汽车减振器外特性仿真与试验分析

基于减振器的工作原理、内部结构和阀系特性,利用环形薄板阀片变形微分方程以及内外径处的边界条件推导环形阀片受均布载荷作用时的挠曲变形解析式,根据流体力学缝隙流动、管嘴流动理论、薄壁小孔节流理论,建立了双筒液压减振器的详细数学模型。采用MATLAB软件进行仿真研究,计算结果与试验数据符合较好。同时用该模型分析减振器补偿阀及流通阀对减振器阻尼力的影响规律及敏感程度,得出的结论可以为减振器的设计和性能预测提供参考。     

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.     

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.     

Magnetic field control of a supersonic nitrogen flow

Magnetohydrodynamic impact on a cold supersonic nitrogen flow with external magnetic field was realized in an experimental complex based on the Big Shock Tube at the Ioffe Physicotechnical Institute. A pulsed supersonic flow with a Mach number of M=4 and steady phase duration of about 1.5 ms was created by expansion of the shock-heated nitrogen flow from a supersonic nozzle. The gas was ionized by pulsed discharge between two electrodes mounted on the nozzle wall so that an electric current of up to ∼500 A passed in the direction perpendicular to the gas flow at the dielectric wall. External magnetic field ∼0.3 T was perpendicular to the gas flow and the current direction. It is established that the magnetic field significantly modifies the shock wave structure in the flow.     

非定常流动中塞式收敛扩张喷管的研究

针对脉冲爆轰发动机的脉动流动特性设计加工了塞式收敛扩张喷管,并对其增推性能和增推机理进行了研究。研究结果表明,塞式收敛扩张喷管可以大幅增加推力,10Hz和15Hz时塞式收敛扩张喷管对发动机的推力增益分别为32.4%和29.52%;塞式收敛扩张喷管扩张段对爆轰室排出的高温高压气体有减压加速作用;塞式收敛扩张喷管塞式结构增加推力壁平台压力值和平台压力持续时间,从而增加发动机推力。     

Unsteady laminar gas flows in an annular nozzle

On the basis of the Navier–Stokes equations, a parametric study of the influence of various factors on the development of initial perturbations caused by starting an air-blown annular nozzle is performed for the laminar model of flow. Flow regimes are found in which the start perturbations accompanying the initiation of the nozzle do not attenuate but pass to a quasi-periodic mode. The frequency Fourier spectrum of pressure fluctuations at the center of the thrust wall and the value of the thrust of the nozzle are determined. Typical pulsed pressure signals obtained in the calculation model and detected in the experiments are presented.     

Effect of the electric discharge on nonstationary processes during supersonic air and methane jet flow over a flat obstacle

The features of supersonic air and methane jet flows over a flat obstacle, accompanied by an electric discharge, were studied. The flow under consideration is characterized by a number of unsteady effects appearing as oscillations of shock-wave fronts with various amplitudes and frequencies depending on the nozzle-obstacle system configuration and jet gas-dynamic parameters. The oscillation frequency of the bow shock wave increases as the obstacle becomes closer to the nozzle edge and the relative obstacle diameter and the supersonic jet stagnation pressure increase. Initiation of the energy release region at the supersonic jet edge causes a change in the oscillation frequency of the bow shock wave; under certain conditions, it causes a change in the entire shock-wave flow pattern.     

Current status and potentialities of wind tunnels with MHD acceleration

The activities aimed at development of hypersonic wind tunnels with MHD gas accelerator started in the late 1950s, when it became clear that the uses of hypersonic wind tunnels of the classical type employing the principle of adiabatic expansion for gas acceleration are subject to limitations. A flow train was developed for such a wind tunnel including a source of conducting gas (electric-arc heater, region behind the reflected shock wave, high-pressure chamber of an impulse wind tunnel, etc.), a system for delivery of readily ionizing seed (K, Na, Cs, and their compounds), a primary supersonic nozzle with a Mach number M ≃1.6-3.0, the MHD-accelerator channel proper, the working section, and a gas exhaust system. In the United States, these studies were performed at the NASA Langley Center, AEDC, and General Electric; in Russia, at the Central Institute of Aerohydrodynamics (TsAGI). Some work was done in France at ONERA and in Germany. This review contains an analysis of various design solutions of the MHD channel proper, seed delivery systems, and systems of electric supply and magnetic field generation, as well as a comparison of the procedures for testing and acquisition and treatment of experimental data. Special note is made of the difficulties confronting the researchers and of the reasons for simultaneous cessation of research activities in the United States at almost all research centers. It is indicated that in Russia, unlike the United States, much more extensive studies were made into the physics of combustion of discharge in gas flows at Mach numbers M = 0–4.5 both with and without a magnetic field. Data are given on the behavior of current distribution in the electrodes, propagation of microarc discharges, boundary layer separation, and magnitude of heat fluxes with the flow parameters corresponding to those of the MHD accelerator. The basic characteristics of the TsAGI hypersonic wind tunnel are given along with the results of its utilization for solving practical problems of aerodynamics. Results are also given of the investigation of a high-enthalpy MHD generator in which the flow from the MHD accelerator is used as the working medium. The advantages are demonstrated of using facilities with MHD gas accelerator in solving the problems of development and testing of scramjet engines (SJE) for transatmospheric flying vehicles, and information is given about the possible parameters (gasdynamic and electrodynamic) of such facilities and their designs. The main problems are listed that must be solved in developing hypersonic facilities with MHD gas accelerator.     

Pressure drop and flashing mechanisms in refrigerant expansion devices

This paper examines a novel pressure drop mechanism as well as flow choking conditions that determine mass flow rate in refrigerant expansion devices. For this study, an ideal situation is considered where an expansion device such as a short tube orifice or a thermostatic expansion valve is modeled as an ideal isentropic nozzle. In addition, a liquid with a certain initial degree of superheat is first expanded in the converging nozzle down to the exit section without any phase transition. At the exit section where the metastable liquid jet flashes to produce a complex axisymmetric two-phase flow, a shock wave may terminate the overall expansion process. The model presented here is based on experimental observations in short nozzles, where the metastable liquid in the central core undergoes a sudden phase transition in the interfacial region, giving rise to a high-speed two-phase flow. A simple 1-D analysis of the radial evaporation wave based on the theory of discontinuities from gas dynamics leads to the Chapman–Jouguet (C-J) solution. Flow choking issues are examined and numerical examples are presented for three common refrigerants: R134a, R-22, and R-600a. Results suggest that the evaporation wave may be the flow controlling mechanism in these devices.     

Scale-up analysis and development of gliding arc discharge facility for volatile organic compounds decomposition

The influences of inlet gas flow rate and reactor configuration on volatile organic compounds (VOCs) decomposition efficiency in a traditional gliding arc (T-GA) facility are studied based on laboratory experiments and numerical simulation. The ratio of the nozzle diameter and the shortest distance of two electrodes should be maintained in a suitable value range to guarantee the decomposition efficiency, which indicates simply enlarging the nozzle inner diameter is not a proper way to raise the T-GA treatment capacity in a fixed supply voltage condition. A developed gliding arc gas discharge (D-GA) reactor based on a modified gas feed system is proposed: small flow rate air goes through the bottom nozzle to process the GA evolution, and high flow rate contaminated gas goes frontal through the plasma region and decomposes. The performances of D-GA reactor in the decomposition of VOCs with relative high gas flow rate, including decomposition efficiency and specific energy consumption, are better than T-GA reactor. D-GA reactor also avoids the drawbacks of the increases of power system amount and electric power consumption in multi-electrode GA system.     

Effect of gas stream swirls on the instability of viscous annular liquid jets

Summary. A linear temporal instability analysis has been carried out for a viscous annular liquid jet moving in two swirling gas streams of unequal velocities with the gas stream swirling motion represented by free-vortex rotation. It is found that two modes of unstable surface waves exist, the para-sinuous and para-varicose mode. The results of the two limiting flow situations, which are a cylindrical liquid jet in a swirling gas stream and a swirling gas jet in a liquid stream, indicate that their instabilities are associated with the para-varicose mode on the outer interface and para-sinuous mode on the inner interface of the annular liquid jet, respectively. It is shown that the centripetal force induced by the inner gas stream rotation is destabilizing and enhances the jet instability, while the centripetal force produced by the outer gas stream rotation is stabilizing and reduces the instability of annular liquid jets. It is interesting to find that for a para-varicose mode an increase in the outer gas rotation not only reduces the upper cut-off wave number, but also increases the lower cut-off wave number, leading to the significant reduction in the unstable wave number range. The stabilizing effect of the outer gas rotation is much more significant for para-varicose mode, and the destabilizing effect of the inner gas rotation is much more influential for para-sinuous mode. In general, the para-sinuous mode has a much larger growth rate and is predominant in the annular liquid jet breakup process. Therefore, increasing the inner gas stream rotation can significantly enhance the breakup of annular liquid jets for practical spray applications.     

Domain-adaptive finite difference methods for collapsing annular liquid jets

A domain-adaptive technique which maps a time-dependent, curvilinear geometry into a unit square is used to determine the steady state mass absorption rate and the collapse of annular liquid jets. A method of lines is used to solve the one-dimensional fluid dynamics equations written in weak conservation-law form, and upwind differences are employed to evaluate the axial convective fluxes. The unknown, time-dependent, axial location of the downstream boundary is determined from the solution of an ordinary differential equation which is nonlinearly coupled to the fluid dynamics and gas concentration equations. The equation for the gas concentration in the annular liquid jet is written in strong conservation-law form and solved by means of a method of lines at high Peclet numbers and a line Gauss-Seidel method at low Peclet numbers. The effects of the number of grid points along and across the annular jet, time step, and discretization of the radial convective fluxes on both the steady state mass absorption rate and the jet's collapse rate have been analyzed on staggered and non-staggered grids. The steady state mass absorption rate and the collapse of annular liquid jets are determined as a function of the Froude, Peclet and Weber numbers, annular jet's thickness-to-radius ratio at the nozzle exit, initial pressure difference across the annular jet, nozzle exit angle, temperature of the gas enclosed by the annular jet, pressure of the gas surrounding the jet, solubilities at the inner and outer interfaces of the annular jet, and gas concentration at the nozzle exit. It is shown that the steady state mass absorption rate is proportional to the inverse square root of the Peclet number except for low values of this parameter, and that the possible mathematical incompatibilities in the concentration field at the nozzle exit exert a great influence on the steady state mass absorption rate and on the jet collapse. It is also shown that the steady state mass absorption rate increases as the Weber number, nozzle exit angle, gas concentration at the nozzle exit, and temperature of the gases enclosed by the annular liquid jet are increased, but it decreases as the Froude and Peclet numbers, and annular liquid jet's thickness-to-radius ratio at the nozzle exit are increased. It is also shown that the annular liquid jet's collapse rate increases as the Weber number, nozzle exit angle, temperature of the gases enclosed by the annular liquid jet, and pressure of the gases which surround the jet are increased, but decreases as the Froude and Peclet numbers, and annular liquid jet's thickness-toradius ratio at the nozzle exit are increased. It is also shown that both the ratio of the initial pressure of the gas enclosed by the jet to the pressure of the gas surrounding the jet and the ratio of solubilities at the annular liquid jet's inner and outer interfaces play an important role on both the steady state mass absorption rate and the jet collapse. If the product of these ratios is greater or less than one, both the pressure and the mass of the gas enclosed by the annular liquid jet decrease or increase, respectively, with time. It is also shown that the numerical results obtained with the conservative, domain-adaptive method of lines technique presented in this paper are in excellent agreement with those of a domain-adaptive, iterative, non-conservative, block-bidiagonal, finite difference method which uncouples the solution of the fluid dynamics equations from that of the convergence length.     

快速热平衡式pVTt法气体流量标准装置的设计与研究

设计了基于单侧溢流式恒温水浴系统的快速热平衡式pVTt气体流量标准装置,对水浴及临界流喷嘴进行了实验研究,采用了五路阀门组合控制技术,实现了预抽气功能,降低了压力波动.装置平衡时间为6 min,与其它pVTt法气体流量标准装置相比,平衡时间至少缩短一倍.     

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.     

The role of vortices in enhancing the action of a pulsed axisymmetric flow upon an obstacle

It is experimentally established that the pressure at the central point of an obstacle oriented perpendicular to the axis of a gas flow emerging from a channel increases when a fluid nozzle formed by the moving primary (head) and secondary vortices reaches the obstacle surface. This phenomenon has been observed in air-flow at a distance of ∼1–4 channel diameters behind the shock wave in the range of subsonic Mach numbers. The obtained experimental data are generalized in the form of dimensionless relationships.     

Investigation of the effect of a pylon and a wing with flaps on the flow within an exhaust jet of a double-flow turbojet engine by a simulation method for large eddies

The effect of a pylon and a wing with deflected flaps on the flow and turbulence characteristics in the exhaust jet of a double-flow turbojet engine (TJE) is investigated with the use of the combined Reynolds Averaged Navier-Stokes/Implicit Large Eddy Simulation (RANS/ILES) method with high resolution. In addition to assessment of the accuracy of the method and comparability, the flow in an axisymmetric nozzle with the same geometry and in its exhaust jet is calculated. All computations are carried out for the flow mode corresponding to the take-off. In the case of the axisymmetric nozzle, good agreement between the computation and the experiment on the distribution of the averaged longitudinal velocity and the turbulence energy in jet cross sections is observed. It is shown that the flap angle and the gap between their internal tips, which the exhaust jet of the TJE passes through, significantly affect the flow and the turbulence level in the jet. Because of the interaction between the jet and tip eddies coming out from the flaps, jet deformation occurs, and a heterogeneous azimuth appears in the distribution of the flow parameters in jet cross sections. The peak turbulence energy increases by a factor of 1.5–2 in comparison with the basic axisymmetric variant. Computations are carried out with meshes containing 2.224 × 10⁶ cells in the case of the axisymmetric nozzle and 3.34 × 10⁶ cells in the case of the nozzle with the pylon and the wing.     

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.     

Numerical simulation of micro-nozzle and micro-nozzle-array flowfield characteristics

Preliminary numerical simulation using a Direct Simulation Monte Carlo (DSMC) method was conducted to elucidate the internal flowfield and external plume characteristics of micro-single-nozzles and micro-nozzle-arrays, since these small-sized nozzles generally undergo a severe viscous loss due to the low Reynolds numbers. This study also contains the investigation on optimization of the geometry and configuration of the micro-nozzles and micro-nozzle-arrays to achieve the improved propulsive performance. Typical sizes of each rectangular nozzle element were 0.1 mm in throat height, 0.36 mm in exit height, and 0.35 mm in length of the divergent part. For the micro-single-nozzles, calculated specific impulses were fairly in good agreement with our previous experimental data, showing a poor nozzle efficiency due to the viscous loss of low Reynolds number. Also, mechanisms of exhaust jet interaction of multi-nozzle-array jets, bringing a significant improvement in thrust performance, were investigated. As a result, it was shown that pressure and temperature increased at the exit and jet boundaries, and then the exhaust multi-jets were not expanded after the exit, or rather being confined, showing possibilities to realize the higher propulsive performance due to the augmented effect of the pressure thrust.     

模拟破片杀伤战斗部空爆冲击波与高速破片群联合作用的等效试验方法

破片杀伤战斗部空爆冲击波与高速破片群联合毁伤作用下目标结构的毁伤特性、防护效能等是当前防护领域的热点和难点,但目前的试验研究手段和方法存在不足,为此,提出采用等效缩比战斗部(其原理为炸药爆炸驱动预制破片分散)来模拟破片杀伤战斗部,可作为进行空爆冲击波与高速破片群对防护结构的联合毁伤作用的实验方法。在确定防御目标战斗部、防御目标弹丸和几何缩尺比的基础上,根据爆炸力学相关经验公式,提出了求解等效缩比战斗部的装药和预制破片的相关参数的等效计算方法。该等效试验方法考虑了多破片侵彻的增强效应以及与爆炸冲击波的联合毁伤增强效应,且等效计算方法参数较少、简单实用。     

The influence of film structure on the interfacial friction in annular two-phase flow under microgravity and normal gravity conditions

Results for the interfacial friction factor and relative interfacial roughness on the gas-liquid interface are reported for an air-water annular flow in a small inner diameter tube (9.53 mm i.d.). The film structure was obtained through processing the time trace signal of film thickness measurements using conductance probes. The interfacial friction factor and the wave height were altered through changing the gravity level and gas Reynolds number. It was found that the wave height decreased with increasing the gas Reynolds number. The wave height in microgravity is less than half of that in normal gravity, while the friction factor was about 10% smaller in microgravity than that in normal gravity. It was shown that the annular two-phase flow friction factor decreased less dramatically as the relative interfacial roughness decreased compared to the single-phase case. It is interesting to note that the interfacial shear stress values at microgravity were very close (or even larger than) those at normal gravity. This was attributed to the thicker substrate at microgravity.