Control of turbulence through a row of Helmholtz resonators

The manipulation of turbulent boundary layers is useful in a variety of situations including drag reduction and separation delay. In this study a passive method of altering the turbulence in a boundary layer is investigated. Ten Helmholtz resonators were imbedded in a spanwise row under a turbulent boundary layer. At certain airspeeds the resonators were strongly excited by the turbulence. In turn, the resonator motions interact to modify the turbulence and mean velocity profiles in the boundary layer. Tests were conducted to measure the response of the resonators as a function of freestream speed. Additional tests, conducted at the conditions for maximum response, documented the affect on the mean and turbulent velocity profiles.