两种燃烧加热风洞参数匹配方案的比较

Comparison of Two Typical Flow-Parameter-Matching Schemes in a Combustion Wind Tunnel

关键词:  燃烧加热风洞  污染  匹配方案  准一维数值模拟

Key words:  Combustion wind tunnel  Vitiation  Matching scheme  Quasi-one-dimensional numerical simulation

摘要:

燃烧加热风洞中的地面高超声速试验通常模拟真实飞行状态下的静温，静压，马赫数(TPM)或总焓，动压，马赫数(h0QM)。为弄清气流参数匹配方式对发动机性能的影响及其机理，基于准一维带化学反应数值模拟对这两种典型匹配方案获得可靠的燃烧室压力分布与发动机推力及比冲的能力进行了比较。结果表明，对于氢燃料加热气流，若燃烧室内未出现明显的局部热壅塞引起的激波结构，TPM匹配方案能较好模拟纯空气流动当量比相同时的压力分布；h0QM匹配方案则能更好模拟燃料量相同的情况；对于模拟燃烧室热壅塞效应，h0QM匹配方案表现更好。从模拟发动机推力的角度来说，两种匹配方案均可通过调整燃油量达到与纯空气结果的较好契合，不管燃烧室内是否出现壅塞激波结构；从模拟燃料比冲的角度来说，则h0QM匹配方案更可靠。燃烧释热比不同是导致两种匹配方案表现不同的关键原因。对于酒精燃料加热气流，两种匹配方案下发动机性能相仿；但此时污染效应更强，给优化匹配方案以准确模拟发动机性能带来更多挑战。

Abstract:

Either the “static temperature + static pressure + flow Mach number (TPM)” or the “total enthalpy + dynamic pressure + flow Mach number (h0QM)” of the real fight conditions is generally simulated in ground-based hypersonic testing in a combustion wind tunnel. To clarify their influence mechanisms on the performance of a scramjet engine，the two typical sets of freestream parameter matching schemes were compared based on quasi-one-dimensional numerical simulation with chemical reaction，in respect of their capability of reliably reproducing the pressure distribution along the combustor and the thrust as well as the specific impulse the engine generates. It was found that for the hydrogen-vitiated flow，it is easier to select the TPM-matched scheme for identical fuel equivalence ratio and the h0QM-matched scheme for identical fuel mass flow rate，to better reproduce the combustor pressure distribution in real flight，if no local thermal-choking-induced shock structure is evident in the combustor. If thermal choking is likely to occur，the h0QM-matched scheme could reproduce the flow pattern more reliably. For the thrust of the engine，good agreement with that in clean air could be achieved by adjusting the fuel mass flow rate for both the two matching schemes，whether or not there is a shock in the combustor. To obtain a reliable fuel-based specific impulse，however，it seems the h0QM-matched scheme is a more appropriate choice. The disparity of combustion heat release ratio in the two matching schemes contributes heavily to the aforementioned differences. For the alcohol-vitiated flow，the engine performance appear nearly the same in the two matching schemes. In this case，the vitiation effect is aggravated so that it is more difficult to reliably reproduce the engine performance by adjusting the freestream parameters.