UBC Theses and Dissertations

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UBC Theses and Dissertations

A potential flow model for separated flow around airfoils Brun, Sarah K.


Continuing the study carried out by Dr. W.W.H. Yeung, a former Ph.D. student in the department of Mechanical Engineering at U.B.C., some new work has been done on the wake source model, a potential flow model for steady separated flow. This work includes some modifications to the model and applications to new geometries. In the wake source model, the body of interest is conformally mapped to a circle. In the transform plane, singularities (most often sources) are used to represent the wake by creating free stream-lines simulating the separating shear layers. The empirical data required by the modelare the positions of separation points and the specification of the pressure coefficient at these points. Applications of this model include the case of flow normal to a flat plate, a separation bubble at the leading edge of a flat plate airfoil, and an airfoil fitted with a Kriiger flap. The case of the normal flat plate was a test case in which the original model was odified in an attempt to specify a constant pressure on the free stream line after separation. This has been achieved to a limited extent by adding sources to the original model. Future work should include the application of the same method to a spoiler and slotted flap air foil configuration. An earlier model using a doublet as singularity was developed by Yeung for the separation bubble case. It showed very good agreement with experiments in terms of the pressure distribution on the wetted surface of the plate but a high suction peak appeared on the bubble boundary, as well as an unsatisfactory bubble shape. In the present study, no improvement has been obtained by using more singularities, unlike the case for thenormal flat plate. For an airfoil with a Kriiger flap, some satisfactory results can be obtained with a model using two doublets, especially at high angles of attack. Results could be improved at moderate incidence with a better estimate of the bubble shape that forms between the flap and the airfoil lower surface. Thus, it is recommended that flow visualization studies be conducted in the future to evaluate this shape. Experiments should also be carefully repeated in order to assess the accuracy of the model.

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