Effect of Flow Oscillations on Cavity Drag and a Technique for Their Control.

Data assimilation of mean velocity from 2D PIV measurements of flow over an idealized airfoil

“…The test section measures 1.6 m in length, 0.46 m in width and 0.5 m in height and the airfoil is mounted vertically so that its span is parallel to the test section height. The flow is conditioned by a perforated plate, a honey-comb mesh, three turbulencereducing screens and a 4-to-1 fifth-order-polynomial contraction (Gharib 1983). The free-stream velocity is 8.1 cm/s and the free-stream turbulence intensity is less than 0.1% at the centerline.…”

“…A large body of work has attempted to investigate this problem which has its roots in the experiments of Strykowski and Sreenivasan (1990), who showed experimentally that for low Reynolds numbers, a small control cylinder inserted in the wake behind a larger cylinder can completely suppress vortex shedding. Numerical studies including Giannetti and Luchini (2007) and Marquet et al (2008) looked at the sensitivity of the cylinder instability to base flow modification and steady forcing near the critical Reynolds number of 47. Meliga et al (2012) and Mettot and Sipp (2014) expanded this framework to higher Reynolds numbers and determined how a small control cylinder could impact the frequency of vortex shedding as predicted by the most unstable global mode of the mean flow.…”

Cavity-based flameholding for chemically-reacting supersonic flows

“…The boundary condition imposed by the cavity length effectively constrains shear layer development and fluid entrainment. Additionally, reasonable cavity length-todepth ratios, i.e., L/Do7-10, resulting in a shear layer that spans the cavity -'open' cavities -prevent the possible transition to large-scale shear layer instabilities that could lead to enhanced bulk mixing but at the expense of increased drag [24,25]. However, even for longer cavities such a transition is less likely due to the increased hydrodynamic stability of the shear layer at the high freestream Reynolds and Mach numbers to be encountered in supersonic combustors [76].…”

Analysis of flow structures in cavity flow with modifications to cavity geometry

“…These oscillations are in turn associated with the presence of a distinct fundamental frequency, which is amplified by the shear layer. Below the minimum cavity length, the shear layer bridges smoothly over the cavity with no distinct oscillation in it [5]. With this minimum cavity length criteria attained, the disturbance can undergo a minimum integrated amplification between separation and impingement.…”

“…At high freestream Mach number of 0.8, intense tonal sounds of cavities can reach 160dB [4]. At freestream Mach number of 0.2, large-amplitude pressure pulses can occur in gas transport systems with closed side branches [5][6].…”