航空油冷三级式无刷发电机流固耦合传热研究及散热优化

Research on Fluid-Solid Coupling Heat Transfer and Optimization of Heat Dissipation in the Aircraft Oil-Cooled Wound Rotor Synchronous Generator

航空三级式无刷发电机具有高电负荷、高磁负荷、体积小、质量轻的特点,导致损耗大和散热困难,因此精确的温度场分析和高效的散热是实现航空三级式无刷发电机高功率密度设计和安全可靠运行的重要基础。该文首先以喷油冷却三级式无刷发电机作为研究对象,分析各级电机损耗的组成与分布特性。构建了考虑到气液两相流的三维全域流固耦合模型,深入探究油气两相混合分布状态。建立三级式无刷发电机温度场模型,研究了各级电机在不同工况下的局部热点分布特性。然后提出一种转子集成甩油盘的散热优化方法,对比研究了优化方法对冷却油分布规律和散热能力的影响,结果显示电机最高温升从71.9℃降到了62.6℃。最后通过样机实验验证了流固耦合传热研究的精确性和散热优化方法的有效性。

The wound rotor synchronous generator(WRSG),with its convenient magnetic field adjustment and brushless power generation features,is widely used in aircraft power systems.The electromagnetic load of the aircraft WRSG is high,leading to high loss density and temperature rise,and the high-temperature environment of the engine compartment also increases the risk of WRSG overheating.Excessive temperature rise can reduce the reliability and even cause WRSG failure in severe cases.Therefore,accurate temperature field modeling and efficient heat dissipation are critical to ensure the safe and stable operation of the WRSG and can also guide heat dissipation design.This paper analyzes the composition and distribution characteristics of WRSG losses and constructs a hybrid cooling method combined with spray oil cooling and cycling oil cooling.Based on the fluid-solid coupled heat transfer model,the uneven distribution characteristics of temperature are studied,and the spray oil method is further optimized to improve heat dissipation.This study focuses on the oil-spray-cooled WRSG as the research object.Firstly,the electromagnetic models of the main generator(MG),main exciter(ME),and permanent magnet generator(PMG)are established through the finite element method.Combined with the theoretical formulas,the loss composition and distribution characteristics of the WRSG are obtained.Considering the heat source distribution,a hybrid cooling structure combining spray oil cooling and cycling oil cooling is designed.The oil flows along the cycling cooling channel to cool the stator assembly of the MG and then enters the hollow shaft.Multiple sets of spray holes are set up in the hollow shaft.Under rotation,oil is sprayed into the WRSG cavity from the spray holes,which can directly contact the heat source of the WRSG,achieving efficient cooling.Then,the fluid-solid coupling model is established based on the parameter transfer relationship of multi-physics fields,and the fluid field of gas-liquid two-phase flow under rotation is numerically simulated based on the Realizable k-εturbulence model and Euler multiphase flow model.The oil friction loss is supplemented by analyzing the mixed distribution state of oil and gas.A three-dimensional temperature field model of the WRSG is established to obtain the temperature rise characteristics of each-stage generator under different working conditions,and the uneven temperature distribution characteristics of the WRSG are studied.The research found that the highest temperature appears at the end of the MG armature winding,followed by the MG excitation winding.In contrast,the temperature of the rotating rectifier and permanent magnet is lower,with a larger temperature rise margin.Further,an optimized method of oil-spray cooling based on the rotor-integrated oil slinger is proposed.Based on the original oil spray cooling,two oil slingers are installed on the spray oil holes on both sides of the MG.The oil slingers are installed coaxially.After the oil sprayed from the spray oil holes at both ends of the MG hits the oil slinger,it is atomized and thrown out by the centrifugal action of the high-speed rotation of the oil slinger.As a result,the situation where the MG excitation winding blocks the single straight-line jet is avoided,which can improve the oil distribution in the cavity.The heat source contacts more oil,improving the heat dissipation effect.Numerical analysis results show that this optimization method improves the oil volume fraction at the end of the MG armature winding and enhances the heat dissipation capacity.The highest temperature rise under rated load and overload has decreased by 18.5%and 12.9%,respectively,and the highest temperature rise of the WRSG has decreased from 71.9℃to 62.6℃.Finally,prototype experiments verify the accuracy of fluid-solid coupling heat transfer research and the effectiveness of oil-spray optimization methods.