可调混压进气道超额定工况黏性作用理解

Understanding on Viscous Effect for a Variable-GeometryMixed-Compression Inlet at Over-Speed Regime

关键词:  超声速混压式进气道  变几何  超额定  黏性效应  数值模拟

Key words:  Supersonic mixed-compression inlet  Variable-geometry  Over-speed regime  Viscous effect  Numerical simulation

摘要:

进气道研制在各阶段均需要好用的设计方法，第一步是用无黏波系理论设计进气道的波系和流道参数。在实际的黏性条件下，超额定工况黏性流场结构非常复杂，基于无黏波系理论的设计方法在逻辑上难以封闭，理解黏性作用的机制和后果，有可能改善无黏方法在超额定工况的适用性，或者提出黏性修正的经验指导。针对设计点马赫数为2.5的可调混压式超声速进气道超额定工况内流道入口波系设计问题，用数值模拟方法，研究理解了超额定工况黏性流场结构生成机制，与无黏设计相比，初始黏性结构（边界层、滑移层）使无黏流道流通能力下降，产生的限流反压迫使上游激波系强化、分离区与激波干扰结构调整，当流动结构产生的溢流量足够大、入流流量与当地流动结构的流通能力相匹配时，即获得新的平衡流场。喉道高度补偿和消除滑移层吞入的尝试验证了上述理解。在反压或限流制造的临界工况，存在局限于内压缩段的“初始不稳定性”（或小喘）现象，可能与滑移层在核心流的摆动范围大有关。在马赫数为3的超额定条件下，喉道补偿系数超过35%可获得期望的波系结构，临界的“初始不稳定性”消失。增大第二级压缩角，使外压缩激波与唇口激波不相交于内流道所在高度范围，消除滑移层生成条件，在相同反压条件下消除了“初始不稳定性”现象，或者说提高了抗反压能力。

Abstract:

Proper (or good) and different design methods are needed for supersonic inlet development in different phases. The first stage is certainly concerned about shock system design with inviscid theory, and inlet geometry as well. However, in the reality of viscous conditions, flow structure is extremely complex at over-speed regime. Therefore inlet design method on the basis of inviscid theory, is unclosed in design logic. Understanding viscous effect and its outcomes may be helpful to improve inviscid theory applicability for over-speed regime at the first stage of inlet design, or may provide some empirical guidances for viscous modification. For a variable-geometry mixed-compression inlet designed at Mach 2.5, this paper investigated the reforming mechanism of viscous flow structure at Mach 3(over-speed regime).Flow structures of some geometry designs are obtained and analyzed. It shows, compared with inviscid flow structure, initial viscous structures, such as boundary layer near walls and free shear layers from shocks intersection point, decrease the transport capability of internal path. The back-pressure resulted from throttling effect compels upstream shocks strengthened, forming separation region and shock interaction structure. New balance is established when spillage is enough and inflow equals local outflow everywhere in virtue of the reformed flow structures. Efforts of compensation for throat height and elimination of shear layer in core flow validate this mechanism understanding. At critical regime induced by back-pressure or throttling there exist a kind of ‘initial instability’ or ‘little buss’ phenomenon, which may be an inhesion resulted from the distinct swings of inflow free shear layers. Designed shock system can be obtained and ‘initial instability’ disappears when throat height compensation rate is over 35%. Increasing the second external compression angle makes the intersection point go away from the region of internal path. So the condition to develop a shear layer is eliminated. ‘Initial instability’ disappears at the same back-pressure, which means the inlet ability has been improved to endure higher back-pressure.