The effect of turbulence on heat transfer from heated cylinders

Abstract

Data were obtained on the effect of free-stream turbulence on heat transfer from heated cylinders placed normal to an air stream. Tests were conducted for a Reynolds number range from 109 000 to 302 000 at values of turbulence intensity from 0·40 to 14·20 per cent. The diameters of the test cylinders used were 4·5 and 7·6 in respectively and the ratio of cylinder diameter to test section width were 0·075 and 0·127. The ratio of turbulence scale to cylinder diameter ranged from 0·015 to 0·095. The scale of turbulence varied from 0·113 to 0·426 in during the study. The structure of the free-stream is characterized and the effects of the artificially induced turbulence on both the local and overall heat transfer are determined. The data are discussed and compared with results of previous studies where appropriate. The results are explained in part by available theory and also indicate areas that require further investigation. A correlation equation is presented that enables the stagnation point heat transfer as a function of turbulence intensity to be determined. The augmentation of heat transfer through the laminar boundary layer as a function of turbulence intensity is also determined. Attempts to determine the effect of turbulence intensity on the overall or average heat transfer were partially successful. A correlation equation for predicting the overall heat transfer as a function of turbulence intensity over a narrow range of correlation parameters is presented.