Simulation and analysis on the motion characteristics of shock train under dynamic throttle
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摘要: 为研究动态反压下的激波串特性，针对一种带凹腔的二元进气道/隔离段构型，在马赫数为6的来流下模拟了堵塞比从0.20增长到0.32再保持不变的动态节流流动，分析了堵塞比增长时间（1～10 ms）对激波串运动的影响。结果表明：激波串在节流变化初期向下游运动，随后向上游运动并最终稳定在某一位置。当堵塞比增长时间在5 ms以内时，激波串向下游和向上游运动的幅度分别为3 mm以内和约18 mm，且激波串运动滞后于节流变化，滞后时间随着增长时间的延长而缩短。当增长时间大于等于6 ms时，激波串可向下游运动到凹腔中部，幅度可达31 mm，并伴随着流动振荡；向上游运动幅度仍约为18 mm，激波串运动与节流变化近似同步。分析表明：较短增长时间工况下，激波串运动滞后主要是因为节流引起反压升高、传播时间大于堵塞比增长时间；较长增长时间工况下，凹腔内流动振荡主要是堵塞比增长初期凹腔亚声速区排出流量增加，回流区横向尺度减小，导致凹腔超声速区膨胀并出现“壅塞”，产生分离激波与回流区相互作用、发生振荡。工程设计时应考虑激波串运动的滞后及其对流动性能的影响。Abstract: To investigate the shock train characteristics under the influence of dynamic backpressure, the dynamic throttle flows of a two-dimensional inlet/isolator configuration were simulated under Mach 6 free steam condition, where the throttle ratio increased from 0.20 to 0.32 and were kept constant. The effects of increasing time （varied from 1–10 ms） of the throttle ratio were analyzed. The results show that the amplitudes of the shock train downstream motion and the upstream motion are within 3 mm and about 18 mm, respectively, as the throttle ratio increases from 0.20 to 0.32 within 5 ms. The shock train motion lag behind the throttle process and the lag time decreases with the prolongation of the throttle variation time. When the increasing time of the throttle ratio was 6 ms and above, the shock train could move downstream to the middle of the cavity and the motion amplitude reached 31 mm, accompanied by flow oscillations. The upstream motion amplitude of the shock train was still about 18 mm and the shock train motion was approximately synchronized with the throttle process. The analysis showes that the lag of the shock train motion is related to the time intervals of back pressure increment and propagation, which is longer than the variation time of the throttle ratio under the condition of short increasing time. Under the long increasing time conditions, the flow oscillations are related to the increase of the mass flowrate in the subsonic section of the cavity, which dominates the shrinkage of the recirculating region in the cavity. This further causes the expansion of the supersonic flows near the cavity and generates choked flows near the throttle region. Therefore, flow oscillations are generated through the interactions between the separated shock wave flows of the choked flows and the cavity recirculating region. The lag of the shock train motion and its influence on flow performance should be considered in engineering design.
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Key words:
- scramjet engine /
- shock train /
- dynamic backpressure /
- hypersonic inlet /
- flow separation
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图 4 定堵塞比下进气道内部流动结构
Figure 4. Internal inlet/isolator flowfield at constant blockage ratios
图 5 定堵塞比工况隔离段下壁面压比曲线
Figure 5. Wall pressure of inlet/isolator section at constant blockage ratios
图 6 ∆t =1 ms工况典型时刻的流场横向密度梯度云图
Figure 6. Contour of transverse density gradient at various times of 1 ms increasing condition
图 7 不同堵塞比增长时间下激波③的流向坐标–时间曲线
Figure 7. Time histories of streamwise coordinate of shock ③ under various increasing time intervals
图 8 Δt=6 ms工况典型时刻的流场横向密度梯度云图
Figure 8. Contour of transverse density gradient at various times under 6 ms increasing time condition
图 9 Δt=10 ms工况典型时刻流场横向密度梯度云图
Figure 9. Contour of transverse density gradient at various times under 10 ms increasing time condition
图 10 节流变化起始和流场稳定状态流动示意图（低速区，vx≤900 m/s）
Figure 10. Flow schematic diagram of the initial and final conditions of dynamic throttle（low speed zone, vx ≤ 900 m/s）
图 11 典型截面质量流量随时间变化曲线
Figure 11. Time histories of mass flowrate of typical cross sections
图 12 典型截面超声速区和亚声速区质量流量随时间变化曲线
Figure 12. Time histories of mass flowrate of supersonic and subsonic regions in typical cross sections
图 13 典型工况下壁面（y=0.06311 m）扰动传播速度x–t云图
Figure 13. Contours of disturbance spread speed on the bottom surface （y=0.06311 m） under typical conditions
图 14 凹腔流动振荡示意图（Δt=6 ms）
Figure 14. Schematic diagram of the cavity oscillation flows （ Δt=6 ms）
表 1 CFD计算工况列表
Table 1. Conditions of CFD simulations
初始堵塞比 结束堵塞比 Δt /ms 0.20 0.32 1、2、4、5、6、8、10 
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表 2 自由来流参数
Table 2. Free stream airflow parameters
变量 参数 马赫数（Ma） 6 静压（p∞）/Pa 1050 静温（T∞）/K 115 速度（v∞）/（m·s−1） 1268 单位雷诺数Reunit/m−1 5.06 ×106
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