On the origin of the double cellular structure of the detonation in gaseous nitromethane and its mixtures with oxygen

An experimental study of the detonation in gaseous nitromethane (NM) and nitromethane-oxygen mixtures has exhibited unambiguously the existence of a double cellular structure in the range of equivalence ratio from 1.3 to 1.75 (NM). Calculations of the reaction zone of the detonation in the same range of equivalence ratio, using a detailed chemical scheme in the ZND model, demonstrate that the chemical energy is released in two main successive distinct exothermic reaction steps characterized by their own induction length which justifies the existence of a two levels detonation cellular structure. This result strengthens the idea that the cellular detonation structure finds its origin in instabilities amplified by delayed local high energy release rate inside the reaction zone.Received: 2 February 2002, Accepted: 27 May 2004, Published online: 7 December 2004[/PUBLISHED]H.-N. Presles: Correspondence to     

Dependence of the stagnation temperature of a jet of gas containing solid particles on the concentration of particles and their velocity

This article gives the results of experiments on the measurement of the stagnation temperature of a two-phase jet, issuing from a nozzle. The experiments were made using a mixture of air and aluminum oxide (particle diameter 50) with a ratio of the mass flow rate of the solid phase to the mass flow rate of the gas equal to 0.3–2.5, and at initial temperatures of the mixture of 150–450°C. It follows from the results of the experiments that the stagnation temperature of a two-phase flow considerably exceeds the temperature of the mixture at the inlet of the nozzle.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 175–176, July–August, 1970.     

Effect of the grain size on the wavelength of localized strain in aluminum specimens in tension

This paper studies the dependence of the wavelength of localized plastic strain at the parabolic stage of strain hardening on the grain size in polycrystal aluminum. This dependence is determined in the grainsize range 10^–2 – 10 mm. The effect of the grain size on the character of the plasticflow curve is studied.     

Shock waves in a mixture of materials. Hydrodynamic approximation

We formulate equations of motion and of hydrodynamics for the calculation of shock adiabats of a mixture of condensed materials under very high pressures, the assumption being made that strength properties can be neglected. Use is made of the general principles for constructing models of interacting continuous media [1–3] systematically presented in [4]. In our calculations we involve the difference of the pressures in the component materials of the mixture. In this regard we invoke the following conditions: the condition of proportional (with respect to mass) shock increase of energy; the consistency condition requiring equality of particle velocities and shock velocity in the individual particles; and, finally, also the condition of proportionality of the pressures in the individual phases. We present numerical calculations for mixtures of tungsten and paraffin and also for mixtures of aluminum and epoxy resin. Our calculations agree with experimental data and also with calculations made upon specifying the equality of the phase pressures [5–8]; they are also in agreement with calculations made in accordance with the additive rule (see [9–11]).Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 113–126, July–August, 1976.     

Dynamics of Brownian particles in a turbulent channel flow

Turbulent channel flows with suspended particles are investigated by means of numerical simulations. The fluid velocity is computed by large eddy simulation. Motion of small graphite particles with diameter of 0.01–10 m, corresponding to the Schmidt number, Sc, of 2.87 × 10²–6.22 × 10⁶ and the particle relaxation time in wall unit, _p⁺, of 9.79 × 10^–5–4.51, is computed by Lagrangian particle tracking. Relation between the particle relaxation time and the computed deposition velocity is found to be in good agreement with an empirical relation. The statistics of the particle motion in the vicinity of the wall are studied. Clear differences are found in dynamical behavior of particles with different sizes. Medium size particles show a strong dependence on the structure of the fluid flow, while small and large particles are considerably less sensitive.     

Pressure and temperature history in diamond silicon mixtures during dynamic compaction

Diamond powders with silicon additives were shock compressed by using a flyer impact technique. Pressure and temperature histories in the powder mixtures were numerically simulated in order to determine the optimum experimental condition which resulted in the highest Vicker's hardness. This was found to be: an initial diamond particle size of 2–4m at 7.2 % silicon by volume. The results of the simulations were consistent with the distribution of the microstructure and the microhardness in the compact.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Pressure pulsations during interaction between a subsonic jet and the subsonic section of a supersonic jeton a flat obstacle

Pressure pulsations were measured during in-leakage of a subsonic jet and the subsonic section of a heated supersonic jet on a flat obstacle. Data have been obtained on the total and spectrum levels of the pressure pulsations at different spacings X of the obstacle from the nozzle exit. It is shown that when the obstacle is disposed at the section of the jet where the local velocity is subsonic, the pulsation levels outside the dependence on the conditions at the nozzle exit (Mach number Maxa 0 a 3.0; stagnation temperature T₀=280–1200K) vary in direct proportion to the local velocity head q. The ratio between the total level and q is (/g)=0.2–0.3. It is established that for a subsonic velocity ahead of the obstacle, all the spectra obtained for different values of M _a , T₀, d _a and X in the coordinates Sh=f(d/V) and (₁*/q)(V/d) will lie on a single generalized spectrum. Here ₁* is the pulsation level in a 1-Hz band, and d and V are, respectively, the jet diameter and velocity directly in front of the obstacle.Translated from Izvestiya Akademiya Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 172–174, September–October, 1975.     

Dual-plane stereo particle image velocimetry (DSPIV) for measuring velocity gradient fields at intermediate and small scales of turbulent flows

A two-frequency dual-plane stereo particle image velocimetry (DSPIV) technique is described for highly resolved measurements of the complete nine-component velocity gradient tensor field u_i/x_j on the quasi-universal intermediate and small scales of turbulent flows. The method is based on two simultaneous, independent stereo particle image velocimetry (PIV) measurements in two differentially spaced light sheet planes, with light sheet characterization measurements demonstrating the required sheet thicknesses, separation, and two-axis parallelism that determine the measurement resolution and accuracy. The present approach uses an asymmetric forward–forward scatter configuration with two different laser frequencies in conjunction with filters to separate the scattered light onto the individual stereo camera pairs, allowing solid metal oxide particles to be used as seed particles to permit measurements in nonreacting as well as exothermic reacting turbulent flows.     

A direct-tension split Hopkinson bar for high strain-rate testing

A direct-tension split-Hopkinson-bar apparatus is introduced. In this apparatus the specimen is loaded by a tensile wave that is generated by the release of a stored load in a section of the input bar. The system can be used for experiments with test durations of up to 500 s. The effect of specimen geometry (length to diameter ratio) is investigated. Consistent results are obtained when the ratio is larger than about 1.60. Results from tests with 6061-T651 aluminum are in agreement with published data.Paper was presented at the 1990 SEM Spring Conference on Experimental Mechanics held in Albuquerque, NM on June 3–6.     

Partition of plastic work into heat and stored energy in metals

This study investigates heat generation in metals during plastic deformation. Experiments were designed to measure the partition of plastic work into heat and stored energy during dynamic deformations under adiabatic conditions. A servohydraulic load frame was used to measure mechanical properties at lower strain rates, 10^–3 s^–1 to 1 s^–1. A Kolsky pressure bar was used to determine mechanical properties at strain rates between 10³ s^–1 and 10⁴ s^–1. For dynamic loading, in situ temperature changes were measured using a high-speed HgCdTe photoconductive detector. An aluminum 2024-T3 alloy and -titanium were used to determine the dependence of the fraction of plastic work converted to heat on strain and strain rate. The flow stress and for 2024-T3 aluminum alloy were found to be a function of strain but not strain rate, whereas they were found to be strongly dependent on strain rate for -titanium.     

Nonisothermal structural regime of motion of a nonlinear viscoplastic medium in a plane channel

The motions of Newtonian and non-Newtonian media with consideration of the heat of friction and temperature dependence of the rheological characteristics of the medium have been examined by many authors [1–6]. A detailed bibliography of these works is given in [3, 5], In the dissertation of one of the authors* an attempt was made to investigate heat transfer during movement of a nonlinear viscoplastic medium with consideration of the temperature dependence of plastic viscosity at a constant value of the ultimate shear stress to. The last assumption is not always justified, since more often cases are found when not only plastic viscosity but also the ultimate shear stress changes with change in temperature. In this article we will examine the effect of the heat of internal friction with consideration of the temperature dependence of plastic viscosity and ultimate shear stress on the hydraulic characteristics of a laminar regime of motion in a plane channel of nonlinear viscoplastic media whose rheological behavior is described by the generalized Casson equation [5]. The upper and lower estimates are found for nonlinear differential equations describing the indicated processes.R. M. Sattarov, Certain isothermal and nonisothermal motions of viscoplastic media, Candidate's Dissertation, Institute of Heat and Mass Transfer, Academy of Sciences of the Belorussian SSR, Minsk (1973).Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 162–166, March–April, 1977.In conclusion the authors thank V. I. Anikin for help in the calculations.     

Mixed convection flow over a vertical plate with localized heating (cooling), magnetic field and suction (injection)

An analysis is carried out to study the effects of localized heating (cooling), suction (injection), buoyancy forces and magnetic field for the mixed convection flow on a heated vertical plate. The localized heating or cooling introduces a finite discontinuity in the mathematical formulation of the problem and increases its complexity. In order to overcome this difficulty, a non-uniform distribution of wall temperature is taken at finite sections of the plate. The nonlinear coupled parabolic partial differential equations governing the flow have been solved by using an implicit finite-difference scheme. The effect of the localized heating or cooling is found to be very significant on the heat transfer, but its effect on the skin friction is comparatively small. The buoyancy, magnetic and suction parameters increase the skin friction and heat transfer. The positive buoyancy force (beyond a certain value) causes an overshoot in the velocity profiles.A mass transfer constant - B magnetic field - C_fx skin friction coefficient in the x-direction - C_p specific heat at constant pressure, kJ.kg^–1.K - C_v specific heat at constant volume, kJ.kg^–1.K^–1 - E electric field - g acceleration due to gravity, 9.81 m.s^–2 - Gr Grashof number - h heat transfer coefficient, W.m².K^–1 - Ha Hartmann number - k thermal conductivity, W.m^–1.K - L characteristic length, m - M magnetic parameter - Nu_x local Nusselt number - p pressure, Pa, N.m^–2 - Pr Prandtl number - q heat flux, W.m^–2 - Re Reynolds number - Re_m magnetic Reynolds number - T temperature, K - T_o constant plate temperature, K - u,v velocity components, m.s^–1 - V characteristic velocity, m.s^–1 - x,y Cartesian coordinates - thermal diffusivity, m².s^–1 - coefficient of thermal expansion, K^–1 - , transformed similarity variables - dynamic viscosity, kg.m^–1.s^–1 - ₀ magnetic permeability - kinematic viscosity, m².s^–1 - density, kg.m^–3 - buoyancy parameter - electrical conductivity - stream function, m².s^–1 - dimensionless constant - dimensionless temperature, K - w, conditions at the wall and at infinity     

Axial damping in metal-matrix composites. II: A theoretical model and its experimental verification

In the companion paper we describe a new experimental technique for resolving the phase difference between two electrical sinusoidal signals to an accuracy of 2/2¹⁶ or 9.587×10^–7 radians. In this paper we demonstrate the use of that technique in measuring the intrinsic material damping of metal-matrix composites in axial tension using strain gages. In particular, the influence of ply, angle, , on the axial damping of a Pitch 55 graphite/6061 aluminum [±]_s laminate is studied at a fixed frequency, a fixed strain level, and at room temperature. Recently, Ni and Adams proposed a model for predicting theflexural damping of a liminate from the flexural damping properties of a lamina. A close agreement between the model and the experiment was observed. As far as we know these are the first measurements of intrinsic material damping of metal-matrix composites.Paper was presented at the 1990 SEM Spring Conference on Experimental Mechanics held in Albuquerque, NM on June 3–6.     

Numerical investigation of nonequilibrium flows of mixtures of fusible metal particles and gases in a laval nozzle

There are numerous papers [1–11] on the determination of the parameters of condensed oxide particles which are formed during combustion of metallized fuels. The ambiguity, and sometimes the contradictoriness, of the test results obtained [3–5, 9–11] indicate the difficulties in conducting correct experimental investigations. In this connection, numerical studies using mixtures of calibrated liquid-metal particles and different gases are of practical interest. Different probes can be calibrated by using calibrated two-phase flows, the two-phase flow around models and probes can be studied, as can the interaction between liquid-metal particles and the front of an aerodynamic compression shock, their intrusion in different entraining media, the interaction between fine particles (particle-projectiles) and large size particles (particle-targets), etc. In many cases, the prehistory of the flow and the parameters of the gas mixture with the particles in the area of the nozzle exit section must be known to investigate the above-mentioned phenomena. The parameters of different nonequilibrium flows of mixtures of gallium particles and gases in a Laval nozzle are investigated numerically in this paper; the maximum diameter (upper boundary of the spectrum) of the particles (d_s = 30 ) which are not destroyed in the nozzle under the effect of the aerodynamic forces and are suitable for use in a calibrated two-phase stream is determined. The computations were carried out in a one-dimensional approximation according to [12–14].Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 86–91, March–April, 1976.The authors are grateful to V. K. Starkov and U. G. Pirumov for discussing the results of the research and to N. M. Alekseev for aid in constructing the graphs.     

Aspects of a method of investigating the distributed load on oscillating wings

The paper discusses the method and technique of an experiment and also some results of the investigation of the unsteady pressure on the surface of a rectangular wing executing oscillations with angular amplitude * = 3° at Strouhal numbers p* = 0.113 (p* = /v, where * is the angular frequency, b is the chord of the wing, and v is the velocity of the oncoming flow).Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 178–181, September–October, 1981.     

Effect of solids concentration in dense suspensions of silica-iron(III) oxide and water

The rheological properties of dense suspensions, of silica, iron (III) oxide and water, were studied over a range of solids concentrations using a viscometer, which was modified so as to prevent settling of the solid components. Over the conditions studied, the material behaved according to power—law flow relationships. As the concentrations of silica and iron(III) oxide were increased, an entropy term in the flow equation was identified which had a silica dependent and an iron (III) oxide dependent component. This was attributed to a tendency to order into some form of structural regularity. A, A, B, C pre-exponential functions (K Pa^–n s^–1) - C _ox volume fraction iron (III) oxide - Q activation energy (kJ mol^–1) - R gas constant (kJ mol^–1 K^–1) - R _v silica/water volume ratio - T temperature (K) - n power-law index - H enthalpy (kJ mol^–1) - S entropy change (kJ mol^–1 K^–1) - shear strain rate (s^–1) - shear stress (Pa)     

气/固/液三相混合物燃烧转爆轰过程实验研究

利用多相燃烧爆炸实验系统,通过高压喷粉/喷雾以及高能点火等过程,对化学当量比条件下3种 典型燃料空气炸药,即硝基甲烷/铝粉/空气、硝酸异丙酯/铝粉/空气、乙醚/铝粉/空气三相混合物的燃烧转爆 轰过程进行了实验研究,同时根据实验结果对比了3种三相混合物的燃爆性能。得到了三相悬浮混合物燃烧 转爆轰过程的宏观规律以及三相混合物燃爆性能随质量浓度变化的规律。     

Calculation of supersonic equilibrium-dissociating air-xenon mixture flow past a blunt body

The flow of an equilibrium-reacting multicomponent three-element air-xenon mixture is numerically investigated. The effect of multicomponent diffusion on the convective heat transfer to the body surface is examined. The dependence of the convective heat transfer to the body surface and the total shock-layer spectral radiation flux P_m on the xenon concentration is obtained. A comparison of the calculated data for P_m and the experimental data of [2] gives good agreement. A simple approximation for the convective heat flux at the stagnation point as a function of xenon concentration is proposed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 156–164, July–August, 1991.In conclusion the authors wish to thank I. A. Sokolova for supplying data on the resistance coefficients of the various mixtures and S. A. Yunitskii for discussing the numerical method.     

Scattering and velocity dispersion of ultrasonic waves in polycrystals of orthorhombic symmetry

The scattering coefficients and the velocity of propagation of longitudinal and transverse ultrasonic waves in polycrystals of orthorhombic and higher symmetry are computed by the method of renormalization of the equations of motion. The formulas thus obtained are compared with the known asymptotic expressions for long and short waves. A numerical computation carried out for aluminum shows that for qa 1 (q is the wave number;a is the correlation scale) the power index determining the frequency dependence of the scattering coefficient decreases monotonically from 4 to 2 for the transverse waves, while for the longitudinal waves this dependence is nonmonotonic, i.e., the power index decreases from 4 to 1, after which it increases again to 2. In the Rayleigh region (q _l a < 1.) the scattering coefficient of the longitudinal waves increases with a power index smaller than 4.Translated from Zhurnal Prikladnoi Mekhanikii Tekhnicheskoi Fiziki, No. 3, pp. 180–190, May–June, 1976.     

Efficient Extreme Value Prediction for Nonlinear Beam Vibrations Using Measured Random Response Histories

Predicted extreme exceedance probabilities associated withexperimental measurements of highly non-linear clamped-clamped beamvibrations driven by band-limited white-noise, are compared using twodifferent approaches for application to short data sets. The firstapproach uses response history measurements to calibrate a discretedynamic model using a Markov moment method appropriately matched toextreme value prediction via finite element solution of theFokker–Planck (FPK) equation. The dynamic model is obtained via theWoinowsky–Krieger equation with added empirical damping. Stationary FPKsolutions are used to obtain mean crossing rates, and for the purpose ofextreme value prediction, crossings are assumed to be independent. Thesecond approach uses a Weissman type I asymptotic estimator, justifiedby use of the Hasofer–Wang hypothesis test. Both methods are comparedwith exceedance probabilities obtained using data from long experiments in which dependence between extreme values is excluded. Thepaper shows that by exploiting the Weissman estimator in a forwardpredictive mode, very accurate exceedance probabilities can be obtainedfrom relatively small amounts of measured data. The calibrated modelbased predictions are consistently in error as a result of non-linearcoupling effects not included in the model – this coupling isimplicitly accounted for in the Weissman predictions.