Three-dimensional wake measurements

Abstract

The performance of a hot wire probe with three wires is investigated for two different flow cases. The wires are made of a platinum/rhodium alloy, and has a diameter of 5 micrometer. The three wires make a probe volume with acrossection of approximately 5 mm. A cosinus fit using the effective angle method gives a deviation of plus/minus 1 degree for a variation of yaw angle equal to plus/minus 20 degrees. First the probe was tested in a fully developed turbulent pipe flow, for Re_D = 10^5. Good results were obtained for |y/R|<0.8, both for mean velocities and turbulent stresses. Closer to the wall the mean flow gradient was to large relative to the probe resolution, giving large errors. The second flow case was a cylinder wake. A traverse of the flow at x/D = 10 was performed at Re_D = 3*10^3. The mean velocities and turbulent stresses was partly found to be in qualitative agreement with results found in litterature. The shear stresses uw and vw were however found to be unphysically large, this is belived to be due to the velocity gradient in the wake. Conditional averaging of the wake results with respect to shedding frequency was also conducted.