The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct. Multiple shock waves are formed inside the duct at a shock Mach number of 1.75. The duct has an exit height of H, and the effect of duct resonance on multiple shock oscillations is investigated by attaching exit ducts of lengths 0H, 50H, and 150H. The downstream disturbance frequency varied from 10 Hz to 200 Hz to explore the oscillation characteristics of the multiple shock waves. The oscillatory response of shock waves under self-excited and forced oscillation conditions are analyzed in terms of wall static pressure, shock train leading-edge location, shock train length, and the size of the separation bubble. The extent of the initial shock location increases with an increase in exit duct length for the self-excited oscillation condition. The analysis of the shock train leading edge and the spectral analysis of wall static pressure variations are conducted. The variation in the shock train length is analyzed using the pressure ratio method for self-excited as well as forced oscillations. The RMS amplitude of the normalized shock train length (ζ_ST) increases with an increase in the exit duct length for the self-excited oscillation condition. When the downstream perturbation frequency is increased, ζ_ST is decreased for exit duct configurations. For all exit duct designs and downstream forcing frequencies, the size of the separation bubble grows and shrinks during the shock oscillations, demonstrating the dependence on duct resonance and forced oscillations.

A pair of unidirectional turbines (UT) can operate in oscillatory airflow without additional units. However, this arrangement suffers from poor flow rectification. A fluidic diode (FD) offers variable hydrodynamic resistance based on the flow direction, and this can be coupled with UT to improve flow rectification. In this work, a numerical investigation on the effect of FD with UT is presented using the commercial fluid dynamics software ANSYS Fluent 16.1 with k-ω SST turbulence closure model. Periodic domains of UT and FD are numerically validated individually with experimental results. Later, both are coupled to obtain the combined effect, and these results are compared with the analytical approach. It was observed that coupling FD with UT improved the unit’s performance at the lower flow coefficient (<1), but its performance decreased as the flow coefficient increased. Due to the diode’s presence, fluid leaving the turbine experiences higher resistance at a higher flow coefficient, which decreases the overall performance of the combined unit.

双平板绕流属于基础流体力学问题，本文对不同端面形状的并列双平板流动与传热特性进行了数值计算。在不同倾角条件下，分析了不同端缘尺寸的倒角结构与圆角结构对并列双平板非稳态流动和传热特性的影响，结果发现，随着端缘尺寸的增加，流动的不稳定性与非定常性减弱；圆角与倒角平板的尾流速度不均匀性逐渐降低；尾流温度的不均匀性在小倾角下先增强后减弱，波动幅度在Srou(Scha)=3时最大，而在大倾角下基本保持单调增加。此外，平板的全局传热特性受端缘改型的影响明显，尤其是倒角结构，随着倒角尺寸的增加，全局努塞尔数基本呈减小趋势。该研究为平板结构在工程领域的应用提供了理论支持。

高温燃气入侵是指主流高温燃气流入涡轮盘腔的现象。以往的研究发现，主流环空压力分布在燃气入侵中起着重要作用，但由于其复杂性，主流流动与燃气入侵的相互作用机制尚不清楚。本文采用URANS数值方法，考虑C_w=0、C_w=500、C_w=5000等3种密封流量下的入侵机制。通过对时间平均主流环空压力的分析表明，随着密封流量的增加，主流压力值减小，并且密封流量对动叶前缘压力分布的影响远大于导叶尾缘压力分布的影响。对主流压力非定常时空分布的分析表明，当密封流存在时，轮缘处压力存在时空倾斜分布。这种现象主要是由于密封流对环空压力场的强反馈机制造成的。对比主流的压力分布和平均径向速度分布可以看出，入侵主要发生在动叶侧，而动叶侧的压力低于导叶侧。为此分析了密封流量C_w=5000时轮缘处的流动特性，提出了压力诱导入侵和通道涡入侵的两种入侵机制。主流在轮缘处的三维效应和惯性效应导致动叶侧分离涡的产生，分离涡的存在导致沿动叶侧入侵。同时，动叶侧的压力会使流体具有径向向内流动的倾向，这将促进分离涡的形成，导致动叶侧高压区域的入侵更加严重。动叶侧压力场比导叶尾缘压力场在轮缘处的入侵过程中更为显著，这有助于解释动叶的存在对燃气入侵的影响这个不确定的问题。