When a wall incurves abruptly, as the rear glass of a car does, the flow is not able to follow the shape of the wall and separates from it: there is flow detachment. Flow separation is involved in many aeronautic applications. The flight domain of an aircraft as well as the working limits of its engines can be limited by this phenomena. That is why studies focus on understanding and predicting flow detachment.
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Strongly detached flow in Onera's hydrodynamic tunnel Thales
The example given in the above picture is related to an experimental study conducted in the Thales hydrodynamic water tunnel. The detachment of the flow leads, close to the lateral walls of the test section, to the formation of a vortex that can be visualized injecting micro air bubbles (on the above picture). Measurements in the flow of mean velocity, pressure or turbulence allow us to constitute a database, useful in the validation of computation codes developed to predict such complex flows. This experimental study takes place in the framework of DESider European project [web site].
Detail of the sloping region of the bump used to cause the flow detachment