高超声速三维热化学非平衡流场的数值模拟

对三维高超声速热化学非平衡流场进行数值模拟,采用双温度热化学非平衡、11组元空气模型,考虑振动-离解耦合．差分格式采用沈清博士提出的“迎风型NND”格式,用熵修正方法消除了高超声速流数值模拟中的“carbuncle现象”．与LU-SGS方法结合,提高了单步计算效率和收敛性．数值模拟结果与文献结果进行了对比,并在弹道靶中进行了钢质圆球的弓形激波位置实验验证．计算结果与文献、实验的对比说明,三维热化学非平衡流计算程序可以精确地捕捉到强弓形激波,得到合理的空气动力系数．     

Measurements of non-equilibrium and equilibrium temperature behind a strong shock wave in simulated martian atmosphere

Non-equilibrium radiation measurements behind strong shock wave for simulated Martian atmosphere are presented in this paper. The shock wave is established in a hydrogen oxygen combustion driven shock tube. Timeresolved spectra of the Δv = 0 sequence of the B ²Σ⁺ → X ²Σ⁺ electronic transition of CN have been observed through optical emission spectroscopy (OES). A new method, which is based on fitting high resolution spectrum for rotational and vibrational temperatures measurement, is proposed to diagnose temperature distribution behind the shock wave. It is estimated that the current scheme has the maximum deviation less than 8% (1σ) for vibrational temperature measurement through detailed analysis of the influence of the uncertainties of spectroscopic constants and spectral resolution. Radiation structure of the shock layer, including induction, relaxation and equilibrium process, and corresponding rotational and vibrational temperatures are obtained through time gating OES diagnostics with sub-microsecond temporal resolution. The present extensive results will strongly benefit the reaction rate estimation and computational fluid dynamics (CFD) code validation in high enthalpy Mars reentry chemistry.     

基于CN自由基的火星再入流场温度测量

利用氰自由基（CN）B2Σ+→X2Σ+ 电子带系的发射光谱温度测量技术诊断模拟火星再入流场高温气体的温度. 以双原子分子光谱理论为基础,通过确定CN 自由基B2Σ+→X2Σ+ 电子带系中 Δv = 0 振动带系发射光谱的跃迁波数、Einstein 跃迁几率以及不同振转能级粒子数等参数,得到了任意转动温度和振动温度下的理论光谱强度分布,结合经窄线宽半导体激光器标定的仪器展宽（Lorentz 线型,半宽度FWHM 为0.154 nm）,为CN自由基B2Σ+→X2Σ+ 电子带系发射光谱测温技术提供理论依据. 利用激波管模拟火星再入流场环境,通过分析激波波后不同时刻处高时间、空间分辨率的CN 自由基发射光谱,得到了激波波后高温气体不同时刻处的转动温度和振动温度,并根据得到的温度信息给出了激波诱导时间和弛豫时间.      

Specific features of modeling of nonequilibrium radiation behind the shock wave in air in the vacuum ultraviolet spectral range

A physical-chemical model of generation of nonequilibrium molecular radiation in the vacuum ultraviolet (VUV) spectral range behind the shock wave in air for shock wave velocities from 4.5 to 9.5 km/s is developed. Experimental results obtained in a shock tube in investigations of photoionization of air ahead of the shock wave front are used for verification of the numerical model of VUV radiation in the wavelength range from 85 to 105 nm. Model calculations show that nonequilibrium VUV radiation arises in a very thin high-temperature layer behind the shock wave front and is affected by heavy particles and electrons.     

Computation and experimental validation of N_{2}-CH_{4}-Ar mixture flows behind normal shock wave

Different vibration-dissociation-vibration coupling models have been used to compute the nonequilibrium N-CH-Ar mixture flow behind a normal shock wave. A three-temperature model was used and the diffuse nature of vibrational relaxation at high temperatures was accounted for. The numerical results obtained with the Treanor and Marrone model (preferential or non preferential) and the Park model of vibration-dissociation-vibration coupling are compared. These results show that the temperatures and the concentrations are mainly affected by the value of the characteristic temperature U in the preferential model of Marrone and Treanor. An assessment of the more realistic model was realized by comparing numerical results with shock tube experiments. The influence of argon addition on the nonequilibrium emission of CN behind the shock wave was also numerically studied and compared to experimental measurements. Received 1 September 1995 / Accepted 10 December 1996     

Monte Carlo analysis of dissociation and recombination behind strong shock waves in nitrogen

Computations are presented for the relaxation zone behind strong, one-dimensional shock waves in nitrogen. The analysis is performed with the direct simulation Monte Carlo method (DSMC). The DSMC code is vectorized for efficient use on a supercomputer. The code simulates translational, rotational and vibrational energy exchange and dissociative and recombinative chemical reactions. A new model is proposed for the treatment of three body recombination collisions in the DSMC technique which usually simulates binary collision events. The new model represents improvement over previous models in that it can be employed with a large range of chemical rate data, does not introduce into the flow field troublesome pairs of atoms which may recombine upon further collision (pseudo-particles) and is compatible with the vectorized code. The computational results are compared with existing experimental data. It is shown that the derivation of chemical rate coefficients must account for the degree of vibrational nonequilibrium in the flow. A nonequilibrium chemistry model is employed together with equilibrium rate data to compute successfully the flow in several different nitrogen shock waves.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Rotation-vibration-dissociation interaction in a multicomponent nonequilibrium viscous shock layer

A new, simple and physically adequate method of calculating vibrationally nonequilibrium dissociation constants is proposed on the basis of a dissociation model which takes into account the equilibrium excitation of the rotational degrees of freedom of the molecules and the nonequilibrium excitation of vibrational quantum states. This rotation-vibration-dissociation interaction model contains only the indeterminacy associated with the indeterminacy of the experimental data on the interaction potentials and the collision cross sections of the components. In the case of thermodynamic equilibrium the model gives values of the dissociation constants close to those generally accepted. The use of this model in multicomponent nonequilibrium total viscous shock layer calculations gives values for the shock detachment distance within 5% of the experimental values. The indeterminacy in the values of the vibrational energy lost by air molecules during dissociation and recovered during recombination does not lead to serious errors in the macrocharacteristics of the flow. The nonequilibrium excitation of vibrational degrees of freedom proves to be not so important in computing the macrocharacteristics of the flow as previously assumed and the existing algorithms for calculating chemically nonequilibrium flows on the assumption of thermodynamic equilibrium can be used with satisfactory accuracy for calculating the values of the heat flux, the position of the shock wave, and the temperature and pressure in the shock layer for partially dissociated and ionized air.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 166–180, November–December, 1994.     

Modeling of vibration-dissociation oxygen kinetics at temperatures of 4,000-11,000 K

The time profiles of vibrational molecular oxygen temperature T _v measured earlier in experiments behind a strong shock wave were used for testing the theoretical and empirical models of thermal nonequilibrium dissociation of molecules. To do this, dissociating gas flows behind the strong shock wave front were calculated with account for these models. If the initial gas temperature behind the wave front T ₀ < 6.5×10³ K, the models well describe changing the temperature with time. However, for T ₀ > 7×10³ K neither of the models tested describes the measured temperature profiles satisfactorily. Using the empirical model proposed in the present study made it possible to satisfactorily describe the vibrational temperature evolution observed in experiments at temperatures up to 11×10³ K.     

One-dimensional nonequilibrium air flow

A solution is found for the problem of steady quasi-one-dimensional air flow in a stream tube with nonequilibrium chemical reactions, ionization reactions, and nonequilibrium excitation of the vibrational degrees of freedom in the molecular components. We consider the inverse problem: for a given pressure distribution find the distributions of all the other gas-thermodynamic quantities and the streamtube sections. The use of an implicit scheme for approximating the equations makes it possible to carry out the calculations over the entire range of variation in the degree of nonequilibrium — from the frozen state to equilibrium. We discuss the nature of the variation in temperature, vibrational energies, and component concentrations along the stream tube. A numerical analysis is made of the transition to equilibrium flow.     

Model of the physico-chemical kinetics behind the front of a very intense shock wave in air

A model of the physico-chemical kinetics of the reactions taking place behind the front of an intense shock wave propagating in air with a speed of 9–14 km/s is proposed. The problem of describing the chemical reactions, namely, molecular dissociation and exchange reactions involving vibrationally excited molecules in the absence of vibrational equilibrium, is solved. The vital role of the vibrational excitation delay in the dissociation of oxygen and nitrogen is established. The rate of the exchange reaction between nitrogen molecules and oxygen atoms in the shock wave depends only slightly on the vibrational excitation level. It is demonstrated that the rate constants for thermally nonequilibrium dissociation reactions can be represented within the framework of the one-temperature approximation at constant vibrational temperatures of the dissociating species satisfying quasi-stationary conditions.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 169–182, March–April, 1995.     

Nonequilibrium viscous shock layer on blunt cones

Some results are given of the numerical investigation into the parameters of the nonequilibrium flow of air in a viscous shock layer in the case of blunt circular cones at zero angle of attack; they are also compared with experimental data obtained during re-entry of ballistic objects into the Earth's atmosphere. The calculations were made with allowance for the nonequilibrium processes of dissociation and ionization, and also vibrational relaxation. The influence of viscosity, heat conduction, and diffusion is taken into account in the complete shock layer. The conditions on the shock wave are posed with allowance for its finite thickness. The characteristic profiles of the velocity, temperature, and electron concentration in the shock layer are given. Good agreement is obtained between the calculated and experimental data on the level and the profiles of the electron concentration. The parameters of the shock layer were determined by a method that is a natural extension of the numerical method of [1] to the case of nonequilibrium flow in a viscous shock layer. Because of this, only the main differences of the method when applied to the calculation of nonequilibrium flows of a multicomponent mixture such as dissociated and ionized air are described.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 15–20, November–December, 1979.     

高速冲击压缩梯恩梯的分子动力学模拟

采用反应力场分子动力学方法模拟了梯恩梯(2,4,6-trinitrotoluene,TNT) 冲击压缩过程. 冲击压缩完全时,体积压缩至原体积40%,梯恩梯分子分解完毕,体系压力达到峰值. 随后稀疏波反向拉伸致大量原子或分子基团飞溅至下游,同时压力开始卸载. 密度及粒子速度剖面显示压缩波后方密度较大,粒子基本处于静止状态,且压缩波内存在较大的粒子速度梯度. 早期化学反应特征是梯恩梯分子在冲击压缩作用下脱落H,O 原子后残基快速聚合形成较大的分子团簇,此阶段和平动—振动弛豫过程相关,并且分子由平动—振动模态转换的时间尺度为0.5 ps. 产物识别分析显示梯恩梯在高速冲击压缩下致C—H,O＝N 键断裂,脱落的原子部分形成OH,H₂,H₂O,N₂,部分H,O 原子游离在体系中. 含碳团簇分析显示,冲击压缩作用致体系中含碳团簇的摩尔质量逐渐累积. 体系内含碳团簇中O/C,H/C,N/C 原子数量比值逐渐趋于平衡(O/C=0.680,H/C=0.410,N/C=0.284),且均小于初始结构中的比值.      

Experimental investigation of CO vibrational deactivation in a supersonic cooling gas flow

Abstract. The vibrational relaxation time of CO molecules at collisions with H atoms was measured in shock tube experiments by means of the CARS-spectroscopy method. The measurements of the CO vibrational temperature at gas temperatures of 1800–3000 K were performed in a supersonic cooling gas flow. The gas was heated behind the incident and reflected shock wave and then flowed out of a wedge-shaped nozzle. H atoms were generated in the reflected shock wave because of dissociation of H and HO admixtures. The extremely high efficiency of H atoms in CO vibrational deactivation was confirmed. Received 1 February 2000 / Accepted 20 February 2000     

Aerodynamic calibration of TCM2 facility and study of a bow shock layer by emission and laser spectroscopy

Flow properties in the TCM2 free piston shock tube/tunnel are determined by time-resolved pressure and heat flux measurements in numerous points of the shock tube and the nozzle, and in the free flow for two stagnation enthalpy conditions (3.5 and 11 MJ/kg). These measurements demonstrate the homogeneity of the flow during more than 1 ms. The cleanness of the useful test time is shown with time-resolved emission measurements at critical wavelengths. NO fluorescence profiles are established with local and planar laser-induced fluorescence in the shock layer around a cylindrical model. It allows to determine the shock stand-off distance for both enthalpy conditions. The problems of quenching and amplified spontaneous emission are considered. The importance of atomic oxygen and atomic nitrogen densities as well as temperature effects is also shown. Evaluation of the temperatures behind the shock front through spectroscopic data agrees with calculations. The proof of the presence of vibrationally excited NO ahead of the shock layer is given. Received 14 March 2000 / Accepted 18 June 2001     

Measurement of the vibrational temperature of oxygen behind a shock wave front under thermal and chemical nonequilibrium conditions

In shock tube experiments the profiles of light absorption in oxygen are obtained for the wavelength interval 200–260 nm over the temperature range 4000–10800 K. Using these data, the vibrational temperature profiles are measured for oxygen molecules behind the shock front. The method of determination of the vibrational temperature of oxygen is based on comparing absorption measurements and detailed absorption spectrum calculations for oxygen in the Schumann-Runge system.     

Nonequilibrium Ionization Behind a Strong Shock Wave in the Mars Atmosphere

The paper reports results of experimental and numerical studies of nonequilibrium ionization behind a strong shock wave in the Mars atmosphere. The calculated kinetic model is verified by measuring the electron concentrations and temperature in the relaxation zone     

热化学非平衡辐射流场数值研究

从耦合辐射的轴对称热化学非平衡N-方程出发,采用双温度、11组元反应气体模型,耦合“线-线”精细辐射模型,利用隐式NND有限差分格式和时间预处理技术数值求解了FIREII飞船热化学非平衡辐射流场,得到了有关辐射和辐射光谱计算结果,并与有关文献的实验结果和计算结果进行了比较。     

Early time spectroscopic measurements during high-explosive detonation breakout into air

Explosive breakout of PBX-9407 into air is examined using time-resolved optical spectroscopy over a period of several microseconds. Emission is monitored over the 250–700 nm range, and several atomic and molecular species are observed including atomic calcium, and copper, as well as OH and CN. Several lines and bands remain unidentified. Fits to Ca and OH spectra suggest that early time temperatures exceed 13,000 K behind the air shock and that temperature decay is fairly rapid over the first $10\,\upmu \mathrm{s}$ . Considering the proposed shock structure of the blast wave, it is likely that these temperatures are confined to a narrow region behind the blast wave, but nevertheless generate emission signatures that dominate the spectra at early times.     

Features of nonequilibrium processes of titrogen oxide formation behind strong shock waves in air

The kinetics of NO and NO₂ of behind shock fronts propagating in air are analyzed. It is shown that in certain cases it is necessary to use fairly detailed chemical reaction schemes involving not only N₂, O₂, NO, N, and O, but also NO₂, N₂O, H₂, OH, and H and to take into account the mutual effects of vibrational relaxation and chemical transformations. It is established that neglecting the chemical processes involving NO₂ only can lead to significant errors in the length of the relaxation zone (up to 25 times), the gasdynamic parameters (up to 20%), and the NO concentration (up to 3 times). Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 132–144, January–February, 1999. The work was carried out with financial support from the Russian Foundation for Basic Research (project No. 96-02-18377).