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Etude expérimentale de la réduction de trainée par injection de bulles dans une couche limite turbulente décollée redéveloppée

Abstract : The bubbly drag reduction in turbulent flow is of significant interest in the navalindustry, particularly to reduce the viscous resistance of ships hulls. This thesis is focused onexperimental observations of the recovery region of a separated turbulent boundary layer in bothsingle-phase and bubbly flows. The experiments were performed in the Cavitation WaterTunnel of the French Navy Academy Research Institute. Air bubbles of intermediate size (0.4-1.3mm) were injected in the recovery region downstream of the recirculating region of a 2Dsquare obstacle (of height h = 16 mm) mounted at the upper wall of the tunnel. The single-phaseflow velocity field was characterized in the vertical plane using Particle Image Velocimetry(PIV) technique in 11 stream-wise measuring stations from upstream of the obstacle down to therecovery region. The gas-phase velocity field in the vertical plane, the gas volume fractiondistribution and the bubble size were characterized by means of Shadowgraphy. A maximumlocal viscous drag reduction DR of 35% is achieved for 6 m/s. The bubbly drag reduction ispromoted by the increase of the velocity and enhanced by increasing the air injection rate. Wesuggest that bubbles can induce a decorrelation between the stream-wise and wall normalfluctuating velocity in the inner layer, but most of the bubbly drag reduction is attributed to thewall normal fluctuating motion of the bubbles.
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  • HAL Id : tel-02591699, version 1

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Jishen Zhang. Etude expérimentale de la réduction de trainée par injection de bulles dans une couche limite turbulente décollée redéveloppée. Autre [cond-mat.other]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2019. Français. ⟨NNT : 2019ENAM0057⟩. ⟨tel-02591699⟩

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