A Study of A Flow through Small Apertures : 2nd Report, Experiments on The Velocity Field

Abstract

The velocity field of an inlet and outlet flow through small orifices was experimentally examined. The velocity along the center line near the orifices was measured with a laser doppler anemometer, stream lines in the whole flow region were photographed, and the following points were clarified : (1) The center line velocities of liquid paraffin agree with the theoretical value of Stokes flow in the region of Reynolds numbers below 10. (2) With distilled water, a diverging angle of the issuing flow from a larger orifice is smaller than that of the issuing flow from a smaller orifice. Furthermore, a characteristic isolated vortex is generated on the downstream side of the orifice at the Reynolds number of from 10 to 30. (3) With ethanol used as a test liquid, the diverging angle of the issuing flow is small even for the Reynolds number of less than 10, and the flow resembles a jet. (4) The magnitude of the diverging angle of the issuing flow have a decisive effect on the value of the excess pressure drop at the same Reynolds number ; the larger the diverging angles is, the smaller the excess pressure drop is. (5) The dimension of the isolated vortex generated with the outlet flow of water is, when non-dimensionalized with the orifice diameter, correlated with a dimensionless number V(λ/ν)^1/2, where V is the mean orifice velocity, λ is a time proper to water and ν is the kinematic viscosity.