The Near-Wall Behavior of Unsteady Vortical Flow Around the Tip of an Axial Pump Rotor Blade

Abstract

Abstract : Experimental study of three-dimensional turbulent tip gap flows in the linear cascade wind tunnel for two different tip gap clearances (t/c=1 .65% and 3.3%). Three experimental techniques are used to measure the tip gap velocity field and static pressure field on the end-wall: a three- orthogonal-velocity- component fiber-optic laser Doppler anemometer (3D-LDA) system, surface oil flow visualization, and a scani-valve pressure measurement system. The end-wall skin friction velocity is calculated from near-wall LDA data and pressure gradient data using the near-wall momentum equation. The statistics of Reynolds stresses and triple products in the two-dimensional turbulent boundary layer and three-dimensional turbulent boundary layer were examined using a velocity fluctuation octant analysis. For the three-dimensional turbulent boundary layer in the moving wall flow, the near-wall shear-flow reinforces the sweep motion to the moving wall and weakens the out-ward ejection motion in the shear flow dominant region. Between the passage flow and the shear flow is the interaction region of the high speed streaks and the low speed streaks. This is the first time that the coherent structure of the three-dimensional turbulent boundary in the linear cascade tip gap has been studied. Experimental study of the downstream behavior of vortex generators used to simulate stator trailing vortices was also done as part of this program and was described in an earlier Technical Report.