HEAT TRANSFER THROUGH INCOMPRESSIBLE LAMINAR BOUNDARY LAYERS

Abstract

This report is an attempt to present the available techniques for calculating heat transfer coefficients through incompressible laminar 'boundary layers. Some of the methods developed for general purpose have been outlined. Two of these have been used to predict the distribution of heat transfer coefficients around a cascade of gas turbine blades of known pressure distr-ibution. After a brief introduction giving the signif" icance of the problem, the equations of boundary layer are stated and a criterion for neglecting frictional heating derived. This is followed by the solution of the problem for the case of a flat plate. Pohihausen's exact solut-ions for the case of an isothermal wall and adiabatic wall have been discussed and subsequently approximate simpler solutions have been presented. The case of arbitrarily varying wall temperatures is dealt with next. DU In the next Chapter, the methods for calculating the heat transfer coefficients for a general two dimen-tional body are given. Starting with the well known wedge flows, the methods of Squire (1942), Lighthill (1950), Smith and Spalding (1958) and Spalding (1958) , ), which is an attempt to improve the Llghthill method, are presented. In order to evaluate the heat transfer coeffic-. cents, the potential velocity distribution is required. Two methods, typical of present day approach, are, therefore, given. The problem of theoretically predict.• ink; the potential flow, outside the boundary layers is complicated t nd the theory formulated is still far from sound. The methods, however, bring out the possi. bility of prediction of the heat transfer coefficients, from entirely theoretical analysis. Due to the reason stated above, the experimental velocity distribution data, published by Pope and Wilson, for a cascade of gas turbine blades, has been used to calculate the heat transfer coefficients by the methods of Smith and Spalding and Spalding. This also facilitates comparison with the published data for heat transfer coefficients by the same authors. The last Chapter deals with these calculations and the conclusions which point towards need for comprehensive experimentation to evaluate the relative accuracy of the methods.