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Detached-Eddy Simulations (DES) of flows over clean and controlled cavities with and without doors are presented in this paper. Mach and Reynolds numbers (based on cavity length) were 0.85 and one million respectively. Spectral analyses showed that the DES computations were able to correctly predict the frequencies of the Rossiter modes for both uncontrolled and controlled cases. Flow visualisations revealed that the impact of the shear layer formed along the cavity on a slanted aft wall no longer creates a large source of acoustic noise. Therefore little acoustic propagation was seen up the cavity. This was confirmed by the analysis of the cavity wall forces, which showed that the oscillations of the shear layer were reduced when the wall was slanted. This aided in reducing the overall Sound Pressure Levels throughout the cavity and far-field. Comparisons of the flow-fields suggested that the addition of the doors also aided in stabilising the shear layer, which was also shown in the analysis of the wall forces. As a result, the addition of the doors was found to affect the clean cavity configuration significantly more than the controlled one.

The implementation of internal store carriage on stealthy military aircraft has accelerated research into transonic cavity flows. Depending on the freestream Mach number and the cavity dimensions, flows inside cavities can become unsteady, threatening the structural integrity of the cavity and its contents (e.g., stores, avionics, etc.). Below a critical length-to-depth ratio, the shear layer formed along the cavity mouth has enough energy to span across the opening. This shear layer impacts the downstream cavity corner and the generated acoustic disturbances propagate upstream, causing further instabilities near the cavity front. Consequently, a self-sustained feedback loop is established. This extreme flow environment calls for flow control ideas aiming to pacify the cavity by breaking the feedback loop and controlling the breakdown of the shear layer. This is the objective of the present work, which aims to assess changes of the cavity geometry and their effect on the resulting flow using detached-eddy simulation. For the cases computed in this work, quantitative and qualitative agreement with experimental data has been obtained. All of the devices tested achieved similar reductions in overall sound pressure level in the rear half of the cavity; however, a slanted aft wall provided the largest noise reduction in the front half of the cavity. Nomenclature A = wall area, m 2 a i t = temporal eigenfunctions C F = force coefficient D = cavity depth, m F, G, H = spatial flux vectors in Navier-Stokes equations f = frequency, Hz L = cavity length, m N = number of snapshots for proper orthogonal decomposition p = pressure, Pa p 0 = unsteady pressure, Pa Q = unsteady terms in Navier-Stokes equations q 1 = freestream dynamic pressure ( 1 2 1 U 2 1 ), Pa Re = Reynolds number Re L = Reynolds number based on cavity length L S = symmetric components of the velocity gradient tensor [Eq. (7)] S = source vector in Navier-Stokes equations [Eq. (1)] T Rossiter1 = time period of the lowest Rossiter mode, s t = time, s u = velocity, m=s x, y, z = Cartesian coordinates, m i = matrix eigenvalues = density, kg=m 3 i x = spatial eigenfunctions = antisymmetric component of the velocity gradient tensor Subscripts rms = root mean square m = mean quantity 1 = freestream value Superscripts inv = inviscid term vis = viscous term

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