A parametric fin structure design study for cooling aerospace electro-mechanical actuators with high-speed axial fans

Despite their advantages compared to hydraulic actuators, electric actuators are prone to overheating due to their high heat dissipation. So, developing reliable cooling systems for electric actuators is a crucial task, especially for aerospace applications which require the fulfillment of high safety requirements. In this paper, an air-cooling system utilizing wing bay air is investigated. An axial fan sucks air to flow through a shrouded-fin surface attached to the motor housing. A CFD model is developed to study the heat transfer and air flow processes over the finned surface. The relation between the fan pressure jump with the volumetric flow rate of a high speed SUNON fan at different rotational speeds and ambient pressures is measured in a fan loop and incorporated in the model. To validate the CFD results, a test rig consisting of a finned surface brazed on a heated aluminum cylindrical block and attached to a fan is built. The predicted and measured temperatures at different locations in the aluminum block show good agreement when the numerical simulation is performed using the k-omega-SST turbulence model. The average discrepancy of the predicted and measured steady state temperature differences (T-T-infinity) reduces from 1.6 degrees C for the k-epsilon Realizable model to 0.31 degrees C for the k-omega SST model. Numerical simulation is performed to predict the effect of fin shape, fin number and fin thickness on the cooling performance of the fin structure. The results show that the straight plate fin configuration outperforms the offset-strip and corrugated fin. Also, it is found that there is an optimum value for the fin number, and this optimum fin number changes with the fan rotational speed and ambient pressure. Reducing the solidity of the fin structure by reducing the fin thickness results in improving the thermal performance when the fan operates at a low ambient pressure (0.2 atm). By comparing all data, it is found that the straight fin structure with 110 fins and fin thickness 0.2 mm is the optimum one. For fan speed of 12,000 rpm, this structure can restrict the thermal resistance between 0.17 degrees C/W at 0.2 atm and 0.047 degrees C/W at 1.0 atm.