Thrust characteristics of an airbreathing pulse detonation engine in flight at mach numbers of 0.4 to 5.0

Multidimensional calculations are performed to demonstrate that, by its characteristics, the pulse detonation engine (PDE) is a unique type of ramjet propulsion system, which can be used in both subsonic and supersonic aircraft. By a number of examples, it is shown that, in various thrust characteristics, such as the specific impulse, specific fuel consumption, and specific thrust, the PDE substantially exceeds ramjet engines.     

Thrust characteristics of an airbreathing pulse detonation engine in supersonic flight at various altitudes

The main thrust characteristics, such as thrust force, specific impulse, specific fuel consumption, and specific thrust, of a pulse detonation engine (PDE) with an air intake and nozzle in conditions of flight at a Mach number of 3 and various altitudes (from 8 to 28 km above sea level) are for the first time calculated with consideration given to the physicochemical characteristics of the oxidation and combustion of hydro-carbon fuel (propane), finite time of turbulent flame acceleration, and deflagration-to-detonation transition (DDT). In addition, a parametric analysis of the influence of the operation mode and design parameters of the PDE on its thrust characteristics in flight at a Mach number of 3 and an altitude of 16 km is performed, and the characteristics of engines with direct initiation of detonation and fast deflagration are compared. It is shown that a PDE of this design greatly exceeds an ideal ramjet engine in specific thrust, whereas regarding the specific impulse and specific fuel consumption, it is not inferior to the ideal ramjet.     

Use of MHD systems in hypersonic aircraft

The possibilities of using magnetohydrodynamic (MHD) systems on hypersonic aircraft are discussed. The distinctive features of using MHD systems in the flow path of ramjet engines are examined. A quasi-one-dimensional mathematical model for the engine is presented which includes the MHD interaction with the flow. It is shown that the specific impulse of an engine system can be raised by using MHD systems. Zh. Tekh. Fiz. 68, 43–47 (November 1998)     

Numerical simulation of the operation process and thrust performance of an air-breathing pulse detonation engine in supersonic flight conditions

Multidimensional simulations of the unsteady gasdynamic flow in the duct of an air-breathing pulse detonation engine (ABPDE) operating on propane gas and the flow around it in supersonic flight at Mach numbers M of 3.0 and an altitude of 9.3 and 16 km are performed. It is shown that, at a length and diameter of the duct of 2.12 m and 83 mm, respectively, an ABPDE with an air intake and a nozzle can operate in a cyclic mode at a repetition frequency of 48 Hz, with a rapid deflagration-to-detonation transition (DDT) occurring at a distance of 5–6 combustion chamber diameters. To determine the thrust performance of the ABPDE in flight conditions, a series of working cycles were simulated with consideration given to the external flow around the engine. Calculations showed that the specific impulse of the ABPDE is approximately 1700 s. This value is much higher than the specific impulse typical of ramjet engines operating on conventional combustion (1200–1500 s) and substantially lower than the specific impulse obtained for the atmospheric conditions at sea level at zero flight velocity (∼2500 s).     

用于高超音速推进的反循环发动机热力性能分析

符号表fIkg空气对应的燃料流量ISP燃料比冲Ti后燃烧室出口温度马比推力，燃料空气当量比WT涡轮输出功MT飞行马赫数＄前登燃烧室出口温度。T涡轮膨胀比H飞行高度T4＊热交换器出口温度7TC压气机压比1引言八十年代以来，美、俄、德、法、英、日等主要空间大国均提出了各自的高超音速计划，如NASP、Sanger、HOTOL、STAR等。各国的方案在Ma＞6．5均采用火箭发动机或超燃冲压发动机，对于Ma＜6．5采用何种方案则分歧较大，有涡轮一冲压组合发动机方案、ATR方案、LACE方案等。本文对反循环发动机（InverseCgcleEngine）方案作了进…     

预注冷质的空气涡轮火箭性能分析研究

提出了压气机进口预注冷质的空气涡轮火箭(MIPCC ATR)循环,拓展了ATR在高飞行马赫数下的工作能力。给出了基于工质组分的变比热ATR循环热力学建模方法和工质物性改变时对部件特性的修正方法,基于所推导的准无量纲关系式讨论了循环参数之间的相互作用及其对性能的影响。研究结果表明预注冷质不仅能有效拓宽ATR的工作包线,而且可以提高单位推力,所需付出的代价是比冲会有一定程度的降低。     

An engineering method for calculating the parameters and characteristics of pulse detonation engines

Theoretical fundamentals for calculating the thermodynamic cycle of engines with fuel detonation (FD cycle), which is realized in the thrust units of pulse detonation engines (PDE), are presented. A system of equations for calculating the parameters of the detonation waves under various conditions of their initiation is derived. These equations were used to examine how various factors influence the parameters of detonation waves and, consequently, the work of the cycle, thermal efficiency, and the specific parameters of the PDE. It was demonstrated that the maximum thermal efficiency of the FD cycle virtually coincides with the minimum losses caused by the irreversibility of heat input into the detonation wave. It was established that the losses are substantially dependent on the temperature of the working substance (compressed air or heated gas) supplied into the thrust units, more specifically, they decrease with increasing temperature.     

Exergy method for estimating the ramjet specific impulse

The exergy method is developed for computing the ramjet thrust-economic characteristics with regard for real thermodynamic properties of combustion products when using as fuel the hydrogen and hydrocarbon fuel for the freestream Mach numbers M = 4 ÷ 14. The estimates for the specific impulse of the given engine using the presented technique are shown to agree with the estimates computed by other authors. The computational method is intended for obtaining the ramjet characteristics and conduction of the parameter analysis at the research initial stage as well as for its use at the conceptual developments of hypersonic flying vehicles.     

Estimation of energetic efficiency of heat supply in front of the aircraft at supersonic accelerated flight. Part 1. Mathematical models

Fuel economy at boost trajectory of the aerospace plane was estimated during energy supply to the free stream. Initial and final flight velocities were specified. The model of a gliding flight above cold air in an infinite isobaric thermal wake was used. The fuel consumption rates were compared at optimal trajectory. The calculations were carried out using a combined power plant consisting of ramjet and liquid-propellant engine. An exergy model was built in the first part of the paper to estimate the ramjet thrust and specific impulse. A quadratic dependence on aerodynamic lift was used to estimate the aerodynamic drag of aircraft. The energy for flow heating was obtained at the expense of an equivalent reduction of the exergy of combustion products. The dependencies were obtained for increasing the range coefficient of cruise flight for different Mach numbers. The second part of the paper presents a mathematical model for the boost interval of the aircraft flight trajectory and the computational results for the reduction of fuel consumption at the boost trajectory for a given value of the energy supplied in front of the aircraft.     

Investigation of the efficiency of regenerative cooling of the ramjet combustor by gasification products of energy-intensive material

The results of mathematical modeling of the thermal state of combustion chambers with regenerative cooling for ramjet engines of promising flying vehicles are presented. The cooling of combustion chambers by the gasification products of a combined charge of the energy-intensive material is considered, where the polyethylene is used as a stuff, and the HMX-based compounds are used as the active substance. The flow rates of the cooling eneregy-intensive material are determined, which provide acceptable levels of temperatures of combustion chambers at various modes of engines operation are determined.     

脉冲爆震发动机性能分析

本文发展了一种新的脉冲爆震发动机性能分析模型,考虑了流体阻力和油珠直径对爆震波速度、压力及脉冲爆震发动机比冲的影响。性能分析模型计算结果与试验结果比较表明,当进行了两相流和流体阻力影响修正后,两者较好。     

考虑气蚀效应的气液两相冲压发动机数值模拟

针对一种新型水下气液两相冲压发动机,综合考虑了湍流效应、气液两相之间的拖曳作用及传热与传质,利用计算流体力学方法研究了气液两相冲压发动机内流场的流动特性随发动机工作条件的变化规律,重点研究了气蚀效应对发动机工作性能的影响.主要结论为:当航行速度大于32 m/s,气液两相冲压发动机入口附近会产生气蚀并造成严重的总压损失,导致扩张段下游产生流动分离,此时发动机无法产生正推力;通过增大气体质量流率,气液两相冲压发动机内流场的压力将会随之升高,气蚀效应被抑制;提高注入发动机气体的温度,发动机的推力及比冲均增大,但是发动机效率急剧降低.      

Estimation of energetic efficiency of heat supply in front of the aircraft at supersonic accelerated flight. Part II. Mathematical model of the trajectory boost part and computational results

The fuel economy was estimated at boost trajectory of aerospace plane during energy supply to the free stream. Initial and final velocities of the flight were given. A model of planning flight above cold air in infinite isobaric thermal wake was used. The comparison of fuel consumption was done at optimal trajectories. The calculations were done using a combined power plant consisting of ramjet and liquid-propellant engine. An exergy model was constructed in the first part of the paper for estimating the ramjet thrust and specific impulse. To estimate the aerodynamic drag of aircraft a quadratic dependence on aerodynamic lift is used. The energy for flow heating is obtained at the sacrifice of an equivalent decrease of exergy of combustion products. The dependencies are obtained for increasing the range coefficient of cruise flight at different Mach numbers. In the second part of the paper, a mathematical model is presented for the boost part of the flight trajectory of the flying vehicle and computational results for reducing the fuel expenses at the boost trajectory at a given value of the energy supplied in front of the aircraft. Sections, formulas, and figures have a numbering continued from the first part of the paper printed in the journal “Thermophysics and Aeromechanics”, 2008, Vol. 15, No. 4, P. 537–548.     

Second-order oriented partial-differential equations for denoising in electronic-speckle-pattern interferometry fringes

We derive the second-order oriented partial-differential equations (PDEs) for denoising in electronic-speckle-pattern interferometry fringe patterns from two points of view. The first is based on variational methods, and the second is based on controlling diffusion direction. Our oriented PDE models make the diffusion along only the fringe orientation. The main advantage of our filtering method, based on oriented PDE models, is that it is very easy to implement compared with the published filtering methods along the fringe orientation. We demonstrate the performance of our oriented PDE models via application to two computer-simulated and experimentally obtained speckle fringes and compare with related PDE models.     

一种改进的非整数自适应时延估计方法*

针对基于时延估计的机电设备故障声定位中的低信噪比和脉冲噪声情况,用α稳定分布建模噪声,改进了非整数自适应时延估计方法。共变相关法对观测序列进行时延估计粗测,将得到的估计值作为非整数自适应时延估计器的初值;将共变相关法中共变序列作为时延估计器的输入信号,在最小平均p范数准则下迭代得到非整数时延估计值。共变序列保留了原始序列间的时延信息,削弱了不相关的噪声。计算机仿真对比实验验证了改进的方法在脉冲环境和低信噪比条件下有更好的性能。     

Optimal constant shape parameter for multiquadric based RBF-FD method

Radial basis functions (RBFs) have become a popular method for interpolation and solution of partial differential equations (PDEs). Many types of RBFs used in these problems contain a shape parameter, and there is much experimental evidence showing that accuracy strongly depends on the value of this shape parameter. In this paper, we focus on PDE problems solved with a multiquadric based RBF finite difference (RBF-FD) method. We propose an efficient algorithm to compute the optimal value of the shape parameter that minimizes the approximation error. The algorithm is based on analytical approximations to the local RBF-FD error derived in [1]. We show through several examples in 1D and 2D, both with structured and unstructured nodes, that very accurate solutions (compared to finite differences) can be achieved using the optimal value of the constant shape parameter.     

多普勒振镜正弦调制多光束激光外差二次谐波测量微冲量

提出了一种正弦调制多光束激光外差二次谐波测量微冲量的新方法,将激光与工质靶作用产生的微冲量转化为扭摆的转动角度测量,基于激光外差技术和多普勒效应,把待测转角信息加载到外差信号的频率差中,经信号解调后可以得到待测转角值,通过多次测量取平均值的方法可以提高待测转角的测量精度,从而提高微冲量的测量精度。利用这种新方法,以PVC+2%C为工质靶,利用MATLAB仿真测量了激光与工质靶作用产生的微冲量,结果表明:该测量的最大相对误差小于0.8%。     

Analysis and algorithms for a regularized cauchy problem arising from a non-linear elliptic PDE for seismic velocity estimation

In the present work we derive and study a non-linear elliptic PDE coming from the problem of estimation of sound speed inside the Earth. The physical setting of the PDE allows us to pose only a Cauchy problem, and hence is ill-posed. However, we are still able to solve it numerically on a long enough time interval to be of practical use. We used two approaches. The first approach is a finite difference time-marching numerical scheme inspired by the Lax–Friedrichs method. The key features of this scheme is the Lax–Friedrichs averaging and the wide stencil in space. The second approach is a spectral Chebyshev method with truncated series. We show that our schemes work because of (i) the special input corresponding to a positive finite seismic velocity, (ii) special initial conditions corresponding to the image rays, (iii) the fact that our finite-difference scheme contains small error terms which damp the high harmonics; truncation of the Chebyshev series, and (iv) the need to compute the solution only for a short interval of time. We test our numerical schemes on a collection of analytic examples and demonstrate a dramatic improvement in accuracy in the estimation of the sound speed inside the Earth in comparison with the conventional Dix inversion. Our test on the Marmousi example confirms the effectiveness of the proposed approach.     

A spectral FC solver for the compressible Navier–Stokes equations in general domains I: Explicit time-stepping

We present a Fourier continuation (FC) algorithm for the solution of the fully nonlinear compressible Navier–Stokes equations in general spatial domains. The new scheme is based on the recently introduced accelerated FC method, which enables use of highly accurate Fourier expansions as the main building block of general-domain PDE solvers. Previous FC-based PDE solvers are restricted to linear scalar equations with constant coefficients. The FC methodology presented in this text thus constitutes a significant generalization of the previous FC schemes, as it yields general-domain FC solvers for nonlinear systems of PDEs. While not restricted to periodic boundary conditions and therefore applicable to general boundary value problems on arbitrary domains, the proposed algorithm inherits many of the highly desirable properties arising from rapidly convergent Fourier expansions, including high-order convergence, essentially spectrally accurate dispersion relations, and much milder CFL constraints than those imposed by polynomial-based spectral methods—since, for example, the spectral radius of the FC first derivative grows linearly with the number of spatial discretization points. We demonstrate the accuracy and optimal parallel efficiency of the algorithm in a variety of scientific and engineering contexts relevant to fluid-dynamics and nonlinear acoustics.