Showing papers by "Terrence W. Simon published in 1991"

Three-Dimensional Flow Near the Blade/Endwall Junction of a Gas Turbine: Application of a Boundary Layer Fence

Abstract: A flow management technique designed to reduce some harmful effects of secondary flow in the endwall region of a turbine passage is introduced. A boundary layer fence in the gas turbine passage is shown to improve the likelihood of efficient film cooling on the suction surface near the endwall. The fence prevents the pressure side leg of the horseshoe vortex from crossing to the suction surface and impinging on the wall. The vortex is weakened and decreased in size after being deflected by the fence. Such diversion of the vortex will prevent it from removing the film cooling flow allowing the flow to perform its cooling function. Flow visualization on the suction surface and through the passage shows the behavior of the passage vortex with and without the fence. Laser Doppler velocimetry is employed to quantify these observations.Copyright © 1991 by ASME

Bypass transition in boundary layers including curvature and favorable pressure gradient effects

Abstract: Recent studies of 2-D boundary layers undergoing bypass transition were reviewed. Bypass transition is characterized by the sudden appearance of turbulent spots in boundary layer without first the regular, observable growth of disturbances predicted by linear stability theory. There are no standard criteria or parameters for defining bypass transition, but it is known to be the mode of transition when the flow is disturbed by perturbations of sufficient amplitude.

On the rotating, slanted, hot-wire technique

Abstract: The purpose of this paper is to convey information and experience gained in the use of a rotating slanted hot-wire probe to measure the complete Reynolds stress tensor and the mean velocity vector The technique is limited to nearly one-dimensional flows with turbulence intensities less than 10% This paper extends the description of the method and discusses potential problems and difficulties one my encounter with this technique In particular, the use of an appropriate least-squares technique (singular value decomposition) is suggested as this gives a more accurate fitting than simply using a matrix inversion of the normal equations The covariance matrix is used to determine the slant angle and rotation positions of the probe most favorable to the least squares fitting and provides a measure of the uncertainties in the solution for the Reynolds stresses The technique presented was used to determine the anisotropy of a turbulent flow with no mean shear The results compare well with cross-wire measurements

Investigation of the effects of flow swirl on heat transfer inside a cylindrical cavity

Abstract: Experiments were conducted to determine local heat transfer coefficients on the inside surfaces of a cylindrical cavity that is cooled by a swirling air flow. Temperature-sensitive liquid crystals were used as temperature sensors. Five blowing (cooling) modes were tested: three with swirl numbers of 0.36, 0.84, and 1.73; a fourth with no swirl (axial flow), and a fifth that was similar to the fourth but had the flow direction reversed. Flow visualization and static pressure measurements were performed to improve understanding of the situation. The smoke-wire technique was successfully used to picture the flow patterns. Plots of local Nusselt number along the cavity surfaces were obtained for the five blowing modes and for three different Reynolds numbers. The swirling cases had similar flow fields with higher heat transfer rates near the cavity top and lower rates near the cavity bottom (the opposite of the nonswirling cases). A tornadolike structure on the cavity bottom was observed in the swirling cases. This structure became stronger and more violent as the degree of swirl and the Reynolds number were increased. The Nusselt number curves for the two nonswirling cases were of similar shape, although the flow direction was reversed.

Hydrodynamic and thermal measurements in a turbulent boundary layer recovering from concave curvature

Abstract: The behavior of a boundary layer on a flat wall downstream of sustained concave curvature is documented. Experiments are conducted with negligible streamwise pressure gradient and a low free-stream turbulence intensity (0.6 percent). The turbulent boundary layer has a moderate strength of curvature (δ/R = 0.024) at the entry to the recovery section. Results show that the skin friction coefficient, which increases over the concave wall, decreases rapidly at first over the recovery wall, then slowly approaches flat-wall values. Stanton number values decrease rapidly, undershooting expected flat-wall values. A discussion of this behavior, supported by profile measurements, is given. Effects include destabilization in the concave-curved flow and rapid streamline readjustment (acceleration) at the end of the curved section. Goertler vortices established on the curved wall persist onto the recovery wall; however, their effects weaken.