高超声速发动机碳氢燃料预冷器换热特性

Heat transfer characteristics of a hydrocarbon fuel precooler for hypersonic engines

将预冷过程引入高超声速涡轮发动机可以降低进入压气机的空气温度,提高可用增压比,增加发动机推力。为研究预冷器热力性能变化规律,对预冷器的结构形式和换热形式进行了分析,建立了以高热沉碳氢燃料为冷源的渐开线型预冷器分段热力计算模型,指出冷热流体均经历大温度变化的预冷器必须分段进行热力计算。研究了燃油流量、空气出口温度、预冷器结构参数等因素对预冷器热力性能的影响,得出结论:由于微细换热管数量达到数万量级,管内流动层流占比较大;燃油流量增加时,预冷器冷却能力增强且重量减轻,但吸热后的燃油不一定能全部用于燃烧,造成推力浪费;降低空气出口温度有助于提升发动机推力性能,但会造成预冷器重量增加和空气压力损失增大;管束横纵向间距均为1.5倍管径时,顺排相比于叉排排列,空气侧对流换热能力差,预冷器重量和空气压降均较大;管束横纵向间距对预冷器热力性能有较复杂影响。研究结论可为未来相似结构管束式预冷器的设计、验证和性能分析提供支撑。

Introducing a pre-cooling process into the air intake of a hypersonic turbine engine can reduce the temperature of the air entering the compressor and increase the available pressure ratio and the engine thrust.To study the thermodynamic performance of the precooler,the structure and heat exchange of the precooler have been investigated in detail,and a segmented thermodynamic calculating model for an involute precooler using high heat sink hydrocarbon fuels as the cold source is established.Results suggest that the thermodynamic calculation for a precooler must be performed in segments when both cold and hot fluids experience large temperature variations.The influence of the fuel mass flow rate,air outlet temperature,and precooler structural parameters on the thermodynamic performance of the precooler are studied.A tremendous amount of micro heat exchange tubes lead to almost laminar flows in the tube.With the increase of the fuel flow rate,the cooling capacity of the precooler is enhanced,and the weight is reduced,but the fuel after heat absorption might not be totally used for combustion,resulting in thrust waste.Lowering the air outlet temperature helps improve the engine thrust performance,but will increase the precooler weight and air pressure loss.When the transverse and longitudinal pitches of the tube bundle both are 1.5 times of the tube diameter,compared with the staggered arrangement,the air-side convection heat transfer capacity for the in-line arrangement deteriorates,and the precooler weight and air pressure loss are both larger.The transverse and longitudinal pitches of the tube bundle have complicated influence on the thermodynamic performance of the precooler.This work can provide strong support for the design,verification,and performance analysis of the tube bundle precooler with similar structures in the future.