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1.
The time and depth of vertical one-dimensional projectile penetration into sandy media in the near shore region are derived.
A precise definition for the physical properties and for the behavior of the sandy medium following the projectile impact
are evaluated. Three separate time intervals following projectile impact are identified. During the first 3 ms of penetration,
the deviatoric friction stress is shown to be negligible and the integrated Mie–Grüneisen equation of state (or, equivalently,
the Hugoniot-adiabat) may be applied to compute the normal penetration resistance force from the sand pressure. In order to
compute sand pressure as a function of the sand density D by the integrated Mie–Grüneisen equation of state, the Mie–Grüneisen
dimensionless constants γ0 and s and the dimensional speed of sound C
0 in the sandy medium are required. In order to illustrate the one-dimensional shock wave propagation in both wet and dry sands,
Hugoniot data for wet and dry silica sands are evaluated by a three degrees of freedom algorithm to compute these required
constants. The numerical results demonstrate that the amplitude of the shock wave pressure in the wet silica sand (41% porosity)
is approximately one-third of the shock wave pressure amplitudes in the dry silica sands (22% and 41% porosity). In addition,
the shock wave pressure dampens quicker in the wet sand than in the dry sands. 相似文献
2.
Experimental investigation of ram accelerator propulsion modes 总被引:1,自引:0,他引:1
Experimental investigations on the propulsive modes of the ram accelerator are reviewed in this paper. The ram accelerator is a ramjet-in-tube projectile accelerator whose principle of operation is similar to that of a supersonic air-breathing ramjet. The projectile resembles the centerbody of a ramjet and travels through a stationary tube filled with a premixed gaseous fuel and oxidizer mixture. The combustion process travels with the projectile, generating a pressure distribution which produces forward thrust on the projectile. Several modes of ram accelerator operation are possible which are distinguished by their operating velocity range and the manner in which the combustion process is initiated and stabilized. Propulsive cycles utilizing subsonic, thermally choked combustion theoretically allow projectiles to be accelerated to the Chapman-Jouguet(C-J) detonation speed of a gaseous propellant mixture. In the superdetonative velocity range, the projectile is accelerated while always traveling faster than the C-J speed, and in the transdetonative regime (85–115 % of C-J speed) the projectile makes a smooth transition from a subdetonative to a superdetonative propulsive mode. This paper examines operation in these three regimes of flow using methane and ethylene based propellant mixtures in a 16 m long, 38 mm bore ram accelerator using 45–90 g projectiles at velocities up to 2500 m/s.This article was processed using Springer-Verlag TEX Shock Waves macro package 1990. 相似文献
3.
This paper describes the components and operation of an experimental setup for the visualization of liquid propellant (LP)
jet combustion at pressures above 100 MPa. The apparatus consists of an in-line ballistic compressor and LP injector. The
ballistic compressor, based on a modified 76 mm gun, provides high-pressure (ca. 55 MPa) clear hot gas for the jet ignition.
A piston (projectile) is fired toward a test chamber beyond the barrel’s end, and its rebound is arrested in a transition
section that seals the test chamber to the barrel. The LP jet is injected once the piston is restrained, and combustion of
the jet further elevates the pressure. At a preset pressure, a disc in the piston ruptures and the combustion gas vents sonically
into the barrel. If a monopropellant is used, the jet injection-combustion process then resembles liquid rocket combustion
but at very high pressures (ca. 140 MPa). This paper discusses the ballistics of the compression and compares experimental
results to those predicted by a numerical model of the apparatus. Experimentally, a pressure of 70 MPa was achieved upon a
12.5 volumetric compression factor by firing a 10 kg piston into 1.04 MPa argon using a charge of 75 g of small-grain M1 propellant.
Received: 16 December 1996/Accepted: 15 July 1997 相似文献
4.
The propagation mechanism of high speed turbulent deflagrations 总被引:2,自引:0,他引:2
The propagation regimes of combustion waves in a 30 cm by 30 cm square cross–sectioned tube with an obstacle array of staggered
vertical cylindrical rods (with BR=0.41 and BR=0.19) are investigated. Mixtures of hydrogen, ethylene, propane, and methane with air at ambient conditions over a range
of equivalence ratios are used. In contrast to the previous results obtained in circular cross–sectioned tubes, it is found
that only the quasi–detonation regime and the slow turbulent deflagration regimes are observed for ethylene–air and for propane–air.
The transition from the quasi–detonation regime to the slow turbulent deflagration regime occurs at (where D is the tube “diameter” and is the detonation cell size). When , the quasi–detonation velocities that are observed are similar to those in unobstructed smooth tubes. For hydrogen–air mixtures,
it is found that there is a gradual transition from the quasi–detonation regime to the high speed turbulent deflagration regime.
The high speed turbulent deflagration regime is also observed for methane–air mixtures near stoichiometric composition. This
regime was previously interpreted as the “choking” regime in circular tubes with orifice plate obstacles. Presently, it is
proposed that the propagation mechanism of these high speed turbulent deflagrations is similar to that of Chapman–Jouguet
detonations and quasi-detonations. As well, it is observed that there exists unstable flame propagation at the lean limit
where . The local velocity fluctuates significantly about an averaged velocity for hydrogen–air, ethylene–air, and propane–air mixtures.
Unstable flame propagation is also observed for the entire range of high speed turbulent deflagrations in methane–air mixtures.
It is proposed that these fluctuations are due to quenching of the combustion front due to turbulent mixing. Quenched pockets
of unburned reactants are swept downstream, and the subsequent explosion serves to overdrive the combustion front. The present
study indicates that the dependence on the propagation mechanisms on obstacle geometry can be exploited to elucidate the different
complex mechanisms of supersonic combustion waves.
Received 5 November 2001 / Accepted 12 June 2002 / Published online 4 November 2002
Correspondence to: J. Chao (e-mail: jenny.chao@mail.mcgill.ca)
An abridged version of this paper was presented at the 18th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Seattle, USA, from July 29 to August 3, 2001. 相似文献
5.
B. F. Boyarshinov 《Journal of Applied Mechanics and Technical Physics》2000,41(4):686-691
It is shown that, for a certain proportion between the rib height (2–15 mm) installed at the test-section entrance and the turbulence level of the main flow (1–26%), there are extrema of parameters that describe mass transfer on the surface of an evaporating liquid fuel. In tests with
and without combustion, discrete changes in the rates of heat and mass transfer are observed. Conditions for their manifestation
are analyzed.
Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from
Prikladnaya Mekhanika i Tekhnicheskava Fizika, Vol. 41, No.4, pp. 124–130, July–August, 2000. 相似文献
6.
This paper reports on progress in the study of the water entry phenomenon. First, an experiment conducted measuring the velocity
of the projectile after water entry. An empirical formula was obtained describing the change of the velocity of an underwater
projectile with water depth. From the formula, the velocity decay coefficient β=0.5ρw
A
o
C
d/m, was determined, where ρw is the water density, A
o is the projection area of the projectile, C
d is the drag coefficient and m is the mass of the projectile. A theoretical model was then presented to describe the motion of the projectile during entry.
Based on the obtained value of β, when the projectile was treated equivalently as a sphere, the theoretical water depth for
deep closure of the cavity was predicted.
Received: 10 February 2000/Accepted: 20 July 2000 相似文献
7.
Experimental studies were carried out to investigate projectile acceleration in a single-stage gun at breech pressures below
50 MPa. The gun was driven by firing either liquid or solid propellant. In-bore projectile velocity was continuously recorded
using the well-known, precise VISAR interferometer technique so that accurate projectile acceleration data could be deduced.
Both the attained projectile acceleration and muzzle exit velocity depend upon the charge-to-mass ratio and the pressure at
which the blow-out disk ruptures. The results obtained from these experiments render information on the interplay between
propellant combustion and projectile acceleration for low in-bore pressure regimes, and they provide the input data required
for adequate numerical simulation. 相似文献
8.
S. G. Subbotin A. V. Proskurin A. Yu. Mel’nikova 《Journal of Applied Mechanics and Technical Physics》2009,50(4):547-552
A method and results of calculation of parameters of long-term shock loading of solids, generated by a gas-dynamic former
containing a combined charge with explosive initiation, are described. A calculation model based on the concepts of the hydrodynamic
theory of detonation and on the theory of combustion of condensed substances is considered. The forcing pressure and the physical
laws of combustion of the combined charge are determined in calculations and experiments. The dynamics of the process is studied
by an example of calculation of parameters of the loaded solid acceleration pulse in the case of initiation and combustion
of a charge consisting of two batches of high explosives: black powder and pyroxylin powder. The effect of the combined charge
parameters and combustion-chamber size on the parameters of the shock loading pulse is studied.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 3–10, July–August, 2009. 相似文献
9.
H. H. Liakos E. P. Keramida M. A. Founti N. C. Markatos 《Heat and Mass Transfer》2002,38(4-5):425-432
Impinging jet combusting flows on granite plates are studied. A mathematical model for calculating heat release in turbulent
impinging premixed flames is developed. The combustion including radiative heat transfer and local extinction effects, and
flow characteristics are modeled using a finite volume computational approach. Two different eddy viscosity turbulence models,
namely the standard k–ɛ and the RNG k–ɛ model with and without radiation (discrete transfer model) are assessed. The heat released predictions are compared with
experimental data and the agreement is satisfactory only when both radiative heat transfer and local extinction modeling are
taken into account. The results indicate that the main effect of radiation is the decrease of temperature values near the
jet stagnation point and along the plate surface. Radiation increases temperature gradients and affects predicted turbulence
levels independently of the closure model used. Also, the RNG k–ɛ predicts higher temperatures close the solid plate, with and without radiative heat transfer.
Received on 13 November 2000 / Published online: 29 November 2001 相似文献
10.
为了研究底排点火具射流蚀剥作用对底排药柱碎块脱落情况及其燃烧性能的影响,采用半密闭爆
发器实验装置模拟底排弹出膛口瞬态卸压工况,借助高速录像记录点火具点火与底排药柱燃烧的序列图像。
建立底排药柱在半密闭爆发器燃烧的数学模型,计算分析了不同碎块脱落质量引起的平均压力、质量流率和
燃烧时间的变化情况。研究结果表明:蚀剥作用发生在点火具点火初期,导致脱落的底排药剂碎块来不及燃
烧;蚀剥作用主要是强点火射流对底排药柱侵蚀与冲击造成的;碎块总量约占底排药柱初始质量的7%~
9%,严重影响点火和燃烧的一致性。计算结果与实验值吻合较好。 相似文献
11.
We strengthen the assertion on the continuous invertibility of the operator
in the space L
2(ℝ, H), where H is a complex Hilbert space and A is a sectorial operator with spectrum in the right half-plane of ℂ.
__________
Translated from Neliniini Kolyvannya, Vol. 9, No. 1, pp. 31–36, January–March, 2006. 相似文献
12.
The classical Fokker–Planck equation is a linear parabolic equation which describes the time evolution of the probability
distribution of a stochastic process defined on a Euclidean space. Corresponding to a stochastic process, there often exists
a free energy functional which is defined on the space of probability distributions and is a linear combination of a potential
and an entropy. In recent years, it has been shown that the Fokker–Planck equation is the gradient flow of the free energy
functional defined on the Riemannian manifold of probability distributions whose inner product is generated by a 2-Wasserstein
distance. In this paper, we consider analogous matters for a free energy functional or Markov process defined on a graph with
a finite number of vertices and edges. If N ≧ 2 is the number of vertices of the graph, we show that the corresponding Fokker–Planck equation is a system of N
nonlinear ordinary differential equations defined on a Riemannian manifold of probability distributions. However, in contrast to stochastic
processes defined on Euclidean spaces, the situation is more subtle for discrete spaces. We have different choices for inner
products on the space of probability distributions resulting in different Fokker–Planck equations for the same process. It
is shown that there is a strong connection but there are also substantial discrepancies between the systems of ordinary differential
equations and the classical Fokker–Planck equation on Euclidean spaces. Furthermore, both systems of ordinary differential
equations are gradient flows for the same free energy functional defined on the Riemannian manifolds of probability distributions
with different metrics. Some examples are also discussed. 相似文献
13.
Yu. A. Gostintsev L. A. Sukhanov P. F. Pokhil 《Journal of Applied Mechanics and Technical Physics》1971,12(5):683-691
It is shown that in order to construct a theory of nonsteady propellant combustion it is necessary to know the steady-state dependences of the burning rate u0 °, surface temperature Ts °, and flame temperature TF ° on the external parameters and the initial temperature of the propellant. The combustion processes in an unbounded space, when one of the external parameters varies according to a harmonic law, are examined within the framework of such a theory.Translated from Zhumal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 60–69, September–October, 1971. 相似文献
14.
This large eddy simulation (LES) study is applied to three different premixed turbulent flames under lean conditions at atmospheric
pressure. The hierarchy of complexity of these flames in ascending order are a simple Bunsen-like burner, a sudden-expansion
dump combustor, and a typical swirl-stabilized gas turbine burner–combustor. The purpose of this paper is to examine numerically
whether the chosen combination of the Smagorinsky turbulence model for sgs fluxes and a novel turbulent premixed reaction
closure is applicable over all the three combustion configurations with varied degree of flow and turbulence. A quality assessment
method for the LES calculations is applied. The cold flow data obtained with the Smagorinsky closure on the dump combustor
are in close proximity with the experiments. It moderately predicts the vortex breakdown and bubble shape, which control the
flame position on the double-cone burner. Here, the jet break-up at the root of the burner is premature and differs with the
experiments by as much as half the burner exit diameter, attributing the discrepancy to poor grid resolution. With the first
two combustion configurations, the applied subgrid reaction model is in good correspondence with the experiments. For the
third case, a complex swirl-stabilized burner–combustor configuration, although the flow field inside the burner is only modestly
numerically explored, the level of flame stabilization at the junction of the burner–combustor has been rather well captured.
Furthermore, the critical flame drift from the combustor into the burner was possible to capture in the LES context (which
was not possible with the RANS plus k–ɛ model), however, requiring tuning of a prefactor in the reaction closure. 相似文献
15.
Large-eddy simulation of a turbulent reactive jet with and without evaporating droplets is performed to investigate the interactions
among turbulence, combustion, heat transfer and evaporation. A hybrid Eulerian–Lagrangian approach is used for the gas–liquid
flow system. Arrhenius-type finite-rate chemistry is employed for the chemical reaction. To capture the highly local interactions,
dynamic procedures are used for all the subgrid-scale models, except that the filtered reaction rate is modelled by a scale
similarity model. Various representative cases with different initial droplet sizes (St
0) and mass loading ratios (MLR) have been simulated, along with a case without droplets. It is found that compared with the bigger, slow responding droplets
(St
0 = 16), smaller droplets (St
0 = 1) are more efficient in suppressing combustion due to their preferential concentration in the reaction zones. The peak
temperature and intensity of temperature fluctuations are found to be reduced in all the droplet cases, to a varying extent
depending on the droplet properties. Detailed analysis on the contributions of respective terms in a transport equation for
grid-scale kinetic energy (GSKE) shows that the droplet evaporation effect on GSKE is small, while the droplet momentum effect
depends on St
0. When the MLR is sufficiently high, the bigger (St
0 = 16) droplets can have profound influence on GSKE, and consequently on the formation and evolution of large-scale flow structures.
On the other hand, the turbulence level is found to be lower in the droplet cases than in the pure flame case, due to the
dissipative droplet dynamic effect. 相似文献
16.
Among many presumed-shape pdf approaches for modeling non-premixed turbulent combustion, the presumed β-function pdf is widely used in the literature. However, numerical integration of the β-function pdf may encounter singularity difficulties at mixture fraction values of Z = 0 or 1. To date, this issue has been addressed by few publications. The present study proposes the Piecewise Integration
Method (PIM), an efficient, robust and accurate algorithm to overcome these numerical difficulties with the added benefit
of improving computational efficiency. Comparison of this method to the existing numerical integration methods shows that
the PIM exhibits better accuracy and greatly increases computational efficiency. The PIM treatment of the β-function pdf integration is first applied to the Burke–Schumann solution in conjunction with the k − ε turbulence model to simulate a CH4/H2 bluff-body turbulent flame. The proposed new method is then applied to the same flow using a more complex combustion model,
the laminar flamelet model. Numerical predictions obtained by using the proposed β-function pdf integration method are compared to experimental values of the velocity field, temperature and species mass fractions
to illustrate the efficiency and accuracy of the present method. 相似文献
17.
S. V. Stankevich G. A. Shvetsov 《Journal of Applied Mechanics and Technical Physics》2009,50(2):342-351
This paper presents a method and results of numerical simulations of current-density, magnetic-field, and temperature distributions
in rail launchers of conducting solids for armatures of various shapes. A comparison is made of the results of calculations
using two-dimensional and three-dimensional models. It is shown that for cylindrical and saddle-shaped armatures, Joule heating
calculations performed by two-dimensional simulation of electromagnetic and thermal phenomena are in good agreement with calculations
for the three-dimensional model.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 205–216, March–April, 2009. 相似文献
18.
A. Marshall P. Venkateswaran D. Noble J. Seitzman T. Lieuwen 《Experiments in fluids》2011,51(3):611-620
Experimental turbulent combustion studies require systems that can simulate the turbulence intensities [u′/U
0 ~ 20–30% (Koutmos and McGuirk in Exp Fluids 7(5):344–354, 1989)] and operating conditions of real systems. Furthermore, it is important to have systems where turbulence intensity can be
varied independently of mean flow velocity, as quantities such as turbulent flame speed and turbulent flame brush thickness
exhibit complex and not yet fully understood dependencies upon both U
0 and u′. Finally, high pressure operation in a highly pre-heated environment requires systems that can be sealed, withstand high
gas temperatures, and have remotely variable turbulence intensity that does not require system shut down and disassembly.
This paper describes the development and characterization of a variable turbulence generation system for turbulent combustion
studies. The system is capable of a wide range of turbulence intensities (10–30%) and turbulent Reynolds numbers (140–2,200)
over a range of flow velocities. An important aspect of this system is the ability to vary the turbulence intensity remotely,
without changing the mean flow velocity. This system is similar to the turbulence generators described by Videto and Santavicca
(Combust Sci Technol 76(1):159–164, 1991) and Coppola and Gomez (Exp Therm Fluid Sci 33(7):1037–1048, 2009), where variable blockage ratio slots are located upstream of a contoured nozzle. Vortical structures from the slots impinge
on the walls of the contoured nozzle to produce fine-scale turbulence. The flow field was characterized for two nozzle diameters
using three-component Laser Doppler velocimetry (LDV) and hotwire anemometry for mean flow velocities from 4 to 50 m/s. This
paper describes the key design features of the system, as well as the variation of mean and RMS velocity, integral length
scales, and spectra with nozzle diameter, flow velocity, and turbulence generator blockage ratio. 相似文献
19.
Heinrich Freistühler Peter Szmolyan 《Archive for Rational Mechanics and Analysis》2010,195(2):353-373
A planar viscous shock profile of a hyperbolic–parabolic system of conservation laws is a steady solution in a moving coordinate
frame. The asymptotic stability of viscous profiles and the related vanishing-viscosity limit are delicate questions already
in the well understood case of one space dimension and even more so in the case of several space dimensions. It is a natural
idea to study the stability of viscous profiles by analyzing the spectrum of the linearization about the profile. The Evans
function method provides a geometric dynamical-systems framework to study the eigenvalue problem. In this approach eigenvalues
correspond to zeros of an essentially analytic function E(rl,rw){\mathcal{E}(\rho\lambda,\rho\omega)} which detects nontrivial intersections of the so-called stable and unstable spaces, that is, spaces of solutions that decay
on one (“−∞”) or the other side (“ + ∞”) of the shock wave, respectively. In a series of pioneering papers, Kevin Zumbrun
and collaborators have established in various contexts that spectral stability, that is, the non-vanishing of E(rl,rw){\mathcal{E}(\rho\lambda,\rho\omega)} and the non-vanishing of the Lopatinski–Kreiss–Majda function Δ(λ,ω), imply nonlinear stability of viscous shock profiles in several space dimensions. In this paper we show that these conditions
hold true for small amplitude extreme shocks under natural assumptions. This is done by exploiting the slow-fast nature of
the small-amplitude limit, which was used in a previous paper by the authors to prove spectral stability of small-amplitude
shock waves in one space dimension. Geometric singular perturbation methods are applied to decompose the stable and unstable
spaces into subbundles with good control over their limiting behavior. Three qualitatively different regimes are distinguished
that relate the small strength e{\epsilon} of the shock wave to appropriate ranges of values of the spectral parameters (ρλ, ρ
ω). Various rescalings are used to overcome apparent degeneracies in the problem caused by loss of hyperbolicity or lack of
transversality. 相似文献
20.
In the paper theoretical and numerical model of two-phase flow of solid granular propellant and its products of combustion in the gun barrel during interior ballistic cycle is given. Two cases are considered: base ignition of propellant charge and ignition by igniter. The theoretical model includes the balance equations of mass, momentum and energy for both phases, as well as necessary constitutive laws. The igniter efflux in the propellant chamber is obtained by incorporation in the model the two-phase flow model of igniter function. The convergent, unconditionally stable, numerical procedure is formed to solve the system of equations of the theoretical model. An original procedure of numerical grid adaptation to the flow field increase, caused by the projectile motion down the gun bore, is developed. The TWOPIB code for the computation of whole interior ballistic cycle of ammunition is developed. Four kinds of experimental investigations were carried out:igniter function in open air, flamespreading through propellant charge in the fibreglass tube during base ignition or during ignition by igniter, and firing of 100 mm APFSDS projectile. Verification of the theoretical–numerical approach by the comparison with experimental data is carried out. The great number of computational results is presented for the parameters that can not be measured, but which are necessary for more complete understanding of examined processes. The presented theoretical–numerical access enables, not only the complete optimisation of propellant charges, but more successful solutions of many interior ballistic problems. 相似文献