AVERAGE OUTSIDE-SURFACE HEAT-TRANSFER COEFFICIENTS AND VELOCITY DISTRIBUTIONS FOR HEATED AND COOLED IMPULSE TURBINE BLADES IN STATIC CASCADES

摘要

A heat-transfer investigation was conducted on cooled as well as heated impulse-type turbine blades in a static cascade to determine the effect of direction of heat flow on convective heat-transfer coeffi-cients. In addition to the heat-transfer data, velocity distributions around the blade were experimentally measured and compared with the velocities calculated 'from a theory derived herein. The experimental heat-transfer coefficients were compared with theoretically derived coefficients that were dependent on the experimental velocity distri-bution around the blade periphery. The investigations were conducted over a range of air temperature from 60° to 600° F. The Reynolds number ranged from 10,000 to 100,000 and the gas-to-blade temperature ratio ranged from 0.9 to 1.1.nIt was found that:n(a) The heated- and cooled-blade heat-transfer coefficients could be correlated by use of a Nusselt, Prandtl, and Reynolds number relation when the Reynolds number was multiplied by the ratio of effective gas temperature to average blade temperature.n(b) The blade peripheral-velocity distributions calculated from theory were approximately 20 percent lower than experimentally measured velocities in the central portion of the blade.n(c) The theoretically predicted heat-transfer rates based on an experimental velocity distribution were within 1 and 4 percent of the experimental heated- and cooled-blade results, respectively, at a Reynolds number of 75,000;but at a Reynolds number of 15,000, these differences were 10 and 23 percent, respectively.n(d) The 23-percent error in gas-to-blade heat-transfer coeffi¬cient could cause an error in the calculation of blade temperatures of the order of 50° F for a blade temperature of 1000° F, turbine-inlet temperature of 1600° F, and a coolant temperature of 500° F. This error is somewhat large. For many materials, a 50°-F change in blade temperature at 1000° F appreciably affects blade life.