Supersonic Gas Flows in Radial Nozzles

Results of experimental investigations and numerical simulations of supersonic gas flows in radial nozzles with different nozzle widths are presented. It is demonstrated that different types of the flow are formed in the nozzle with a fixed nozzle radius and different nozzle widths: supersonic flows with oblique shock waves inducing boundary layer separation are formed in wide nozzles, and flows with a normal pseudoshock separating the supersonic and subsonic flow domains are formed in narrow nozzles (micronozzles). The pseudoshock structure is studied, and the total pressure loss in the case of the gas flow in a micronozzle is determined.     

Mixing Characteristics in a Supersonic Combustor with Gaseous Fuel Injection Upstream of a Cavity Flameholder

Non-reacting experiments and numerical simulations have been performed to investigate the mixing characteristics in a supersonic combustor with gaseous fuel injection upstream of a flameholding cavity in a supersonic vitiated air flow with stream Mach number 1.7. Using helium as simulated fuel, the acetone vapor is adulterated into the fuel jet. The fuel distribution in spanwise and streamwise direction is imaged by the planar laser-induced fluorescence (PLIF) measurement. According to the similarity of experimental observations with different cavities, the typical L/D = 7 cavity with aft wall angle 45° is chosen and the flowfield with the injection is calculated by Large Eddy Simulation. Experimental and numerical results have shown that most of the fuel flow away upon the open cavity with the lifting counter-rotating vortex structures induced by the transverse jet. Only a small portion of the fuel is convected into the cavity shear layer by the vortex interaction of the jet with cavity shear layer, and then transported into the cavity due to the cavity shear layer motion and the interaction of the shear layer with the cavity trailing edge.     

Numerical Investigation of Supersonic Flows Around Hyperelliptic Cones

The results of numerical simulation of supersonic flows around hyperelliptic cones with different cross-sections are presented. For solving the problem within the inviscid gas model, the finite volume method based on an integral approximation of the Euler equations is used. The steady-state solution is found using the saturation method. The flow pattern is studied and it is shown that bodies with integral geometric characteristics (midsection area, volume, etc.) similar to those of the elliptic cone but with a more uniform flowfield over most of the lower surface can be constructed.     

Numerical Simulations of High-Speed Turbulent Cavity Flows

Detached-Eddy Simulations (DES) of flows over clean and controlled cavities with and without doors are presented in this paper. Mach and Reynolds numbers (based on cavity length) were 0.85 and one million respectively. Spectral analyses showed that the DES computations were able to correctly predict the frequencies of the Rossiter modes for both uncontrolled and controlled cases. Flow visualisations revealed that the impact of the shear layer formed along the cavity on a slanted aft wall no longer creates a large source of acoustic noise. Therefore little acoustic propagation was seen up the cavity. This was confirmed by the analysis of the cavity wall forces, which showed that the oscillations of the shear layer were reduced when the wall was slanted. This aided in reducing the overall Sound Pressure Levels throughout the cavity and far-field. Comparisons of the flow-fields suggested that the addition of the doors also aided in stabilising the shear layer, which was also shown in the analysis of the wall forces. As a result, the addition of the doors was found to affect the clean cavity configuration significantly more than the controlled one.     

Existence of Stationary Supersonic Flows Past a Pointed Body

In this paper we study the mathematical aspects of the stationary supersonic flow past a non-axisymmetric curved pointed body. The flow is described by a steady potential flow equation, which is a quasilinear hyperbolic equation of second order. We prove the local existence of the solution to this problem with a pointed shock attached at the tip of the pointed body, provided the pointed body is a perturbation of a circular cone, and the vertex angle of the approximate cone of the pointed body is less than a critical value. The solution is smooth in between the shock and the surface of the body. Consequently, such a structure of flow near the tip of the pointed body and its stability is verified mathematically. Accepted October 13, 2000?Published online January 22, 2001     

Thermal Vibrational Convection in a Cavity under Nontranslational Oscillations

Thermal vibrational convection in a cavity subjected to combined translational-rotational high-frequency vibrations is investigated theoretically and experimentally. Attention is concentrated on convection in a plane layer and a coaxial gap. It is shown that the vibrational action of the combined vibration differs qualitatively from purely translational or rotational vibration, being more efficient. The experimental results and theoretical calculations carried out using the averaged equations of thermovibrational convection are found to be in good agreement.     

Modeling of Supersonic Turbulent Flows in the Vicinity of Axisymmetric Configurations

Calculation results of turbulent flows in the vicinity of axisymmetric configurations of the cylinderflare type for Mach numbers M = 3, 5, and 7 are presented. The calculations are performed for conditions of real physical experiments. The mathematical model is based on the averaged Navier–Stokes equations supplemented by the Wilcox turbulence model. The calculated and experimental distributions of pressure on the body surface, velocity fields, and heattransfer coefficients are compared.     

Maintenance of Oscillations in Three-Dimensional Traveling Waves in Plane Poiseuille Flows

Two solutions of three-dimensional Navier–Stokes equations are studied numerically. These solutions describe the fluid motion in a plane channel, are of the traveling-wave form, and are periodic in the streamwise and spanwise directions. It is shown that, in each solution, the oscillations arise as a result of linear instability in the streamwise averaged velocity field. This instability is due to the existence of streamwise streaks known as the regions where the velocity is higher or lower than the mean velocity. A mechanism for the maintenance of streamwise vortices causing the formation of streaks is revealed. The obtained results confirm and extend the existing knowledge about the mechanism for the formation of near-wall turbulent structures.     

Existence and Stability of Supersonic Euler Flows Past Lipschitz Wedges

It is well known that, when the vertex angle of a straight wedge is less than the critical angle, there exists a shock-front emanating from the wedge vertex so that the constant states on both sides of the shock-front are supersonic. Since the shock-front at the vertex is usually strong, especially when the vertex angle of the wedge is large, then a global flow is physically required to be governed by the isentropic or adiabatic Euler equations. In this paper, we systematically study two-dimensional steady supersonic Euler (i.e. nonpotential) flows past Lipschitz wedges and establish the existence and stability of supersonic Euler flows when the total variation of the tangent angle functions along the wedge boundaries is suitably small. We develop a modified Glimm difference scheme and identify a Glimm-type functional, by naturally incorporating the Lipschitz wedge boundary and the strong shock-front and by tracing the interaction not only between the boundary and weak waves, but also between the strong shock-front and weak waves, to obtain the required BV estimates. These estimates are then employed to establish the convergence of both approximate solutions to a global entropy solution and corresponding approximate strong shock-fronts emanating from the vertex to the strong shock-front of the entropy solution. The regularity of strong shock-fronts emanating from the wedge vertex and the asymptotic stability of entropy solutions in the flow direction are also established.     

以压力为基本求解变量数值模拟粘性超、跨音速流动

应用以压力为基本求解变量的SIMPLE方法 ,对一双喉喷管中的层流超音速流动和一扩压器中的紊流跨音速流动进行了数值计算。计算结果显示 ,本文的计算结果与文献数据及实验结果相符很好。表明本文方法对可压缩流动有很高的模拟精度。进而表明经过可压缩推广的SIMPLE方法适用于任何马赫数的流动计算     

Supersonic Inviscid Corner Flows with Regular and Irregular Shock Interaction

The results of a numerical and analytical investigation of steady-state supersonic inviscid flows in corners formed by intersecting compression wedges are presented. The flows considered are symmetric about the corner bisector. The distinctive features of flow pattern formation related with the reflection of wedge-generated shocks from the bisector plane are studied. The wedge angles at which transition from regular to irregular shock reflection occurs are determined both numerically and analytically using the criteria available for plane flows; the data thus obtained are found to be in agreement. Flow patterns with irregular shock reflection, namely, single, transitional, and double Mach, as well as von Neumann reflection, are identified; they are similar to the known types of reflection for plane quasi-steady-state flows. Varieties of these types not observed in the plane flows are found to exist. The effects of the angle of inclination of the plane surfaces of the corner to the freestream direction, the sweep angle of the leading edges, and the dihedral angle are investigated. Some previously unknown parameters of corner configurations for which transition may occur in accordance with the von Neumann criterion are determined.     

Steady Flows in an Oscillating Spheroidal Cavity with Elastic Wall

The steady flow arising in a spheroidal cavity with periodically-deformed elastic wall is studied experimentally. It is found that average flows whose intensities and structures depend on the wall oscillation frequency and amplitude can develop in the fluid. The average flow is generated in the Stokes boundary layer whose relative thickness is characterized by the dimensionless frequency of the vibrational action. Flow in the form of a pair of toroidal vortices which occupy the entire cavity volume can be observed over the range of low dimensionless frequencies when the boundary layer thickness is comparable with the characteristic cavity dimension. Increase in the dimensionless frequency (decrease in the relative thickness of the Stokes layers) leads to a displacement of the primary vortices towards the cavity boundary. In this case secondary vortices with opposite swirling are formed in the central part of the cavity above the primary vortices. The further increase in the dimensionless frequency leads to development of the secondary vortices and growth of the flow intensity. The large-scale secondary vortices occupy almost the entire cavity volume over the range of high dimensionless frequencies. The dependences of the regimes of average flows and their intensities on the control dimensionless parameters, the oscillation amplitude and frequency, are found on the basis of the results of the investigation.     

Triple-Diffusive Mixed Convection in a Porous Open Cavity

The triple-diffusive mixed convection heat and mass transfer of a mixture is analyzed in an enclosure filled with a Darcy porous medium. The mass transfer buoyancy effects due to concentration gradients of the dispersed components (pollutant components) are taken into account using the Boussinesq approximation model. The governing equations are transformed into a non-dimensional form, and six groups of non-dimensional parameters, including Darcy–Rayleigh number, Peclet number, two Lewis numbers for pollutant components 1 and 2 and two buoyancy ratio parameters for pollutant components 1 and 2, are introduced. The governing equations are numerically solved for various combinations of non-dimensional parameters using the finite element method. The effect of each group of non-dimensional parameters on the pollutant distribution and the heat transfer in the cavity is discussed. The results indicate that the presence of one pollutant component can significantly affect the pollutant distribution of the other component. When the Lewis number of a pollutant component is small, the increase in the bouncy ratio parameter of the proposed component always increases the Nusselt and Sherwood numbers in the cavity.     

Flows of Supersonic Underexpanded Jets on the Range of Moderate Reynolds Numbers

The results of an experimental investigation of the gasdynamic structure of supersonic underexpanded air jets flowing out of a sonic nozzle into a low-pressure medium are presented. This setting of the experimentmakes it possible to achieve high values of the nozzle-to-ambient pressure ratio at moderate outflow Reynolds numbers characteristic of underexpanded jets issuing from micronozzles. The data on the supersonic core length, the laminar-turbulent transition location, and the jet flow characteristics are obtained. The results are compared with those obtained in microjets flowing out of sonic nozzles. Emphasis is placed on the earlier discovered effect of inverse transition of a turbulent jet into the laminar flow regime with increase in the Reynolds number.     

TVD格式在超音速喷管三维粘性流动求解中的应用

详细给出了任意三维曲线坐标系中Ｎｏｖｉｅｒ－Ｓｔｏｋｅｓ方程的对流项ＴＶＤ格式的构造过程，建立了数值求解三维粘性流动的计算方法，应用该方法对三维超音速喷管中有激波及无激波情况下的两种工况的层流流场进行了数值求解，并与实验做了对比。结果表明本文建立的计算方法具有较高的精度，同时也证明ＴＶＤ格式具有分辩率高，稳定收敛等优点，为进一步开展叶栅流场及紊流的研究打下了基础。     

导流板对腔口流体自持振荡影响的研究

腔口流体动力自持振荡的频率和导流板的长度有一定关系。本文通过对跨越腔口非稳定层和自持振荡的理论分析，并通过对不同长度导流板的腔、低速流激自持振荡均方压力谱分析的实验研究，给出流激自持振荡的频率与导流板长度之间的关系。流体动力振荡和腔的声驻波共振耦合时，腔内振荡的均方压力达到最大值。根据流速变化时，均方压力谱峰值频率的偏移，分析了导流板长度对流引起的流一腔系统耦合共振的影响。     

Synthesis of Diamonds from the Microwave Plasma with the Use of Supersonic Gas Flows

A new method of deposition of diamond films with the use of supersonic gas flows activated by a microwave discharge is implemented for the first time. The operation principle of the proposed gas-discharge system is similar to that of a microwave electrothermal thruster. A mixture of hydrocarbons and hydrogen is used as a plasma-forming gas. It is demonstrated that the proposed method allows the plasma-forming gas to be used at pressures far above the upper limit of the pressure range of modern microwave plasma systems for chemical vapor deposition of diamond films (approximately 40 000 Pa).     

Investigation of the Flow in an Annular Cavity in a Cylindrical Body in a Supersonic Stream

The results of an experimental investigation of the flow over an annular cavity in a cylindrical body are presented; the cavity-to-body diameter ratio was 0.7 and the incident flow Mach number was 2.84. Using the data on the pressure distribution and optical measurements of the flow pattern, the structure of the flow inside the cavity was studied on the relative cavity length range from 0.5 to 14 including the regimes with both open and closed separation zones.     

开式空腔流动的蒙特卡罗直接模拟

蒙特卡罗直接模拟(Direct Simulation Monte-Carlo)方法是一种基于分子动力论的随机性数值模拟方法，它在各类稀薄气体流动模拟中得到了广泛应用。本文首先讨论了DSMC方法的基本原理，引用文献结果论述了DSMC方法与Boltzmann方程的内在一致性，采用DSMC方法从分子运动论层次对过渡区开式空腔流动进行精细模拟，再现空腔内旋涡的形成及发展过程，了解复杂流场的流场特性。模拟和分析了空腔的形状(展弦比)、壁温以及Knudsen数(稀薄性)等因素对空腔内流动和旋涡结构的影响。研究表明，空腔的展弦比、壁面温度以及流动Knudsen数等因素对空腔内旋涡的大小、形状、位置、个数都有极大的影响，应用DSMC方法可以真实再现稀薄条件下的开式空腔流动。