强梯度复杂流场中的粒子动力学响应试验研究

示踪粒子在(高)超声速流场中的动力学响应是粒子成像测速等粒子示踪测量技术的关键问题之一.现有文献对粒子动力学响应的试验测量往往是通过单个斜激波响应的测量方法.然而,当示踪粒子用于测量高速飞行器发动机内部复杂的激波串流场时,粒子将经历由多道激波导致的速度、压力、黏性等剧烈变化.本文结合目前(高)超声速飞行器的研究热潮,重点关注示踪粒子在应用于发动机内部具有连续激波的复杂流场测量中存在的跟随性评估方面,开展了一系列的相关试验研究.包括测量超声速风洞的喷管出口速度分布以验证测试系统的性能,在马赫4.2和3.0流场中测量了粒子对二维10°和15°单斜劈绕流中的斜激波动力响应,并测量了模拟发动机内部连续梯度的双斜劈粒子斜激波动力响应.结合粒子动力学的理论模型,得到了各状态的粒子弛豫时间、弛豫距离、Stokes数.基于图像方法、统计学规律分析了激波非定常抖动对测量结果的影响,并对测量结果进行了修正.结果显示,相同斜劈角度下,马赫数越高,粒子的弛豫时间、弛豫距离就越大.但是在相同的来流马赫数下,斜劈角度越大,粒子的弛豫时间、弛豫距离反而减小.在强梯度之后由于流场的雷诺数和黏性系数变化剧烈,粒子的跟随性降低了大约5.7%,stokes数增加了约1%.虽然在本文条件下Stokes数仍满足超声速流场对粒子跟随性的要求,但粒子响应的降低无疑是值得关注的,尤其是当其被应用于具有更多连续梯度的复杂流场测量中.

Experimental study on of dynamics of particles in the flow filed with intensive gradients

The dynamic response of particles in hyper/supersonic flow is one of the key points of techniques using tracer particles, such as particle image velocimetry (PIV). In the literature, it is validated by the single oblique shock response testing. However, particles suffer intensive variation of velocity, density and viscosity, when used to trace and measure the complex flow field in the high speed vehicle engine. To test and validate the dynamics of particles in such a flow field with intensive gradient, in this paper we conduct a series experiments dealing with this issue. The study includes the measurements on the velocity field at the exit of the wind tunnel nozzle to testify the performance of PIV system, the measurements on the oblique shock response of particles in Mach 4.2 and Mach 3.0 supersonic flows over a 10° wedge and a 15° wedge respectively, and measurements on the double oblique shock response of particles in the flow field which is designed to simulate the flow field inside the vehicle engine with gradients and without the influence of expansion wave. Based on the particle dynamic models, the relaxation time, relaxation distance, Stokes numbers of different cases can be gained. And the influence of unstable shock oscillation is analyzed and revised based on image method and statistic analysis. It can be found that the relaxation time and distance increase with the Mach number, given the same wedge degree. However, with the same incoming Mach number, the relaxation time and distance drop when the wedge degree increases. Due to the intensive variation of Reynolds number and viscosity, the results show that in a certain extent particles lose their following ability by 5.7%, while its Stokes number increases by 1%. In the flow condition herein, the Stokes number still meets the requirement of supersonic flow. However the decrease of particle following ability is worth being concerned, especially when using particles in the complex flow field with more intensive gradients.
Keywords： particle dynamics supersonic flow shock waves measurement