Analyse physique d'écoulements décollés fortement tridimensionnels par expérimentation. Structuration spatio-temporelle et sensibilité à une turbulence amont

Abstract : This work aims to study conical vortices generated from a generic model representing the A-pillar of an automotive vehicle. This vortex structure is responsible of strong fluctuations on the side window and generates noise in the cabin. As these vehicles are subjected to the turbulent wind, the sensitivity of vortex structure dynamics to an upstream turbulence was studied by adding a grid at the test section entrance of the wind tunnel.The spatial and temporal properties of the velocity fields and the wall pressure were studied by simultaneously combining High Speed Stereo-PIV and wall fluctuating pressure measurements with distant sensors. It is shown that a moderate level of upstream turbulence (6% of intensity) results in a very significant change of the vortex dynamics and the associated wall fluctuating pressure. Our assumption is that in the absence of external turbulence, the main Cp’ contributionis linked to the footprint of the vortex core and of the induced secondary separation. On the contrary, in the presence of upstream turbulence, the strong increase of Cp’ seems to be associated with a global response of the vortex structure. The study of the spatio-temporal dynamics withpressure-velocity correlations allowed highlighting the strong coupling between the dynamics ofthe shear layer and of the core of the vortex structure. Thus, there is a modulation of the flapping frequency of the vortex controlled by the geometry of the model and by the characteristics ofthe upstream turbulence (intensity and integral length scale).
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Faisal Affejee. Analyse physique d'écoulements décollés fortement tridimensionnels par expérimentation. Structuration spatio-temporelle et sensibilité à une turbulence amont. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2015. Français. ⟨NNT : 2015ESMA0008⟩. ⟨tel-01226473⟩

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