3-DIMENSIONAL MEASUREMENT OF VELOCITY, VELOCITY-GRADIENTS AND RELATEDPROPERTIES IN TURBULENT FLOWS

A finite difference method for the simultaneous measurement of the thr ee-dimensional velocity vector and its gradient tensor in turbulent ai rflow is presented and verified. The method relies upon the simultaneo us measurement of the velocity vector at different locations of the fl ow field using a twenty-hotwire probe consisting of five orthogonal fo ur-hotwire subprobes. Evaluation of velocity vectors for each subprobe is performed in three-dimensional space using a trivariate approximat ion procedure of the probe calibration data. With this technique exten sive measurements of three-dimensional velocity, its spatial derivativ es and other related properties as three-dimensional vorticity, local dissipation, vorticity production and turbulent length scales have bee n carried out in the wind tunnel. The flows investigated have been qua si-isotropic turbulent grid flow and turbulent boundary layer at moder ate Reynolds numbers. The results obtained are satisfactory and in goo d agreement to theory and ether experimental and computational investi gations known from literature.