Laminar velocity profiles in developing flows using a laser doppler technique

Abstract

Abstract A laser doppler flowmeter is used to obtain velocity profiles in circular glass tubes downstream from a plug composed of brass screens. The apparatus for measuring point velocities of particles suspended in a fluid is described. Measurements were made very close to the plug at Reynolds numbers of 16.5, 47, and 274, and the flow development followed down the tube. The results show that the entrance flow development is dependent on the inlet profile shape and the Reynolds number for Reynolds numbers below 300. The flow development at Reynolds numbers less than 300 was considerably slower than that predicted by the boundary‐layer solution of the equations of motion starting with a flat profile.