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
Effect of Squealer Cavity Depth and Oxidation on Turbine Blade Tip Heat Transfer
An experimental study has been performed to investigate the effect of squealer cavity depth on the detailed distribution of convective heat transfer coefficients of a turbine blade tip surface. This paper presents full surface information on heat transfer coefficients within a blade cascade which develops an appropriate pressure distribution about an airfoil blade tip and shroud model. A stationary blade cascade experiment has been run consisting of three airfoils, the center airfoil having a variable tip gap clearance. The airfoil models the aerodynamic tip section of a high pressure turbine blade with inlet Mach number of 0.21, exit Mach number of 0.74, pressure ratio of 1.41, Reynolds number of 2.8•106, and total turning of about 100 degrees. The cascade inlet turbulence intensity level is 9%. Tip surface heat transfer coefficient distributions are first shown for a flat, square-edge tip with a clearance gap of 2.03 mm. Heat transfer distributions are then shown for full-perimeter squealer tip cavities having the same clearance gap above the squealer rim, and clearance-to-cavity depth ratios from 0.67 to 2. Regionally averaged heat transfer coefficients are analyzed to discern a relationship between tip heat transfer and cavity depth. Further tests demonstrate the effect of partial squealer rim oxidation, or material loss, on the surface heat transfer distributions.Copyright © 2001 by ASME
DEM generation from new VIR sensors: IKONOS, ASTER and Landsat-7
DEM generation is a living R&D topic since new-launched satellite images can be used to generate stereoscopic images. Using a coplanarity equation model developed at CCRS and an automatic matching method developed at PCI, DEMs are generated with new VIR stereo data. Accuracy of 4.9 m with high-resolution IKONOS images, and 33 m and 101 m with medium-resolution ASTER and Landsat-7 ETM/sup +/ images respectively are obtained. The same matching accuracy of one-pixel is translated into worse results with Landsat due to a small B/H ratio of 0.15.