Effect of the Laminar Separation Bubble Induced Transition on the Hydrodynamic Performance of a Hydrofoil
Résumé
The present study deals with the effect of the laminar separation bubble (LSB) induced transition on the lift, drag and moment coefficients of a hydrofoil. A 2D numerical study, based on the SST transition model of ANSYS-CFXr, is conducted on a NACA66 hydrofoil. Angles of attack range from -4° to 14° and the Reynolds number is Re=7.5.10e5.An experimental investigation is carried out in the French naval academy research institute’s hydrodynamic tunnel based on the measurements of lift and drag. Experiments on a smooth, mirror finished, hydrofoil enable comparison with the transition model. Experiments with a roughness added on the leading edge enable comparison with the SST fully turbulent model. For angles of attack below 6°, the LSB triggered laminar to turbulent transition of the boundarylayers of the suction and pressure sides is located near the trailing edge of the smooth NACA66. As the angle of attack reaches 6°, the LSB suddenly moves to the leading edge on the suction side while transition is located at the trailing edge on the pressure side. The smooth hydrofoil shows higher CL and CM and lower CD than the rough leading edgeone from -4° to 6°. Both experiments lead to the same coeffcients from 6° to 14°. The calculations show that both models are in good agreement with their respective experiments. The SST transition model proves to be a relevant, even essential, prediction tool for lifting bodies operating at a moderate Reynolds number.
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