Numerical Prediction of Heat Transfer Coefficient by Karman's Analogy and an Application for Air-Cooled Motorcycle Engines

Abstract

Cooling performance is a significant issue for air-cooled motorcycle engines, because its performance depends on the vehicle motion. Commonly, a heat transfer coefficient is calculated by heat flux and temperature difference, which are solved by energy equation under conjugated condition between a solid and a fluid. However, this method is complicated. Therefore, Karman's analogy based on a relation between the fluid friction and the heat transportation was used to obtain a heat transfer coefficient without solving an energy equation. Partial Cells in Cartesian coordinate method was employed as a CFD (Computational Fluid Dynamics) method for an efficient calculation around complex obstacles. Characteristics of heat transfer in a straight pipe were confirmed by a comparison with the Colburn's empirical formula. The results showed good agreement within ±10% differences under Pr=0.7 and 104<Re<1.2×105. Furthermore, a calculation result of local heat transfer coefficients of an air-cooled motorcycle engine was shown. From the above, a new approach of heat analysis by a CFD was proposed.