Numerical study on similarity of plume infrared radiation between reduced-scale solid rocket motors

This study seeks to determine the similarities in plume radiation between reduced and full-scale solid rocket models in ground test conditions through investigation of flow and radiation for a series of scale ratios ranging from 0.1 to 1. The radiative transfer equation(RTE) considering gas and particle radiation in a non-uniform plume has been adopted and solved by the finite volume method(FVM) to compute the three dimensional, spectral and directional radiation of a plume in the infrared waveband 2–6 μm. Conditions at wavelengths 2.7 μm and 4.3 μm are discussed in detail, and ratios of plume radiation for reduced-scale through full-scale models are examined. This work shows that, with increasing scale ratio of a computed rocket motor, area of the hightemperature core increases as a 2 power function of the scale ratio, and the radiation intensity of the plume increases with 2–2.5 power of the scale ratio. The infrared radiation of plume gases shows a strong spectral dependency, while that of Al_2O_3 particles shows spectral continuity of gray media.Spectral radiation intensity of a computed solid rocket plume's high temperature core increases significantly in peak radiation spectra of plume gases CO and CO_2. Al_2O_3 particles are the major radiation component in a rocket plume. There is good similarity between contours of plume spectral radiance from different scale models of computed rockets, and there are two peak spectra of radiation intensity at wavebands 2.7–3.0 μm and 4.2–4.6 μm. Directed radiation intensity of the entire plume volume will rise with increasing elevation angle.     

Infrared radiation characteristics of a hypersonic vehicle under time-varying angles of attack

Hypersonic vehicles emit strong infrared(IR) radiation signatures that can be treated as a detecting source for object identification and routine diagnosis. This paper is aimed at examining the intrinsic radiation characteristics of a Boost-Glide Vehicle(BGV) under the condition of various Angles of Attack(AOAs). A two-temperature model considering the thermal and chemical nonequilibrium effects is coupled with Navier-Stokes equations solved by the finite volume technique.A gas–solid conjunction heat transfer model is also added into the fluid solver to simulate the surface temperature of the vehicle. The radiative transfer equation is solved with Line of Sight(LOS)algorithm. The computational results for a Hypersonic Technology Vehicle-2(HTV-2) type vehicle show that radiances of the vehicle are strongly dependent on the surface temperature. The presence of AOA results in the significant difference of the surface temperature. Infrared radiation characteristics are also changed in intensity and spectral band due to the AOA. Simulations are performed with two time-varying AOAs. Transient results indicate that the variation of AOA does have a great effect on the infrared radiance and is closely related to observation angle, spectral band, angle size,angular velocity and time history.     

Bernoulli particle flter with observer altitude for maritime radiation source tracking in the presence of measurement uncertainty

For maritime radiation source target tracking in particular electronic counter measures（ECM）environment,there exists two main problems which can deteriorate the tracking performance of traditional approaches.The frst problem is the poor observability of the radiation source.The second one is the measurement uncertainty which includes the uncertainty of the target appearing/disappearing and the detection uncertainty（false and missed detections）.A novel approach is proposed in this paper for tracking maritime radiation source in the presence of measurement uncertainty.To solve the poor observability of maritime radiation source target,using the radiation source motion restriction,the observer altitude information is incorporated into the bearings-only tracking（BOT）method to obtain the unique target localization.Then the two uncertainties in the ECM environment are modeled by the random fnite set（RFS）theory and the Bernoulli fltering method with the observer altitude is adopted to solve the tracking problem of maritime radiation source in such context.Simulation experiments verify the validity of the proposed approach for tracking maritime radiation source,and also demonstrate the superiority of the method compared with the traditional integrated probabilistic data association（IPDA）method.The tracking performance under different conditions,particularly those involving different duration of radiation source opening and switching-off,indicates that the method to solve our problem is robust and effective.     

Thermodynamic Characteristic Study of a High-temperature Flow-rate Control Valve for Fuel Supply of Scramjet Engines

Thermodynamic characteristics are of great importance for the performance of a high-temperature flow-rate control valve,as high-temperature environment may bring problems,such as blocking of spool and increasing of leakage,to the valve.In this paper,a high-temperature flow-rate control valve,pilot-controlled by a pneumatic servo system is developed to control the fuel supply for scramjet engines.After introducing the construction and working principle,the thermodynamic mathematical models of the valve are built based on the heat transfer methods inside the valve.By using different boundary conditions,different methods of simulations are carried out and compared.The steady-state and transient temperature field distribution inside the valve body are predicted and temperatures at five interested points are measured.By comparing the simulation and experimental results,a reasonable 3D finite element analysis method is suggested to predict the thermodynamic characteristics of the high-temperature flow-rate control valve.     

A new model to simulate infrared radiation from an aircraft exhaust system

A multi-scale narrow band correlated-k distribution(MSNBCK) model is developed to simulate infrared radiation(IR) from an exhaust system of a typical aircraft engine.In this model,an approximate approach instead of statistically uncorrelated assumption is used to treat overlapping bands in gas mixture.It significantly reduces the requirement for computing power through converting the exponential increase of computing power consumption with the increase of participating gas species to linear increase.Besides,MSNBCK model has a great advantage compared with conventional methods which can estimate each species' contribution to the total gas mixture radiation intensity.Line by line(LBL) results,experimental data and other results in the references are used to evaluate this new model,which demonstrates its advantage in terms of accuracy and computing efficiency.By coupling this model and finite volume method(FVM) into radiative transfer equation(RTE),a comparative study is conducted to simulate IR signature from the exhaust system.The results indicate that wall's IR emission should be considered in both 3-5 μm and8-14 μm bands while gases' IR emission plays an important role only in 3-5 μm band.For plume IR radiation,carbon dioxide's emission is much more significant than that of water vapor in both3-5μm and 8-14 μm bands.Especially in 3-5 μm band,the water vapor's IR signal can even be neglected compared with that of carbon dioxide.     

Investigation on plume interference effect of solid propellant micro-thruster

The three-dimensional numerical simulation of two-phase plume flow of solid propellant micro-thrusters was developed. Then it was used to investigate the plume interference effect by combining the direct simulation Monte Carlo (DSMC) method for multi-component gas flow with the two-way coupling model for two-phase rarefied flow. At different space between the two micro-thrusters and different wall temperature,the plume interference effect was analyzed specifically. The results show that under the plume interference effect the gas is compressed and the flow direction is changed,which resulted in the increasing of gas pressure and temperature; solid phase made no significant effect on the flow parameters of gas phase; with the rising of the space between the two micro-thrusters,the maximum pressure decreased and the maximum temperature increased in the domain under the plume interference effect; the wall temperature could influence the temperature of the gas which is extremely close to the wall,but not the gas pressure.      

Extension of the low diffusion particle method for near-continuum two-phase flow simulations

The low diffusion (LD) particle method, proposed by Burt and Boyd, is modified for the near-continuum two-phase flow simulations. The LD method has the advantages of easily coupling with the direct simulation Monte Carlo (DSMC) method for multi-scale flow simulations and dramatically reducing the numerical diffusion error and statistical scatter of the equilibrium particle methods. Liquidor solid-phase particles are introduced in the LD method. Their velocity and temperature updating are respectively, calculated from the motion equation and the temperature equation according to the local gas properties. Coupling effects from condensed phase to gas phase are modeled as momentum and energy sources, which are respectively, equal to the negative values of the total momentum and energy increase in liquid or solid phase. The modified method is compared with theoretical results for unsteady flows, and good agreements are obtained to indicate the reliability of the one-way gas-to-particle coupling models. Hybrid LD-DSMC algorithm is implemented and performed for nozzle discharging gas-liquid flow to show the prospect of the LD-DSMC scheme for multi-scale two-phase flow simulations.     

An optimization method for metamorphic mechanisms based on multidisciplinary design optimization

The optimization of metamorphic mechanisms is different from that of the conventional mechanisms for its characteristics of multi-configuration. There exist complex coupled design variables and constraints in its multiple different configuration optimization models. To achieve the compatible optimized results of these coupled design variables, an optimization method for metamorphic mechanisms is developed in the paper based on the principle of multidisciplinary design optimization（MDO）. Firstly, the optimization characteristics of the metamorphic mechanism are summarized distinctly by proposing the classification of design variables and constraints as well as coupling interactions among its different configuration optimization models. Further, collaborative optimization technique which is used in MDO is adopted for achieving the overall optimization performance. The whole optimization process is then proposed by constructing a two-level hierarchical scheme with global optimizer and configuration optimizer loops. The method is demonstrated by optimizing a planar five-bar metamorphic mechanism which has two configurations,and results show that it can achieve coordinated optimization results for the same parameters in different configuration optimization models.     

Combustion modeling in a model combustor

The flow-field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically studied.Results obtained from four combustion models,combined with the re-normalization group(RNG) k-ε turbulence model,discrete ordinates radiation model and enhanced wall treatment are presented and discussed.The results are compared with a comprehensive database obtained from a series of experimental measurements.The flow patterns and the recirculation zone length in the combustion chamber are accurately predicted,and the mean axial velocities are in fairly good agreement with the experimental data,particularly at downstream sections for all four combustion models.The mean temperature profiles are captured fairly well by the eddy dissipation(EDS),probability density function(PDF),and laminar flamelet combustion models.However,the EDS-finite-rate combustion model fails to provide an acceptable temperature field.In general,the flamelet model illustrates little superiority over the PDF model,and to some extent the PDF model shows better performance than the EDS model.      

Calculation of high-temperature insulation parameters and heat transfer behaviors of multilayer insulation by inverse problems method

In the present paper, a numerical model combining radiation and conduction for porous materials is developed based on the finite volume method. The model can be used to investigate high-temperature thermal insulations which are widely used in metallic thermal protection systems on reusable launch vehicles and high-temperature fuel cells. The effective thermal conductivities（ECTs） which are measured experimentally can hardly be used separately to analyze the heat transfer behaviors of conduction and radiation for high-temperature insulation. By fitting the effective thermal conductivities with experimental data, the equivalent radiation transmittance, absorptivity and reflectivity, as well as a linear function to describe the relationship between temperature and conductivity can be estimated by an inverse problems method. The deviation between the calculated and measured effective thermal conductivities is less than 4%. Using the material parameters so obtained for conduction and radiation, the heat transfer process in multilayer thermal insulation（MTI） is calculated and the deviation between the calculated and the measured transient temperatures at a certain depth in the multilayer thermal insulation is less than 6.5%.     

SCC investigation of low alloy ultra-high strength steel 30CrMnSiNi2A in 3.5wt%NaCl solution by slow strain rate technique

To evaluate stress corrosion cracking(SCC) mechanism of low alloy ultra-high strength steel 30CrMnSiNi2 A in environment containing NaCl, SCC behavior of the steel in 3.5wt% NaCl solution is investigated by slow strain rate technique(SSRT) with various strain rates and applied potentials, surface analysis technique, and electrochemical measurements. SCC susceptibility of the steel increases rapidly with strain rate decreasing from 1 · 10 5s 1to 5 · 10 7s 1, and becomes stable when strain rate is lower than 5 · 10 7s 1. SCC propagation of the steel in the solution at open circuit potential(OCP) needs sufficient hydrogen which is supplied at a certain strain rate.Fracture surface at OCP has similar characteristics with that at cathodic polarization 1000 mVSCE, which presents characteristic fractography of hydrogen induced cracking(HIC).All of these indicate that SCC behavior of the steel in the solution at OCP is mainly controlled by HIC rather than anodic dissolution(AD).     

Radical recombination in a hydrocarbon-fueled scramjet nozzle

To reveal the radical recombination process in the scramjet nozzle flow and study the effects of various factors of the recombination, weighted essentially non-oscillatory(WENO)schemes are applied to solve the decoupled two-dimensional Euler equations with chemical reactions to simulate the hydrocarbon-fueled scramjet nozzle flow. The accuracy of the numerical method is verified with the measurements obtained by a shock tunnel experiment. The overall model length is nearly 0.5 m, with inlet static temperatures ranging from 2000 K to 3000 K, inlet static pressures ranging from 75 k Pa to 175 k Pa, and inlet Mach numbers of 2.0 ± 0.4 are involved.The fraction Damkohler number is defined as functions of static temperature and pressure to analyze the radical recombination progresses. Preliminary results indicate that the energy releasing process depends on different chemical reaction processes and species group contributions. In hydrocarbon-fueled scramjet nozzle flow, reactions with H have the greatest contribution during the chemical equilibrium shift. The contrast and analysis of the simulation results show that the radical recombination processes influenced by inflow conditions and nozzle scales are consistent with Damkohler numbers and potential dissociation energy release. The increase of inlet static temperature improves both of them, thus making the chemical non-equilibrium effects on the nozzle performance more significant. While the increase of inlet static pressure improves the former one and reduces the latter, it exerts little influence on the chemical non-equilibrium effects.     

Progress in helicopter infrared signature suppression

Due to their low-attitude and relatively low-speed fight profiles, helicopters are subjected to serious threats from radio, infrared(IR), visual, and aural detection and tracking. Among these threats, infrared detection and tracking are regarded as more crucial for the survivability of helicopters. In order to meet the requirements of infrared stealth, several different types of infrared suppressor(IRS) for helicopters have been developed. This paper reviews contemporary developments in this discipline, with particular emphasis on infrared signature suppression, advances in mixer-ejectors and prediction for helicopters. In addition, several remaining challenges, such as advanced IRS, emissivity optimization technique, helicopter infrared characterization, etc., are proposed, as an initial guide and stimulation for future research. In the future, the comprehensive infrared suppression in the 3–5 lm and 8–14 lm bands will doubtfully become the emphasis of helicopter stealth. Multidisciplinary optimization of a complete infrared suppression system deserves further investigation.     

Ignition enhancement of ethylene/air by NOx addition

Recently, non-equilibrium plasma assisted combustion (PAC) has been found to be promising in reducing the ignition delay time in hypersonic propulsion system. NO x produced by non-equilibrium plasma can react with intermediates during the fuel oxidation process and thereby has influence on the combustion process. In this study, the effects of NO x addition on the ignition process of both the homogeneous ethylene/air mixtures and the non-premixed diffusion layer are examined numerically. The detailed chemistry for ethylene oxidization together with the NO x sub-mechanism is included in the simulation. Reaction path analysis and sensitivity analysis are conducted to give a mechanistic interpretation for the ignition enhancement by NO x addition. It is found that for both the homogenous and non-premixed ignition processes at normal and elevated pressures, NO 2 addition has little influence on the ignition delay time while NO addition can significantly promote the ignition process. The ignition enhancement is found to be caused by the promotion in hydroxyl radical production which quickly oxidizes ethylene. The promotion in hydroxyl radical production by NO addition is achieved in two ways:one is the direct production of OH through the reaction HO2+NO = NO2+OH, and the other is the indirect production of OH through the reactions NO+O2=NO2+O and C2H4+O = C2H3+OH. Moreover, it is found that similar to the homogeneous ignition process, the acceleration of the diffusion layer ignition is also controlled by the reaction HO2+NO = NO2+OH.     

An approach for parameter estimation of combined CPPM and LFM radar signal

In this paper, the problem of parameter estimation of the combined radar signal adopting chaotic pulse position modulation (CPPM) and linear frequency modulation (LFM), which can be widely used in electronic countermeasures, is addressed. An approach is proposed to estimate the initial frequency and chirp rate of the combined signal by exploiting the second-order cyclostationarity of the intra-pulse signal. In addition, under the condition of the equal pulse width, the pulse repetition interval (PRI) of the combined signal is predicted using the low-order Volterra adaptive filter. Simulations demonstrate that the proposed cyclic autocorrelation Hough transform (CHT) algorithm is theoretically tolerant to additive white Gaussian noise. When the value of signal noise to ratio (SNR) is less than 4 dB, it can still estimate the intra-pulse parameters well. When SNR = 3 dB, a good prediction of the PRI sequence can be achieved by the Volterra adaptive filter algorithm, even only 100 training samples.     

Springback prediction of thick-walled high-strength titanium tube bending

Significant springback occurs after tube rotary-draw-bending （RDB）, especially for a high-strength Ti-3A1-2.5V tube （HSTT） due to its high ratio of yield strength to Young＇s modulus. The combination scheme of explicit and implicit is preferred to predict the springback. This simulation strategy includes several numerical parameters, such as element type, number of elements through thickness （NEL）, element size, etc. However, the influences of these parameters on spring- back prediction accuracy are not fully understood. Thus, taking the geometrical specification 9.525 mm × 0.508 mm ofa HSTT as the objective, the effects of numerical parameters on prediction accuracy and computation efficiency of springback simulation of HSTT RDB are investigated. The simulated springback results are compared with experimental ones. The main results are： （1） solid and continuum-shell elements predict the experimental results well; （2） for C3DSR elements, NEL of at least 3 is required to obtain reliable results and a relative error of 29% can occur as NEL is varied in the range of 1-3; （3） specifying damping factor typically works well in Abaqus/Emplicit simulation of springback and the springback results are sensitive to the magnitude of damping factor. In addition, the explanations of the effect rules are given and a guideline is added.     

Experimental investigations on the power extraction of a turbine driven by a pulse detonation combustor

In order to grasp the interaction mechanism between the pulse detonation combustor（PDC）and the turbine,the experimental work in this paper investigates the key factors on the power extraction of a turbocharger turbine driven by a PDC.A PDC consisting of an unvalved tube is integrated with a turbocharger turbine which has a nominal mass flow rate of 0.6 kg/s and50000 r/min.The PDC-turbine hybrid engine is operated on gasoline-air mixtures and runs for6＋min to achieve a thermal steady state,and then the engine performance is evaluated under different operating conditions.Results show that the momentum difference per unit area between the turbine inlet and outlet plays an important role in the power extraction,while the pressure peak of the detonation has little effect.The equivalence ratio of fuel and air mixture and the transition structure between PDC and turbine are also important to the power extraction of the turbine.The present work is promising as it suggests that the performance beneft of a PDC-turbine hybrid engine can be realized by increasing the momentum difference per unit area through the optimal design of transition section between the PDC and turbine.     

Parametric analyses for synthetic jet control on separation and stall over rotor airfoil

Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier–Stokes equations coupled with a k x shear stream transport turbulence model are employed to accomplish the flowfield simulation of rotor airfoils under jet control. Additionally,a velocity boundary condition modeled by a sinusoidal function is developed to fulfill the perturbation effect of periodic jets. The validity of the present CFD procedure is evaluated by the simulated results of an isolated synthetic jet and the jet control case for airfoil NACA0015. Then, parametric analyses are conducted specifically for an OA213 rotor airfoil to investigate the effects of jet parameters(forcing frequency, jet location and momentum coefficient, jet direction, and distribution of jet arrays) on the control effect of the aerodynamic characteristics of a rotor airfoil. Preliminary results indicate that the efficiency of jet control can be improved with specific frequencies(the best lift-drag ratio at F+= 2.0) and jet angles(40 or 75) when the jets are located near the separation point of the rotor airfoil. Furthermore, as a result of a suitable combination of jet arrays, the lift coefficient of the airfoil can be improved by nearly 100%, and the corresponding drag coefficient decreased by26.5% in comparison with the single point control case.     

Fatigue crack propagation of new aluminum lithium alloy bonded with titanium alloy strap

A new type of aluminum lithium alloy (Al-Li alloy) Al-Li-S-4 was investigated by test in this paper. Alloy plate of 400 mm · 140 mm · 6 mm with single edge notch was made into samples bonded with Ti-6Al-4V alloy (Ti alloy) strap by FM 94 film adhesive after the surface was treated. Fatigue crack growth of samples was investigated under cyclic loading with stress ratio (R) of 0.1 and load amplitude constant. The results show that Al-Li alloy plate bonded with Ti alloy strap could retard fatigue crack propagation. Retardation effect is related with width and thickness of strap. Flaws have an observable effect on crack propagation direction.