EFFECT OF VORTEX CORE DISTORTION ON BLADE-VORTEX INTERACTION

The effect of vortex distortion on the flow arising from the interaction of a convecting vortex and an airfoil is analyzed for two-dimensional, incompressible, inviscid flow. Significant distortion of the vortex structure, owing to interaction with the airfoil, can occur, especially during close interactions. The vorticity field is represented by multiple vortex elements. Vortex instability and diffusion, resulting from discretization in space and time, are discussed. An integral-boundary-element method is used to represent the airfoil surface and its effect on the flowfield. The body panels are redistributed on the surface as the vortices are convected past the airfoil to calculate the effect of the vorticity field more accurately. The method is applied to several cases to examine effects of vortex strength, distribution, and initial separation position. The distortion, even splitting, of the vortex core is observed for the case of close interaction. However, the extent of distortion depends strongly on the initial size and strength of the vortex. Also, the unsteady pressure term contributes significantly to both the surface-pressure distribution and total lift in addition to the quasisteady term. Circulation around the airfoil is also presented.