Boundary Element Method Applied to the 2D Foil with Oscillating Heave and Pitch Motions

Abstract

When an oscillating foil is placed in a uniform and steady flow, due to its heave and pitching motion, it produce a downstream flow at trailing edge, which leads to a forward force or thrust. Many fishes or insects use this phenomenon to move in air/water. It has proved that the heave and pitch frequency is very important parameter to produce thrust which should be chosen sharply. In this paper a 2D airfoil with oscillating movement was simulated and power/thrust coefficient was calculated. An unsteady numerical model based on boundary element method (BEM) was developed to simulate the flow around the foil. Two different conditions (with different angles of attack, =5, 10) were chosen for the flapping airfoil. For each condition, the foil was oscillated with 8 different frequencies to draw the thrust and power coefficients. The results were compared with experimental data and a finite volume-based solver. It could be seen that however FVM is more precisions to simulate such a hydrodynamics cases but for lifting bodies objects such as airfoil, BEM offers reasonable accuracy. In addition, one of the best advantages of BEM is its speed in calculation. Considering BEM just used 100 boundary cells in simulations, it is about 30 times faster than FVM, which means BEM could be used in rough estimations and preliminary calculations.