The subject under investigation is very important to the gas turbine industry, and the derivation of a correlation for the oil chamber wall heat transfer coefficient is long past overdue. The complexity, however, is that the correlation needs to represent the two-phase flow regime (liquid oil + air) along the chamber wall which changes with engine operating conditions. Therefore, the proposed correlation in this paper requires further validation in order to delineate the effect of two-phase flow regime. Would the authors comment on why the definition of the Reynolds number (Eq. (12)) is not based on local tangential velocity ns×rs but rather a pseudo tangential velocity based on circumference ns×2πrs. Also, if the chamber circumference is U=πDh, why are the Reynolds numbers of Eqs. (15) and (16) written without the π?

Busam, S., Glahn, A., and Wittig, S., 2000, ASME JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER , 122, No. 2, pp. 316–322.