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Étude expérimentale du frottement pariétal instationnaire

Abstract : The aim of this thesis is to find out experimentally the temporal evolution of unsteady skin friction in the presence of a propagation of pressure wave. The transient flow is obtained downstream sudden valve closure. The experimental study of the transient flow is carried out by Ultrasonic pulsed Doppler velocimetry to measure the instantaneous velocity profiles and by the polarographic method to determine the local skin friction. These measurements made it possible to highlight the effect of the waves of pressure on the velocity profiles and skin friction. The results made it possible to show that the quasi-steady approach to determine the unsteady friction is valid only if the characteristics of the flow vary little. When the flow is subjected to strong accelerations and decelerations, this approach is not applicable. This study made it possible to confirm all while specifying them, certain models based on the instantaneous acceleration. The analysis of the results shows that the empirical coefficient of the instantaneous acceleration used in many models depends closely on the nature of the transient event, of the intensity of accelerations or decelerations and the time. It is shown that the scale of time of a transient event is an essential parameter of which it is necessary to hold account for a better prediction of skin friction in a transient flow
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Hamid Zidouh. Étude expérimentale du frottement pariétal instationnaire. Mécanique [physics.med-ph]. Université de Valenciennes et du Hainaut-Cambrésis, UVHC, (France), 2007. Français. ⟨NNT : 2007VALE0045⟩. ⟨tel-02997730⟩

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