Influence of velocity gradients on measurements of velocity and streamwise vorticity with hot-wire X-array probes

An analysis and measurement of the effects of the streamwise velocity gradients, ∂U/∂y and ∂U/∂z, on the velocity components, U, v, and w, and the streamwise vorticity component, ω_x, measured in turbulent flow with a pair of orthogonal hot-wire X arrays, is presented. It is shown that these gradients, which can have the same order of magnitude instantaneously as the mean shear stress at the wall, cause extremely large errors in the measured instantaneous cross-stream velocity and streamwise vorticity components.