部分预混超声速燃烧火焰面模式研究综述

采用部分预混火焰面模式建模与仿真已经成为超声速燃烧数值研究的主要趋势之一.系统回顾了超声速燃烧火焰面模式的发展历程,针对其应用的两个基本问题进行总结:一是火焰面模式在超声速燃烧中的物理存在问题,二是超声速燃烧火焰面模式的建模问题.重点分析了火焰面模式应用于超声速燃烧的难点,提出了超声速燃烧火焰面模式建模应兼顾的问题.     

SUPERSONIC BIPLANE —— A POSSIBLE BOOMLESS CONFIGURATION

超声速双翼机的概念由德国空气动力学家阿道夫$\cdot$布兹曼于1935年提出。近年来, 面对超声速运输机低声爆、低超声速巡航阻力的需求, 超声速双翼机重新进入了航空科学家的视野。本文概述了典型超声速双翼机的工作机理, 介绍了超声速双翼机应用所面对的基本问题————非设计点特性、三维问题等的研究进展。最后对超声速双翼机下一步需要重点研究的问题及其应用前景进行了展望。     

Solution of the problem of the supersonic laminar off-design jet in a parallel flow using a difference method

A finite difference method is proposed for solving the simplified Navier-Stokes equations for the case of a supersonic laminar off-design jet issuing into a parallel supersonic stream. Calculations are made of underexpanded and overexpanded jets for various Reynolds numbers.     

Study on the mechanisms and quantitative law of mode I supersonic crack propagation

Continuum mechanics predicts that the propagation speed of non-equilibrium information in solids is limited by the longitudinal wave speed, so is crack propagation. However, solids are essentially discrete systems. In this paper, via theoretical analysis and numerical simulations, it is demonstrated in a straightforward way that non-equilibrium disturbance (e.g. force, displacement, energy, and so on) can propagate at a supersonic speed in discrete systems, although the magnitude of the disturbance attenuates very quickly. In dynamic fracture, a cascade of atomic-bond breaking events provides an amplification mechanism to counterbalance the attenuation of the disturbance. Therefore, supersonic crack propagation can be realized in a domino way. Another key factor for supersonic crack propagation is to ensure sufficient energy flowing into the crack tip. Since most energy can only be transferred at a speed limited by the longitudinal wave speed, the conditions for the occurrence of supersonic crack propagation are not easily met in most situations, unless there is high pre-stored energy along the crack path or continuous energy supply from the loading concomitantly moving with the crack tip. A quantitative relation between supersonic crack propagation speed and material properties and parameters is given, which implies that knowing all the classical macroscopic quantities is not enough in determining the supersonic crack propagation speed, and the microstructure does play a role. Moreover, it is interesting to note that fracture toughness affects the crack propagation speed in the subsonic regime, but not in the supersonic regime, because the deformation/stress is uniform in front of a supersonic crack where strength criterion dominates.     

Spatial interaction of jets propagating in an accompanying supersonic flow

A numerical method of calculating a three-dimensional laminar supersonic underexpanded jet escaping into an accompanying supersonic flow is developed. The simplified Navier-Stokes equations for a steady-state three-dimensional flow are employed. Numerical calculations are carried out for several cases relating the outflow of jets from a four-nozzle assembly into an accompanying supersonic flow, and a number of the characteristics of three-dimensional flows of this kind are presented.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 88–93, November–December, 1972.     

Effect of Condensation on the Length of Strongly Underexpanded Jets Exhausting Into a Rarefied Submerged Space

Exhaustion of supersonic argon and nitrogen jets through sonic and supersonic nozzles into a rarefied submerged space at high stagnation pressures is studied experimentally. The shapes and lengths of the jets are visualized by means of detecting radiation excited in the considered flow by an electron beam. Dependences of the geometric parameters of the jets on exhaustion and clusterization conditions at low Reynolds numbers based on the reference length of the jet are obtained. It is found that the coefficient of proportionality between the length of the first “barrel” of the supersonic jet and the degree of jet expansion increases with an increase in the stagnation pressure. Empirical dependences of the proportionality coefficient on the size of clusters formed in supersonic flows are derived for the first time.     

Investigation of the Flow Structure on a Miniature Gas-Dynamic Setup: Identification of the Secondary Flow in a Clustered Supersonic Jet Escaping Into a Rarefied Space

A possibility of using small-scale vacuum setups for experimental investigations of supersonic jets escaping from supersonic nozzles into vacuum or rarefied space is considered. Results of studying the structure of the secondary supersonic flow formed in supersonic jets with developed condensation, which is detected for the first time, are reported. The present investigations are carried out with the use of photometry and spectrometry of jets with the use of radiation excited by an electron beam; flow visualization is also performed. The results obtained in the study are analyzed; capabilities and specific features of various methods of flow registration are considered. An empirical model, which establishes the dependence between the detected secondary flow and the process of formation of large clusters in the flow, is developed and justified.     

Nozzle startup in an oncoming flow

Three variants of the startup of an axisymmetric convergent-divergent nozzle are considered with the static pressures at the entry and exit of the nozzle being the same at the beginning of the process. The subsonic startup corresponds to open nozzle acceleration in air. The supersonic startup simulates the sudden opening of a cover at the nozzle inlet under supersonic flight conditions. A successful nozzle startup with the formation of steady supersonic flow along the whole channel is realized in the third variant of supersonic startup with gas injection through a small region of the wall of the divergent nozzle section. The investigation is performed numerically, on the basis of the Euler equations for axisymmetric gas flows.     

Propagation of an underexpanded turbulent jet in a parallel supersonic flow

The characteristics of supersonic off-design turbulent jets discharging into parallel supersonic flows are investigated numerically using approximate equations for the effective turbulent viscosity which are derived by analysis of the experimental data.     

SWT-120风洞稳定段的性能测量

在普通超音速风洞中,由于受到噪声干扰,很难进行有效的边界层转捩特性试验研究,针对超声速流动特点发展较低噪声风洞十分必要,而稳定段设计的好坏直接影响到下游试验段噪声水平。本文介绍一座低噪声风洞稳定段的结构和性能测量结果。先对稳定段的结构设计做了简单介绍,然后对实验结果进行分析,实验结果表明在大角度扩散段内装置孔锥,稳定段安装消音夹层和阻尼网组等部件后,气流的速度脉动和压力脉动明显降低,其中压力脉动降低一个量级,速度脉动为1%。进一步优化设计和改进工艺,速度脉动还可进一步降低。测量结果表明SWT-120稳定段的设计是成功的,对我们以后发展更高性能的静风洞有借鉴和参考价值。     

Development of a Parachute System for Deceleration of Flying Vehicles in Supersonic Regimes

Aerodynamic problems arising during design and development of braking systems for re-entry vehicles are analyzed. Aerodynamic phenomena and laws valid in a supersonic flow around a pair of bodies having different shapes are studied. Results of this research can be used in solving application problems (arrangement and optimization of experiments; design and development of various braking systems for re-entry vehicles moving with supersonic speeds in the atmosphere).     

Supersonic rarefied gas flow through a wire grid

The direct simulation Monte Carlo method is used to study a plane-parallel supersonic gas flow through a grid formed by a series of parallel infinite cylinders. Characteristic features of the shock disturbance formation during the interaction of a supersonic flow with a permeable grid and the effect of this disturbance on the flow parameters behind the grid are revealed. The boundaries of the domain of supersonic flow breakup ahead of the grid and the laws of the total momentum loss on the grid are obtained. Kinetic and energetic characteristics of the flow behind the grid are determined.     

化学反应对超音速混合层发展的影响分析

超音速混合层流动发展的研究对于了解超音速燃烧过程具有重要意义.基于耦合详细化学反应动力学机理的高精度数值模拟,分析了化学反应对超音速混合层发展过程的影响.主要分析了在两种燃烧状态下化学反应对混合层的演化过程和混合层厚度的影响.此外从涡动力学角度,分析了化学反应对混合层厚度的影响机理.     

Mechanism of self-oscillations in a supersonic jet impact onto an obstacle 1. Obstacle with a spike

Results of numerical simulations and experimental investigations of self-oscillations arising in the case of impingement of an overexpanded or underexpanded jet onto an obstacle with a spike are reported. The mechanisms of the emergence and maintaining of self-oscillations for overexpanded and underexpanded jets are elucidated. It is demonstrated that self-oscillations are caused by disturbances in a supersonic jet, which induce mass transfer between the supersonic flow and the region between the shock wave and the obstacle. The feedback is ensured by acoustic waves generated by the radial jet on the obstacle. These waves propagate in the gas surrounding the jet, impinge onto the nozzle exit, and initiate disturbances of the supersonic jet parameters. In the overexpanded jet, these disturbances penetrate into the jet core, where they are amplified in oblique shock waves.     

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.     

Computation of the stability derivatives via CFD and the sensitivity equations

The method to calculate the aerodynamic stability derivates of aircrafts by using the sensitivity equations is ex- tended to flows with shock waves in this paper. Using the newly developed second-order cell-centered finite volume scheme on the unstructured-grid, the unsteady Euler equations and sensitivity equations are solved simultaneously in a non-inertial frame of reference, so that the aerodynamic stability derivatives can be calculated for aircrafts with complex geometries. Based on the numerical results, behavior of the aerodynamic sensitivity parameters near the shock wave is discussed. Furthermore, the stability derivatives are analyzed for supersonic and hypersonic flows. The numerical results of the stability derivatives are found in good agree- ment with theoretical results for supersonic flows, and variations of the aerodynamic force and moment predicted by the stability derivatives are very close to those obtained by CFD simulation for both supersonic and hypersonic flows.     

纳米示踪平面激光散射技术在激波复杂流场测量中的应用

在激波以及激波边界层相互作用这类含激波的复杂流场中,流场结构具有明显的三维特征.研究这类流场,采用纹影、阴影和干涉等传统流动显示技术空间分辨率较低,难以分辨流场的三维特性.基于纳米示踪的平面激光散射技术(nano-tracer planar laser scattering,NPLS),是作者近年来开发的一种新的研究超声速流场的测试与显示技术,可对超声速复杂三维流场进行高时空分辨率流动显示与测量.NPLS技术的特点使其成为测量激波复杂流场的有力手段.近年来,作者以NPLS技术为主要手段,对航空航天领域典型的激波复杂流场进行了试验研究,包括超声速弹头绕流、超声速混合层、超声速边界层,以及激波边界层相互作用流场,显示出NPLS技术在激波复杂流场精细测试与流动显示中优势.本文简要介绍NPLS技术在激波复杂流场测量中应用的研究进展.      

Evolution of disturbances in a laminarized supersonic boundary layer on a swept wing

Experimental data on stability of a three-dimensional supersonic boundary layer on a swept wing are presented. The experiments are performed on a swept wing model with a lenticular profile with a 40° sweep angle of the leading edge at a zero angle of attack. The supersonic boundary layer on the swept wing was laminarized with the use of distributed roughness. A pioneering study of interaction of traveling and stationary disturbances is performed. Some specific features of this interaction are identified. The main reason for turbulence emergence in a supersonic boundary layer on a swept wing is demonstrated to be secondary crossflow instability. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 40–46, March–April, 2008.     

Shock capturing for steady,supersonic, two-dimensional isentropic flow

A finite difference scheme is presented for the solution of the two-dimensional equations of steady, supersonic, isentropic flow. The scheme incorporates numerical characteristic decomposition, is shock-capturing by design and incorporates space marching as a result of the assumption that the flow is wholly supersonic in at least one space dimension. Results are shown for problems involving oblique hydraulic jumps and reflection from a wall.     

Experiments on free and impinging supersonic microjets

The fluid dynamics of microflows has recently commanded considerable attention because of their potential applications. Until now, with a few exceptions, most of the studies have been limited to low speed flows. This experimental study examines supersonic microjets of 100–1,000 μm in size with exit velocities in the range of 300–500 m/s. Such microjets are presently being used to actively control larger supersonic impinging jets, which occur in STOVL (short takeoff and vertical landing) aircraft, cavity flows, and flow separation. Flow properties of free as well as impinging supersonic microjets have been experimentally investigated over a range of geometric and flow parameters. The flowfield is visualized using a micro-schlieren system with a high magnification. These schlieren images clearly show the characteristic shock cell structure typically observed in larger supersonic jets. Quantitative measurements of the jet decay and spreading rates as well as shock cell spacing are obtained using micro-pitot probe surveys. In general, the mean flow features of free microjets are similar to larger supersonic jets operating at higher Reynolds numbers. However, some differences are also observed, most likely due to pronounced viscous effects associated with jets at these small scales. Limited studies of impinging microjets were also conducted. They reveal that, similar to the behavior of free microjets, the flow structure of impinging microjets strongly resembles that of larger supersonic impinging jets.