Generating controllable velocity fluctuations using twin oscillating hydrofoils: experimental validation

A method for generating controllable two-dimensional velocity fluctuations using two pitching foils was derived theoretically in a previous companion paper. The present work describes the experimental implementation of the method. The experiments are carried out in a re-circulating water channel optimised to provide low turbulence intensity in the incoming flow. Velocities are measured using an acoustic Doppler velocimeter (ADV). The pitching motions of the foils are position-controlled using a closed-loop control system. Two velocity fluctuation patterns are investigated. They consist of a combination of sinusoidal components. Theoretical predictions and experimental measurements are compared in the time and frequency domain. Although some discrepancies are observed, the agreement is generally good and therefore validates the theoretical method for the conditions investigated.