Ultrasound (US) neuromodulation, especially sonogenetics, has been demonstrated with potential applications in noninvasive and targeted treatment of various neurological disorders. Despite the ...growing interest, the mechanism for US neuromodulation remains elusive, and the optimal condition for eliciting a neural response with minimal adverse effect has not been identified. Here, we investigate the Piezo1 activation and intracellular calcium response elicited by acoustical streaming induced shear stress under various US exposure conditions. We find that Piezo1 activation and resultant intracellular calcium response depend critically on shear stress amplitude and pulse length of the stimulation. Under the same insonification acoustic energy, we further identify an optical pulse length that leads to maximum cell deformation, Piezo1 activation, and calcium response with minimal injury, confirmed by numerical modeling of Piezo1 channel gating dynamics. Our results provide insight into the mechanism of ultrasonic activation of Piezo1 and highlight the importance of optimizing US exposure conditions in sonogenetics applications.
Presently, hydropower is the world's largest source of renewable energy. Pump Storage Power Plant develops the rapidly because of its effective electricity storage and becomes the most part of ...hydropower. A pump turbine is the vital component of a Pump Storage Power Plant. To obtain efficient generation, safe and stable operation of a pump turbine is pretty important. However, the existence of the hump characteristics of a pump-turbine in pump mode usually leads to operating instability. Thus it is necessary to analyze regions of the hump characteristics. In this research experimental investigation and numerical simulation are employed in order to study the hump characteristics. Unsteady incompressible turbulent flow simulations for the full pump turbine model water domain are performed using the SST k–ω turbulence model. A refinement grid is generated, which allows the corresponding y-plus values of the runner blades, stay vanes and guide vanes less than 2 in average. Calculation results of torque in different discharges as well as head and efficiency in the small discharge regions are in solid agreement with the experimental data. The results show that there are three vortex groups which distribute in the tandem cascade passages when entering the hump region. They are equally located in the circumferential direction in the tandem cascade, and one vortex group is located in two passages of the special stay vane. The strength and range of the vortex group change with different discharges. It also shows certain instability during one runner revolution. This work can provide a basic understanding for the improvement of the stable operation of a pump turbine.
•A refinement grid where average y-plus on blades surface less than 2 is generated.•We simulate the hump characteristics curve according to the experimental data.•Hump characteristic mechanism is analyzed based on unsteady simulations.•The effect of vortex formation in the tandem cascade leads to hump region.
This paper performs numerical investigations on the interaction of shock wave with an ellipsoidal bubble in liquid medium. The governing equations, including the conservative Euler equations and the ...non-conservative transport equation of the liquid volume fraction, are discretized based on the finite volume method. A tangent of hyperbola for interface capturing (THINC) interface reconstruction scheme is employed for the phasic densities and the liquid volume fraction to maintain the interface sharpness. The major-axis (z-axis) of the bubble is parallel to the incident planar shock wave. Different collapse behaviors are observed for two ellipsoidal geometries, named as the disk-like bubble and rugby-like one. Different collapse patterns of an initial ellipsoidal bubble are presented and the manifestation is that the transverse jets pierce the bubble differently, classified as along the centerline, off-centerline along the circumferential direction or along the meridian line if the aspect ratio is varied. For the disk-like bubble, it presents the strongest collapsing process under certain eccentricity, characterized by the highest water hammer pressure under the same incident shock strength. The second sheeting jet is an important factor that leads to the collapse of the remaining bubbles pierced by the first transverse jet.
The hump characteristic is one of the main problems for the stable operation of pump turbines in pump mode.However,traditional methods cannot reflect directly the energy dissipation in the hump ...region.In this paper,3D simulations are carried out using the SST k-ω turbulence model in pump mode under different guide vane openings.The numerical results agree with the experimental data.The entropy production theory is introduced to determine the flow losses in the whole passage,based on the numerical simulation.The variation of entropy production under different guide vane openings is presented.The results show that entropy production appears to be a wave,with peaks under different guide vane openings,which correspond to wave troughs in the external characteristic curves.Entropy production mainly happens in the runner,guide vanes and stay vanes for a pump turbine in pump mode.Finally,entropy production rate distribution in the runner,guide vanes and stay vanes is analyzed for four points under the 18 mm guide vane opening in the hump region.The analysis indicates that the losses of the runner and guide vanes lead to hump characteristics.In addition,the losses mainly occur in the runner inlet near the band and on the suction surface of the blades.In the guide vanes and stay vanes,the losses come from pressure surface of the guide vanes and the wake effects of the vanes.A new insight-entropy production analysis is carried out in this paper in order to find the causes of hump characteristics in a pump turbine,and it could provide some basic theoretical guidance for the loss analysis of hydraulic machinery.
•Shock waves from toroidal bubble collapse is imperative for kidney stone dusting.•Progressively intensified collapse of toroidal bubbles boosts shock wave emission.•The shock waves, not jet impact, ...are vital for cavitation damage in laser lithotripsy.•The leaky Rayleigh waves may contribute to superficial material removal.
Holmium:yttrium–aluminum-garnet (Ho:YAG) laser lithotripsy (LL) has been the treatment of choice for kidney stone disease for more than two decades, yet the mechanisms of action are not completely clear. Besides photothermal ablation, recent evidence suggests that cavitation bubble collapse is pivotal in kidney stone dusting when the Ho:YAG laser operates at low pulse energy (Ep) and high frequency (F). In this work, we perform a comprehensive series of experiments and model-based simulations to dissect the complex physical processes in LL. Under clinically relevant dusting settings (Ep = 0.2 J, F = 20 Hz), our results suggest that majority of the irradiated laser energy (>90 %) is dissipated by heat generation in the fluid surrounding the fiber tip and the irradiated stone surface, while only about 1 % may be consumed for photothermal ablation, and less than 0.7 % is converted into the potential energy at the maximum bubble expansion. We reveal that photothermal ablation is confined locally to the laser irradiation spot, whereas cavitation erosion is most pronounced at a fiber tip-stone surface distance about 0.5 mm where multi foci ring-like damage outside the thermal ablation zone is observed. The cavitation erosion is caused by the progressively intensified collapse of jet-induced toroidal bubble near the stone surface (<100 μm), as a result of Raleigh-Taylor and Richtmyer-Meshkov instabilities. The ensuing shock wave-stone interaction and resultant leaky Rayleigh waves on the stone surface may lead to dynamic fatigue and superficial material removal under repeated bombardments of toroidal bubble collapses during dusting procedures in LL.
This paper performs a numerical study on the interaction of a planar shock wave with a water column embedded with/without a cavity of different sizes at high Weber numbers. The conservative-type ...Euler and non-conservative scalar two-equations representing the transportation of two-phase properties consist of the diffusion interface capture models. The numerical fluxes are computed by the Godunov-type Harten-Lax–van Leer contact Riemann solver coupled with an incremental fifth-order weighted essentially non-oscillatory (WENO) scheme. A third-order total variation diminishing (TVD) Runge–Kutta scheme is used to advance the solution in time. The morphology and dynamical characteristics are analysed qualitatively and quantitatively to demonstrate the breakup mechanism of the water column and formation of transverse jets under different incident shock intensities and embedded-cavity sizes. The jet tip velocities are extracted by analysing the interface evolution. The liquid column is prone to aerodynamic breakup with the formation of micro-mist at later stages instead of liquid evaporation because of the weakly heating effects of the surrounding air. It is numerically confirmed that the liquid-phase pressure will drop below the saturated vapour pressure, and the low pressure can be sustained for a certain time because of the focusing of the expansion wave, which accounts for the cavitation inside the liquid water column. The geometrical parameters of the deformed water column are identified, showing that the centreline width decreases but the transverse height increases nonlinearly with time. The deformation rates are nonlinearly correlated under different Mach numbers. The first transverse jet is found for a water column with an embedded cavity, whereas the water hammer shock and second jet do not occur under the impact of low intensity incident shock waves. The
$x$
-velocity component recorded at the rear stagnation point can remain unchanged for a comparable time after a declined evolution, which indicates that the downstream wall of the shocked water ring somehow moves uniformly. It can be explained that the acceleration of the downstream wall is balanced by the trailing shedding vortex, and this effect is more evident under higher Mach numbers. The increased enstrophy, mainly generated at the interface, demonstrates the competition of the baroclinic effects of the shock wave impact over dilatation.
As the pump turbine tends to be operated with high head and high rotational speed, the study of stability problems becomes more important. The pump turbine usually works at operating conditions where ...the guide vanes experience strong vibrations. However, most traditional studies were carried out based on constant GVO（guide vane opening） simulations. In this work, dynamic analysis on pressure fluctuation in the vaneless region of a pump turbine model was conducted using a dynamic mesh method in turbine mode. 3D unsteady simulations were conducted where GVO was closed and opened by 1° from the initial 18°. Detailed time domain and frequency domain characteristics on pressure fluctuation in the vaneless region under different guide vane rotational states compared with constant GVO simulations were investigated. Results show that, during the guide vanes oscillating process, the low and intermediate frequency components in the vaneless region are significantly different. The amplitudes of pressure fluctuation are higher than those with constant GVO simulations, which agree better with the experimental data. In addition, the pressure fluctuation increases when GVO is opened, and vice versa. It can be concluded that pressure fluctuation in the vaneless region is strongly influenced by the oscillating of the guide vanes.
To investigate the effects of fiber lateral scanning speed across the stone surface (
) and fiber standoff distance (SD) on dusting efficiency during short pulse holmium (Ho): YAG laser lithotripsy ...(LL), pre-soaked BegoStone samples were treated in water using 0.2 J/20 Hz at SD of 0.10~0.50 mm with
in the range of 0~10 mm/s. Bubble dynamics, pressure transients, and stone damage were analyzed. To differentiate photothermal ablation vs. cavitation damage, experiments were repeated in air, or in water with the fiber tip at 0.25 mm proximity from the ureteroscope end to mitigate cavitation damage. At SD = 0.10 mm, the maximum dusting efficiency was produced at
= 3.5 mm/s, resulting in long (17.5 mm), shallow (0.15 mm), and narrow (0.4 mm) troughs. In contrast, at SD = 0.50 mm, the maximum efficiency was produced at
= 0.5 mm/s, with much shorter (2.5 mm), yet deeper (0.35 mm) and wider (1.4 mm), troughs. With the ureteroscope end near the fiber tip, stone damage was significantly reduced in water compared to those produced without the ureteroscope. Under clinically relevant
(1~3 mm/s), dusting at SD = 0.5 mm that promotes cavitation damage may leverage the higher frequency of the laser (e.g., 40 to 120 Hz) and, thus, significantly reduces the procedure time, compared to at SD = 0.1 mm that promotes photothermal ablation. Dusting efficiency during short pulse Ho: YAG LL may be substantially improved by utilizing an optimal combination of
, SD, and frequency.
Supersonic spray combustion is one of the most significant physiochemical processes that occurs in the scramjet propulsion system, and related research can motivate the development of scramjet ...engines. This paper reviews the research on supersonic spray combustion that has been conducted in the past few decades and focuses on the key physiochemical processes and associated fluid physical mechanisms. Supersonic spray combustion involves not only the typical processes during the combustion of liquid fuel, such as atomization, dispersion, evaporation, mixing and ignition, but also complicated interactions among the spray, turbulence, shock waves and chemical reactions in supersonic flows. The interactions commonly affect the combustion performance in terms of ignition, stability and efficiency. The present work outlines the current research status for spray combustion in subsonic flows. Then a brief description of the basic features of supersonic flow and combustion is provided. For the supersonic combustor in the scramjet engine, the research results and challenges regarding supersonic flow and spray in mixing layers and jets are discussed. The stabilization of supersonic spray combustion and the control methods are introduced and summarized. An outline of the effects of shock waves on combustion, and the shock-induced deflagration and detonation is provided as an overview of the research and development progress since shock waves typically occur in supersonic combustors. Finally, the potential challenges and issues that are encountered in the fundamental research, including numerical models and approaches and experimental techniques and databases, and the applications of supersonic spray combustion are highlighted.
•This work provides theoretical solutions to shock reflection off gas-liquid two-phase interface for the fast-slow case.•The shock polar analysis is proposed to obtain the analytical solution of the ...critical angle when the reflection transits from a regular to an irregular type.•The interface deflection angle, pressure ratio across the transmitted shock wave and post-shock velocity of the transmitted shock wave are obtained theoretically, which are identical to the numerical simulation results.
The wave patterns of shock wave interaction with multi-material interface have been studied in the past decades. Interactions between shock waves and interfaces can be classified as slow-fast and fast-slow case depending on the relative acoustic impedance of two mediums as shock passes from one to another. In this paper, the fast-slow case of shock passes from water to air is studied and the refraction wave patterns includes regular and irregular types, which have been identified from previous studies. The analytical solutions are emphasized with the incident shock angle ranging from 0∘ to 90∘ and the shock strength from 0.2 GPa to 5.0 GPa. By applying the Tait equation, the shock relations as well as the Prandtl-Meyer relations in water is obtained, both of which are used to complete the polar diagrams for the incident shock wave, the reflected Prandtl-Meyer fan and the transmitted shock wave for the fast-slow case. This has not yet been reported in previous studies. The critical angle is obtained when the reflection transits from a regular to an irregular type and the inclination angle of the incident shock wave at the interaction point after the reflection is found for irregular reflection. The interface deflection angle, the pressure ratio across the transmitted shock wave and the post-shock velocity of the transmitted shock wave are derived analytically with varying incident shock angles and strengths. Numerical simulations are performed to compare with the analytical solutions and the refraction wave patterns are consistent with the analytical results. The analytical interface deflection angles and transmitted shock angles overlap well with the numerical results.
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