APPLICATION OF AN INVERSE MASS-TRANSFER METHOD TO THE MEASUREMENT OF TURBULENT FLUCTUATIONS IN THE VELOCITY-GRADIENT AT THE WALL

The frequency response of the concentration boundary-layer is often a concern when flush mounted mass transfer probes are used to measure turbulent fluctuations in the velocity gradient at a wall. Present practice involves the use of a solution of the mass balance equation which is linear in the fluctuating quantities. An inverse mass transfer method is explored in this paper, which avoids the linearization assumption. Improved measurements of the amplitude probability distribution and of the frequency spectrum of the streamwise component of the fluctuating velocity gradient are presented. In particular, values of rms level, skewness and flatness of 0.37, 0.96, 4.2 are obtained, in good agreement with a recent study by Alfredson, Johansson, Haritonidis and Eckelmann.