Étude expérimentale d'un jet plan turbulent se développant dans un flux uniforme en co-courant

Abstract : This experimental study focuses on the measurement and analysis of the behaviour of a vertical, downwardblowing plane jet when it develops inside a uniform co-flowing stream. The ratio r between the velocities of the co-flow and the jet is considered in the range [0, 0.3] which includes the case of the classical plane jet without co-flow (r = 0). The motivation of the study was to develop a specific knowledge on air curtains classically used for the control of cold and clean local environments in the food industry. This study focuses on the isothermal case, with no temperature difference between the jet and the co-flow, the non-isothermal cases being only introduced in the last chapter (Chapter IV) in view of further studies on the high Richardson number cases. The study is turbulence-oriented, with an analysis mainly based on quantities and properties related to turbulence, like the Reynolds stresses profiles and the characteristic scales. The analysis of the evolution of the mean quantities, in particular the expansion of the mean velocity profile, was conducted in relation with their dependence on turbulence. The main measurement technique used was ×-wire Hot Wire Anemometry operated in Constant Temperature mode (CTA). Particle Image Velocimetry (PIV) was used for the reduced investigations on non-isothermal cases, in Chapter IV, taking advantage of its insensitivity to temperature. The experiment was carried out in a specific vertical wind tunnel, the test section of which had an effective length of two meters (Chapter II). The initial literature review (Chapter I) highlights the specificities of plane jets as regards the mean and turbulent behavior. In (Chapter III), the isothermal case is studied with a special focus on the influence of the velocity ratio r and the Reynolds number. It is shown that choosing a global normalization to describe the behaviour of the jet leads to a generic model valid for the entire set of eleven different conditions investigated. The model appears to correctly account for the influence of the ratio r on the evolution of the mean velocity on the axis, the expansion of the thickness of the jet and the evolution of rms velocity fluctuations. The model gives, in addition, a means to assess, for r = 0, the characteristics of the limit case of a plane jet without co-flow. The thorough set of data obtained with ×-wires probes finally enables, at the end of chapter III, an analysis of the characteristic turbulence scales in that specific flow. It appears that the integral scales are in direct relation with the jet thickness and that the Kolmogorov scales are linked to the integral scales through a universal scale ratio depending on the local Reynolds number.
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Jean Youssef. Étude expérimentale d'un jet plan turbulent se développant dans un flux uniforme en co-courant. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2012. Français. ⟨NNT : 2012ESMA0022⟩. ⟨tel-00784840⟩

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