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.     

Detonation combustion of hydrogen in a convergent-divergent nozzle with a central coaxial cylinder

The feasibility of steady detonation combustion of a hydrogen-air mixture entering at a supersonic velocity in an axisymmetric convergent-divergent nozzle with a central coaxial cylinder is considered. The problem of the nozzle starting and the initiation of detonation combustion is numerically solved with account for the interaction of the outflowing gas with the external supersonic flow. The modeling is based on the gasdynamic Euler equations for an axisymmetric flow. The calculations are carried out using the Godunov scheme on a fine fixed grid which allows one to study in detail the interaction of an oblique shock wave formed in the diffuser with the nozzle axis. It is shown that a central coaxial cylinder ensures the starting with the formation of supersonic flow throughout the entire nozzle and stable detonation combustion of a stoichiometric hydrogen-air mixture in the divergent section of the nozzle.     

Detonation combustion of hydrogen in a Laval nozzle under rarefied atmosphere conditions

Detonation combustion of a hydrogen-air mixture entering an axisymmetric convergent-divergent nozzle at a supersonic velocity is considered under atmospheric conditions at altitudes up to 24 km. The investigation is carried out on the basis of the two-dimensional gasdynamic Euler equations for a multicomponent reacting gas. The limiting altitude ensuring detonation combustion in a Laval nozzle of given geometry is numerically established for freestream Mach numbers 6 and 7. The possibility of the laser initiation of detonation in a supersonic flow of a stoichiometric, preliminarily heated hydrogen-air mixture is experimentally studied. The investigation is carried out in a shock tube under conditions simulating a supersonic flow in the nozzle throat region.     

Stabilization of detonation combustion in a high-velocity flow of a hydrogen-oxygen mixture

The flow of a hydrogen-oxygen mixture diluted with argon in a supersonic axisymmetric nozzle consisting of an inlet cylinder, a convergent region, a cylindrical throat, and a divergent region is considered. The supersonic flow enters the channel along the axis of symmetry. The flow structure is calculated with allowance for hydrogen ignition. A possibility of stabilizing the combustion zone is studied and the forces acting on the nozzle from the flow are determined. The problem is solved in the two-dimensional approximation with account for detailed combustion kinetics.     

Detonation combustion of hydrogen in an axisymmetric channel with a central body

The problem of initiation and stabilization of detonation combustion of a hydrogen–air mixture injected into an axisymmetric channel with a finite-length central body in a flow with a Mach number M₀ = 5–9 is solved. It is numerically demonstrated that the presence of the central body both in a convergent–divergent nozzle and in an expanding channel leads to stabilization of detonation combustion of a stoichiometric hydrogen–air mixture at free-stream Mach numbers M₀ > 7. Various channel configurations that ensure different values of thrust generated by detonation combustion of a stoichiometric hydrogen–air mixture are compared.     

Profiling of a Supersonic Combustion Chamber and Nozzle Under Constraints on the Total Length

A method of combined profiling of a combustion chamber and two-dimensional supersonic nozzle with a given total length is demonstrated with reference to a hydrogen/air hypersonic ramjet. The possibility of a considerable increase in thrust is illustrated by various devices designed within the framework of the method developed.     

Nozzle design study for a quasi-axisymmetric scramjet-powered vehicle at Mach 7.9 flight conditions

A nozzle shape optimization study for a quasi-axisymmetric scramjet has been performed for a Mach 7.9 operating condition with hydrogen fuel, aiming at the application of a hypersonic airbreathing vehicle. In this study, the nozzle geometry which is parameterized by a set of design variables, is optimized for the single objective of maximum net thrust using an in-house CFD solver for inviscid flowfields with a simple force prediction methodology. The combustion is modelled using a simple chemical reaction code. The effects of the nozzle design on the overall vehicle performance are discussed. For the present geometry, net thrust is achieved for the optimized vehicle design. The results of the nozzle-optimization study show that performance is limited by the nozzle area ratio that can be incorporated into the vehicle without leading to too large a base diameter of the vehicle and increasing the external drag of the vehicle. This study indicates that it is very difficult to achieve positive thrust at Mach 7.9 using the basic geometry investigated.     

高速液体受限射流扩展形态研究

采用一种火药燃烧驱动液体喷射的新装置及其测试系统，研究受限空间中高速惰性液体射流的扩展结构。观察了环境反压、液体粘性、喷嘴结构等参量对射流扩展形态的影响，分析了射流雾化机理。研究结果对改进燃烧室设计及控制燃烧稳定性有一定的指导意义。     

Flow of gas with a cellular vortical structure through a nozzle

The operation of rocket motors is often accompanied by the development of powerful secondary vortices in the combustion chamber [1–3], The superposition of the secondary vortices on the main flow leads to the formation of a cellular flow structure. Each of the cells represents a three-dimensional vortical circulation of the gas, and this causes a change in the working conditions of the nozzle. The model of helical motion [4] is used in this paper in considering the influence of the three-dimensional behavior of an adiabatic flow on the flow and traction characteristics of the nozzle.     

含能气体射流与液体相互作用的实验研究

为了研究整装式液体发射药的燃烧稳定性的控制方法,设计了点火喷射模拟装置及4种多级渐扩型观察室,利用数字高速摄像系统,观察含能气体射流在液体模拟工质中的扩展过程,并对实验中出现的喷孔壅塞现象进行了分析.结果表明:射流在渐扩型结构中扩展稳定,喷射压力、喷孔直径和渐扩结构对射流扩展形态和气液掺混过程有显著影响,通过合理调整这些参数,可以实现对射流扩展过程的有效控制;喷孔壅塞时射流扩展形态非对称,影响气液掺混,不利于控制射流的稳定性.     

Numerical modeling of the processes within the combustion chamber of a solid propellant rocket engine during the stabilization of the design operation mode

Comprehensive numerical modeling of the processes occurring in the combustion chamber of a solid propellant rocket engine during the stabilization of the design operation mode is performed. The self-consistent problem considered includes nonstationary operation of an ignition device, warmup and ignition of a solid propellant charge followed by its nonstationary burning, nonstationary threephase homogeneous-heterogeneous flow of the combustion products in the combustion chamber, in the nozzle, and behind the engine nozzle unit, engine depressurization, and nozzle unit plug blowing-out. The results of the calculations are presented.     

Experimental Study on Bubble Movement Characteristics during Underwater Pyrotechnic Combustion

High-speed photography was used to study bubble movement characteristics during underwater pyrotechnic combustion. The results show that bubble behaviors include bubble formation at the nozzle, departure from the nozzle, bubble coalescence, and bubble breakup. Compared with cavitation bubbles and fluidization bubbles, the nozzle bubbles formed during underwater pyrotechnic combustion feature larger diameters, up to centimeters, and darker, and more irregular shapes. During large bubble coalescence, two bubbles approach each other, generate a channel for transfer of mass and heat, and finally coalesce. The bubbles contain high-temperature gases and solid residues generated during pyrotechnic combustion, which lead to non-uniform forces on the bubble surface and make the bubbles more prone to breakup. Because of the high-temperature solid grains, the surrounding liquid vaporizes to form bubbles.     

Revised model coefficients for vibrational relaxation in a nitrogen–oxygen gas mixture

A numerical investigation of thermal non-equilibrium flows requires species specific relaxation rates, which are often calculated using the Landau–Teller model. This model requires the determination of collision specific relaxation times, which can be computed using Millikan and White’s empirical formula. The coefficients used in this formula for each specific collision pair form a set of coefficients, which are assessed here. The focus of the investigation lies on their performance in hypersonic low-temperature (300–2,500?K) flows that occur at shock-tunnel nozzle exits or in supersonic combustion ramjets (scramjets) before combustion. Two experimental validation cases are chosen; a shock-tunnel nozzle and a sharp cone in hypersonic cross-flow experiment. A comparison of the experimentally measured vibrational temperatures at the nozzle exit against numerical data shows large discrepancies for two commonly used coefficient sets. A revised set of coefficients is proposed that greatly improves the agreement between the numerical and experimental results. Furthermore, the numerically generated shock shape over the sharp cone using the revised set of coefficients correlates well with the experimental measurements.     

Isothermal mass transfer in annular liquid jets with Sievert's solubility law

Summary A study of isothermal gas absorption by underpressurized, axisymmetric, thin, inviscid, incompressible, annular liquid jets which form enclosed volumes, where hazardous wastes may be burned, is presented. The study considers the nonlinear dynamical coupling between the fluid dynamics of, and the gases enclosed by, the annular liquid jet. It assumes equilibrium conditions at the interfaces, and employs Sievert's solubility law to determine the gas concentration at the gas-liquid interfaces. Both steady-state and transient conditions are considered. Under steady-state conditions, the fluid dynamics and mass transfer phenomena are uncoupled, and the rate of generation of combustion gases is equal to the mass absorption rate by the liquid. The transient behaviour of the annular jet is determined from initial conditions corresponding to steady-state operation, once there is no gas generation by the combustion of hazardous wastes. It is shown that, for most of the conditions considered in this paper, there is no leakage of gaseous combustion products through the jet's outer interface, and that the amount of gases dissolved in the liquid at the nozzle exit and the solubility ratio play a paramount role in determining the mass fluxes of hazardous combustion products at the annular jet's interfaces.The research reported in this paper was supported by Project PB91-0767 from the C.I.C.Y.T. of spain.     

Two-dimensional radiation MHD modeling assessment of designs for argon gas puff distributions for future experiments on the refurbished Z machine

Argon Z-pinch experiments are to be performed on the refurbished Z machine (which we will refer to as ZR here in order to distinguish between pre-refurbishment Z) at Sandia National Laboratories with a new 8 cm diameter double-annulus gas puff nozzle constructed by Alameda Applied Sciences Corporation (AASC). The gas exits the nozzle from an outer and inner annulus and a central jet. The amount of gas present in each region can be varied. Here a two-dimensional radiation MHD (2DRMHD) model, MACH2-TCRE, with tabular collisional radiative equilibrium atomic kinetics is used to theoretically investigate stability and K-shell emission properties of several measured (interferometry) initial gas distributions emanating from this new nozzle. Of particular interest is to facilitate that the distributions employed in future experiments have stability and K-shell emission properties that are at least as good as the Titan nozzle generated distribution that was successfully fielded in earlier experiments on the Z machine before it underwent refurbishment. The model incorporates a self-consistent calculation for non-local thermodynamic equilibrium kinetics and ray-trace based radiation transport. This level of detail is necessary in order to model opacity effects, non-local radiation effects, and the high temperature state of K-shell emitting Z-pinch loads. Comparisons of radiation properties and stability of measured AASC gas profiles are made with that of the distribution used in the pre-refurbished Z experiments. Based on these comparisons, an optimal K-shell emission producing initial gas distribution is determined from among the AASC nozzle measured distributions and predictions are made for K-shell yields attainable from future ZR experiments.     

AEROELASTICITY ANALYSIS OF AN INDUSTRIAL GAS TURBINE COMBUSTOR USING A SIMPLIFIED COMBUSTION MODEL

Lean premixed industrial gas turbine combustors are susceptible to flame instabilities, resulting in large unsteady pressure waves that may cause the discharge nozzle to experience excessive vibration levels. A detailed aeroelasticity analysis, aimed at investigating possible structural failure mechanisms, was undertaken using a time-accurate unsteady flow representation, a simplified combustion disturbance and a structural model of the discharge nozzle. The computational domain included the lower part of the combustor geometry as well as the nozzle guide vanes (NGVs) at the HP turbine inlet. A pressure perturbation, representing the unsteadiness due to the combustion process, was applied below the tertiary fuel inlet and its frequency was set to each structural natural frequency in turn. The propagation of the pressure perturbation through the combustor nozzle, its reflection from the NGVs and further reflections were monitored using two different models. The first one, the so-called “open” system, ignored the reflections from the upper part of the combustion chamber while the second one, the “closed” system, assumed full reflection with an appropriate time shift. The calculations have shown that the imposed excitation could generate unsteady pressure shapes that were correlated with the “flap” modes of the discharge nozzle. In addition, an acoustic resonance condition was observed when the forcing pressure wave had a frequency close to 550 Hz, the experimentally observed failure frequency of the nozzle. The co-existence of these two factors, i.e., excitation/structural-mode match and the possibility of acoustic resonance, was thought to have the potential of producing very high vibration response.     

点火过程和初始条件对燃烧轻气炮内弹道性能的影响

采用计算流体力学方法对燃烧轻气炮膛内燃烧过程进行数值模拟,分析不同的点火点数目和点火能量以及初始温度和压力对燃烧轻气炮内弹道特性的影响。结果表明,采用合理的点火点数目、初始温度和压力条件可以有效控制氢气的燃烧过程,减弱燃烧室内的压力波动。模拟结果对燃烧轻气炮膛内燃烧过程控制具有重要参考价值。     

Analysis of Unsteady Motion with Respect to Noise Sources in a Gas Turbine Combustor: Isothermal Flow Case

In order to evaluate the direct and indirect contributions to the total combustion noise emission, a combustion chamber consisting of a swirl burner and an exit nozzle of Laval-shape, representing a gas turbine combustor, is investigated by means of experiments and large eddy simulation. Focused on the isothermal flow case first and encouraged by a good overall agreement between the LES and the experimental data for the flow field, a first characterisation of the flow with respect to noise sources is performed. To analyse acoustic properties of the flow, time and length scales are evaluated inside the combustor. Furthermore, the evidence for the existence of a precessing vortex core (PVC), typical for configurations with swirl, is revealed. Finally, the effect of the PVC on the flow inside the Laval nozzle is discussed.     

不同发射深度下导弹水下点火气水流体动力计算

从流体动力角度研究了不同发射深度下，导弹水下点火这一非定常非线性过程。整个系统分为外部水流场、喷管流场和燃气泡流场三个区域加以考虑。水流场采用不可压势流模型，用边界元方法求解；喷管内流场采用非定常一元流动模型，用特征线差分法求解，并设置了激波检测功能；燃气泡采用基于质量和能量守恒的零维计算模型。在时间域中用步进方法实现了三个流场的耦合求解。给出了四种发射深度下的数值计算结果，展示了导弹水下点火的一