Influence of the flow velocity on a Kovasznay type vorticity probe

Abstract

The output signal of a Kovasznay type vorticity probe is in first-order approximation proportional to the longitudinal component of the vorticity omegax= partial differentialw/ partial differentialy- partial differentialv/ partial differentialz and does not depend on the two transverse components of the flow velocity v, w. An experimental investigation of the influence of all three fluctuating velocity components on the longitudinal vorticity signal showed that their influence may not be neglected. The error in the probe response caused by the longitudinal component of the flow velocity was easily corrected using the instantaneous longitudinal velocity component and digital measuring techniques. On the other hand, the error caused by the two transverse velocity components could not be corrected. The contamination of the vorticity signal produced by the two transverse velocity components has been calculated by considering first- and second-order terms. The agreement between the calculations and experimental measurements is good. It is concluded that in a turbulent flow field this probe cannot be used without the simultaneous knowledge of the instantaneous transverse velocity components.