Magnetohydrodynamic control of supersonic flow past bodies: Possibilities and undesirable effects

Basic problems of super-and hypersonic magnetohydrodynamics (MHD) associated with the determination of the integral characteristics of bodies and vehicles inside which there are systems generating a uniform magnetic field are considered. Three classes of flows, namely, flow in a hypersonic multimode fixed-geometry air-intake; internal and external flow in a model of a hypersonic vehicle containing an air-intake with an MHD generator, a combustion chamber, and a supersonic nozzle; and hypersonic flow past a blunt cone are studied using numerical simulation and theoretical analysis (on the basis of the complete averaged system of Navier-Stokes equations and the electrodynamic equations). Attention is concentrated on the presence of an additionalmagnetic force acting on the system generating themagnetic field and, consequently, on the body and initiating an additional drag (in the case of a vehicle-reducing its thrust). Attractive possibilities for MHD flow control, namely, an increase in the degree of flow compression in the air-intake, a reduction in the ignition length in the combustion chamber, and a decrease in the heat flux to the nose of the body, are noted, as well as negative effects associated with the action of the magnetic force on the bodies considered.     

Review on the application and prospect of magnetohydrodynamics in aeronautical engineering

介绍了磁流体动力学在航空工程中的主要应用方式,主要包括：磁流体冲压组合发动机、磁流体涡轮组合发动机、燃烧室后磁流体发电、表面磁流体发电、磁流体加速风洞、磁流体推力矢量、进气道大尺寸磁流体流动控制、边界层分离流动控制、边界层转捩控制、飞行器头部热流控制等;探讨了磁流体技术在应用中存在的关键科学与技术问题,对导电流体的产生、磁流体实验设备与实验技术、多场耦合机理及数值模拟方法等进行了分析;最后对磁流体技术在航空工程上的应用与发展进行了总结与展望.     

Numerical modeling of detonation combustion of hydrogen-air mixtures in a convergent-divergent nozzle

The flow of igniting hydrogen-air mixtures entering an axisymmetric convergent-divergent nozzle at a supersonic velocity is considered. A possibility of stabilizing detonation combustion is numerically investigated at different freestream Mach numbers with account for nonuniform distribution of hydrogen concentration at the nozzle entry. The investigation is performed on the basis of the two-dimensional gasdynamic Euler equations for a multicomponent reacting gas. A detailed model of chemical reactions is used. The calculated thrust is compared with the drag of a conical housing containing the supersonic nozzle considered.     

Hall效应对三维磁流体发生器的影响

应用三维非理想低磁雷诺数磁流体五方程模型发展了对带有强制项的Navier-Stokes方程组采用熵条件格式, 对椭圆型电势方程采用SOR进行迭代的数值方法,研究了Hall效应对磁流体旁路超燃冲压发动机中磁流体发生器流动及性能的影响.磁流体发生器采用电子束获得有效可靠的电导率. 计算结果表明,Hall效应可引起流场和电场的扭曲, 从而诱导出不稳定二次流的发展与演变,并破坏Joule热的分布. 对这些磁流体现象作出了较详细的分析.最后计算了磁流体发生器的性能参数, 说明Hall效应将导致磁流体发生器的性能下降.      

Supersonic combustion and hypersonic propulsion

50 多年的努力和曲折经历证明了超声速燃烧冲压发动机概念的可行性. 本文对影响超燃冲压发动机技术成熟的主要因素作了扼要的分析. 高超声速推进的首要问题是净推力, 利用超声速燃烧获得推力遇到各种实际问题的制约, 它们往往互相牵制. 几次飞行试验表明高超声速飞行需要的发动机净推力仍差强人意, 液体碳氢燃料(煤油) 超燃冲压发动机在飞行马赫数5 上下的加速和模态转换过程, 成为高超声速吸气式推进继续发展的瓶颈. 研究表明, 利用吸热碳氢燃料不仅是发动机冷却的需要也是提高发动机推力和性能的关键举措, 燃料吸热后物性改变对燃烧性能的附加贡献对超燃冲压发动机的净推力至关重要.当前, 实验模拟技术和测量技术相对地落后, 无法对环境、尺寸和试验时间做到完全的模拟. 计算流体动力学(Computational Fluid Dynamics, CFD) 逐渐成为除实验以外唯一可用的工具, 然而, 超声速燃烧的数值模拟遇到湍流和化学反应动力学的双重困难. 影响对发动机的性能作正确可靠的评估.提出双模态超燃冲压发动机模态转换、吸热碳氢燃料主动冷却燃料催化裂解与超声速燃烧耦合、燃烧稳定性、实验模拟技术与装置、内流场特性和发动机性能测量、数值模拟中的湍流模型、煤油替代燃料及简化机理等研究前沿课题, 和未来5~10 年重点发展方向的建议.     

Gas-Dynamic Processes in Two-Phase Flows in MHD Generators

A plane problem of a two-phase monodisperse flow of combustion products of plasma-forming composite solid propellants in the duct of a Faraday's MHD generator with continuous electrodes, including an accelerating nozzle, MHD channel, and diffuser, is considered. An algorithm based on the pseudo-transient method is developed to solve the system of equations describing the two-phase flow. Gas-dynamic processes in the channels of the Pamir-1 setup are numerically studied. It is shown that shock-free deceleration of a supersonic flow to velocities close to the equilibrium velocity of sound in a two-phase mixture and significantly lower than the velocity of sound in the gas is possible in two-phase flows.     

Problem of Deceleration of a Supersonic Conducting Channel Flow by a Magnetic Field

Problems of the deceleration of a supersonic conducting flow by a magnetic field are investigated. A conducting gas flow in a circular tube is considered in the presence of an axisymmetric magnetic field induced by a unit current loop or solenoid of finite length. The analysis is carried out on the basis of both the Euler equations (inviscid gas) and the complete system of Navier-Stokes equations for laminar viscous gas flow and turbulent flow using a one-parameter turbulence model. The numerical simulation is based on an implicit relaxation finite-difference scheme which is a modification of the Godunov method. The total pressure losses are determined for various values of the magnetohydrodynamic (MHD) interaction, the initial Mach number, and different magnetic field geometries and it is shown that the irreversible losses are significant in MHD supersonic flow deceleration.     

磁流体动力学在航空工程中的应用与展望

介绍了磁流体动力学在航空工程中的主要应用方式,主要包括:磁流体冲压组合发动机、磁流体涡轮组合发动机、燃烧室后磁流体发电、表面磁流体发电、磁流体加速风洞、磁流体推力矢量、进气道大尺寸磁流体流动控制、边界层分离流动控制、边界层转捩控制、飞行器头部热流控制等;探讨了磁流体技术在应用中存在的关键科学与技术问题,对导电流体的产生、磁流体实验设备与实验技术、多场耦合机理及数值模拟方法等进行了分析;最后对磁流体技术在航空工程上的应用与发展进行了总结与展望.     

Technique for experimental determination of the total thrust-aerodynamic characteristics of aircraft models

A method of experimental determination of the force characteristics of nozzles (thrust, lift, and pitching moment) simultaneously with the aerodynamic characteristics of an aircraft model in a supersonic flow in proposed. The tests were conducted for a special methodical model, with equilibrium of the thrust and drag jorces being reached. It is shown that the internal force characteristics of the nozzle and the drag of the model, as well as the effective lift and pitching moment (with account of propulsion), can be determined from the measured thrust of the propulsion simulator. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 73–82, November–December, 1999.     

Model of Formation of the Electric Current in Aircraft Jet Engine Ducts

A possible mechanism of formation of electric currents (engine currents) in aircraft engine jets (with subsequent charging of the aircraft) is investigated. This mechanism is a result of the presence of electrons and ions at concentrations of 10⁷–10¹⁰cm^-3 in the gas flow in the engine duct. The electrons and ions are formed in the fuel combustion chamber as a result of chemo- ionization reactions. The wall flow zones in which the electrical quasi-neutrality of the medium is violated are considered. In these zones a nonzero normal component of the electric current is formed on the wall surface and a streamwise electric current develops in the duct. A general functional dependence of the engine current on the basic dimensionless parameters is obtained on the basis of similarity theory and dimensional analysis. Within the framework of electrical diffusion boundary layer theory a model problem of formation of the maximum possible engine current is formulated. A universal system of equations and boundary conditions, which contains no dimensionless parameters, is obtained and investigated. The engine current is qualitatively estimated for real engines and the calculation results are compared with the experimental data obtained under airfield conditions.     

高亚声速运输机后体减阻措施研究

为了降低高亚声速运输机的阻力,改善飞机的气动性能,本文在某一典型运输机机身外形的基础上,研究了后体参数和涡流发生器对机身后体流场及阻力的影响。通过数值模拟计算,得出了不同外形的后体流态分布及阻力特性数据。结果表明,小的上翘角和收缩比、大的扁平度和长细比能够显著地减小压差阻力,而涡流发生器能够有效地减小摩擦阻力。该结果可为后续的型号研制提供参考。     

Effect of Gas Non-Ideality on the Performance of Laval Nozzles with an Abrupt Constriction

The flows in Laval nozzles with a ero-length region of abrupt constriction and in nozzles with smooth entrance regions are studied on the basis of the Reynolds equations supplemented by a differential turbulence model. It is established that the viscosity effect does not lead to flow separation in the vicinity of the minimum section of optimal nozzles with an abrupt constriction. In all the examples calculated, the thrust of these nozzles is greater than that of nozzles with smooth a constriction and an optimally contoured supersonic part, the flow rate through the nozzle being larger when viscosity is taken into account than in the ideal (inviscid) case.     

Experimental study of extreme thrust on a tidal stream rotor due to turbulent flow and with opposing waves

Time-varying thrust has been measured on a rotor in shallow turbulent flow at laboratory scale. The onset flow has a turbulence intensity of 12% at mid depth and a longitudinal turbulence length scale of half the depth, about 5 times the vertical scale, typical of shallow flows. The rotor is designed to have thrust and power coefficient variations with tip speed ratio close to that of a full-scale turbine. Three extreme probability distributions give similar thrust exceedance values with the Type 1 Pareto in mid range which gives 1:100, 1:1000 and 1:10 000 exceedance thrust forces of 1.38, 1.5 and 1.59 times the mean value. With opposing waves superimposed the extreme thrust distribution has a very similar distribution to the turbulent flow only. Exceedance forces are predicted by superposition of a drag force with drag coefficient of 2.0 based on the wave particle velocity only and with an unchanged mean thrust coefficient of 0.89. These values are relevant for the design of support structures for marine turbines.     

超声速钝体逆向喷流减阻的数值模拟研究

为研究逆向喷流技术对超声速钝体减阻的影响,采用标准k-ε湍流模型,通过求解二维Navier-Stokes方程对超声速球头体逆向冷喷流流场进行了数值模拟,并着重分析了喷口总压、喷口尺寸对流场模态和减阻效果的影响。计算结果显示:随着喷流总压的变化,流场可出现两种流动模态,即长射流穿透模态和短射流穿透模态;喷流能使球头体受到的阻力明显减小;存在最大减阻临界喷流总压值(在所研究参数范围内最大减阻可达51.1%);在其它喷流物理参数不变时,随着喷口尺寸的增大,同一流动模态下的减阻效果下降。本文的研究对超声速钝体减阻技术在工程上的应用具有一定的参考价值。     

Stabilization of propane combustion in a supersonic air flow using a nonequilibrium longitudinal discharge and a coaxial local low-pressure zone

The results of the experimental investigation of the flow in the vicinity of an electric-discharge module having a low aerodynamic drag and intended for igniting hydrocarbon fuel and stabilizing its burning in a supersonic flow at low initial static temperature and pressure are presented. The distinctive feature of the module is that the combustion zone is not attached to the combustion chamber walls. Due to a certain geometric connection between different regions of the module anode, an interference of shock and expansion waves occurs in its vicinity. This leads to the formation of a local longitudinal low-pressure zone behind the anode, the convergence of individual fuel jetlets injected through orifices in the anode in this zone, the formation precisely there of a longitudinal nonequilibrium discharge, and the intensification of fuel mixing and plasmochemical reactions. The gasdynamic features of supersonic flow past the module are numerically investigated. The dynamics of electrical discharge formation and the combustion zones thus formed are studied under particular conditions. The data on the stagnation temperature distribution in the discharge wake are obtained.     

Boundary layer development in an MHD duct

This study presents a method of calculation for two-dimensional, steady-state, laminar flow in the entrance region of an MHD duct. The electrically conducting fluid in the free stream is compressible whereas the medium in the boundary layer itself is taken to be incompressible. Thus, the density is variable in the axial direction of the duct only, and the momentum and energy equations for the boundary layer are uncoupled. These equations are solved using an extended Von Kármán-Pohlhausen method as described by U. P. Hwang for a compressible MHD flow with zero electric field. In this study, however, the electric field is essentially not zero and the MHD duct can work as a generator. The equations of the insulator boundary layer are solved in the assumption that the displacement thickness of the electrode boundary layer equals that of the insulator boundary layer, so the total influence of the varying effective crossection on the free stream is taken into account. In this way a quick method of calculating the MHD flow in the entrance region of a duct is obtained.     

Hysteresis phenomena in a plane rotatable nozzle

The flow in a rotatable nozzle is calculated within the framework of the Reynolds equations and the Spalart-Allmaras turbulence model on the pressure difference range 1.1 < π < 5 for four configurations of the nozzle with the area ratio ε = 1.52 and two angles of the nozzle axis rotation. The flow structure is determined and the thrust characteristics and the angles of the thrust vector rotation are obtained. It was found that in the overexpansion regime the flows in plane symmetric and rotatable nozzles involve hysteresis phenomena due the Coanda effect and the interaction between the boundary layer and a shock generated within the nozzle on its supersonic walls. The hysteresis phenomena detected provide an up-to-4% divergence in the thrust coefficient for the same problem parameters. The results of the numerical modeling are compared with the experimental data and the results of calculations in accordance with Sekundov’s model.     

Introduction of turbulent model in a mixed finite volume/finite element method

The aim of this work is to present a new numerical method to compute turbulent flows in complex configurations. With this in view, a k-? model with wall functions has been introduced in a mixed finite volume/finite element method. The numerical method has been developed to deal with compressible flows but is also able to compute nearly incompressible flows. The physical model and the numerical method are first described, then validation results for an incompressible flow over a backward-facing step and for a supersonic flow over a compression ramp are presented. Comparisons are performed with experimental data and with other numerical results. These simulations show the ability of the present method to predict turbulent flows, and this method will be applied to simulate complex industrial flows (flow inside the combustion chamber of gas turbine engines). The main goal of this paper is not to test turbulence models, but to show that this numerical method is a solid base to introduce more sophisticated turbulence model.     

Comparison Between Numerically Simulated and Experimentally Measured Flowfield Quantities Behind a Pulsejet

Pulsed combustion is receiving renewed interest as a potential route to higher performance in air breathing propulsion and ground based power generation systems. Pulsejets offer a simple experimental device with which to study unsteady combustion phenomena and validate simulations. Previous computational fluid dynamics (CFD) simulations focused primarily on pulsejet combustion and exhaust processes. This paper describes a new inlet sub-model which simulates the fluidic and mechanical operation of a valved pulsejet head. The governing equations for this sub-model are described. Sub-model validation is provided through comparisons of simulated and experimentally measured reed valve motion, and time averaged inlet mass flow rate. The updated pulsejet simulation, with the inlet sub-model implemented, is validated through comparison with experimentally measured combustion chamber pressure, inlet mass flow rate, operational frequency, and thrust. Additionally, the simulated pulsejet exhaust flowfield, which is dominated by a starting vortex ring, is compared with particle imaging velocimetry (PIV) measurements on the bases of velocity, vorticity, and vortex location. The results show good agreement between simulated and experimental data. The inlet sub-model is shown to be critical for the successful modeling of pulsejet operation. This sub-model correctly predicts both the inlet mass flow rate and its phase relationship with the combustion chamber pressure. As a result, the predicted pulsejet thrust agrees very well with experimental data.     

Features of internal and external flows in high-speed vehicles with a magnetohydrodynamic air-intake

The features of the internal and external flows in high-speed vehicles with a magnetohydrodynamic air-intake ensuring additional deceleration of the supersonic flow are considered. Preliminary investigations carried out earlier showed that this MHD flow control makes it possible significantly to increase the gasdynamic component of the vehicle thrust. However, there are significant negative effects, mainly the development of an additional vehicle drag force associated with the magnetic field. Thus, there arises a complex of interrelated problems with opposite effects on the resulting characteristics of the vehicle. In the present study these questions are investigated both on the basis of developed physicomathematical models and numerical methods and by means of the combined optimization of the internal duct profile and the external configuration of the vehicle. It is shown that a strategy for improving the vehicle characteristics can only be chosen by simultaneously analyzing the features of the internal (magnetohydrodynamic) and external (gasdynamic) flows.