Gouttes et films liquides en aérodynamique automobile

Abstract : The aim of this work is to contribute experimentally to the development of a liquid film model in automobile aerodynamics. We present here typical experiments on flow of drops and liquid films relevant to industrial situations. The dynamics of liquid films and drops on a car windscreen under a rainy weather are very important for safety issues. We describe in a first part the flow of a liquid film on an inclined glass substrate. This study leads us to develop an original technique for measuring liquid film thicknesses and waves speeds. We characterize the falling film flow and highlight different wave development regimes. When a counter-current airflow is added, we characterize the critical flooding regime at the transition from a flow driven by gravity to a film entrained by the airflow. This gas-liquid flow configuration is particularly unstable due to wetting conditions and leads in general to drops, meandering rivulets and puddles. We focus in the second part of this study on the dynamics of drops. We show that due to the hysteresis of the contact angle, the drops start to move beyond a certain wind velocity. The drops dynamics is then predicted as a function of three non-dimensional numbers, which take into account viscous, aerodynamics, gravity and capillary forces. We also show that the contra-intuitive recirculation inside the drops is very slow; thus the drag coefficient depends essentially on the shape of the drop. We finally describe the evolution of droplet shape and the interaction between neighboring droplets.
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Submitted on : Thursday, November 25, 2010 - 11:51:53 AM
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  • HAL Id : pastel-00539839, version 1

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Ady Kevin Njifenju. Gouttes et films liquides en aérodynamique automobile. Milieux fluides et réactifs. Université Pierre et Marie Curie - Paris VI, 2010. Français. ⟨pastel-00539839⟩

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