The Richtmyer–Meshkov instability of a 'V' shaped air/helium interface subjected to a weak shock

The Richtmyer-Meshkov instability ofa ‘V＇ shaped air/helium gaseous interface subjected to a weak shock wave is experimentally studied. A soap film technique is adopted to create a ‘V＇ shaped interface with accurate initial conditions. Five kinds of ‘V＇ shaped interfaces with different vertex angles are formed to highlight the effects of initial conditions on the flow characteristics. The results show that a spike is generated after the shock impact, and grows constantly with time. As the vertex angle increases, vortices generated on the interface become less noticeable, and the spike develops less pronouncedly. The linear growth rate of interface width after compression phase is estimated by a linear model and a revised linear model, and the latter is proven to be more effective for the interface with high initial amplitudes. The linear growth rate of interface width is, for the first time in a heavy/light interface configuration, found to be a non-monotonous function of the initial perturbation amplitude-wavelength ratio.

Life test research of a high specific impulse Hall thruster HEP-140MF

In this study,a high specific impulse Hall thruster,HEP-140 MF,having a high discharge voltage,was used to accelerate ions.We aimed to obtain a high specific impulse and an acceleration zone moving downstream toward the channel exit to reduce wall sputtering erosion of the walls of the discharge channel,hence ensuring an enhanced lifetime.To study the lifetime characteristics of the high specific impulse Hall thruster,a life test was performed on the HEP-140 MF thruster for the first time,and performance parameters,such as thrust,specific impulse,and efficiency,were measured.Changes in the performance parameters and evolutions in the surface profiles of the discharge channel wall were summarized.The reasons contributing to these changes during the life test were analyzed.Moreover,the accelerated life test method was validated on the HEP-140 MF.

The View of Micropropulsion Technology for China’s Advanced Small Platforms in Deep Space

In this paper,micropropulsion systems are analyzed in conjunction with the various mission requirements of China’s deep space exploration.As a great challenge facing the world,deep space exploration can be enabled only in a few countries with a success rate of around 50%.With the advancement of spacecraft and scientific instruments,it is now feasible to build small and low-cost spacecraft for a variety of deep space missions.As spacecraft become smaller,there is a need for proper micropropulsion systems.Examples of propulsion system selections for deep space exploration are discussed with a focus on products developed by Beijing Institute of Control Engineering(BICE).The requirements for propulsion systems are different in lunar/interplanetary exploration and gravitational wave detection.Chemical propulsion is selected for fast orbit transfer and electric propulsion for increasing scientific payloads.Cold gas propulsion and microelectric propulsion are good choices for space-based gravitational wave detection due to the capability of variable thrust output at the micro-Newton level.The paper also introduces the sub-1-U micropropulsion modules developed by BICE with satisfactory performance in flight tests,which are promising propulsion systems for small deep space platforms.A small probe with an electric sail propulsion system has been proposed for the future solar system boundary exploration of China.The electric sail serves as not only a propellant-free thruster but also a detector probing the properties of the space medium.

High temperature effects in moving shock reflection with protruding Mach stem

The influence of high temperature effects on the protrusion of Mach stem in strong shock reflection over a wedge was numerically investigated. A two-dimensional inviscid solver applies finite volume method and unstructured quadrilateral grids were employed to simulate the flow. Theoretical analysis was also conducted to understand the phenomenon. Both numerical and theoretical results indicate a wall-jet penetrating forward is responsible for the occurrence of Mach stem protrusion. The protrusion degree seems to depend on the thermal energy buffer capacity of the testing gas. Approaches to increase the energy buffer capacity, such as vibrational relaxation, molecular dissociation, and increase of frozen heat caoacitv, all tend to escalate the orotrusion effect.

Numerical study on shock-dusty gas cylinder interaction

The interaction of a planar shock wave with a dusty-gas cylinder is numerically studied by a compressible multi-component solver with an adaptive mesh refinement technique. The influence of non-equilibrium effect caused by the particle relaxation, which is closely related to the particle radius and shock strength, on the evolution of particle cylinder is emphasized. For a very small particle radius, the particle cloud behaves like an equilibrium gas cylinder with the same physical properties as those of the gas-particle mixture. Specifically, the transmitted shock converges continually within the cylinder and then focuses at a region near the downstream interface, producing a local high pressure zone followed by a particle jet. Also, noticeable secondary instabilities emerge along the cylinder edge and the evident particle roll-up causes relatively large width and height of the shocked cylinder. As the particle radius increases, the flow features approach those of a frozen flow of pure air, e.g., the transmitted shock propagates more quickly with a weaker strength and a smaller curvature, resulting in an increasingly-weaken shock focusing and particle jet. Also, particles would escape from the vortex core formed at late stages due to the larger inertia, inducing a greater particle dispersion. It is found that a large particle radius as well as a strong incident shock can facilitate such particle escape. The theory of Luo et al.(J. Fluid Mech., 2007) combined with the SZ circulation model ( J. Fluid Mech., 1994) can reasonably explain the high dependence of particle escape on the particle radius and shock strength.

On transition of type V interaction in double-wedge flow with non-equilibrium effects

The transition between regular reflection （RR） and Mach reflection （MR） of type V shock-shock interaction on a double-wedge geometry with high temperature non-equilibrium effects is investigated by extended shock-polar method and numerical simulation. First, the critical angles of transition from detachment criterion and yon Neumann criterion are determined by the extended shock-polar method considering the non-equilibrium effects. Then wave patterns and the transition process are numerically obtained. Results of the critical transition angles from shock-polar calculation and numerical simulation show evident disagreement, indicating transition mechanism between RR and MR of type V interaction is changed. By comparing with the frozen counterpart, it is also found that non-equilibrium effects lead to a larger critical wedge angle and a larger hysteresis interval.

Review on hydrodynamic instabilities of a shocked gas layer

Hydrodynamic instabilities induced by a shock wave can be observed in both natural phenomena and engineering applications,and are frequently employed to study gas dynamics, vortex dynamics, and turbulence. Controlling these instabilities is very desirable, but remains a challenge in applications such as inertial confinement fusion. The field of “shock-gas-layer interaction” has experienced rapid development, driven by advances in experimental and numerical techniques as well as theoretical understanding. This domain has uncovered a diverse array of wave patterns and hydrodynamic instabilities, such as reverberating waves, feedthrough, abnormal and freeze-out Richtmyer-Meshkov instability, among others. Studies have shown that it is possible to suppress these instabilities by appropriately configuring a gas layer. Here we review the recent progress in theories,experiments, and simulations of shock-gas-layer interactions, and the feedthrough mechanism, the reverberating waves and their induced additional instabilities, as well as the convergent geometry and reshock effects, are focused. The conditions for suppressing hydrodynamic instabilities are summarized. The review concludes by highlighting the challenges and prospects for future research in this area.

Mode coupling in converging Richtmyer-Meshkov instability of dual-mode interface

The converging Richtmyer-Meshkov(RM)instability on single-and dual-mode N2/SF6 interfaces is studied by an upwind conservation element and solution element solver.An unperturbed case is first considered,and it is found that the shocked interface undergoes a long-term deceleration after a period of uniform motion.The evolution of single-mode interface at the early stage exhibits an evident nonlinearity,which can be reasonably predicted by the nonlinear model of Wang et al.(Phys Plasmas 22:082702,2015).During the deceleration stage,the perturbation amplitude drops quickly and even becomes a negative(phase inversion)before the reshock due to the Rayleigh-Taylor(RT)stabilization.After the reshock,the interface experiences a phase inversion again or does not,depending on the reshock time.The growth of the second-order harmonic in the deceleration stage clearly reveals the competition between the RT effect and the nonlinearity.For dual-mode interfaces,the growth of the first mode(wavenumber k1)relies heavily on the second mode(wavenumber k2)due to the mode coupling effect.Specifically,for cases where k2 is an even or odd multiple of k1,the growth of the first mode is inhibited or promoted depending on its initial amplitude sign and the phase difference between two basic waves,while for cases where k2 is a non-integer multiple of k1,the second mode has negligible influence on the first mode.Through a systematic study,signs of perturbation amplitudes of the generated k2−k1 and k2+k1 waves are obtained for all possible dual-mode configurations,which are reasonably predicted by a modified Haan model(Phys Fluids B 3:2349-2355,1991).

Energy convergence effect and jet phenomenon of shock-heavy spherical bubble interaction

We present computational results on the evolution of the shock-accelerated heavy bubbles surrounded by nitrogen with the Atwood number At = 0.497–0.677 and the emphasis is on the jet phenomenon caused by the shock focusing. The multi-fluid Eulerian equation is solved by a finite volume method based on MUSCL-Hancock approach. Based on the numerical schlieren and the distributions of density and pressure, it is found that there are three typical jet structures(outward jet, no jet, inward jet) for different combinations of gas mixture inside the bubble which determine the position of shock focusing relative to the downstream pole of the heavy bubble(upstream of the pole, at the pole, downstream the pole). Compared with the inward jet, the velocity of outward jet is obviously larger. As At increases, the moment of jet formation is postponed, and the maximal values and magnifications of pressure and density increase distinctly. Therefore, the energy convergence effects are heavily enhanced with the increase of bubble gas density.

平面激波冲击双层重/轻界面的不稳定性研究

采用可压缩多组分流动高精度求解器数值研究平面激波冲击SF_(6)/Ar/He双层界面(SF_(6)/Ar界面有正弦扰动,Ar/He界面无扰动)的不稳定性问题,重点考察激波强度和界面间距对不稳定性发展的影响.结果表明,在入射激波冲击后第一道界面振幅会逐渐减小到零(反相),随后在相反的方向上持续增长.从第二道界面上反射回来的稀疏波促进或抑制第一道界面的扰动发展,这取决于界面间距D.具体地说,如果D很小,稀疏波在到达第一道界面时界面还没有完成反相,那么会促进第一道界面的扰动发展;如果D很大,稀疏波到达时第一道界面已完成反相,那么会抑制第一道界面的扰动发展.对于任意初始条件,存在一个临界距离,在此距离下稀疏波作用第一道界面时界面刚好完成反相.本文提出了计算这一临界距离的理论模型,为调控第一道界面的扰动增长速率提供了理论支撑.第二道界面的失稳是由扰动透射激波冲击无扰动界面引起的,属于非标准Richtmyer-Meshkov(RM)不稳定性问题,其扰动增长速率强依赖于冲击界面时扰动激波的相位.本文发现Ishizaki模型由于忽略斜压涡量的影响,不能准确预测第二道界面上的扰动增长.综合考虑斜压涡量、速度扰动和压力扰动的影响,本文提出了一个修正的非标准RM不稳定性理论模型,可以对第二道界面的扰动发展给予有效预测.