The local heat transfer coefficient, for air flowing through a pipe with a swirling motion, was measured at various stations downstream of the swirling air inlet. The swirling motion of the air was produced by a single tangential slot, initially at 90 deg to the pipe axis, through which the air was introduced. The dimensions of the slot and the angle of tangency were varied and the resultant flow field inside the pipe was measured and expressed in the form of local “swirl numbers”. The augmentation of heat transfer was found to be a function of the swirl number and a correlation for this function is presented. At some locations, the augmentation can be as much as eight times the value for fully developed nonswirling turbulent flow.
The influence of injection of cooling films through a row of holes on the heat transfer coefficient on a flat plate is investigated for a range of mass flux ratio using a heat-mass transfer analogy. Injection angles of 35 deg and 90 deg are covered. The experimental technique employed uses a swollen polymer surface and laser holographic interferometry. The results presented show the change in local heat transfer coefficient over the no-injection values at the centerline and off-centerline locations for various streamwise stations. The effect of injection on laterally averaged heat transfer coefficients is also assessed.
Published information on the discharge coefficient of film cooling holes is classified in terms of the hole geometry, the external flow conditions at inlet and outlet, and the method of evaluation. This may be either theoretical or experimental. The information is reviewed primarily in the context of its use for evaluating discharge coefficients for conditions not directly covered by published data. It is shown that potential flow analyses can give acceptable accuracy for simple geometries with crossflows, while more complex cases require the use of correlated data, which may be incorporated in a range of predictive schemes. Deficiencies and inconsistencies in the published information are highlighted, and future developments are discussed.
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