Experiments on the Forced Wake of an Airfoil

Abstract

Presented here is an experimental effort which attempts to understand the nature of the wake of an airfoil in a controlled environment. The frequency of oscillation in the wake (the vortex shedding frequency) is controlled through the introduction of an external perturbation. Strip heaters are used to introduce waves into the top and bottom boundary layers of a thin symmetric airfoil which are amplified and introduced to the wake. The linear and nonlinear interactions of these waves in the wake are studied in detail. Three modes of interaction have been observed through flow visualization and velocity measurements: frequency locking in which the vortex shedding frequency is the same as the forcing frequency, quasiperiodic vortex interaction in which periodic clusters of vortices are observed in the wake, and chaotic vortex interaction in which the vortices in the wake have a three dimensional random structure.

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