1 PRESSURE SENSITIVE PAINT FOR ANALYSIS OF FILM-COOLING EFFECTS ON A GAS TURBINE BLADE TIP
This paper deals with the implementation of Pressure Sensitive Paints (PSP) in turbomachinery and other aero-thermal research studies. A specific calibration setup developed at the Pennsylvania State University and the applications of PSP are discussed in detail. PSP is an experimental technique for mapping pressure distributions on any aerodynamic body. It requires coating the surface of the body with a special paint that exhibits luminescence when it is exposed to light of appropriate frequency. The intensity of the exposed light is then used as a measure of the pressure at that point. In order to draw up a reference criteria, calibration of the paint was carried out in a specially designed chamber. The paper provides details about the calibration procedure as well as the setup. Although in the recent years PSP has been used for the investigation of high speed flows, its low-speed applications are also being investigated. The current effort aims at using PSP technology in exploring film-cooling effectiveness and the pressure loss characteristics associated with the use of flat as well as squealer tip rotor blades in an axial flow turbine. In conclusion, this paper attempts at establishing PSP as a simple, cost effective and highly efficient means of experimental verification of computational results along with proposing this technique as a substitute for the expensive wind tunnel testing of various aerodynamic bodies. Introduction Any increase in the thermal efficiency of a gas turbine engine is contingent on a corresponding increase in the turbine inlet temperature. However, at the same time an increased turbine inlet temperature leads to enhanced heat transfer and thermal stresses on the blade surface. In order for the blade to withstand such adverse environment and avoid any material failure, it becomes essential to provide an arrangement for cooling the system. Of the various cooling mechanism available, film-cooling has come to be widely accepted as one of the more useful active cooling methods. In case of film-cooling, relatively cooler air is passed through several small discreet holes onto the surface of the blade. This generates a protective film between the hot mainstream flow and the blade surface which protects the surface of the blade by keeping it at a lower temperature. The coolant used in film cooling is actually bled air from the compressor. Hence, although it protects the turbine components and allows for an increased turbine inlet temperature, excessive use of the coolant leads to a decrease in the overall thermal efficiency of the system as we have a higher percentage of compressor air being bled and greater mixing of cooler air into the hot mainstream air taking place. Thus the best configuration would have to be the one yielding the maximum increase in the turbine inlet temperature with the expense of least coolant possible. Many research efforts have been Paper Ref. # 335
Turbine Nozzle Film Cooling Study Using the Pressure Sensitive Paint (PSP) Technique
The use of pressure sensitive paint (PSP) to measure film cooling effectiveness on a turbine nozzle surface was demonstrated in a high speed wind tunnel. Film cooling effectiveness was measured from a single row of holes located on a turbine vane suction surface with a shaped exit. Nitrogen gas was used to simulate film cooling flow as well as a tracer gas to indicate oxygen concentration such that film effectiveness by the mass transfer analogy could be obtained. Three blowing ratios were studied for each of the five freestream conditions: a reference condition, a reduced and an increased Reynolds number condition, and a reduced and an increased Mach number condition. The freestream turbulence intensity was kept at 12.0% for all the tests. The PSP was calibrated at various temperatures and pressures to obtain better accuracy before being applied to the airfoil surface. The film effectiveness increased with blowing ratio for all the freestream conditions. The effects of secondary flow and freestream Mach number and Reynolds number on turbine nozzle suction surface film cooling are also discussed.Copyright © 1999 by ASME
Investigation of a Tip Clearance Cascade in a Water Analogy Rig
The tip clearance flow region of high pressure axial turbine blades for small gas turbine engines has been investigated in a water flow cascade. The blade model features variable clearance and variable endwall speeds. The cascade is scaled for Reynolds number and sized to give velocities suitable for visualization. Pressure profiles were measured on one blade, and correlated with the visualization. Unloading is found to be a major feature of the pressure field at both tip and midspan, and is intimately connected with scraping effects and the behavior of the clearance vortex. Some initial hot film velocity measurements are also presented.Copyright © 1985 by ASME