High-resolution simulations of cylindrical void collapse in energetic materials: Effect of primary and secondary collapse on initiation thresholds

Kumar, Nirmal; Schmidt, Martin; Udaykumar, H. S.

doi:10.1103/physrevfluids.2.043202

Cited by 69 publications

(54 citation statements)

References 33 publications

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“…7b. From stages 44 onward, the temperature is first seen to increase in a hill-like form (labelled as 8 ), then decreases taking a well-like form ( 9 ) and then increases again taking the form of a hill, but with a shallower gradient than before ( 10 ). This is because at these late stages, the Mach stem feature has attained a horn-like shape and it is advected upwards.…”

Section: Evolution Along Constant Latitude Linesmentioning

confidence: 84%

“…Kapila et al [7] presented the collapse process and the detonation generation in an exemplary explosive and studied the effect of cavity shape in the detonation generation using a pressuredependent reaction rate. In an elastoplastic framework, Tran and Udaykumar [8] studied the response of reactive HMX with micron-sized cavities, while Rai et al [9,10] considered the resolution required for reactive cavity collapse simulations and the sensitivity behaviour of elongated cavities in HMX.…”

Section: Introductionmentioning

confidence: 99%

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The evolution of the temperature field during cavity collapse in liquid nitromethane. Part II: reactive case

Michael

Nikiforakis

2018

Shock Waves

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This work is concerned with the effect of cavity collapse in non-ideal explosives as a means of controlling their sensitivity. The main objective is to understand the origin of localised temperature peaks (hot spots) which play a leading order role at the early stages of ignition. To this end, we perform two-and three-dimensional numerical simulations of shock-induced single gas-cavity collapse in liquid nitromethane. Ignition is the result of a complex interplay between fluid dynamics and exothermic chemical reaction.In the first part of this work, we focused on the hydrodynamic effects in the collapse process by switching off the reaction terms in the mathematical formulation. In this part, we reinstate the reactive terms and study the collapse of the cavity in the presence of chemical reactions. By using a multi-phase formulation which overcomes current challenges of cavity collapse modelling in reactive media, we account for the large density difference across the material interface without generating spurious temperature peaks, thus allowing the use of a temperature-based reaction rate law. The mathematical and physical models are validated against experimental and analytic data. In Part I, we demonstrated that, compared to experiments, the generated hot spots have a more complex topological structure and that additional hot spots arise in regions away from the cavity centreline. Here, we extend this by identifying which of the previously determined hightemperature regions in fact lead to ignition and comment on the reactive strength and reaction growth rate in the distinct hot spots. We demonstrate and quantify the sensitisation of nitromethane by the collapse of the isolated cavity by comparing the ignition times of nitromethane due to cavity collapse and the ignition time of the neat material. The ignition in both the centreline hot spots and the hot spots generated by Mach stems occurs in less than half the ignition time of the neat material. We compare two-and three-dimensional simulations to examine the change in topology, temperatures, and reactive strength of the hot spots by the third dimension. It is apparent that belated ignition times can be avoided by the use of three-dimensional simulations. The effect of the chemical reactions on the topology and strength of the hot spots in the timescales considered is also studied, in a comparison between inert and reactive simulations where maximum temperature fields and their growth rates are examined.

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Section: Evolution Along Constant Latitude Linesmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

The evolution of the temperature field during cavity collapse in liquid nitromethane. Part II: reactive case

Michael

Nikiforakis

2018

Shock Waves

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“…For a PBX explosive, one kind of typical heterogeneous solid explosives, the pore collapse that including the viscoplastic deformation, the hydrodynamic micro-jetting, the compression of gas in cavities and the shear bandings is a dominant mechanism of "hot-spot" formation during the shock initiation process [13,14], and the explosive maybe enter the detonation growth process once the "hot-spot" is ignited, which is mainly described by the surface combustion mechanism [15,16]. Generally, the reactive hot spots in PBX have the temporal and spatial scales on the order of nanosecond and micron, respectively [17,18], and it is suggested that the shock intensity, the material viscosity, and the initial pore's size and shape all have noticeable effect [ [19][20][21][22][23][24]. To quantitatively describe the reactive flow field of the shock initiation and detonation processes in heterogeneous solid explosives, a number of reaction rate models have been proposed over the years, included mainly the empirical macroscopic models [25][26][27][28], the statistical models [29][30][31] and the mesoscopic models [14,15,32,33].…”

Section: Introductionmentioning

confidence: 99%

Comparative Analysis of Detonation Growth Characteristics between HMX‐ and TATB‐based PBXs

Bai

Duan

Luo

et al. 2019

Propellants Explo Pyrotec

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This paper offers a new method for calculating the reaction rate based on the pore collapse “hot‐spot” ignition mechanism in multi‐component polymer bonded explosives (PBXs), and proposes a mesoscopic reaction rate model that allows us to predict the shock initiation and detonation behaviors of multi‐component PBXs with any explosive component proportion and explosive particle size. The pressure‐time histories in PBXC03 (87 % HMX, 7 % TATB, and 6 % Viton by weight) and PBXC10 (25 % HMX, 70 % TATB, and 5 % Kel‐F800 by weight) are calculated by using the new mesoscopic reaction rate model, and the numerical results are found to be in good agreement with the experimental data. It is found that the shock initiation and detonation behaviors of PBXC03 with the dominant component of HMX is mainly controlled by the hot‐spot ignition. The subsequent combustion reacts fast once the hot‐spot is ignited and shows an accelerated reaction characteristic. While, with the dominant component of insensitive TATB, the critical initiation pressure of PBXC10 is high enough to make almost saturated reactive hot spots just behind the precursory shock‐wave front, and the shock initiation behavior is basically determined by the combustion reaction, which is characterized by a stable reaction due to the slow combustion‐wave velocity.

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“…8b. New waves, S 21 and S 22 , are generated by more transmission/reflection processes at the lobe boundary, and S 22 is also split into two parts, S 22A and S 22B , due to its interaction with the upstream-travelling wave generated upon cavity collapse, namely S 10 (Fig. 8c).…”

Section: Late Stages Of the Three-dimensional Cavity Collapsementioning

confidence: 99%

“…Limited results on the shock-cavity collapse in nitromethane were presented by Michael and Nikiforakis [15], in HNS by Kittel and Yarrington [16], and in HMX by Menikoff [17]. In an elastoplastic framework, Tran and Udaykumar [18,19] and Kapahi and Udaykumar [20] studied the response of inert and reactive HMX with micron-sized cavities, while Rai et al [21,22] considered the resolution required for simulations of reactive cavity collapse and the sensitivity behaviour of elongated cavities in HMX.…”

Section: Introductionmentioning

confidence: 99%

The evolution of the temperature field during cavity collapse in liquid nitromethane. Part I: inert case

Michael

Nikiforakis

2018

Shock Waves

View full text Add to dashboard Cite

This work is concerned with the effect of cavity collapse in non-ideal explosives as a means of controlling their sensitivity. The main objective is to understand the origin of localised temperature peaks (hot spots) which play a leading order role at the early stages of ignition. To this end, we perform two-and three-dimensional numerical simulations of shock-induced single gas-cavity collapse in liquid nitromethane. Ignition is the result of a complex interplay between fluid dynamics and exothermic chemical reaction. In order to understand the relative contribution between these two processes, we consider in this first part of the work the evolution of the physical system in the absence of chemical reactions. We employ a multi-phase mathematical formulation which can account for the large density difference across the gas-liquid material interface without generating spurious temperature peaks. The mathematical and physical models are validated against experimental, analytic, and numerical data. Previous inert studies have identified the impact of the upwind (relative to the direction of the incident shock wave) side of the cavity wall to the downwind one as the main reason for the generation of a hot spot outside of the cavity, something which is also observed in this work. However, it is also apparent that the topology of the temperature field is more complex than previously thought and additional hot spot locations exist, which arise from the generation of Mach stems rather than jet impact. To explain the generation mechanisms and topology of the hot spots, we carefully follow the complex wave patterns generated in the collapse process and identify specifically the temperature elevation or reduction generated by each wave. This enables tracking each hot spot back to its origins. It is shown that the highest hot spot temperatures can be more than twice the post-incident shock temperature of the neat material and can thus lead to ignition. By comparing two-dimensional and three-dimensional simulation results in the context of the maximum temperature observed in the domain, it is apparent that three-dimensional calculations are necessary in order to avoid belated ignition times in reactive scenarios.

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High-resolution simulations of cylindrical void collapse in energetic materials: Effect of primary and secondary collapse on initiation thresholds

Cited by 69 publications

References 33 publications

The evolution of the temperature field during cavity collapse in liquid nitromethane. Part II: reactive case

The evolution of the temperature field during cavity collapse in liquid nitromethane. Part II: reactive case

Comparative Analysis of Detonation Growth Characteristics between HMX‐ and TATB‐based PBXs

The evolution of the temperature field during cavity collapse in liquid nitromethane. Part I: inert case

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