Interference of nonstationary oblique shock waves

Special features of calculation of the flow parameters behind a nonstationary oblique shock wave moving in a stream of absolutely nonviscous gas are considered. The wave intensity at which the stream behind the shock wave may exhibit singularities is determined. The problem of calculating a nonstationary shock wave configuration formed during the interaction of a supersonic jet with an obstacle is solved.     

Relaxation of the shock-wave configuration in a diffuser after termination of the action of magnetic and electric fields

The pulsed interaction of an ionized gas flow in a full-internal-compression diffuser with magnetic and electric fields has been experimentally studied. The interaction is determined by the shape of the electric current pulse between electrodes situated in the initial part of a hypersonic diffuser. It is established that, after termination of the current pulse, some characteristics of the shock wave front configuration in the gas flow exhibit relaxation with a significant delay to the unperturbed values.     

Experimental and numerical simulation of the flow in a driving module with an annular and linear double-slot nozzle

This paper presents the results of numerical and experimental studies of the flow and comparison of propulsion performance characteristics of a model of a jet engine exhaust system equipped with an annular or (equivalent in gas consumption) linear double-slot nozzle with an inner cavity and circular segment deflector in the axial section. Calculations performed for the annular nozzle and double-slot nozzle corresponding to it in geometric parameters demonstrate that a flow similar to the flow in nozzles with a central body is formed in the exhaust system. According to the data obtained, the initial turn of the flow takes place in the oblique shock wave. In the double-slot nozzle, the final turn of the flow in the direction of the thrust vector occurs in a configuration of four shock waves positioned downwards in the flow; in the annular nozzle, it is in the intense barrel shock wave. It was established that the exhaust system with an annular of the linear doubleslot nozzle develops a thrust and specific impulse that exceed the corresponding values for the sonic nozzle equivalent in gas consumption by almost a factor of 2.     

The effect of MHD interactions on the input shock waves in a supersonic diffuser

The interaction with an external magnetic field modifies the variation of the shock wave configuration in a pure inert gas plasma at the entrance of a supersonic diffuser. The phenomenon was studied using an experimental setup based on a shock tube with a flat nozzle and the model supersonic diffuser. The experiments were conducted in krypton, for the shock wave Mach number in the shock tube M=7.8 and the Mach number at the nozzle exit M=4.2. The gasodynamic discontinuities and their structural variations induced by the magnetic induction changes were by visualized by the schlieren method and by photography of the intrinsic emission accompanying the process. Three regions of the MHD interaction affecting the shock wave configuration in the gas flow were revealed.     

Shock wave reflection and diffraction on a convex double wedge

We have numerically simulated the interaction of a shock wave with a convex double angle within the framework of a model of inviscid non-heat-conducting gas. The main attention is paid to the stage of a two-shock diffraction configuration on the second face of the wedge. Special features of flow under various condi-tions of diffraction are revealed. We also propose an explanation of the appearance and behavior of a purely gasdynamic layer formally resembling the viscous boundary layer.     

管路噪声的降噪方案

国内大型钢铁厂、发电厂、制药厂因输送煤气、空气，蒸汽等介质，在厂房内外布满了大直径、大流量的管道，阀门。这些管路在原设计中大多很少考虑到噪声对环境污染的问题，而管路空变、拐弯以及流速高、三通阀门组等更会因湍流、涡流等引发的振动而加大噪声值。我们在这方面经近半年多的实践，摸索出一套简单实用造价低的治理方法，更为突出的是治理效果有较大突破，可供有关单位借鉴。     

Sensor Fusion Methodology to Overcome Cross-Axis Problem for Micromachined Thermal Gas Inertial Sensor

Micromachined thermal gas inertial sensors are novel devices that take advantages of simple configuration, large working range, high shock resistance, and good reliability in virtue of using gaseous medium instead of mechanical proof mass as key moving and sensing elements. Basing on multidimentional movements of gas flow in a small chamber, the sensor generally undergoes a cross-axis problem. In this paper, a study on the cross-axis sensitivity of the thermal gas rotation sensor is reported. The cross-axis problem of the sensor is resulted from the multidimensional coupling movement of the convection flow in the sensor chamber and possibly be diminished by a tailored structural design. Unlike using a complex scheme on the mechanical structure, combining more than two sensors to form an integrated compensation system and using a fusion methodology to decouple cross rotations are proposed in this paper. The method helps to enhance practical applications for thermal rotation sensors.      

Experimental investigation of drag reduction by forward facing high speed gas jet for a large angle blunt cone at Mach 8

Substantial aerodynamic drag, while flying at hypersonic Mach number, due to the presence of strong standing shock wave ahead of a large-angle bluntcone configuration, is a matter of great design concern. Preliminary experimental results for the drag reduction by a forward-facing supersonic air jet for a 60° apexangle blunt cone at a flow Mach number of 8 are presented in this paper. The measurements are carried out using an accelerometer-based balance system in the hypersonic shock tunnel HST2 of the Indian Institute of Science, Bangalore. About 29% reduction in the drag coefficient has been observed with the injection of a supersonic gas jet.     

The structure of gasdynamic flow in a supersonic separator of natural gas

Results are given of calculations of flow within the two-dimensional Euler model of supersonic swirling flow of gas in a supersonic separator of natural gas. The formulation of the problem is given, numerical experiment is performed, and the basic parameters of gas flow (velocity components, pressure, and so on) are obtained as functions of radius. The process of relaxation of flow to steady state with the formation of shock wave is considered, and the shock wave structure is determined. The behavior of gasdynamic parameters is analyzed under conditions of separation in the region of shock wave and behind it.     

Formation of triple shock configurations with negative reflection angle in steady flows

Triple configurations of shock waves with negative reflection angles are considered. These configurations have been observed in quasi-steady cases of shock wave reflection from a planar wedge in real gases, while in steady cases three-shock configurations are only known to occur with positive reflection angles. Boundaries for the appearance of a three-shock configuration with a negative reflection angle in steady cases are analytically determined as dependent on the initial Mach number of the flow, angle of incidence, and adiabatic index. The formation of a three-shock configuration with a negative reflection angle in a steady flow must lead to a change in the character of the wave pattern, and under certain conditions it can lead to instability.     

Approximate analytical solutions for self-similar flows of a dusty gas with variable energy

Approximate analytical solutions are obtained for the unsteady one dimensional self-similar flow behind a strong shock wave propagating in a mixture of a gas and small solid particles at rest. It is assumed that variable energy is deposited at the shock and the total energy of the flow behind the shock is assumed to be varying with shock radius obeying a power law. The initial density of the medium is taken to be a constant. A simple integral method is employed to study the adiabatic and isothermal flows. The effect of the parameter characterizing the variation of total energy of the flow, on solutions of the flow field is investigated in detail. It as also shown that the similarity solutions of perfect gas with variable energy can be obtained as a particular case of this problem by taking the initial volume fraction of solid particles in the mixture as zero. Approximate solutions are compared with the numerical solutions and found a good agreement between them.     

The normal shock waves of real gases and the generalized isentropic exponents

When a supersonic gas flow is choked or otherwise disturbed, a shock wave appears. When this shock wave is perpendicular to the direction of the one-dimensional flow, a normal shock wave transforms the flow to a subsonic one. The thermodynamic variables involved are five, i.e. the pressure, the specific volume, the temperature, the enthalpy and the velocity of the flow. To determine their values after the normal Shock, five relations are used namely the equation of state, the enthalpy equation, the laws of conservation of impulse and energy, and the continuity of mass. For the simple case of a perfect gas, these relations are explicit and allow a straightforward solution of the system of the five equations. In the case of a real gas flow the system is solved numerically. The present work considers two other possibilities, i.e. the use of perfect gas like equations describing the phenomenon or the use of the Redlich-Kwong equation of state. Perfect gas like equations may be used now, to describe the phenomenon, after it has been shown that there exist three isentropic exponents, instead of the one used until now, and after it has been observed that the mathematical form of the perfect gas equations fit the real gas isentropic expansion when suitable numerical values of the corresponding constants and exponents are used. The other possibility, the use of the Redlich-Kwong equation of state, allows the calculation of the state variables after the normal shock when only the two constants of this equation and the specific heat of the corresponding perfect gas state (pressure approaching zero) are available. Both methods presented here require the numerical solution of a onevariable equation. In the first method the variable is the Mach number while in the second the specific volume.     

气调包装机气体置换结构优化与内部三维流场模拟

目的 针对现有的气体置换装置存在工作过程中气体置换精度不高、置换率低、内部流场复杂紊乱等问题,对DF-520型气调包装机气体置换装置结构进行了改进以及内部流场数值模拟。方法 运用FLUENT软件在进口压力为20 kPa,混配O2体积分数为2%、CO2体积分数为28%、N2体积分数为70%的边界条件下对新旧2种换气装置进行数值模拟和对比分析,进一步通过样机试验对比分析2种模型的气体置换率和气体置换精度。结果 数值模拟结果表明,与旧构型相比,新构型置换腔内部气体流速较平均、强流区面积小、漩涡区少、气体流向一致性高、气体置换速度快;样机试验结果表明,新旧构型气体置换装置平均气体置换率分别为99.2%和95.6%,新构型目标气体体积分数标准差、平均相对偏差以及变异系数更小。结论 本研究表明,优化后的气体置换装置气流分布更稳定,置换精度达到设计要求,工作效率更高,适用于气调包装机的包装工作,能为后续研究提供思路。     

Self-similar piston problem in non-ideal gas

Self-similar flows of a non-ideal gas driven by an expanding piston are studied. The equation of state for such gases is taken in the best suitable form that is found to be fairly accurate at low density region. The shock is assumed to be strong and propagating in a uniform medium at rest. The total energy of the flow between the shock and piston is assumed to be varying with shock radius obeying a power law. Both approximate analytical and numerical solutions are obtained for various values of the parameter that characterises the non-ideal nature of the gas. The influence of this parameter on not only the flow field but also on the shock density ratio, drag coefficient and pressure distribution on the piston surface is studied.     

On one case of interaction of stationary plane oblique shock waves in a polytropic gas

The interaction of plane oblique shock waves, one of which overtakes the other, at an arbitrary angle in a polytropic gas with a constant polytropic index has been considered in the context of the hydrodynamic theory of shock waves. The pattern of the decay of a discontinuity arising in this case and the dependence of its dynamics on the angle of interaction of the waves have been investigated on the basis of numerical calculations. The characteristic angles at which a shock-wave configuration develops and their dependence on the velocity of initial shock waves have been determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 1, pp. 90–95, January–February, 2006.     

Numerical simulation of the interaction between reflected shock wave and near-wall boundary layer

The interaction of a shock wave, reflected from the flat end of a cylindrical shock tube, with a cocurrent gas flow at the side wall, is considered in the axisymmetric case. The Navier-Stokes system of equations has been numerically integrated in the thin layer approximation using a predictor-corrector scheme. The appearance of a recirculation gas flow structure behind the reflected shock front and the evolution of this structure in the reflected wave going away from the tube end are analyzed. The corresponding patterns of constant density lines and the velocity vector field are presented.     

Nonstandard analysis of a converging shock wave in a nonideal gas

The problem of propagation of strong plane and converging shock waves in an unsteady inviscid nonideal gas is studied. A nonstandard analysis is used to derive the jump conditions for both shock waves. It is assumed that the jump occurs on an infinitesimal interval and jump functions in the flow parameters are smooth across this interval. The distribution of the flow parameters across the shock wave is expressed in terms of the Heaviside functions. Numerical computation to study the distribution of the flow parameters is performed.     

Intensification of mixing of parallel compressible flows using a localized pulse-periodic energy supply

The possibility of intensification of the mixing of supersonic and subsonic low-density gas jets that interact with an oblique shock with an ambient cocurrent supersonic flow using a localized pulse-periodic energy supply is demonstrated by means of numerical simulation. It is shown how an energy source located in front of the shock at the jet axis and also in an external flow affects the generation of large-scale vortex structures that favor the mixing process intensification.     

The attenuation of shock waves in a nonequilibrium gas

The evolution of weak shock waves in nonequilibrium gas media with fluctuating parameters is investigated. Two-dimensional nonlinear, evolution equations are derived for the averaged parameters of an acoustic field induced by a body in a supersonic flow of active medium. A possible mechanism of reduction of the amplitude and broadening of the front of weak shock waves in nonequilibrium gas media is discussed.     

TNT炸药爆炸场中三波点的数值模拟

准确预测三波点的位置和揭示三波点的规律,对工程防护和实现弹药的高效损伤有着重要作用。基于LS-DYNA有限元软件,利用数值模拟方法研究了TNT炸药在混凝土地面上形成爆炸冲击波的三波点运动轨迹,并初步揭示了炸高、药量和炸药形状等因素对三波点高度的影响。研究表明:在爆炸场中,爆炸冲击波以炸药为中心向四周传播,三波点轨迹的高度均呈现逐渐增高的变化趋势。不论改变炸药的药量还是炸高,三波点高度的增速在中场(4.0~7.0 m)都较缓,而进入远场(7.0 m)增速骤增。当炸药的炸高和药量相同,炸药形状不同时,圆柱状炸药在中场爆炸形成的三波点高度比长方体炸药略高,且高度增速都较缓;而在远场三波点的高度基本相等,且增速急剧上升,趋于定值。与炸药形状的影响相比,炸高和药量对TNT炸药爆炸冲击波的三波点高度的影响较大。