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Analyse et contrôle de l'écoulement turbulent affleurant une cavité profonde

Abstract : Deep cavities are present in many industrial processes. The aero-acoustic coupling and the high increase in the skin friction coefficient downstream from the cavity results in resonance of high pressure level as well as strong vibration and structural fatigue. The present experimental investigation shows the effect of a deep cavity on a turbulent boundary layer. A control device using spanwise cylinder is conducted. LDV measurements, conducted in a water tunnel, evidenced that the skin friction coefficient increases downstream from the cavity. With same flow conditions, drag increase is lower for deep cavities than for shallow ones studied in the literature. The high values of skewness and flatness coefficients are related to intermittent ejections of flow from the downstream part of the cavity. This hypothesis was confirmed thanks to PIV measurements. Pressure measurements are conducted in two large deep cavity configurations (L/H = 0.2 et 0.41) in a large wind tunnel. Oscillations of discrete frequencies are produced inside the cavity when the free-stream velocity becomes higher than a minimum value which depends on the cavity length L. The hydrodynamic mode of the cavity shear layer is well predicted by the Rossiter model the convection velocity is measured and when the empirical time delay is neglected. Time-resolved PIV measurements show that for L/H = 0.2 and U₀ = 43 m/s only one vortical structure is formed at the cavity leading edge. This vortex grows while convecting downstream along the shear layer. A cylinder placed spanwisely near the cavity leading edge removes the resonance and highly modifies the behavior of the shear layer flow. Reductions in sound pressure levels (SPL) of up to 36 dB is obtained for optimal position of 1.67 diameter of the cylinder from the wall. Moreover, a shaped cylinder was also studied and shows that the attenuation of tones is not due to high frequency pulsing as suggested in literature, but to higher stability of the shear layer due to the change in the mean axial velocity profiles and the increase in the shear layer thickness.
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Submitted on : Tuesday, November 17, 2020 - 2:23:34 PM
Last modification on : Friday, November 27, 2020 - 5:04:48 PM


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Mouhammad El Hassan. Analyse et contrôle de l'écoulement turbulent affleurant une cavité profonde. Mécanique des fluides [physics.class-ph]. Université de Valenciennes et du Hainaut-Cambrésis, 2008. Français. ⟨NNT : 2008VALE0019⟩. ⟨tel-03009826⟩



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