Measurements of a Separating Turbulent Boundary Layer.
Abstract
The problem of turbulent boundary layer separation due to an adverse pressure gradient is an old but still important problem in many fluid flow devices. The directionally-sensitive laser anemometer now provides the ability to accurately measure the instantaneous flow direction and magnitude. The experimental results described in this report are concerned with a nominally two-dimensional separating turbulent boundary layer for an airfoil-type flow in which the flow was accelerated and then decelerated until separation. Upstream of separation single and cross-wire hot-wire anemometer measurements are also presented. Measurements obtained in the separated zone with a directionally-sensitive laser anemometer system are presented. Results lead to significant conclusions about the nature of the separated flow when the thickness of the backflow region is small as compared with the shear layer thickness. The backflow is controlled by the large-scale outer region flow. The small mean backflow does not come from far downstream, but appears to be supplied intermittently by large-scale structures as they pass through the separated flow. Downstream of fully-developed separation, the mean backflow appears to be divided into three layers: a viscous layer nearest the wall that is dominated by the turbulent flow unsteadiness but with little Reynolds shearing stress effects; a rather flat intermediate layer that seems to act as an overlap region between the viscous wall and outer regions; and the outer backflow region that is really part of the large-scaled outer region flow.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1980
- Accession Number
- ADA095252
Entities
People
- B. G. Shivaprasad
- Roger L. Simpson
- Y.-t. Chew
Organizations
- Purdue University