Detonation Propagation Research Articles

New effects of stratified gas detonation

28 In this paper, we consider problems on initiated detonation in a supersonic flow and in a quiescent sto� ichiometric propane-air mixture that partly or entirely fills in the cross section of a plane channel. In this flow, the detonation initiation occurs due to a shelf or a wall completely closing the channel, whereas in a quiescent medium, an explosion is used. The study is conducted in the framework of the singlestage com� bustion kinetics by the numerical method based on Godunov's scheme. We have also determined the crit� ical conditions for the detonation initiation, which are associated with both the incidentflow velocity and the explosion energy. In all processes under consideration, we found the mechanism of the detonation propaga� tion, which had not been known previously. The mechanism is stipulated by the formation of a compli� cated waveflow structure. For this structure, the pen� etration of the shock wave propagating through inert gas into the layer ahead of the detonation wave is char� acteristic. As a result, inert gas is heated and inflamed. Thus, the process is of a periodic nature that differs from the usual cellular detonation in a homogeneous

406 障害物と希釈剤による爆轟波伝播への影響(OS5 衝撃波と燃焼)

406 障害物と希釈剤による爆轟波伝播への影響(OS5 衝撃波と燃焼)

Utilizing unsteady curved detonation analysis and detailed kinetics to study the direct initiation of detonation in H 2–O 2 and H 2–Air mixtures

In the present paper, utilizing a detailed chemical kinetics, the simplified unsteady reactive Euler equations are solved in the reaction zone of a curved detonation, to derive the relation between detonation propagation velocity ( D) with its acceleration ( D ˙ ) and front curvature ( κ), that is the so called D ˙ − D − κ relation. Then, this relation is used for tracking the detonation front and to study the onset of a self sustained near CJ detonation. The reaction-zone history is studied to understand the events that happen during the onset of a detonation in Hydrogen/Oxygen mixtures. It is observed that the relative movement of the location of the peak of the thermicity function with respect to the front, and its absolute value, are two parameters that determine the physics of the onset. Utilizing the D ˙ − D − κ relation based on the detailed chemical kinetics, the critical initiation energy is calculated for the H 2–O 2 and H 2–Air mixtures. Although, the previous studies by single step kinetics [A. R. Kasimov, PhD Thesis, Univ. of Illinois at Urbana-Champaign] and the present results both predict the critical initiation energy with acceptable accuracy, however, the present work makes a better prediction of the equivalence ratio at which the H 2–O 2 mixture experiences its minimum critical energy. Also the present predictions are more accurate for the lean H 2–O 2 and H 2–Air mixtures. Using the present method, the effect of initial pressure on the critical initiation energy of H 2–O 2 mixture is well predicted compared to empirical results.

Specifics of the detonation of mixtures of powerful high explosives with W and Pb high-density inert additives

Results of experimental and theoretical studies of the unusual detonation properties of mixtures of high explosives (HEs) with high-density inert additives (W and Pb) were analyzed and systematized. Typical examples of the nonideal detonation of composite explosives for which the measured detonation pressure is substantially lower while the detonation velocity is higher than the values calculated within the framework of the hydrodynamic model, with the specific heat ratio for the detonation products being ∼6–8, are presented. Mathematical models capable of qualitatively and quantitatively describing the specificity of the propagation of detonation in HE-W mixtures. Mechanisms of formation of anomalous pressure and mass velocity profiles, which explain why the correlation between the Chapman-Jouguet pressure for HE-W and HE-Pb mixtures, the velocity of the free surface of duralumin target, and the depth of the dent imprinted in steel witness plates, are described.

Evolution of detonation propagation through an annular gap into a combustion chamber

Some results of theoretical studies of detonation processes in combustible gaseous mixtures are discussed for a model geometry of large combustion chambers of detonation engines in the case of mixtures of hydrogen and oxygen-enriched air. The effect of geometric characteristics on the operation of pulse detonation engines is analyzed. In particular, the propagation of detonation waves in tubes of small diameter to larger volumes and the evolution of detonation under the action of converging shock waves are considered.

Self-organized generation of transverse waves in diverging cylindrical detonations

Self-organized generation of transverse waves associated with the transverse wave instabilities at a diverging cylindrical detonation front was numerically studied by solving two-dimensional Euler equations implemented with an improved two-step chemical kinetic model. After solution validation, four mechanisms of the transverse wave generation were identified from numerical simulations, and referred to as the concave front focusing, the kinked front evolution, the wrinkled front evolution and the transverse wave merging, respectively. The propagation of the cylindrical detonation is maintained by the growth of the transverse waves that match the rate of increase in surface area of the detonation front to asymptotically approach a constant average number of transverse waves per unit length along the circumference of the detonation front. This cell bifurcation phenomenon of cellular detonations is discussed in detail to gain better understanding on detonation physics.

Influence of the initial gas pressure on the detonation limits and parameters of low-density secondary explosives in an inert porous medium

This paper reports the results of an experimental study of the detonation of low-density (3–40 mg/cm3) secondary high explosives (HEs) in evacuated and gas-filled inert porous media. A convective-jet mechanism of detonation propagation was found to occur under all conditions studied. The effects of the type of HE and initial gas pressure on the critical density of the HE and detonation parameters were elucidated. It is shown that, in the presence of air, detonation can occur at a lower volume-averaged density of the HE than in the case of the evacuated media and there are two limits (minimal and maximal) for the initial gas pressure. As the volume-averaged density HE decreases, the limits approach each other and, for a certain critical density of the HE, detonation exists only at one value of the initial pressure.

Formation of unburnt pockets in gaseous detonations

Formation of unburnt pockets in gaseous detonations is caused by two mechanisms: longitudinal and transverse mechanisms. The longitudinal mechanism is based on longitudinal instability of the detonation front. In the transverse mechanism, interactions between transverse waves lead to the formation of unburnt pockets. In this paper, the transverse mechanism is investigated via two-dimensional numerical simulations of propagation of gaseous detonation in a channel. A front structure that includes triple points, transverse waves, the incident shock, and the Mach stem is formed, as the detonation propagates in the channel. The origin of unburnt pockets is explained by the interaction between transverse waves or corresponding triple points that detach a portion of the reactant from the detonation front. It is observed that the size of the unburnt pockets and the depth of penetration to the products increase with increasing activation energy and that the shape of the pockets also changes with activation energy.

Nitrous acid under high temperature and pressure – From atomistic simulations to equation of state for thermochemical modeling

Complex thermochemistry modeling in the wake of a detonation or shock propagation requires accurate equations of state (EOS) for the resulting chemical species under high temperature and pressure. Nitrous acid (HONO or HNO 2) has been shown to be an important post-detonation product for many energetic compounds. Given that its EOS has not been determined so far, either experimentally or theoretically, we develop a class II force field to model both conformers (i.e. cis and trans) of HONO, and compute the EOS using classical molecular dynamics simulations. We then show that this EOS can be well represented within a thermodynamics theory framework previously applied to other polar fluids.

Spinning detonation and velocity deficit in small diameter tubes

Detonation velocities and soot patterns of H 2/O 2 mixtures were measured in glass tubes of 3, 6 and 10 mm diameters at pressures ranging from 70 to 400 Torr and equivalence ratios of 0.5–1.5. It was confirmed that the transition from a multi-head to a spinning detonation occurred at the pressure where the cell size is equal to the length of circumference. At this transition pressure, the velocity was 95% of the C-J detonation. Stable spinning detonations were observed at wide range of initial pressures below the transition point. Detonation velocities were continuously decreasing with decreasing initial pressures in this pressure region. Spinning detonations with velocities down to 85% of the C-J detonation were observed. Those deficits in detonation velocities were well predicted by the modified ZND model with full detailed chemical kinetics. Heat and momentum losses were taking into account in this model. Validity of the modified ZND model to define the limit of detonation propagation was discussed.

Detonation in gases

We review recent progress in gaseous detonation experiment, modeling, and simulation. We focus on the propagating detonation wave as a fundamental combustion process. The picture that is emerging is that although all propagating detonations are unstable, there is a wide range of behavior with one extreme being nearly laminar but unsteady periodic flow and the other chaotic instability with highly turbulent flow. We discuss the implications of this for detonation propagation and dynamic behavior such as diffraction, initiation, and quenching or failure.

LES model of large scale hydrogen–air planar detonations: Verification by the ZND theory

The large eddy simulation (LES) model of hydrogen–air detonation at very large scales, which doesn't require Arrhenius chemistry, is presented. The progress variable equation is applied for the first time to simulate propagation of a reaction front following and coupled with a leading shock. The gradient method, based on a product of pre-shock mixture density and detonation velocity, is employed as a source term in the progress variable equation. Chemical kinetics enters the combustion model only through its influence on the detonation velocity and modelling of detailed chemistry is omitted. The LES model is verified against theoretical solution by the Zel'dovich–von Neumann–Doring (ZND) theory for a case of planar 29.05% hydrogen–air detonation in elongated 3 × 3 × 100 m calculation domain. Thermodynamically calculated values of the specific heats ratio for burned mixture γ = 1.22 and the standard heat of combustion Δ H c = 3.2 MJ/kg are applied without any adjustment often applied in other models. Numerical simulation reproduced theoretical values of von Neumann spike, Chapman–Jouguet pressure, Taylor wave and detonation propagation velocity. There are no adjustable parameters in the model. Practically no grid sensitivity for the planar detonation wave is demonstrated by the LES model. Detonation velocity and pressures are shown to be nearly independent of the computational cell size in a wide range of cell sizes 0.1–1.0 m. Impulse depends to some extent on a cell size. Three-dimensional version of the LES model is under development to simulate pressure effects and identify design solutions, including mitigating techniques, for hydrogen safety engineering. There is no intention to use this oriented on large scale applications engineering LES model to reproduce fine structure of the detonation wave.

Shock and detonation wave diffraction at a sudden expansion in gas–particle mixtures

Numerical modeling of the propagation of shock and detonation waves is carried out in a duct with an abrupt expansion for a heterogeneous mixture of fine particles of aluminum and oxygen. A considerable difference from corresponding flows in pure gas is found. The influence of the size and mass loading of particles on the flow and shock wave structure behind the backward-facing step is determined. As in gaseous detonations, three types of scenarios of detonation development are obtained. Specific features of the flow structure are revealed such as deformation of the combustion front due to interaction between the relaxation zone and the vortex structure. The influence of particle size and channel width on detonation propagation is analyzed.

A study of detonation propagation and diffraction with compliant confinement

Previous computational studies of diffracting detonations with the ignition-and-growth (IG) model demonstrated that, contrary to experimental observations, the computed solution did not exhibit dead zones. For a rigidly confined explosive it was found that while diffraction past a sharp corner did lead to a temporary separation of the lead shock from the reaction zone, the detonation re-established itself in due course and no pockets of unreacted material remained. The present investigation continues to focus on the potential for detonation failure within the IG model, but now for a compliant confinement of the explosive. The aim of the present paper is two-fold. First, in order to compute solutions of the governing equations for multi-material reactive flow, a numerical method is developed and discussed. The method is a Godunov-type, fractional-step scheme which incorporates an energy correction to suppress numerical oscillations that occur near material interfaces for standard conservative schemes. The accuracy of the solution method is then tested using a two-dimensional rate-stick problem for both strong and weak confinements. The second aim of the paper is to extend the previous computational study of the IG model by considering two related problems. In the first problem, the corner-turning configuration is re-examined, and it is shown that in the matter of detonation failure, the absence of rigid confinement does not affect the outcome in a material way; sustained dead zones continue to elude the model. In the second problem, detonations propagating down a compliantly confined pencil-shaped configuration are computed for a variety of cone angles of the tapered section. It is found, in accord with experimental observation, that if the cone angle is small enough, the detonation fails prior to reaching the cone tip. For both the corner-turning and the pencil-shaped configurations, mechanisms underlying the behaviour of the computed solutions are identified.

A new reduced network to simulate detonations in superbursts from mixed H/He accretors

We construct a new reduced nuclear reaction network able to reproduce the energy production due to the photo-disintegration of heavy elements such as Ru, which are believed to occur during superbursts in mixed H/He accreting systems. We use this network to simulate a detonation propagation, inside a mixture of C/Ru. As our reference, we use a full nuclear reaction network, including 14758 reactions on 1381 nuclides. Until the reduced and full networks converge to a good level of accuracy in the energy production rate, we iterate between the hydrodynamical simulation, with a given reduced network, and the readjustment of a new reduced network, on the basis of previously derived hydrodynamical profiles. We obtain the thermodynamic state of the material after the passage of the detonation, and the final products of the combustion. Interestingly, we find that all reaction lengths can be resolved in the same simulation. This will enable C/Ru detonations to be more easily studied in future multi-dimensional simulations, than pure carbon ones. We underline the dependence of the combustion products on the initial mass fraction of Ru. In some cases, a large fraction of heavy nuclei, such as Mo, remains after the passage of the detonation front. In other cases, the ashes are principally composed of iron group elements.

Gaseous detonation propagation in a bifurcated tube

Gaseous detonation propagation in a bifurcated tube was experimentally and numerically studied for stoichiometric hydrogen and oxygen mixtures diluted with argon. Pressure detection, smoked foil recording and schlieren visualization were used in the experiments. Numerical simulation was carried out at low initial pressure (8.00kPa), based on the reactive Navier–Stokes equations in conjunction with a detailed chemical reaction model. The results show that the detonation wave is strongly disturbed by the wall geometry of the bifurcated tube and undergoes a successive process of attenuation, failure, re-initiation and the transition from regular reflection to Mach reflection. Detonation failure is attributed to the rarefaction waves from the left-hand corner by decoupling leading shock and reaction zones. Re-initiation is induced by the inert leading shock reflection on the right-hand wall in the vertical branch. The branched wall geometry has only a local effect on the detonation propagation. In the horizontal branch, the disturbed detonation wave recovers to a self-sustaining one earlier than that in the vertical branch. A critical case was found in the experiments where the disturbed detonation wave can be recovered to be self-sustaining downstream of the horizontal branch, but fails in the vertical branch, as the initial pressure drops to 2.00kPa. Numerical simulation also shows that complex vortex structures can be observed during detonation diffraction. The reflected shock breaks the vortices into pieces and its interaction with the unreacted recirculation region induces an embedded jet. In the vertical branch, owing to the strength difference at any point and the effect of chemical reactions, the Mach stem cannot be approximated as an arc. This is different from the case in non-reactive steady flow. Generally, numerical simulation qualitatively reproduces detonation attenuation, failure, re-initiation and the transition from regular reflection to Mach reflection observed in experiments.

Modeling of weakly nonideal detonation of condensed high explosives with a high content of carbon

A numerical model of weakly nonideal detonation of plastic-bounded TATB is proposed, which alleviates the requirements to the computational grid and necessary computational resources. The model is tested against the experimental results on the dependence of the detonation velocity on the charge diameter and detonation propagation in an annular charge.

Numerical prediction of concrete slab response to blast loading

In this paper, a dynamic plastic damage model for concrete material has been employed to estimate responses of both an ordinary reinforced concrete slab and a high strength steel fibre concrete slab subjected to blast loading. In the concrete material model, the strength envelope is a damage-based modified piece-wise Drucker–Prager model; the strain rate effect on tension and compression are considered separately; the damage variable is based on Mazars’ damage model, which is a combination of tensile and compressive damage. The equation of state (EOS) is also a combination of the porous and solid EOS of concrete with different forms for tension and compression states. The interaction between the blast wave and the concrete slab is considered in the 3D simulation. In the first stage, the initial detonation and blast wave propagation is modelled in a 2D simulation before the blast wave reaches the concrete slab, then the results obtained from the 2D calculation are remapped to a 3D model. The calculated blast load is compared with that obtained from TM5-1300. The numerical results of the concrete slab response are compared with the explosive tests carried out in the Weapons System Division, Defence Science and Technology Organisation, Department of Defence, Australia. Repetitive applications of blast loading on slabs are also simulated and the results compared with test data.

An Improved CE/SE Scheme and Its Application to Detonation Propagation

An improved two-dimensional space-time conservation element and solution element (CE/SE) method with second-order accuracy is proposed, examined and extended to simulate the detonation propagations using detailed chemical reaction models. The numerical results of planar and cellular detonation are compared with corresponding results by the Chapman–Jouguet theory and experiments, and prove that the method is a new reliable way for numerical simulations of detonation propagation.

Gas detonation in a channel with transverse ribs

Results of experiments on detonation propagation in a rectangular horizontal channel with high ribs on the lower wall are presented. The experiments were performed with acetylene-oxygen mixtures. An interval of initial pressures is found, in which low-velocity detonation with a steady velocity of 0.38–0.55 of the Chapman-Jouguet velocity without losses exists. This detonation wave is a system consisting of a shock wave and a flame. Owing to gas outflow to the layer occupied by the ribs, the flame is maintained at a constant distance from the shock wave, which is approximately equal to the free transverse size of the channel. This distance weakly decreases with increasing initial pressure and is almost independent of the burning rate of the gas at standard temperature.