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 Blade Tip Geometry on Tip Flow and Heat Transfer for a Blade in a Low Speed Cascade
A comprehensive investigation of the effect of various tip sealing geometries is presented on the blade tip leakage flow and associated heat transfer of a scaled up HPT turbine blade in a low-speed wind tunnel facility. The linear cascade is made of four blades with the two corner blades acting as guides. The tip section of a HPT first stage rotor blade is used to fabricate the 2-D blade. The wind tunnel accommodates an 116° turn for the blade cascade. The mainstream Reynolds number based on the axial chord length at cascade exit is 4.83 × 105 . The upstream wake effect is simulated with a spoked wheel wake generator placed upstream of the cascade. A turbulence grid placed even farther upstream generates the required free-stream turbulence of 4.8%. The center blade has a tip clearance gap of 1.5625% with respect to the blade span. Static pressure measurements are obtained on the blade surface and the shroud. The effect of crosswise trip strips to reduce leakage flow and associated heat transfer is investigated with strips placed along the leakage flow direction, against the leakage flow and along the chord. Cylindrical pin fins and pitch variation of strips over the tip surface are also investigated. Detailed heat transfer measurements are obtained using a steady state HSI-based liquid crystal technique. The effect of periodic unsteady wake effect is also investigated by varying the wake Strouhal number from 0. to 0.2, and to 0.4. Results show that the trip strips placed against the leakage flow produce the lowest heat transfer on the tips compared to all the other cases with a reduction between 10–15% compared to the plain tip. Results also show that the pitch of the strips has a small effect on the overall reduction. Cylindrical pins fins and strips along the leakage flow direction do not decrease the heat transfer coefficients and in some cases enhance the heat transfer coefficients by as much as 20%.Copyright © 2003 by ASME
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.