Numerical and experimental analysis of rounded fins for high speed air-cooled heat exchangers

Abstract

The implementation of Surface Air-Cooled Oil Coolers (SACOCs) in new generation of turbofans is becoming more and more common. The main reason behind this is the need of improving the engine thermal management system as lubricants and components are working under increasingly severe demands. The idea of using the cold air from the bypass duct as a cold sink not only can be beneficial to cool down the oil, but because the enthalpy can be released into this flow to enhance the propulsion. However, it is extremely important to maintain the aerodynamic impact of the heat exchanger to its minimum so the propulsive efficiency is not worsened.In this investigation, the effect of rounding the sharp edges of a finned heat exchanger working under realistic conditions of very high Reynolds numbers is addressed. Firstly, a parametric study to determine the blend radius was numerically conducted and then, both geometries were experimentally tested for different Reynolds. The rounded version presented not only better results in terms of heat exchange, but also a considerable reduction in the aerodynamic impact of the fins. A detailed numerical analysis of both cases under nominal conditions showed that rounding the sharp edges enables the airflow to remain better attached to the fins, decreasing thus the aerodynamic impact in terms of velocities and vorticity and improving the thermal performances.