Experimental and numerical investigation on conjugate performance of fan and heat exchanger of helicopter oil cooling system

Abstract

In this article, a combined experimental and numerical study has been performed to investigate the operating performance of axial fan and oil cooling system. A test rig was established, and six types of plate-fin heat exchangers (HEs) with offset strip and rectangular fins and three different flow lengths of 30 mm, 60 mm and 90 mm at air side were designed and manufactured. The performance of an axial fan with front guide vane was experimentally studied by two different adjusting modes: gradually increasing and decreasing air flow rate. The conjugate performances of the axial fan and different HEs were discussed in detail. Moreover, a three-dimensional (3D) model was developed to investigate the flow distribution of the system including fan and 30 mm offset strip fins HE at different flow rates. The results show that: (1) the total pressure performance curve of the axial fan under two adjusting modes could form a hysteresis region near the stall boundary. In the hysteresis region, the fan performance curves showed significant difference under both adjusting modes; (2) when the offset strip fins HE with large flow resistance is considered, the system could have two theoretical working points in the hysteresis region. For the case of HE with 90 mm offset strip fins, the flow rates of the system at two theoretical working points were 25.1 m³/min and 34.2 m³/min, and the heat transfer capacity of the HE were 23.1 kW and 27.5 kW, respectively. In the current experiment, it was found that the system operated at the point with smaller flow rate; (3) when the HE flow resistance exceeded a certain value, the boundary layer separation of the airflow could occur at the rotor blade. The separation had a small effect on the inlet airflow due to its turbulence kinetic energy was low and basically the same at each blade passage. Therefore, the system did not surge or stall at small flow rate.