Shock Wave Propagation Research Articles

Flow structure and parameter evaluation of conical convergent–divergent nozzle supersonic jet flows

Supersonic gas jets in conical convergent–divergent nozzles are studied numerically using the OpenFOAM rhoCentralFoam solver. The spatiotemporal evolution of the jet flow field is analyzed. The influence of the operating conditions on the flow field is studied parametrically, including the nozzle pressure ratio (NPR), area ratio, and throat position. The behaviors and mechanisms of the double-diamond structure, throat wave, and exit wave are interpreted in detail. The results show that a conical convergent–divergent nozzle always generates shock waves. The throat shock reaches its maximum length during the initial stage, then becomes slightly shorter before becoming stationary, dominated by the exit velocity. Furthermore, it is shown that the jet flow changes from overexpansion to underexpansion with increasing NPR. With an increasing area ratio, the trend is the opposite. The throat position affects the jet divergence angle at the nozzle exit, consequently causing a variation in the core radius of the jet. It is further shown that the double-diamond structure does not always appear. The throat shock angle, exit wave angle, and shear layer width directly affect the shape of the double-diamond structure. The favorable pressure gradient of the nozzle ultimately dominates the changes in the length of the throat wave and exit wave.

Setting up experiments with laser plasma clouds to simulate the generation of quasi-spherical collisionless shock waves in cosmic plasma, based on calculations by the particle (ion) method using a hybrid model

Setting up experiments with laser plasma clouds to simulate the generation of quasi-spherical collisionless shock waves in cosmic plasma, based on calculations by the particle (ion) method using a hybrid model

The Effect of Explosions on the Protective Wall of a Containerized Hydrogen Fuel Cell System

With the development of hydrogen energy, containerized hydrogen fuel cell systems are being used in distributed energy-supply systems. Hydrogen pipelines and electronic equipment of fuel cell containers can trigger hydrogen-explosion accidents. In the present study, Computational Fluid Dynamics (CFD) software was used to calculate the affected areas of hydrogen fuel cell container-explosion accidents with and without protective walls. The protective effects were studied for protective walls at various distances and heights. The results show that strategically placing protective walls can effectively block the propagation of shock waves and flames. However, the protective wall has a limited effect on the reduction of overpressure and temperature behind the wall when the protective wall is insufficiently high. Reflected explosion shock waves and flames will cause damage to the area inside the wall when the protective wall is too close to the container. In this study, a protective wall that is 5 m away from the container and 3 m high can effectively protect the area behind the wall and prevent damage to the container due to the reflection of shock waves and flame. This paper presents a suitable protective wall setting scheme for hydrogen fuel cell containers.

Study on the characteristics of initial shock waves generated by cylindrical charge for underwater explosion

In order to provide a theoretical basis for studying the shock wave propagation and evolution generated by cylindrical charge of near-field underwater explosion, the characteristics of initial shock waves generated by cylindrical charge are studied. First, a new theoretical model for initial shock waves is proposed by the polar curve method. Based on the theoretical model and the simulated results, the influences of incident angle, length-to-diameter ratio and type of charge on the initial shock waves are analysed. Then the experiments of underwater explosion load tests are carried out to verify the theoretical and simulation results. Finally some instructive conclusions are drawn: i) The two-dimensional theoretical model can calculate the initial underwater shock wave pressure and its direction of cylindrical charge through detonation velocity, detonation pressure, explosive density and incident angle, which is provides a theoretical basic for studying the shock wave propagation and evolution studies. By comparing the theoretical results with the numerical results verified by experiments, the maximum error is not more than 9.93%. ii) Increasing the incident angle α 0 will reduce the initial shock wave pressure of cylindrical charge and make its direction deflect towards the material interface. When the incident angle α 0 is in the range of 0 - 10°, increasing the incident angle makes the initial shock wave pressure decrease rapidly as a power function. With the increasing of the incident angle, the attenuation rate of the initial shock wave firstly decreases and then increases when the incident angle α 0 is in the range of 10 - 72°. This phenomenon explains the reason that the axial and radial initial shock wave pressures are much higher than those in other directions after the central initiation of cylindrical charge. iii) According to the geometric relationship, the length-to-diameter ratio of the charge will limit the range of the incident angle. The length-to-diameter ratio will affect the initial shock wave pressure at the same initiation time. The pressure decreases with the increase of the length-to-diameter ratio when the initial shock wave is formed on the cylindrical surface of the charge.

Controllability of shock waves in one-dimensional polariton condensates

In one-dimensional incoherent pumped exciton–polariton condensates, we realize the generation and control of supersonic shock waves. By choosing a suitable initial input wave, we obtain the region of existence of various shock waves as a function of the phase of the initial wave, the coefficient of polariton interaction, the coefficient of the interaction between polariton and reservoir and the condensation rate and intensity of pumping. Using these results, we discuss the effect of different parameters on shock waves composed of two shock waves, and find that the gain and loss will result in a sloping platform between two waves. In addition, we also consider the effect of the non-adiabatic approximation and the diffusion coefficient of the reservoir on the profiles of the shock waves. We find that the non-adiabatic approximation will result in some small oscillations on the uniform background, and the platform between two waves becomes flat; however, the diffusion effect of the reservoir will clear these small oscillations and tilt the platform. Our results may pave the way to control shock waves in an incoherent pumped exciton–polariton system.

(003) New Treatment Approach for Female Sexual Dysfunction by Transvaginal Shockwave Therapy (TVST)

Abstract Introduction Female Sexual Dysfunction (FSD) is a common condition of women especially following menopause. In recent years, energy-based devices (EBD), such as lasers and radio-frequencies, have been marketed for vaginal rejuvenation and FSD. Low-intensity shockwave therapy (LIST) has been introduced as a treatment for male erectile dysfunction and may hold promise for FSD. In women energy has to be delivered to the vaginal wall to manifest its tissue regenerative potential. In this pilot study, we evaluated a specially designed transvaginal probe, which is able to deliver shockwave energy to the vaginal wall and the external genitalia. Objective To evaluate the safety and therapeutic efficacy of LIST, when applied transvaginally for the treatment of FSD and incontinence. We call this approach transvaginal shockwave therapy (TVST). Methods The study was a single-arm, pilot study conducted between February-August 2021. Fifteen female patients aged 45-61 years (mean age: 52.7 years) were recruited and 78.6% of them were post-menopausal. All women presented with sexual dysfunction and 7 of them (46.7%) also reported urinary incontinence. Treatment was performed with the MoreNova system (Hikkonu Ltd., Israel), an electromagnetic low-intensity shockwave generator, using a novel transvaginal probe. Energy flow density was 0.09 mJoule/mm2 and intensity was gradually increased to the maximal tolerable level (1.6-1.8). Each session delivered 400 shockwaves to 6 predefined anatomical areas: the frontal vaginal wall (11 and 1 o' clock positions), the labia minora and majora (left, right). Patients underwent a total of 6 treatment sessions over the course of three weeks (2 per week). Statistical analysis was performed using student’s t-test (paired, one-tail, significance at p<0.05). Results Sexual dysfunction was assessed with the Female Sexual Function Index (FSFI) and incontinence with the ICIQ-UI Short-Form. Evaluations were performed at baseline and at 1 and 3 month post treatment. One patient aborted (for reasons unrelated to treatment) and was excluded from analysis. No patient complained of pain or discomfort during or after treatment and no side-effects were reported. Mean total FSFI score at baseline was 13.93, increased significantly to 22.66 at 1 month and slightly decreased to 20.88 at 3 months post treatment. All domains of the FSFI were significantly improved both at 1 and 3 month follow-ups compared to baseline. Percentage of patients achieving minimally clinically important differences (MCID) of the FSFI domains (Krychman et al, 2018) was also estimated. It was found that at 1 month follow-up more than 70% of patients achieved improvements exceeding the MCID in the pain, orgasm and lubrication FSFI domains. At 3 months, this significant improvement was sustained in the pain and orgasm domains. Mean ICIQ-UI was 3,53 at baseline and decreased to 3 at 3 months and 2.28 at 3 months post treatment. Conclusions There is a great need for new, effective and safe therapies for FSD. Quite often FSD is not reported by the patients and disregarded by physicians who are not involved in sexual medicine. Robust scientific evidence as to the efficacy of EBDs is also lacking. In our study, we found that TVST is safe and very well-tolerated by the patients. It improved FSD up to 3 months post treatment and this improvement was evident in all domains of the FSFI. There was also improvement in incontinence, as documented by the ICIQ-UI index. This observation surely warrants further investigation. Our data, although limited, underline the need for large scale, controlled studies ideally targeting different genito-urinary conditions. Disclosure Yes, this is sponsored by industry/sponsor: Direx Clarification Industry funding only - investigator initiated and executed study.

Dynamic Process and Damage Evaluation Subject to Explosion Consequences Resulting from a LPG Tank Trailer Accident

The involvement of liquefied petroleum gas (LPG), which is highly combustible and explosive, greatly increases risk in road transport. A 3D numerical model was conducted in FLACS, which depicts the dynamic process and variation of combined effects along the multi-directions of LPG explosion under an actual case. With the simulation of scenarios, power-law explosion and fireball models were used to reproduce the results, and the dynamic evolution of specific parameters during the LPG explosion process was analyzed. The results reveal that the LPG explosion’s expansion around the expressway moved along the spaces between obstacles, while conditions at the site of the accident had an enhancement effect on LPG/air mixture accumulation. The propagation trajectory of the shock wave in the horizontal direction presented a regular circle within 623.73 ms, and the overpressure was enough to lead to extensive damage to surrounding structures. Further, shock wave-driven overpressure brought hazards to buildings further afield with multiple peak values. The influence of the LPG explosive fireball evolution is significantly reflected in the injury range of the heat flux; the maximum diameter of the on-site fireball eventually extended to 148.19 m. In addition, the physical effect indicated that the turbulence intensity induced by the surrounding buildings in the accident site significantly promoted the interaction between the shock wave and flame propagation. This research proposes a detailed analysis of damage coupling characteristics caused by an LPG tank trailer explosion integrated with a FLACS-mirrored model, which are useful for blast-resistant design and disposal planning under similar accidental circumstances.

Numerical investigation on jet penetration capacity of hypervelocity shaped charge in underwater explosion

Shaped charges are widely employed in both military and civilian applications owing to their strong penetration capacities, such as weapon production, oil exploitation, mining, and tunneling. To augment the armor-breaking capability of a shaped charge, it is of utmost significance to enhance the velocity of the metal jet. Therefore, the hypervelocity shaped charge (HSC) has been proposed as a potential solution. Compared with ordinary shaped charges, HSCs can cause severer damage to the target owing to the faster velocity of its jet head. The Eulerian Finite Element Method (EFEM) is developed to build the axisymmetric numerical model, and it can simulate shockwave propagation, jet penetration, and target destruction. The model is validated by the experiments, and the convergence analysis is also performed. And the fundamental characteristics of HSC in underwater explosions including the metal jet and shockwave are investigated. Subsequently, the HSCs with the different liner truncation heights HL and liner materials are simulated to obtain the optimal parameter (range) for penetration capacity. Analyzing the numerical results, when 8mm≤HL≤13mm or the liner is made of aluminum, the metal jet generated by HSC will have a greater penetration capacity to the steel plate through the comparison of the crevasse diameter and residual velocity.

Self-ignition and flow characteristics of pressurized hydrogen in Y-shaped tubes

The geometrical diversion of combustible gas molecules notably affects their self-ignition in high-pressure tubes. This study investigates the propagation of shock waves and flame induced by a sudden pressure release of hydrogen in various Y-shaped tubes. The impact of the initial burst pressure, downstream tube length, and bifurcation angle (60°, 120°) were analyzed by recording the pressure signals, photoelectric curves, and jet fire evolution. The results showed that the gas diversion caused by the Y-shaped structure significantly reduces the maximum overpressure of the hydrogen jet, the intensity, and the velocity of the leading shock wave. Also, it was indicated that increasing the Y-shaped tube's length downstream of the bifurcation point could enhance the strength of leading and reflected shock waves after the Y-bifurcation, making self-ignition more likely to happen. Applying a 60°-bifurcation angle could create stronger leading and reflected shock waves during the propagation downstream of the bifurcation point, while a 120°-bifurcation angle could make a more substantial reflected shock wave propagating upstream. It leads to the re-ignition downstream of the bifurcation in the 60°-bifurcation tube after the flame quenching and stronger far-field jet fire outside the tube.

Exceptionally bright optical emission from a rare and distant gamma-ray burst

Long $\rm \gamma$-ray bursts (GRBs) are produced by the dissipation of ultra-relativistic jets launched by newly-born black holes after the collapse of massive stars. Right after the luminous and highly variable $\gamma$-ray emission, the multi-wavelength afterglow is released by the external dissipation of the jet in circumburst medium. We report the discovery of a very bright ($\rm \sim 10$ mag) optical emission $\rm \sim 28$ s after the explosion of the extremely luminous and energetic GRB 210619B located at redshift 1.937. Early multi-filter observations allowed us to witness the end of the shock wave propagation into the GRB ejecta. We observed the spectral transition from a bright reverse to the forward shock emission, demonstrating that the early and late GRB multi-wavelength emission is originated from a very narrow jet propagating into an unusually rarefied interstellar medium. We also find evidence of an additional component of radiation, coming from the jet wings which is able explain the uncorrelated optical/X-ray emission.

Modeling and simulation of laser shock waves in elasto-plastic polycrystalline microstructures

We study the propagation of elasto-plastic shockwaves induced by high power laser impacts in 2D polycrystalline metallic alloys in order to investigate the influence of the material microstructure on the fields of plastic strain and subsequent residual stresses. Implementing a visco-plastic constitutive relation at the grain scale accounting for two dislocation slip systems into a finite volume numerical scheme, simulations on single crystal specimens with different lattice orientations show that plastic strain is concentrated in narrow bands originating at the edges of the laser impact and parallel to the slip planes. In the case of polycrystalline microstructures composed of randomly oriented grains, it is found that the microstructure morphology is the origin of a heterogeneous distribution of the residual plastic strain and stress fields, which thus departs from the residual stress fields usually modeled when the microstructure is not accounted for. To account for the random character of polycrystal microstructures, we perform a statistical analysis of the mechanical fields over a large number of microstructures to quantify the dispersion of the results. It is found that even though the residual stresses induced by a laser impact are in compression on average at the center of the laser impact, some realizations of the microstructures can lead to localized concentrations of less compressive, or even tensile, residual stresses at the surface, thus probably reducing the fatigue resistance of the shocked material.

Molecular Dynamics Simulation of Shock Wave Propagation in Aluminum Single Crystal

The characteristics of shock wave propagation in aluminum single crystal are simulated by using the molecular dynamics (MD) method based on the embedded atom method (EAM) potential function. The structure of the shock front and the Hugonoit relation are obtained. The simulated results show that a two-wave structure exists in the aluminum single crystal for the particle velocity bellower than 2 km/s and the velocity of the elastic wave increases slightly with the shock loading. While only plastic wave exists in the aluminum single crystal for the particle velocity higher than 2 km/s and the width of the shock front decreases by exponent with the normal stress. The MD simulation results are basically consistent with the experimental results.

Propagation of shock waves in a non-ideal gas with dust particles in an interstellar medium

Propagation of shock waves in a non-ideal gas with dust particles in an interstellar medium

Benchmarks of generalized hydrodynamics for one-dimensional Bose gases

The results of benchmarks of the recent theory of generalized hydrodynamics (GHD) in the context of the dynamics of the 1D Bose gas described by the Lieb-Liniger model are reported. Through comparisons against several alternative, well-established computational approaches, the range of applicability of GHD in some of the most challenging out-of-equilibrium scenarios, such as propagation of quantum shock waves and collisional relaxation, is verified and validated and, additionally, some of the methods limitations are pointed out.

Study on the liquid jet and shock wave produced by a near-wall cavitation bubble containing a small amount of non-condensable gas

The liquid jet and shock wave produced by a near-wall cavitation bubble are two major reasons resulting in material-wall damage. To better understand the destructive mechanism, the complete process of action of the multi-cycle cavitation bubble collapsing on the nearby wall with the effect of non-condensable gas under different stand-off distances was numerically investigated. For this purpose, a fully compressible solver is further developed with the implementation of a modified phase-change model. Validations were conducted by comparing the numerical results with the experimental data. Furthermore, the high-pressure zones on the wall induced by the shock wave and liquid jet are carefully analyzed. Numerical results reveal that the bubble behavior, shock wave propagation, and liquid jet types are highly associated with the stand-off distance. Finally, the potential material-wall damage is estimated by using the pressure impulse, and the relationship between the pressure impulse at the central point and the stand-off distance is quantitatively analyzed. It is found two pressure impulse peaks are at the central point.

Influence of equivalence ratio and H2 blended ratio on explosion propagation characteristics of DME/H2 blended gas in closed narrow space

To reveal the explosion risk and propagation law of dimethyl ether (DME)/hydrogen (H2) blended gas, the explosion propagation characteristics of DME/H2 blended gas under different equivalence ratio (Φ) and hydrogen blended ratio (λ) was investigated based on experimental research and theoretical analysis. The results show that the peak overpressure (Pp), the peak pressure rise rate (dP/dt)p and the peak shock wave propagation velocity (Vp) show an increasing and then decreasing trend with the increase of Φ, and reach the maximum at Φ = 1.0. The effect of a little addition of H2 on the explosion hazards of blended gas is small, but when λ > 10%, the explosion hazards increase significantly. The magnitude of increase of Pp, (dP/dt)p and Vp is different with the increase of λ. Compared with the enhancement effect on Pp and (dP/dt)p, the enhancement effect on Vp is more obvious with the continuous blend of H2. Comprehensive analysis of the thermodynamic and chemical kinetic parameters of H2, the chemical kinetic parameters of H2 play a dominant role in the explosion risk of hydrogen-blended gases.

Investigation of the formation and evolution of over-tip shock waves in the pressure-driven tip leakage flow by time-resolved schlieren visualization

Time-resolved schlieren visualization and transonic wind tunnel are used to investigate tip leakage flows (TLFs) over several generic blade tip models. Focus is on the generation and evolution of the over-tip shock waves in the clearance region. A multi-cutoff superposition technique is developed to improve the schlieren system for better visualization. Unsteady flow structures, such as over-tip shock oscillation, shear-layer flapping, and vortex shedding, are revealed by Fourier analysis and dynamic mode decomposition. To predict the generation and decaying of over-tip shocks, a simplified model is proposed by analogizing the shock system to be an N-shaped sawtooth wave. The results show that (1) the proposed model is able to capture the main features of the generation and decaying of over-tip shock waves. The processes of shock generation, decaying, and fading-out are dominated by the mean background flow, the shock state, and the flow fluctuations, respectively. Adding extra coming flow fluctuations can be an efficient way to control the evolution of over-tip shock system. (2) The shock-oscillating frequency is kept the same with the shear-layer flapping, and shock waves with a given oscillating frequency range is constrained to a specific position range. This is termed the “lock-in effect,” which is also observed in TLFs over contoured blade tips. The non-uniformity generation and the nonlinear propagation of shock waves are responsible for this effect. Constrained by this effect, the evolution of over-tip shock waves is separated into four discrete phases. Thus, this effect can be applied for the control of TLFs.

Poster Session 1

Although the shock wave propagation in the dusty gas medium is widely used in research, astrophysics, military, and industrial applications, the shock wave in a self-gravitating mixture of van der Waals gas and a pseudo-fluid of inert solid particles in a rotating medium, is not well understood. In the present paper, the strong exponential shock wave propagation in a self-gravitating mixture of non-ideal gas and a pseudo-fluid of small solid particles is modelled for unsteady adiabatic and isothermal flows in a rotating medium. In our model, the solid particles are considered as chemically inert pseudo-fluid, and the equilibrium flow conditions hold in the entire flow field region. The similarity solutions are derived for isothermal and adiabatic flows. The vorticity vector components, and isothermal and adiabatic compressibility's are also taken into account. It is shown that the zero-temperature gradient supposition brings the reflective changes in pressure, axial vorticity vector, density, and compressibility distributions in contrast to the adiabatic flow. The shock strength decreases, and the compressibility increases due to the zero-temperature gradient consideration. Also, the effects of the problem parameters on shock waves and the distributions of the flow variables velocity, density, etc., are discussed in detail. It is remarkable to note that due to the consideration of a self-gravitating mixture or with an increase in the ratio of the density of solid particles to the initial density of the gas, the shock strength increases; whereas due to the consideration of non-idealness of the gas or rotating medium the shock strength decreases.

On the propagation and interaction of ion-acoustic solitary, periodic, shock, and breather waves in a non-Maxwellian electron–positron–ion magnetoplasma

This investigation analyzes the propagation of nonlinear ion-acoustic waves (IAWs) in an unmagnetized, collisionless plasma composed of inertial positive ions and inertialess Maxwellian positrons as well as the inertialess non-Maxwellian electrons that obey (r, q)-distribution. To observe the impact of particle trapping on the nonlinear IAWs in an electron–positron–ion plasma, the Korteweg–De Vries (KdV) and modified KdV (mKdV) equations are derived using a reductive perturbation method. In the distribution function, the spectral parameters (r, q) put up their contribution to the flatness and high-energy tails, respectively. An important aspect of this investigation is the determination of well-known quasi-periodic solutions, multi-soliton solutions, breathers, and shocks under the variation of different physical parameters, especially spectral indices (r, q). Finally, the interaction of solitons is also presented for discussion of the complete profile. In addition, a detailed comparison, especially in a periodic wave, is made between the generalized (r, q)-distribution and the limiting cases of Kappa and Maxwellian distributions. The results presented in this study contribute to a better understanding of the characteristics of both high- and low-energy parts of the electron distribution function as well as the formation of periodic, soliton, multi-soliton, breathers, and shocks in space and astrophysical plasmas.

Baroclinic interaction of forced shock waves with random thermal gradients

Density gradients aligned at an angle to pressure gradients result in baroclinic torque in fluid flows, generating vorticity. In this work, we study the vorticity generated by the baroclinic torque exerted by the interaction of pressure jumps across random two-dimensional shock waves with density gradients. A field of random two-dimensional shock waves has acoustic spectral energy scaling as Êk∼ε2/3ℓ−1/3k−2, where k is the wavenumber, ε is the energy dissipation, and ℓ is the integral length scale of the field. Since the acoustic energy is broadband, pressure and velocity gradients exist in a wide range of length scales. We study the interaction of these broadband gradients with isobaric thermal gradients localized at a length scale in the spectral space. We show that the method of generating shock waves or injection of wave energy in the system governs the baroclinic interactions. For stochastically forced shock waves, baroclinic terms are negligible. Broadband vorticity with energy at least two orders of magnitude smaller is generated due to continuous variation in curvature of shock waves caused by stochastic forcing. On the other hand, shock waves maintained by energy rescaling result in the generation of coherent vorticity. We also discuss the relative magnitude of the baroclinic torque generated due to total density gradients compared to the one generated due to non-isentropic density gradients within the shock waves interacting with the pressure gradients.