Eulerian–Lagrangian multiscale numerical analysis of multimodal partial shedding dynamics

Dynamics of unsteady compressible cavitating flows associated with the cavity shedding

Numerical investigation of the shock wave propagation in cavitating flow around NACA66 hydrofoil based on a compressible method

Comparative study between turbulence models in unsteady cavitating flow with special emphasis on shock wave propagation

Experience using pressure-based CFD methods for Euler–Euler simulations of cavitating flows

The objective of this article is to investigate the flow structure of the ventilated cavitation around an under-water vehicle. In the experiments, a high-speed camera system is used to observe cavity evolution of the unsteady cavitation flow, the velocity field is measured by the particle image velocimetry technique, and dynamic pressure measurement systems are used to measure pressure fluctuations under different cavitation numbers. We seek to investigate the mechanism of the re-entrant flow and shock wave phenomenon during the cavity evolution. The study concludes that the ventilated cavity is insufficient to overcome the re-entrant jet intrusion and the re-entrant jet moves upstream straightly as well as curvilinearly. Then, the vortex structure rotating clockwise forms on the vehicle surface and the cavity area with low velocity represents the vortex. The re-entrant jet rolls back after the re-entrant jet reaches the front of the cavity. The experimental results also show that the pressure signals at different instants destabilize on the vehicle surface; fluctuant pressure peak is detected at the closure region of the cavity and pressure peak increases as the cavitation number is decreased. Surface pressure fluctuations travel on the vehicle surface from the collapse of cloud cavitation. The variation in shedding frequency for different cavitation numbers is discussed at the end of the article.

Dynamics of the closing of pores at the shock wave front: PMM vol. 43, no. 3, 1979, pp. 511–518

gas ahead of the gaseous driver piston, i . e . , the discharge plasma [1]. Separation of the discharge plasma from the thermal plasma is observed only for initial pressures above 0.05-1 mm Hg, and Mach numbers in air below 30-35, and below 10-15 in argon [2,3]. The use of an electrodeless (inductive) discharge to obtain shock waves, as will be shown below, does not remove this kind of restriction nor does it obviate the difficulty. The existence of appreciable deviations from uniformity and regularityrof the flow in electric shock tubes imposes special requirements for control of the state of the gas behind the generated shock waves, and measurements of the gas temperature distribution are of paramount importance in this regard. In this paper we present results of systematic measurements of plasma temperature distribution behind strong shock waves in air and argon, obtained by three independent methods. A justification is given for the "hydrodynamic" method of measuring temperature in a supersonic plasma stream, as described in [4, 5], based on a comparison with simultaneous spectrographic measurements. A discussion is given of the peculiarities of formation and propagation of shock waves in electrodeless discharge Dlbes~ 1. Description of Equipment and Methods of Measurement. The tests were carried out on the equipment shown schematically in Fig. 1. A 1-pF capacitor, charged to 30 kV, is discharged through an 8turn coil of length 10 era, located at the end of a glass tube of diameter 8.6 era. The period of oscillation of the discharge circuit is 22 gsee, and rupture occurs at pressures of air or argon (usually with addition of, l% hydrogen) in the range 1-10 -s mm Hg. Measurement of electron temperature distribution behind the shock wave was performed by the method in which one uses the relative intensities of two spectral lines of hydrogen (H$ and Ha), the light flux being limited by two slits of width 0.5 mm at the entrance of an ISP-81 spectrograph (chamber with ] = 270 mm at a mean dispersion of about 30 %/ram): Separate measurements of the light as a function of time are carried out by means of two photomultipliers. The reduction of the oscillograms, calibration of the channels, and corn-

The objective of this work is to investigate experimentally controlling cavitating flow over NACA66 (MOD) hydrofoils by means of an active water injection along its suction surface. The continuous water vertically jets out of the chamber inside the hydrofoil through evenly distributed surface holes. Experiments were carried out in cavitation water tunnel, using high-speed visualization technology and the particle image velocimetry (PIV) system to study the sheet/cloud cavity behaviors. We studied the effects of this active control on cavity evolution with four kinds of jet flow at two different jet positions. We analyzed the effect of water injection on the mechanism of the cavitating flow control. The results were all compared with that for the original hydrofoil without jet and show that the active jet can effectively suppress the sheet/cloud cavitation characterized by shrinking the attached cavity size and breaking the large-scaled cloud shedding vortex cavity into small-scaled ones. The optimum effectiveness of cavitation suppression is affected by the jet flow rates and jet positions. The water injection at flow rate coefficient 0.0245 with the jet position of 0.45C reduces the maximum sheet cavity length by 79.4 $$\%$$ and the cavity shedding is diminished completely, which gives the most superior effect of sheet cavitation suppression. The jet blocks the re-entrant jet moving upstream and weakens the power of re-entrant jet and thus restrains the cavitation development effectively and stabilizes the flow field.

Numerical investigation of cavitation vortex dynamics in unsteady cavitating flow with shock wave propagation

The formation of dispersive shock waves in one-dimensional Bose gas represents a limitation of Generalized Hydrodynamics (GHD) due to the coarse-grained nature of the theory. Nevertheless, GHD accurately captures long-wavelength behavior, thus indicating an implicit knowledge of the underlying microscopic physics. Such representations are already known through the Whitham modulation theory, where dispersionless equations describe the evolution of the slowly varying shock wave parameters. Here we study the correspondence between Whitham's approach to the Gross-Pitaevskii equation and GHD in the semiclassical limit and beyond. Our findings enable the recovery of the shock wave solution directly from GHD simulations, which we demonstrate for both zero and finite temperature. Additionally, we study how free expansion protocols affect the shock wave density and their implications for experimental detection. The combined picture of Whitham and GHD lends itself to additional physical interpretation regarding the formation of shock waves. Published by the American Physical Society 2024

Modification of titanium microstructure after propagation of a melting shock wave (SW) generated by a femtosecond laser pulse is investigated experimentally and analyzed using hydrodynamic and atomistic simulations. Scanning and transmission electron microscopy with analysis of microdiffraction is used to determine the microstructure of modified subsurface layers of titanium. We found that two layers are modified beneath the surface. A top surface polycrystalline layer of nanoscale grains is formed from shock-molten material via rapid crystallization. In a deeper subsurface layer, where the shock-induced melting changes into plastic deformation due to attenuation of SW, the grain structure of solid is considerably affected, which results in a grain size distribution differing from that in the intact titanium. Molecular dynamics simulation of single-crystal titanium reveals that the SW front continues to melt even after its temperature drops below the melting curve Tm(P). The enormous shear stress of ∼12 GPa generated in a narrow SW front leads to free slip of atomic planes, collapse of the crystal lattice, and formation of a supercooled metastable melt. Such melt crystallizes in an unloading tail of SW. The mechanical melting ceases after drop in the shear stress giving rise to the shock-induced plastic deformation. The last process triggers a long-term rearrangement of atomic structures in solid. The overall depth of modified layers is limited by SW attenuation to the Hugoniot elastic limit and can reach several micrometers. The obtained results reveal the basic physical mechanisms of surface hardening of metals by ultrashort laser pulses.

This paper proposes a new lattice Boltzmann (LB) method for the study of shock wave propagation in elastic solids. The method, which implements a flux‐corrected transport (FCT) algorithm, contains three stages: collision, streaming, and correction. In the collision stage, distribution functions are updated. In the streaming stage, the distribution functions are shifted between lattice points. Generally, a partial differential equation (PDE) is solved in the streaming stage, and finite element methods are employed to support the use of unstructured meshes in the LB method. The FCT algorithm is used in the correction stage to revise the distribution functions at lattice points, so fluctuations behind shock wave fronts can be eliminated efficiently. In this method, schemes for shock wave reflection at fixed and free boundaries are developed based on the bounce‐back technique. A similar technique is used to treat wave reflection and transmission at material interfaces of composites. Several one‐dimensional examples show that this LB‐FCT method can provide ideal depictions of shock wave propagation in structures, especially composite structures. Copyright © 2006 John Wiley & Sons, Ltd.

This research experimentally examines the influence of viscoelastic dilute water solutions of polyethylene oxide on Venturi cavitation. Variations in solutions are engineered to manipulate the viscoelastic properties that in turn affect cavitation patterns and attributes. The consequences of viscoelasticity and flow conditions on cavitation are quantified using dimensionless numbers, including the elasticity number (El), the Reynolds number (Re), and the pressure ratio (κ). The experiment identifies three distinct cavitation patterns in the solutions, with their transitions being impacted by alterations in El and κ. As El amplifies, the cavitation bubbles expand and get smoother, and the reentrant jet thickens and amplifies. The behavior of cavitation aligns with the model proposed by Zhang et al. [Phys. Fluids 31, 097107 (2019)], suggesting the critical role of the reentrant jet in the shedding of the cavity cluster. The study also substantiates that the reentrant jet intensifies with ascending El or Re. The collective influence of El, Re, and κ is discovered to shape the cavitation length and shedding frequency of cavity clusters. An increased El or a decreased Re reinforces the vorticity and the reentrant jet, which inevitably leads to a reduction in cavitation lengths and an uptick in the shedding frequency. Conversely, a larger El results in a more gradual response of the bubble to pressure alterations and pronounced rebounds, extending the cavitation length.

Shock waves have not previously been used as a treatment modality for lesions in the brain and skull because of the lack of a suitable shock wave source and concerns about safety. Therefore, the authors have performed experiments aimed at developing both a new, compact shock wave generator with a holmium:yttrium-aluminum-garnet (Ho:YAG) laser and a safe method for exposing the surface of the brain to these shock waves. Twenty male Sprague-Dawley rats were used in this study. In 10 rats, a single shock wave was delivered directly to the brain, whereas the protective effect of inserting a 0.7-mm-thick expanded polytetrafluoroethylene (ePTFE) dural substitute between the dura mater and skull before applying the shock wave was investigated in the other 10 rats. Visualizations on shadowgraphy along with pressure measurements were obtained to confirm that the shock wave generator was capable of conveying waves in a limited volume without harmful effects to the target. The attenuation rates of shock waves administered through a 0.7-mm-thick ePTFE dural substitute and a surgical cottonoid were measured to determine which of these materials was suitable for avoiding propagation of the shock wave beyond the target. Using the shock wave generator with the Ho:YAG laser, a localized shock wave (with a maximum overpressure of 50 bar) can be generated from a small device (external diameter 15 mm, weight 20 g). The placement of a 0.7-mm-thick ePTFE dural substitute over the dura mater reduces the overpressure of the shock wave by 96% and eliminates damage to surrounding tissue in the rat brain. These findings indicate possibilities for applying shock waves in various neurosurgical treatments such as cranioplasty, local drug delivery, embolysis, and pain management.

Shock wave formation and acceleration in a high-aspect ratio cross section shock tube were studied experimentally and numerically. The relative importance of geometric effects and diaphragm opening time on shock formation are assessed. The diaphragm opening time was controlled through the use of slit-type (fast opening time) and petal-type (slow opening time) diaphragms. A novel method of fabricating the petal-type diaphragms, which results in a consistent burst pressure and symmetric opening without fragmentation, is presented. High-speed schlieren photography was used to visualize the unsteady propagation of the lead shock wave and trailing gas dynamic structures. Surface-mounted pressure sensors were used to capture the spatial and temporal development of the pressure field. Unsteady Reynolds-Averaged Navier–Stokes simulation predictions using the shear-stress-transport turbulence model are compared to the experimental data. Simulation results are used to explain the presence of high-frequency pressure oscillations observed experimentally in the driver section as well as the cause of the initial acceleration and subsequent rapid decay of shock velocity measured along the top and bottom channel surfaces. A one-dimensional theoretical model predicting the effect of the finite opening time of the diaphragm on the rate of driver depressurization and shock acceleration is proposed. The model removes the large amount of empiricism that accompanies existing models published in the literature. Model accuracy is assessed through comparisons with experiments and simulations. Limitations of and potential improvements in the model are discussed.