Comparison of two axial fans for cooling of electromechanical actuators at variable pressure

Abstract Electro-Mechanical Actuators (EMAs) in the aerospace field will provide major benefits to reduce overall weight, cost, and easier maintenance when servicing the aircraft. In the present study, two cooling fans were tested experimentally to determine the effects of the blade count and ambient pressure on the fan performance and efficiency. Both fans were tested at the same rotational speed of 13,000 rpm and four pressure conditions, (1, 0.7, 0.5, 0.3) atm. The lowest ambient pressure tested was 0.3 atm. Typical commercial aircraft operate at this ambient pressure at cruising altitudes. Selecting a 2-bladed and 7-bladed fan accommodates for testing of the extrema in terms of solidity, fan performance, and efficiency. The 7-bladed fan yielded the best performance to the 2-bladed fan in terms of static pressure to the volumetric flow rate, but the 2-bladed fan demonstrated to operate more efficiently than the 7-bladed fan in some ambient pressure conditions. The 7-bladed fan demonstrated turbulent flow regimes with Reynolds numbers, Re ≫ 4000, for all cases except for at the high resistance when operating at 0.3 atm.; on the other hand, the 2-bladed fan-operated in the laminar and transitional flow regimes for 0.3 atm. and during shutoff conditions at 0.5 atm. The higher Reynolds numbers allow for more air mixing which will, in turn, enhance the cooling of the system. In terms of volumetric flow rate delivery, the higher blade counts can deliver higher volumetric flow rates. The smaller blade counts perform more efficiently at (0.7, 0.5) atm which is due to lower power requirement to drive the blades. The current work addresses the effects of pressure on fan efficiency and performance. Both fans demonstrated higher efficiencies at pressure lower than ambient pressure due to the density changes at the lower pressure conditions.

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