栅格绕流数值模拟研究

栅格长宽比是影响栅格翼气动特性的重要参数,为研究它对栅格翼气动特性的影响规律,本文通过求解NS方程数值模拟研究单栅格长宽比对栅格气动特性的影响,并且对栅格边框厚度和形状对阻力的影响,在亚、跨、超声速多个马赫数下进行了数值模拟.结果显示,在所选择的长宽比范围内,长宽比对阻力的影响不大,对法向力有明显的影响,选择适当的栅格边框外形和厚度,可以大大减小栅格的阻力.     

Laser Shock Peening of Aluminum Alloy 7050 for Fatigue Life Improvement

The effects of laser shock peening (LSP) on improving fatigue life of aluminum alloy 7050 are investigated.Surface hardness is increased corresponding to a high dislocation density induced by LSP.The X-ray diffraction stress measurement shows that LSP results in prominent increase of surface compressive stress,quasi-symmetrically distributed in the laser peened region.The fatigue life of the alloy 7050 in rivet fastener hole structure is notably improved owing to LSP.The sequence of LSP and fastener hole preparation also influence the fatigue cycle life of the alloy.     

RANS/LES在超声速突起物绕流中的应用研究

安装在超声速/高超声速飞行器表面的突起物如机翼、控制舵等通常会导致复杂的激波/边界层干扰,对突起物的局部气动特性甚至飞行器整体的气动特性产生较大的扰动.在采用计算流体力学(CFD)数值模拟此类问题时,传统的求解雷诺平均Navier-Stokes(RANS)方程方法由于不能准确预测湍流脉动流场并且精度有限,在应用上受到一定的限制.本文在研究B-L (Baldwin-Lomax)内层模型和Smagorinsky亚格子模型优缺点的基础上,提出了一种新型的RANS/LES(Large Eddy Simulation)混合模型,并进行了算例验证,证实了该方法的可行性.在此基础上,对火箭表面突起物的干扰流场进行了数值模拟研究,细致地刻画了突起物附近的激波/边界层干扰、剪切层失稳和底部分离涡形成的非定常过程,获得了突起物及火箭表面上的压力脉动历程并进行了频谱分析.研究发现,相对于突起物底部的非定常分离流动,突起物前缘的激波和边界层相互干扰的非定常过程是突起物周围压力脉动的主导因素,这种高频的压力脉动可能对火箭内设备的正常工作产生不利的影响.     

高超声速激波/边界层干扰流动数值模拟研究

在基于Roe格式的全Navier-Stokes方程计算流体力学(CFD)代码中,发展了一种局部熵修正方法,克服了传统熵修正方法在边界层流动模拟中耗散过大的缺点,可用于更加准确的模拟激波/边界层干扰的复杂高超声速流动。对典型高超声速双锥边界层分离与激波干扰的复杂流动进行了模拟,研究了网格密度和熵修正方法耗散性对计算结果的影响。研究表明:高超声速双锥边界层分离与激波干扰流动的数值模拟结果对网格具有很强的敏感性,过稀的网格将产生严重的分离流动预测偏差;低耗散性的局部熵修正方法能更加准确地模拟复杂的高超声速激波与边界层分离流动干扰现象。     

热激励在超声速进气道内对激波诱导的边界层分离的控制机理

通过数值模拟的方法研究了马赫5的超声速进气道内,热激励对激波/边界层相互作用的控制机理。研究了热激励器放热功率(E)、热激励器展向放置数目(N)和热激励器到控制激波的距离(S)三个参数在超声速进气道内激波控制和边界层分离改善中的表现。分别针对以下四种条件进行了数值模拟:1)E=2k W、N=2、S=0.02m;2)E=3k W、N=2、S=0.02m;3)E=2k W、N=3、S=0.02m;4)E=2k W、N=2、S=0m。分析发现:在以上四种条件下,均可观察到热激励在控制激波和改善激波诱导边界层分离上有着显著的效果。热激励器的放热功率对激波的控制效果有着明显的影响,在本文所考虑的热激励能量范围内,放热功率越大,原激波角的改变越大,最终分离区的改变越明显;展向放置的热激励器数目N影响着输入到流场的能量密度,并且N越大,壁面附近的激波面越趋于平面。尽管N对上壁面沿展向的压力分布无明显影响,但对上壁面分离区大小有明显的影响;对比条件1和4下的计算结果,发现S=0.02m可以得到很好的控制效果,而S=0m时流场结构几乎没有变化,这就表明热激励器必须放置在控制激波上游的一定距离处才会有预期的效果。     

Thermal shock damage behavior of CVD ZnS by oxygen propane flame：A numerical and experimental study

Chemical vapor deposition zinc sulfide （CVD ZnS） is widely used as an infrared window material to transmit infrared signals, keep the aerodynamic shape and protect its imaging system, which often suffers high temperature and complicated thermal stresses. The purpose of this paper is to investigate the thermal shock damage of CVD ZnS through a finite element method and oxygen propane flame experiments. The finite element model is developed to simulate the temperature and thermal stress fields by an oxygen propane flame. Then, the thermal shock experiments are performed to investigate the thermal shock damage behavior. The results show that the temperature rising rate of the shock surface is fast during the initial heating stage resulting in high thermal stress. After the thermal shock experiment, the scanning electron microscope （SEM） photographs shows that the shock surface of the specimen becomes rough and the microcracks occur in the thermal shock zone. Good agreements are achieved between the numerical solutions and the experimental results.     

激波诱导矢量喷管动态数值模拟

对一二元收扩激波诱导矢量喷管进行了二维动态数值模拟,研究了不同落压比、不同次流加速时间下,喷管气动特性和流场结构随次流增加的变化规律。结果表明:喷管在过膨胀状态下,次流流量达到一定值时,其推力会有较强的振荡;在完全膨胀和欠膨胀状态下,振荡较小。其原因是,次流增加过程中,喷管出口附近有复杂波系存在和回流产生,而回流对提高推力和增加矢量角有益。     

降落伞充气理论的发展

综述了降落伞充气理论的研究成果与发展状况，内容涉及以质量守恒方程为基础的降落伞充气理论；以伞衣径向运动方程为基础的伞衣充气理论；流固耦合的伞衣充气理论。在介绍各种研究方法的同时，阐述了降落伞充气过程包含的复杂物理现象、研究难点及解决方法，最后指出了当前充气过程研究的热点及发展趋势。     

Implications of a weak termination shock

Recent observations from the Voyager spacecraft have suggested that the spectrum of the anomalous cosmic ray component is relatively steep at the termination shock, which is believed to be responsible for accelerating these particles. This conclusion argues that the termination shock must be weak, which in turn requires that the upstream Mach number in the solar wind must be quite low, 2.4. It is pointed out that such conditions are unlikely to prevail at all locations along the shock front. However, it is possible for such conditions to exist at the interface between high speed streams at high heliographic latitudes and the region at low latitudes where high and low speed streams have interacted and come into equilibrium. This discussion suggests a preferred location for the injection of the anomalous component into the shock acceleration process.     

激波绕射方台的非定常流场研究

本文以数值方法研究了运动激波绕射矩形突台的非定常流场发展过程。计算中采用ＴＶＤ格式，得到了清晰的流场变化图谱。从流场图中可分辨出旋涡的形式过程及分离域形态。研究结果表明，本方法可以很好地描述激波绕射方台形成的复杂流动过程，对流场间断有较高的捕获力。