STAGNATION REGION GAS FILM COOLING: SPANWISE ANGLED INJECTION FROM MULTIPLE ROWS OF HOLES
Abstract
An experimental investigation was conducted to model the film cooling performance for a turbine vane leading edge using the stagnation region of a cylinder in cross-flow. Experiments were conducted with both a single row and multiple rows of spanwise angled coolant holes for a range of the coolant blowing ratio with a freestream-to-wall temperature ratio (DBLTURN) 1.7 and Re(,D) = 90000, characteristic of the gas turbine environment. The objective of the investigation was to obtain data for the local convective heat transfer rates to a highly cooled, curved surface exposed to a turbulent hot mainstream flow and a secondary, film coolant flow. Because the leading edge of the first stage, inlet turbine vane experiences some of the most severe thermal loads found in the turbine engine, effective film cooling is most important in this area. Experiments were conducted in a rectangular duct using a cylindrical test surface. A gas turbine combustor provided heated air flow to simulate the Reynolds number and internal convection cooling of the cylinder allowed the freestream-to-wall temperature of 1.7 to be achieved. The film coolant, injected at room temperature, passed through coolant holes angled 25(DEGREES) from the surface. The cylindrical test surface was instrumented with miniature heat flux gages and wall thermocouples to determine the percentage reduction in the Stanton number as a function of the distance downstream of injection (x/d(,0)) and the location between adjacent holes (z/S). Data from local heat flux measurements are presented for single row and multiple row injection configurations. The single injection row was positioned at the angular locations ((theta)(,i)) occupied by the film coolant rows in the multiple row configurations (5(DEGREES), 22.9(DEGREES), 40.8(DEGREES), 58.7(DEGREES) from stagnation). Two hole spacing ratios, S/d(,0) = 5 and 10, were studied with single row injection. Three multiple row configurations, shown below, were investigated. (1) Five Row Configuration S/d(,0) = P/d(,0) = 5 First Row at (theta)(,1) = 5(DEGREES) (2) Three Row Configuration S/d(,0) = P/d(,0) = 10 First Row at (theta)(,1) = 5(DEGREES) (3) Two Row Configuration S/d(,0) = P/d(,0) = 10 First Row at (theta)(,2) = 22.9(DEGREES) The multiple row studies involved the use of a uniform M (constant (rho)(,c)V(,c)/(rho)(,(INFIN))V(,(INFIN))) blowing distribution across the rows of holes and a non-uniform blowing distribution that modeled the use of a common plenum. The results present the downstream and spanwise variations of the film cooling performance for both single row and multiple row injection. The data demonstrated a lack of lateral spreading by the coolant jets as they passed downstream. It was possible to estimate the optimum coolant blowing ratio independent of the row location. Heat flux levels larger than those without film cooling were produced directly behind the coolant holes as the blowing ratio was increased beyond a particular value. This blowing rate was found to be dependent on row location. The multiple row results showed good agreement with the single row data. Most variations were discovered at the downstream rows in the multiple row configurations. The major influence of upstream blowing on downstream injection was to effectively lower the optimum coolant blowing ratio and the blowing ratio where the level of heat flux surpassed the non-film cooled condition. The blowing distributions modeling a common plenum supply exhibited large blowing ratios. These blowing rates generated heat flux levels behind the hole in excess of the non-film cooled values. An increase in the freestream turbulence intensity from 4.4% to 9.5% was found to have a negligible effect on the film cooling performance.
Degree
Ph.D.
Subject Area
Mechanical engineering
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