Effect of nonisothermal conditions of skin friction in subsonic turbulent channel flows

A number of different approaches are available in current literature to the theoretical determination of skin friction in nonisothermal flows in channels and pipes. Some of these (e.g., [1–3]) predict an appreciably stronger dependence of skin friction on temperature ratio =T_w/T (T_w is the wall temperature; T is the core fluid temperature), than those indicated by experimental results [4–7]. Significantly better agreement with existing experimental results is achieved in [8, 9] based on comprehensive numerical analysis of a system of integrodifferential equations. However, the assumptions they make are not always sound nor physically clear. Besides, the use of numerical methods does not allow the authors to relate their analysis to known limiting laws and simultaneously develop reliable numerical expressions to generalize experimental data. Physically quite clear results have been obtained in [10–12] and, in particular, very simple limiting laws for skin friction have been established. At the same time, it appears that based on the same physically clear assumptions, it is possible to obtain even more general results which agree well with experimental data. Simultaneously, these results which coincide with the limiting values at infinite Reynolds number make it possible to indicate the limits of applicability of these laws and extend them to finite Reynolds number range.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 69–76, January–February, 1984.