Flow Visualization and Radial Velocity Measurements of Entrainment in an Axisymmetric Turbulent Jet
Abstract
A submerged, axisymmetric turbulent jet of water was studied using a laser Doppler anemometer (LDA). Mean radial and turbulent radial velocity profiles within the irrotational ambient region (external to the jet) and rotational region (within the jet) were measured up to 40 jet diameters. Flow visualization studies (photographs and video) were conducted using incandescent light sheets with LDA tracer particles. These visual observations reveal detailed turbulent flow structure. Trailing ends of turbulent eddies at the jet edge travel opposite to the mean axial flow. The intermittency surface undulates irregularly and resembles a violently perturbed boundary layer between two immiscible liquids. Irrotational ambient fluid follows parabolic streamlines into the jet, but only when perceived as a time average. Mean radial velocity profiles, measured with an LDA, followed typical "Double S" curves. The mean radial velocity in the irrotational region of the jet was found to be an inverse function of radial distance measured from the jet axis, for any given axial location. This evidence proves there is no entrainment velocity that is directly proportional to the local axial velocity: the key assumption to jet entrainment theory.
- Publication:
-
APS Division of Fluid Dynamics Meeting Abstracts
- Pub Date:
- November 1998
- Bibcode:
- 1998APS..DFD..AB01F