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Surface Air Cooled Oil Cooler (SACOC) is a widely used oil cooler for turbofan engines. While SACOC has a simple configuration of air-cooling fins on oil passages, the cooling performance is not sufficiently clarified because the coolant air is of high-Reynolds number. In the present study, a numerical analysis was conducted to identify the impact of inflow swirl angle and inflow turbulence intensity on the cooling performance of SACOC. From the results, it was found that the cooling performance was not sensitive to either swirl angle or turbulence intensity. A simple numerical method for a crossflow type heat exchanger was also developed in this study to avoid simulating several hundreds of air-side and oil-side passages. With the developed method, the thermal resistance of the oil passage of SACOC was investigated, which was usually ignored in industrial investigations, and a possibility of improving the cooling performance was found in oil-side devices. INTRODUCTION Thermal management is one of the critical technology issues in developing modern turbofans. In recent years, the introduction of a fan drive gear drastically increased the amount of dissipated heat. The severe situation is thought to be more challenging in the future; new electric systems require additional cooling capacity (Morioka et al., 2018). In a turbofan, lubricating oil works as a heat transfer medium and is finally cooled by oil coolers. A turbofan usually has two types of oil coolers: an air-cooling system and a fuel-cooling system. For the air-cooling system, Surface Air Cooled Oil Cooler (SACOC) is installed in a modern turbofan. Figure 1 shows the schematics of SACOC. SACOC is a crossflow heat exchanger with aircooling fins, and oil flows in the plate-like structure with corrugated fins inside. The system is installed at the downstream of fan exit guide vanes. SACOC is widely used because of its advantages of less aerodynamic losses and lighter weight than compact heat exchangers. However, there is an emerging issue, that is, modern turbofan engines are equipped with so many SACOC’s almost to the limit of available areas in the fan duct. Moreover, because the reduction in fuel consumption limits the capacity of the fuel cooling system, the air-cooling system has to manage more heat load than ever. Therefore, the cooling characteristics of SACOC should be clarified precisely to develop an efficient thermal management system for future engines. There are a few previous reports about the cooling fins for SACOC. Outirba & Hendrick (2013) showed that the thermal performance of cooling fins was not effectively improved by the refinement of fin shape under high velocity flow situation. Sousa et al. (2014) tested the fin array in a wind tunnel with spiral passage to reproduce Figure 1 Schematics of SACOC, Left: Installation Position, Right: Flow Passages

proceedings

Numerical Study on the Impact of Air-Side Inflow Condition and Oil-Side Thermal Boundary Layer on a Cooling Performance of Surface Air Cooled Oil Cooler