluctuations of the flow by introducing spanwise variations in the flow fields. For turbulent flows at M∞ = 0.6 and 1.4, the spanwise variations in the flow fields are also captured, but the influence of cavity width on velocity fluctuations is moderate, as the dominant spanwise fluctuations are triggered from turbulent mixing. However, streamwise velocity fluctuations decrease in the finite-span cavity compared to the cavity with spanwise periodic boundary condition.

Numerical Simulations of Subsonic and Transonic Open-Cavity Flows

Two-dimensional open-cavity flows for free stream Mach number of 0.1 to 1.6 are investigated with direct numerical simulations for cavities of aspect ratio 2 and 6 to characterize the flow stability. We determine the neutral stability curve over a wide range of Mach numbers and Reynolds numbers. In particular, we examine the effects of compressibility on the flow in transonic regime at low Reynolds numbers. Rossiter modes are identified by spectral analysis. The corresponding spatial structures associated with the dominant and subdominant Rossiter modes are extracted with dynamic mode decomposition. The nature of these structures provides us insight to their contribution to instability of the flow. The interaction between the shock waves and the shear layer modes for the transonic flows are investigated.

Biglobal instabilities of compressible open-cavity flows

The stability characteristics of compressible spanwise-periodic open-cavity flows are investigated with direct numerical simulation and biglobal stability analysis for rectangular cavities with aspect ratios of

Spanwise effects on instabilities of compressible flow over a long rectangular cavity

L/D=2

Active attenuation of a trailing vortex inspired by a parabolized stability analysis

and 6. This study examines the behavior of instabilities with respect to stable/unstable steady states in the laminar regimes for subsonic and transonic conditions where compressibility plays an important role. It is observed that an increase in Mach number destabilizes the flow in the subsonic regime and stabilizes the flow in the transonic regime. Biglobal stability analysis is conducted to extract 2D and 3D eigenmodes for prescribed spanwise wavelengths about the 2D steady state. The properties of 2D eigenmodes agree well with those observed in the 2D nonlinear simulations. In the analysis of 3D eigenmodes, it is found that an increase of Mach number stabilizes dominant 3D eigenmodes. For a short cavity with

Suppression of Cavity Oscillations via Three-Dimensional Steady Blowing

L/D=2

Effects of sidewalls and leading-edge blowing on flows over long rectangular cavities

, the 3D eigenmodes primarily stem from centrifugal instabilities. For a long cavity with

Resolvent Analysis of Compressible Flow over a Long Rectangular Cavity

L/D=6

3D Printing of Fluid Flow Structures

, other types of eigenmodes appear whose structures extend from the aft-region to the mid-region of the cavity. A selected number of 3D DNS are performed at

Effects of spanwise instabilities on the suppression of wake mode in flow over a long rectangular cavity

M_\infty=0.6