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随着高超声速飞行器的不断更新换代, 对成像窗口提出了新的设计要求, 即共形窗口以提高气动特性, 这要求在超声速气膜和光学窗口需要与飞行器机身保持相同的曲率外形. 在马赫数 Ma= 6高超声速静风洞中开展了凸曲率壁面(CV)混合层稳定性研究. 采用基于纳米粒子的平面激光散射技术捕获到混合层流场结构, 结合分形维数对混合层失稳规律进行研究. 使用数值模拟技术得到了压力、压缩冲量( I p)沿流向演化结果. 结果表明: 随着来流总压( P 0)的增大, 静压比(RSP)减小, 混合层失稳位置延迟, 典型涡结构移动速度增大. CV壁面由于顺压梯度的存在使得压力沿流向下降, 沿壁面切向的超声速气膜处于工作状态时, 可以提升壁面压力, 随着 P 0增大, RSP随之降低, 提升效果下降; 流动受到CV的膨胀效应影响, I p沿流向下降, 超声速气膜可以削弱CV上的膨胀效应从而抑制 I p的下降; 压缩冲量的变化率Δ I p受 P 0影响显著, 在弯曲冲量| I Φ| = 0.191—3.624内, 当 P 0= 0.5 MPa, Δ I p从178.67%降至12.02%; 当 P 0= 1.0 MPa, Δ I p从40.38%降至5.64%. Δ I p随| I Φ|增大而降低, 随着 P 0增大, 降低幅度减小. 结果揭示凸曲率影响下的高超声速混合层流动演化规律, 对高超声速飞行器实现气动减阻与防热特性的外形设计提供一定参考.With the continuous upgrading of hypersonic vehicles, a new requirement for designing imaging window i.e. conformal window for improving aerodynamic characteristics, is put forward, in which the supersonic cooling film and optical window are required to maintain the same curvature shape as the aircraft body. In this work, the mixed-layer flow evolution on a convex wall (CV) is investigated. A nanoparticle-based planar laser scattering technique is used to design the flow field structure of the mixed layer in Ma= 6 hypersonic static wind tunnel, and the location of the mixed-layer instability is studied by combing fractal dimension. The results of pressure, and impulse of compression ( I p) evolution along the flow direction are obtained by numerical simulation, showing that the total incoming pressure ( P 0) has a significant effect on the flow evolution of the mixed layer: as P 0increases, the ratio of static pressure (RSP) decreases, that the position of the mixed-layer instability is delayed, and that the flow velocity of the typical vortex structure increases. The favorable gradient existing at the CV wallleads the pressure to drop along the flow direction, and the pressure is enhanced when the supersonic air film along the tangential direction of the wall is under the operating condition. However, as P 0increases, the RSP decreases, and the lifting effect of the pressure on the CV decreases. The flow field is affected by the expansion effect of the CV, and I pdecreases along the flow direction. The supersonic air film can weaken the expansion effect on the CV and thus suppressing the decrease of I p. The change rate of I p(Δ I p) is significantly affected by P 0, in a range of bending impulse | I Φ| = 0.191–3.62, Δ I pdecreases from 178.67% to 12.02% when P 0= 0.5 MPa, and Δ I pdecreases from 40.38% to 5.64% when P 0= 1.0 MPa. Δ I pdecreases as | I Φ| increases, but the decrease becomes less as P 0increases. The results reveal the flow evolution law of hypersonic mixed layer under the influence of convex curvature, and provide a certain reference for designing the shape of hypersonic vehicle to achieve aerodynamic drag reduction and thermal protection characteristics.
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Keywords:
- hypersonic/
- mixed layer/
- fractal dimension/
- impulse of compression
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