Aerodynamics - Control of Surface Shear Stress of Fluctuations in Turbulent Boundary Layers.
Abstract
An experimental study of techniques for modifying the surface shear stress, both mean and fluctuating, in turbulent boundary layers is reported. The surface shear along the test section of a 45.7cm square wind tunnel, with a downstream expansion section, was determined by means of surface-hot-wire-heat-transfer-gauges. Turbulent boundary layers in both zero and adverse pressure gradients were evaluated. The mean and fluctuating surface shear in a zero pressure gradient can be effectively reduced by employing a set of closely spaced fins. The fins protruded from the surface up through the sublayer. The fins produced an effective momentum defect for the boundary layer near the surface, which reduced the surface shear fluctuations by as much as 75 percent, two boundary layer thicknesses downstream, and 52 percent 15 boundary layer thicknesses downstream (the limit of the present experiment). The mean surface shear was also reduced by 35 to 25 percent for the same 2 to 15 boundary thicknesses downstream. The fins do not appear to produce a large increase in the thickness of the layer. No small size device, which could be mounted in the sublayer, was found that could develope a persistent increase in either the mean or fluctuating surface shear. Small scale vortex generators had no measureable effect on the flow for downstream distances greater than approximately 4 to 5 boundary layer thicknesses. Only the large scale vortex generator, normally use to delay boundary layer separation, produced an increase in surface shear at large distances downstream. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1981
- Accession Number
- ADA103354
Entities
People
- V. A. Sandborn
Organizations
- Colorado State University