Three-dimensional measurement of velocity, velocity gradients and related properties in turbulent flows

Abstract

A finite difference method for the simultaneous measurement of the three-dimensional velocity vector and its gradient tensor in turbulent airflow is presented and verified. The method relies upon the simultaneous measurement of the velocity vector at different locations of the flow field using a twenty-hotwire probe consisting of five orthogonal four-hotwire subprobes. Evaluation of velocity vectors for each subprobe is performed in three-dimensional space using a trivariate approximation procedure of the probe calibration data. With this technique extensive measurements of three-dimensional velocity, its spatial derivatives and other related properties as three-dimensional vorticity, local dissipation, vorticity production and turbulent length scales have been carried out in the wind tunnel. The flows investigated have been quasi-isotropic turbulent grid flow and turbulent boundary layer at moderate Reynolds numbers. The results obtained are satisfactory and in good agreement to theory and other experimental and computational investigations known from literature.