scholarly journals Investigation of Shock Initiation in Covered Charges under Shock Wave and Fragment Impacts

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Xingwang Chen ◽  
Jinxiang Wang ◽  
Kui Tang ◽  
Hongfei Wang ◽  
Yuanbo Li
Keyword(s):  
Shock Wave ◽  
Theoretical Model ◽  
Numerical Simulations ◽  
High Speed ◽  
Least Squares Method ◽  
Strong Shock ◽  
Protective Function ◽  
Shock Initiation ◽  
Metal Plates ◽  
The Impact

In the current work, a series of step-by-step research methods have been applied to address the damaging effects of near-field strong shock waves and high-speed fragments on covered charge. In the first step, the defects of covered plates due to high-speed fragments were simplified to penetrated notches, and then, these notches were used to evaluate the impact of shock wave loads on charges covered with metal plates. In the next step, we developed a theoretical model to take into account the shock initiation of charges covered with defected metal plates. Explosive initiation standards coupled with shock wave evolution characteristics were applied to specify the crucial conditions of explosive detonation. Finite element program, for instance, was applied for the simulation of shock initiation processes in pressed charges (when TNT was covered with a steel plate containing a penetrated notch), and then, numerical simulations were validated by experimental findings. Finally, the results obtained from the numerical simulations and theoretical model were applied to evaluate the impacts of shock wave intensity, the thickness of covered metal plate, and the geometrical features of penetrated notch on pressed charge shock initiation. The least squares method was applied to determine critical initiation criteria (n and K). Theoretical calculation results were found to be highly consistent with those obtained from numerical simulations, indicating that covered metal plates significantly contributed to charge protection. The results also revealed that notches could undermine the protective function of covered plates and the size and shape of notch significantly affected charge critical detonation distance. Critical detonation distances of noncontact explosions were found to be 25 and 81 mm for a 3 mm thick pressed TNT in the presence and absence of 45# steel-covered plate, respectively. According to the results, increase in the diameter of covered plates containing a cylindrical notch increased pressed TNT critical detonation distance. When dealing with a covered plate containing a normally reflected frustum notch, however, we figured out that any increase in normal reflection slope could decrease pressed TNT critical detonation distance.

Numerical simulation of humidification and heating during inspiration within an adult nose

2012 ◽  
Vol 50 (2) ◽  
pp. 157-164
Author(s):  
F. Sommer ◽  
R. Kroger ◽  
J. Lindemann
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Middle Turbinate ◽  
Multislice Ct ◽  
Respiratory Cycle ◽  
In Vivo Measurements ◽  
Airflow Distribution ◽  
The Impact ◽  
Human Nose

Background: The temperature of inhaled air is highly relevant for the humidification process. Narrow anatomical conditions limit possibilities for in vivo measurements. Numerical simulations offer a great potential to examine the function of the human nose. Objective: In the present study, the nasal humidification of inhaled air was simulated simultaneously with temperature distribution during a respiratory cycle. Methods: A realistic nose model based on a multislice CT scan was created. The simulation was performed by the Software Fluent(r). Boundary conditions were based on previous in vivo measurements. Inhaled air had a temperature of 20(deg)C and relative humidity of 30%. The wall temperature was assumed to be variable from 34(deg)C to 30(deg)C with constant humidity saturation of 100% during the respiratory cycle. Results: A substantial increase in temperature and humidity can be observed after passing the nasal valve area. Areas with high speed air flow, e.g. the space around the turbinates, show an intensive humidification and heating potential. Inspired air reaches 95% humidity and 28(deg)C within the nasopharynx. Conclusion: The human nose features an enormous humidification and heating capability. Warming and humidification are dependent on each other and show a similar spacial pattern. Concerning the climatisation function, the middle turbinate is of high importance. In contrast to in vivo measurements, numerical simulations can explore the impact of airflow distribution on nasal air conditioning. They are an effective method to investigate nasal pathologies and impacts of surgical procedures.

High Speed Liquid Impact Onto Wetted Solid Surfaces

1994 ◽  
Vol 116 (2) ◽  
pp. 345-348 ◽  
Author(s):  
H. H. Shi ◽  
J. E. Field ◽  
C. S. J. Pickles
Keyword(s):  
Shock Wave ◽  
Liquid Layer ◽  
Solid Surface ◽  
High Speed ◽  
Shear Failure ◽  
Soda Lime ◽  
Liquid Jet ◽  
Soda Lime Glass ◽  
The Impact

The mechanics of impact by a high-speed liquid jet onto a solid surface covered by a liquid layer is described. After the liquid jet contacts the liquid layer, a shock wave is generated, which moves toward the solid surface. The shock wave is followed by the liquid jet penetrating through the layer. The influence of the liquid layer on the side jetting and stress waves is studied. Damage sites on soda-lime glass, PMMA (polymethylmethacrylate) and aluminium show the role of shear failure and cracking and provide evidence for analyzing the impact pressure on the wetted solids and the spatial pressure distribution. The liquid layer reduces the high edge impact pressures, which occur on dry targets. On wetted targets, the pressure is distributed more uniformly. Despite the cushioning effect of liquid layers, in some cases, a liquid can enhance material damage during impact due to penetration and stressing of surface cracks.

Evolution of enstrophy in shock/homogeneous turbulence interaction

2012 ◽  
Vol 707 ◽  
pp. 74-110 ◽  
Author(s):  
Krishnendu Sinha
Keyword(s):  
Shock Wave ◽  
Numerical Simulations ◽  
High Speed ◽  
Isotropic Turbulence ◽  
Stokes Equations ◽  
Interaction Analysis ◽  
Direct Numerical Simulations ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Flow ◽  
Linear Interaction

AbstractInteraction of turbulent fluctuations with a shock wave plays an important role in many high-speed flow applications. This paper studies the amplification of enstrophy, defined as mean-square fluctuating vorticity, in homogeneous isotropic turbulence passing through a normal shock. Linearized Navier–Stokes equations written in a frame of reference attached to the unsteady shock wave are used to derive transport equations for the vorticity components. These are combined to obtain an equation that describes the evolution of enstrophy across a time-averaged shock wave. A budget of the enstrophy equation computed using results from linear interaction analysis and data from direct numerical simulations identifies the dominant physical mechanisms in the flow. Production due to mean flow compression and baroclinic torques are found to be the major contributors to the enstrophy amplification. Closure approximations are proposed for the unclosed correlations in the production and baroclinic source terms. The resulting model equation is integrated to obtain the enstrophy jump across a shock for a range of upstream Mach numbers. The model predictions are compared with linear theory results for varying levels of vortical and entropic fluctuations in the upstream flow. The enstrophy model is then cast in the form of$k$–$\epsilon $equations and used to compute the interaction of homogeneous isotropic turbulence with normal shocks. The results are compared with available data from direct numerical simulations. The equations are further used to propose a model for the amplification of turbulent viscosity across a shock, which is then applied to a canonical shock–boundary layer interaction. It is shown that the current model is a significant improvement over existing models, both for homogeneous isotropic turbulence and in the case of complex high-speed flows with shock waves.

scholarly journals Numerical and experimental evaluation of shock dividers

Shock Waves ◽  
2022 ◽  
Author(s):  
M. Rezay Haghdoost ◽  
B. S. Thethy ◽  
M. Nadolski ◽  
B. Seo ◽  
C. O. Paschereit ◽  
...  
Keyword(s):  
Shock Wave ◽  
Shock Waves ◽  
Numerical Simulations ◽  
Total Pressure ◽  
High Speed ◽  
Pressure Probe ◽  
Width Ratio ◽  
Pressure Pulsations ◽  
Pulse Detonation ◽  
Shock Dynamics

AbstractMitigation of pressure pulsations in the exhaust of a pulse detonation combustor is crucial for operation with a downstream turbine. For this purpose, a device termed the shock divider is designed and investigated. The intention of the divider is to split the leading shock wave into two weaker waves that propagate along separated ducts with different cross sections, allowing the shock waves to travel with different velocities along different paths. The separated shock waves redistribute the energy of the incident shock wave. The shock dynamics inside the divider are investigated using numerical simulations. A second-order dimensional split finite volume MUSCL-scheme is used to solve the compressible Euler equations. Furthermore, low-cost simulations are performed using geometrical shock dynamics to predict the shock wave propagation inside the divider. The numerical simulations are compared to high-speed schlieren images and time-resolved total pressure recording. For the latter, a high-frequency pressure probe is placed at the divider outlet, which is shown to resolve the transient total pressure during the shock passage. Moreover, the separation of the shock waves is investigated and found to grow as the divider duct width ratio increases. The numerical and experimental results allow for a better understanding of the dynamic evolution of the flow inside the divider and inform its capability to reduce the pressure pulsations at the exhaust of the pulse detonation combustor.

scholarly journals Early-time jet formation in liquid–liquid impact problems: theory and simulations

2018 ◽  
Vol 856 ◽  
pp. 764-796 ◽  
Author(s):  
R. Cimpeanu ◽  
M. R. Moore
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Early Stage ◽  
Early Time ◽  
Leading Order ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Jet Velocity ◽  
The Impact ◽  
Wagner Theory

We perform a thorough qualitative and quantitative comparison of theoretical predictions and direct numerical simulations for the two-dimensional, vertical impact of two droplets of the same fluid. In particular, we show that the theoretical predictions for the location and velocity of the jet root are excellent in the early stages of the impact, while the predicted jet velocity and thickness profiles are also in good agreement with the computations before the jet begins to bend. By neglecting the role of the surrounding gas both before and after impact, we are able to use Wagner theory to describe the early-time structure of the impact. We derive the model for general droplet velocities and radii, which encompasses a wide range of impact scenarios from the symmetric impact of identical drops to liquid drops impacting a deep pool. The leading-order solution is sufficient to predict the curve along which the root of the high-speed jet travels. After moving into a frame fixed in this curve, we are able to derive the zero-gravity shallow-water equations governing the leading-order thickness and velocity of the jet. Our numerical simulations are performed in the open-source software Gerris, which allows for the level of local grid refinement necessary for a problem with such a wide variety of length scales. The numerical simulations incorporate more of the physics of the problem, in particular the surrounding gas, the fluid viscosities, gravity and surface tension. We compare the computed and predicted solutions for a range of droplet radii and velocities, finding excellent agreement in the early stage. In light of these successful comparisons, we discuss the tangible benefits of using Wagner theory to confidently track properties such as the jet-root location, jet thickness and jet velocity in future studies of splash jet/ejecta evolution.

On high-speed impingement of cylindrical droplets upon solid wall considering cavitation effects

2018 ◽  
Vol 857 ◽  
pp. 851-877 ◽  
Author(s):  
Wangxia Wu ◽  
Gaoming Xiang ◽  
Bing Wang
Keyword(s):  
Phase Transition ◽  
Shock Wave ◽  
High Speed ◽  
Solid Wall ◽  
Fluid Model ◽  
Droplet Diameter ◽  
Droplet Surface ◽  
Rarefaction Waves ◽  
Two Phase ◽  
The Impact

The high-speed impingement of droplets on a wall occurs widely in nature and industry. However, there is limited research available on the physical mechanism of the complicated flow phenomena during impact. In this study, a simplified multi-component compressible two-phase fluid model, coupled with the phase-transition procedure, is employed to solve the two-phase hydrodynamics system for high-speed cylindrical droplet impaction on a solid wall. The threshold conditions of the thermodynamic parameters of the fluid are established to numerically model the initiation of phase transition. The inception of cavitation inside the high-speed cylindrical droplets impacting on the solid wall can thus be captured. The morphology and dynamic characteristics of the high-speed droplet impingement process are analysed qualitatively and quantitatively, after the mathematical models and numerical procedures are carefully verified and validated. It was found that a confined curved shock wave is generated when the high-speed cylindrical droplet impacts the wall and this shock wave is reflected by the curved droplet surface. A series of rarefaction waves focus at a position at a distance of one third of the droplet diameter away from the top pole due to the curved surface reflection. This focusing zone is identified as the cavity because the local liquid state satisfies the condition for the inception of cavitation. Moreover, the subsequent evolution of the cavitation zone is demonstrated and the effects of the impact speed, ranging from $50$ to $200~\text{m}~\text{s}^{-1}$ , on the deformation of the cylindrical droplet and the further evolution of the cavitation were studied. The focusing position, where the cavitation core is located, is independent of the initial impaction speed. However, the cavity zone is enlarged and the stronger collapsing wave is induced as the impaction speed increases.

scholarly journals Experimental study of Richtmyer-Meshkov instability in a cylindrical converging shock tube

2014 ◽  
Vol 32 (3) ◽  
pp. 343-351 ◽  
Author(s):  
Ting Si ◽  
Zhigang Zhai ◽  
Xisheng Luo
Keyword(s):  
Shock Wave ◽  
Shock Tube ◽  
Test Section ◽  
High Speed ◽  
Mie Scattering ◽  
Gas Bubble ◽  
Reflected Shock ◽  
Gas Cylinder ◽  
Converging Shock Waves ◽  
The Impact

AbstractThe interaction of a cylindrical converging shock wave with an initially perturbed gaseous interface is studied experimentally. The cylindrical converging shock is generated in an ordinary shock tube but with a specially designed test section, in which the incident planar shock wave is directly converted into a cylindrical one. Two kinds of typical initial interfaces involving gas bubble and gas cylinder are employed. A high-speed video camera combined with schlieren or planar Mie scattering photography is utilized to capture the evolution process of flow structures. The distribution of baroclinic vorticity on the interface induced by the cylindrical shock and the reflected shock from the center of convergence results in distinct phenomena. In the gas bubble case, the shock focusing and the jet formation are observed and the turbulent mixing of two fluids is promoted because of the gradually changed shock strength and complex shock structures in the converging part. In the gas cylinder case, a counter-rotating vortex pair is formed after the impact of the converging shock and its rotating direction may be changed when interacting with the reflected shock for a relatively long reflection distance. The variations of the interface displacements and structural dimensions with time are further measured. It is found that these quantities are different from those in the planar counterpart because of the shock curvature, the Mach number effect and the complex shock reflection within the converging shock tube test section. Therefore, the experiments reported here exhibit the great potential of this experimental method in study of the Richtmyer-Meshkov instability induced by converging shock waves.

On the Fragmentation of Drops

1986 ◽  
Vol 108 (1) ◽  
pp. 109-114 ◽  
Author(s):  
M. J. Tan ◽  
S. G. Bankoff
Keyword(s):  
Shock Wave ◽  
Shock Tube ◽  
Weber Number ◽  
High Speed ◽  
Strong Shock ◽  
High Speed Camera ◽  
Pressure Shock ◽  
Critical Weber Number ◽  
Strong Shock Waves

Fragmentation of mercury drops falling through a bubbly aqueous liquid by a pressure shock wave was investigated by means of a shock tube capable of operating at driver pressures up to 3 MPa. The responses to moderately strong shock waves (up to 1.7 MPa) were photographed by a high-speed camera at rates of up to 4400 frames per second. The results show the existence of a critical Weber number, (We)cr = 17, for drop fragmentation. Qualitative characterization of the shock-drop interactions for single mercury drops is provided.

A Shock Wave Parameters Control by its Interaction with the Low Density Gas Layer

2013 ◽  
Vol 8 (4) ◽  
pp. 49-63
Author(s):  
Tatyana Bobarykina ◽  
Vladimir Chirkashenko
Keyword(s):  
Shock Wave ◽  
Numerical Simulations ◽  
Stokes Equations ◽  
Substantial Reduction ◽  
Experimental Studies ◽  
Navier Stokes ◽  
Low Density ◽  
Thermal Layer ◽  
Gas Layer ◽  
The Impact

Wind tunnel research with a supersonic (M = 2) flow (~ 0.1 m in diameter) and the numerical simulations using the two-dimensional Navier – Stokes equations were conducted to substantiate conditions sufficient to substantially reduce a shock wave intensity at its interaction with a layer of low-density gas. The results of experimental studies of the interaction of a shock wave with a gas layer heated by the combustion of hydrogen and air are shown. Numerical simulations resulted in data about the efficiency of the impact thermal layer/shock wave in a wind range of determining parameters. Also the parameters of the flow in the thermal layer providing substantial reduction in the intensity of the shock wave were determined

Erosion and accretion by cratering impacts on rocky and icy bodies: Formulation of scaling relations for high-speed ejecta

2021 ◽  
Author(s):  
Hidenori Genda ◽  
Ryuki Hyodo
Keyword(s):  
Point Source ◽  
Numerical Simulations ◽  
High Speed ◽  
Scaling Law ◽  
Large Body ◽  
Target Material ◽  
Target Surface ◽  
Impact Angle ◽  
Material Strength ◽  
The Impact

<p>Numerous small bodies inevitably lead to cratering impacts on large planetary bodies during planet formation and evolution. As a consequence of these small impacts, a fraction of the target material escapes from the gravity of the large body, and a fraction of the impactor material accretes onto the target surface, depending on the impact velocities and angles. Here, we study the mass of the high-speed ejecta that escapes from the target gravity by cratering impacts when material strength is neglected. We perform a large number of cratering impact simulations onto a planar rocky and icy targets using the smoothed particle hydrodynamics method. We show that the escape mass of the target material obtained from our numerical simulations agrees with the prediction of a scaling law under a point-source assumption when <em>v</em><sub>imp</sub> > ~ 10 <em>v</em><sub>esc</sub>, where <em>v</em><sub>imp</sub> is the impact velocity and <em>v</em><sub>esc</sub> is the escape velocity of the target. However, we find that the point-source scaling law overestimates the escape mass up to a factor of ~ 70, depending on the impact angle, when <em>v</em><sub>imp</sub> < ~ 10 <em>v</em><sub>esc</sub> (Figure 1). Using data obtained from numerical simulations, we derive a new scaling law for the escape mass of the target material

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