Water Hammer Shock Research Articles

Investigations on the shock wave induced by collapse of a toroidal bubble.

When bubbles collapse near a wall, they typically experience an asymmetric deformation. This collapse leads to the creation of a jet that strikes the bubble interface, causing the formation of a toroidal bubble and the subsequent release of a water-hammer shock. In this study, we present a systematic analysis of the collapse of a toroidal bubble in an open field or adjacent to a flat wall using high-fidelity numerical simulation. To maintain the sharpness of the interface, we employ the interface compression technique and the boundary variation diminishing approach within the two-phase model. Our findings demonstrate that shock waves emitted from the toroidal bubble consistently propagate toward the central axis of the torus, resulting in significant pressure shocks along the axis, similar to the water-hammer shock formed during the collapse of a spherical bubble. In contrast, weak pressure waves are generated in the transverse directions, leading to relatively weaker pressure peaks. Furthermore, the wall-pressure peak induced by the toroidal bubble is approximately three times higher than that induced by the spherical bubble. Based on the directional characteristics of pressure wave propagation from collapsing toroidal bubbles, toroidal-shaped pressure vessels can be designed as buoyancy materials for deep submersibles. This design enables the focused release of energy in a specific direction, effectively minimizing the destructive chain reaction caused by the implosion.

Introducing a Novel Innovative Technique for the Recording and Interpretation of Dynamic Coronary Angiography.

In the study of coronary artery disease (CAD), the mechanism of plaque formation and development is still an important subject for investigation. A limitation of current coronary angiography (CAG) is that it can only show static images of the narrowing of arterial channels without identifying the mechanism of the disease or predicting its progression or regression. To address this limitation, the CAG technique has been modified. The new approach emphasizes identifying and analyzing blood flow patterns, employing methodologies akin to those used by hydraulic engineers for fluid or gas movement through domestic or industrial pipes and pumps. With the new technique, various flow patterns and arterial phenomena-such as laminar, turbulent, antegrade, retrograde, and recirculating flow and potentially water hammer shock and vortex formation-are identified, recorded, and classified. These phenomena are then correlated with the presence of lesions at different locations within the coronary vasculature. The formation and growth of these lesions are explained from the perspective of fluid mechanics. As the pathophysiology of CAD and other cardiovascular conditions becomes clearer, new medical, surgical, and interventional treatments could be developed to reverse abnormal coronary flow dynamics and restore laminar flow, leading to improved clinical outcomes.

Compressible multicomponent flow simulations and data-driven modeling of high-speed liquid droplet impingement

Accurate prediction of the force exerted on a droplet during high-speed liquid droplet impingement (LDI) is challenging yet important for the safety management of nuclear/fossil power plants. This paper describes compressible multicomponent flow simulations and data-driven modeling of high-speed LDI. The compressible multicomponent flow simulations are conducted for various impact Mach numbers ranging from Ma = 0.045 to 0.077. Whereas the peak force associated with the water hammer shock exhibits dependency on the impact Mach number, a self-similar structure for the pressure field within the small region about the impact plane is observed during high-speed LDI. An important observation is that the nondimensional mass-averaged droplet velocity does not vary with the impact Mach number. Finally, a data-driven LPP approach is presented to obtain fast and highly realistic simulations of high-speed LDI.

Time-dependent force in high-speed liquid droplet impacting on a wet wall

Recent research (Fujisawa, 2022a) has shown that the time-dependent force exerted on a droplet during high-speed [O (100 m/s)] impact on a planar rigid wall is quite different from that of low-speed [O (1 m/s)] impact case owing to the compressibility of the droplet. Here, we consider a more general case of a high-speed liquid droplet impacting a wall where a liquid film is present on the wall surface. Three-component Euler simulations were performed to determine the characteristics of the time-dependent force exerted on the droplet during high-speed liquid droplet impact on a planar rigid wet wall. Several initial liquid film thicknesses were considered. The strength of the force exerted on the droplet decreases in magnitude as the liquid film thickness increases, whereas the total force increases with increasing liquid film thickness owing to the presence of a water hammer shock that is reflected inside the liquid film.

Questions on the Genesis and Growth of Coronary Lesions and their Answers Based on Fluid Mechanics Engineering: A New Dynamic Angiography Analysis

In the continuing debate regarding the mechanism of atherosclerotic plaque formation in arteries, one question remains unanswered: While all arteries in a patient are exposed to the same systemic risk factors (hypertension, diabetes, aging, nicotine of cigarettes, etc.), why do plaques frequently present in the coronary arteries, and to a lesser extent in the arteries of the lower extremities, and still less in the carotid or renal arteries? Over the past five years, in order to find an answer to the above question, there has been a radical shift in our research strategy: The principles of fluid dynamics in industrial and domestic pipes/pipelines were employed to decipher changes in the cardiovascular system. The types of flow under investigation included laminar, entrance, turbulent, and helical flows in systole and diastole, as well as the interface between antegrade and retrograde flows resulting in water hammer shock and cavitation phenomena. We aim to highlight the similarities and differences among flow types in arteries and pipes and apply the same methodologies to study the formation, growth, and rupture of coronary plaques leading to inactive and active clinical syndromes and the beneficial mechanism of percutaneous coronary interventions (PCI). In this article, we list the questions and the answers based on the primary data of several completed studies and the preliminary results of ongoing projects from a fluid mechanics perspective. The angiographic coronary images of recirculation flow, vortex formation, collision, hammer water shock, and cavitation will be showcased in detail, and their videos in slow motion are uploaded in the addendum for further in-depth review.

Effect of impact velocity on time-dependent force and droplet pressure in high-speed liquid droplet impingement

In this study, the effect of the impact velocity of a droplet on the time-dependent force exerted on the droplet and droplet pressure during high-speed [O (100 m/s)] liquid droplet impingement (LDI) on a planar rigid wall is numerically investigated. The force exerted on the droplet and droplet pressures are computed as a function of time, and its frequency spectrum is analyzed to explain the physical mechanisms that occur during high-speed LDI. The results show that high-speed LDI involves the formation of a water hammer shock and its reflection on the free surface of the droplet and wall, resulting in sustained reverberation inside the droplet. Therefore, the force curve shows oscillatory behavior and is quite different from that of the low-speed [O (1 m/s)] impact case. Finally, the force and the droplet pressure are computed for various impact velocities of the droplet.

Abstract 12211: Water Hammer Shock Causing Rupture Of Vulnerable Cap Of Culprit Lesions In Acute Coronary Syndrome: An Angiographic And Machine Learning Analysis

Introduction: Acute coronary syndrome (ACS) is caused by rupture of coronary plaques. What triggers these ruptures? Hypothesis: In the field of hydraulics, in a setting of a tank and draining pipe, if the valve at the distal end of the pipe is open, the fluid flows normally. If the valve closes abruptly, the flow next to the valve stops. However the fluid from the tank continues to flow forward and can collide with the distal stationary fluid. This is called water hammer shock. Could the same event happen in coronary arteries? The contraction of the left ventricle (LV) is similar to the abrupt closure of a valve, stopping the myocardial capillary flow. Could the systolic LV contraction trigger water hammer shock? Methods: Angiograms with culprit lesions of ACS (recorded at 15 images/second or 0.06 second per image) were reviewed. The first image was of the artery completely filled with contrast. The subsequent images showed the blood in white color blood moving in over a background of black contrast. The normal flow was laminar. When there was retrograde on top of turbulent flow, this was evidence of a collision between antegrade and retrograde flow (or water hammer shock). The measurements by visual angiographic evaluation and by Machine Learning (ML) included (1) the duration and (2) size of coronary segment with turbulence. The ML program had 2 models (build on Python). Model 1 was built based on U-net and Densenet-121 for vessel segmentation. Model 2 was used for classification of flow. The model 2 was trained based on the convolutional neural network. Results: Angiograms of 20 ACS patients showed laminar flow (90%) in diastole. The flow became turbulent during systole with retrograde flow. The area of collision or water hammer shock showed diffuse coarse mixing of black (contrast) and white (blood). The presence of turbulence matched the location of 85% of ruptured plaques. The duration of turbulence lasted 80% of systole. Special protocols were used successfully to train AI to recognize the lesions, retrograde and turbulent flow. Conclusions: With the new angiographic technique, detailed images of water hammer shock matched the location of ruptured plaques in ACS patients. These results may help to understand the genesis and offer precise prevention and treatment for ACS

Abstract 11177: Uncontrolled Systolic Hypertension Exaggerates the Effect of Water Hammer Shock from a Retrograde Direction While Diastolic Hypertension Aggravates the Injury from an Antegrade Direction: New Mechanism of Coronary Artery Disease by Angiographic and Machine Learning Investigation

Introduction: Hypertension (HTN) is a strong risk factor of coronary artery disease. Hypothesis: Based on the damages induced by flow abnormalities in pipes, our research is built on the hypothesis that flow disturbances start the atherosclerotic process. Our strategy is to use today’s practice of fluid mechanics to unlock the mechanism of HTN on coronary plaques. Methods: All patients with uncontrolled HTN and unstable angina underwent coronary angiography and were selected if they had 1 or 2 moderate lesions. At first. contrast was injected until the index artery was completely opacified. As the injection stopped, the blood moved in and displaced the contrast. The movements and interactions of the blood flow in white color above a black background could be clearly analyzed. At the same time, Artificial Intelligence (Machine Learning (ML algorithms) program had 2 models built on Python. Model 1 was based on U-net and Densenet-121 for vessel segmentation. Model 2 was used for classification and movement of flow. Model 2 was trained based on the convolutional neural network. The main measurements were the types, durations and directions of flows. Results: 20 patients were enrolled. 80% of lesions happened at the mid right coronary artery, near the bifurcation of the left anterior descending artery and diagonal, and of the circumflex artery and obtuse marginal. At the locations of lesions, 100% patients had turbulence caused by collision of the antegrade against the retrograde flow (water hammer shock). If there was excessive diastolic HTN >100mmHg, the duration of retrograde flow was short (<0.18 sec) and 75% turbulence happened DISTAL to the collision/bifurcation site. It happened due to higher gradient from proximal to distal. In severe systolic HTN, the duration of retrograde flow was longer (> 0.30 sec) and 80% turbulence happened PROXIMAL to the collision/bifurcation site due to higher gradient from distal to proximal. Conclusions: Uncontrolled diastolic HTN exaggerated the strength of antegrade flow and turbulence DISTAL to the collision/bifurcation site while uncontrolled systolic HTN intensified the retrograde flow and turbulence PROXIMAL to the collision/bifurcation site. Both inflicted damage on the intima and started the atheroslerotic process.

Numerical study of the shock wave and pressure induced by single bubble collapse near planar solid wall

Bubble collapse is one of the leading causes for the cavitation erosion of submerged structures. For better understanding of the destructive mechanism of cavitation, high-fidelity simulation is performed to simulate the complete process of single bubble collapse near a planar solid wall. The wave propagation method with the approximate Riemann solver Harten Lax and van Leer Contact is adopted to solve the compressible two-phase five-equation model. We implement fifth-order weighted essentially non-oscillatory scheme with the block-structured adaptive mesh method to resolve shock waves and moving interface with high-resolution. We simulate single bubble collapsing in free-field to validate the present numerical methods and solver. Our results (e.g., averaged bubble-interior pressure and the radius variation) are found in excellent agreement with the theoretical Keller–Miksis solutions. In this study, the shock wave transmitted inside the bubble and the water-hammer shock formed in the liquid are under quantitative investigation. Numerical results reveal that the interactions between the shock wave and bubble interface give rise to peak pressures of liquid phase, and the initial stand-off distances have important influence on shock wave pattern, wall peak pressure, and bubble dynamics.

Studying the Effect of Water Hammer Shock Wave on Composite Repaired Patches Based on ASME PCC-2

Pipelines are identified as one of the most important elements in the transmission of energy worldwide, and hence, their maintenance is of great importance. Accordingly, many standards have been developed to maintain these pipelines in services, such as ASME B31G and ASME PCC2. In recent years, composite patches are increasingly utilized to repair damaged areas Therefore, there are many studies carried out on this repair system. However, the behavior of the patches and repaired pipes has rarely been studied under dynamic pressures and water hammer phenomenon conditions. The main objective of this paper is to study the effect of the water hammer phenomenon on the damaged area of the steel pipe. Moreover, the behavior of the composite patch, which was used for repairing, after the passage of the pressure wave is studied. Furthermore, the effect of strain rates on composite patch damage is investigated by a specific VUMAT subroutine in the numerical model. It was found that despite the good resistance of the steel pipe in the damaged area, the composite patch is very vulnerable and fails after the water hammer shock wave. Therefore, it is recommended that for all pipelines where there is a risk of water hammer impact, repaired patches, based on ASME PCC2, should be re-examined and restored.

Curved surface effect on high-speed droplet impingement

Abstract

Experimental and empirical study of large transverse deformation of triangular plates subjected to water hammer shock loading

In this paper, the dynamic plastic response of isosceles triangular plates under hydrodynamic loads was investigated experimentally using a drop hammer machine. To do this, a series of experimental tests were carried out on mild steel triangular plates with different thicknesses to bring insight into the effect of geometry and mechanical properties of the plate on the deformation of specimens, which were impacted by a piston-induced pressure wave inside a water tube. The effects of various impact loads originated from different drop hammer standoff distances, and hammer weights concerning variations of deflection of the center of mass were described. The experimental results were presented in terms of deflection of the center of mass of the plates and deflection profiles. The experimental results showed that the plate with lower thickness experienced higher deflection-to-thickness ratio. An empirical model was also proposed based on new dimensionless numbers for triangular plates in order to predict the ratio of deflection of the center of mass to thickness. The dimensionless numbers considered the effects of plate geometry, hydrodynamic applied load, and mechanical properties of materials. Comparison between the experimental results and empirical predictions demonstrated that the suggested model is accurate enough to predict of the response of isosceles triangular plates under hydrodynamic loads.

Impingement of high-speed cylindrical droplets embedded with an air/vapour cavity on a rigid wall: numerical analysis

The high-speed impingement of hollow droplets embedded with a cavity has fundamental applications in various scenarios, such as in spray coating and biomedical engineering. The impingement dynamics is modulated by the wrapping medium, different from that of denser solid droplets. With air and vapour cavities, the impingement of two kinds of hollow cylindrical droplets is simulated in the present study to investigate the morphology and physical mechanisms regarding droplet and cavity dynamics. The compressible two-phase Eulerian model is used to couple with the phase transition procedure. The results detail the evolution of droplets and collapsing dynamics of the two kinds of cavities. Processes are captured in which the impinging water-hammer shock wave interacts with the cavity, and vertical liquid jets are induced to impact the embedded cavity. For the case of the air cavity, a transmitted shock wave is formed and propagates inside the cavity. The air cavities are compressively deformed and broken into a series of small cavities. Subsequently, a range of intermittent collapsing compression wavelets are generated due to the interface collapse driven by local jets. As for the vapour cavity in the saturated state, initially, once it is impacted by the impinging shock wave, it gradually shrinks accompanied by local condensation but without generation of transmitted waves. Following the first interaction between the lower and upper surfaces of the cavity, the vapour cavity undergoes continuous condensation and collapse with repeated interface fusion. The vapour cavity finally turns into liquid water blended into the surroundings, and the strong collapsing shock waves are expanded inside the droplet. The radius ratios and initial impinging speeds are chosen to analyse the variation of the collapsing time, maximum collapsing pressure and mean pressure on the rigid wall. The pressure withstood by the wall due to the collapsing cavity increases with the initial size of the cavity and initial impinging speed. The maximum local pressures in the entire fluids and the mean pressure on the wall during the collapsing of the vapour cavities are higher than those for the air cavities.

Simulation of high-speed droplet impact against a dry/wet rigid wall for understanding the mechanism of liquid jet cleaning

Physical cleaning techniques are of great concern to remove particulate contamination because of their low environmental impact. One of the promising candidates is based on water jets that often involve fission into droplet fragments. Particle removal is believed to be achieved by droplet-impact-induced wall shear flow. Here, we simulate a high-speed droplet impact on a dry/wet rigid wall to investigate the wall shear flow as well as water hammer after the impact. The problem is modeled by the axisymmetric compressible Navier–Stokes equations and solved by a finite volume method that can capture both shocks and material interface. As an example, we consider the impact of a spherical water droplet (200 µm in diameter) at velocity from 30 to 50 m/s against a dry/wet rigid wall. In our simulation, we can reproduce both acoustic and hydrodynamic events. In the dry wall case, the strong wall shear appears near the moving contact line at the wetted surface. On the other hand, once the wall is covered with the liquid film, the wall shear stress gets weaker as the film thickness increases—a similar trend holds for the water-hammer shock loading at the wall. According to the simulated base flow, we compute hydrodynamic force acting on small particles that are assumed to be attached at the wall, in a one-way-coupling manner. The hydrodynamic force acting on the particles is estimated under Stokes’ assumption and compared to particle adhesion of van der Waals type, enabling us to derive a simple criterion of the particle removal.

Numerical study of a planar shock interacting with a cylindrical water column embedded with an air cavity

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.

Design of Reverse Flow Blockage Device for Reactor Coolant Pumps

Future Sodium cooled Fast Reactors (SFR) in India, are being designed with 3 Reactor Coolant Pumps (RCP). Reactor Coolant Pumps (RCP) are used in pumping the coolant fluid through the reactor core. As the RCPs are operating in parallel, failure of one pump will result in a significant portion of the pumped coolant to bypass the core via tripped RCP. Thus, the reactor has to be shut down and the tripped RCP has to be replaced, which results in down time. Operation of reactor with only two RCP (2/3 mode) will supplement the power generation. Henceforth, if the flow path through the tripped RCP is made highly resistant as compared to the core, then eventually, flow from the two operating RCPs will go through reactor core. Such a flow blocking/resisting arrangement can also provide the flexibility during reactor startup. A cylindrical shell is designed for closing the suction passage of the pump and the shell is raised or lowered from above the roof slab with the help of tie-rods. The cylindrical shell (sleeve shell) is designed to withstand water hammer shock due to inadvertent sudden closure of the suction passage. To determine the shell thickness, pump performance curves are developed based on reactor operating conditions. The sleeve shell will not be able to perfectly close the suction passage as space is required for movement of sleeve shell over the pump shell, thus a study is performed on incorporating a labyrinth to minimize the leakage.

Numerical investigation of shock induced bubble collapse in water

A semi-conservative, stable, interphase-capturing numerical scheme for shock propagation in heterogeneous systems is applied to the problem of shock propagation in liquid-gas systems. The scheme is based on the volume-fraction formulation of the equations of motion for liquid and gas phases with separate equations of state. The semi-conservative formulation of the governing equations ensures the absence of spurious pressure oscillations at the material interphases between liquid and gas. Interaction of a planar shock in water with a single spherical bubble as well as twin adjacent bubbles is investigated. Several stages of the interaction process are considered, including focusing of the transmitted shock within the deformed bubble, creation of a water-hammer shock as well as generation of high-speed liquid jet in the later stages of the process.

Experimental and theoretical study of large deformation of rectangular plates subjected to water hammer shock loading

This paper presents experimental and analytical investigation of the dynamic inelastic response of rectangular metal plates subjected to liquid shock loading. A series of experimental results on fully clamped aluminum alloy and mild steel rectangular plates of different thickness and varying standoff distance of hammer is reported. The effect of varying both shock load and the plate material on the deflection is described. Also, an analytical procedure based on an upper bound solution is used to theoretically study the dynamic behavior of uniform impacted plates. In the present model, effects of strain rate and bending/membrane strain are assumed. The results of the analytical model and the experimental data have good agreement. So, this model can be useful for predicting deformation of rectangular plates under low impact loading.

Mechano-chemical pathways to H2O and CO2 splitting

The shock-induced collapse of CO2-filled nanobubbles is investigated using molecular dynamics simulations based on a reactive force field. The energetic nanojet and high-pressure water hammer shock formed during and after collapse of the nanobubble trigger mechano-chemical H2O-CO2 reactions, some of which lead to splitting of water and formation of O2 molecules. The dominant pathways through which splitting of water molecules occur are identified.

Numerical simulations of non-spherical bubble collapse.

A high-order accurate shock- and interface-capturing scheme is used to simulate the collapse of a gas bubble in water. In order to better understand the damage caused by collapsing bubbles, the dynamics of the shock-induced and Rayleigh collapse of a bubble near a planar rigid surface and in a free field are analysed. Collapse times, bubble displacements, interfacial velocities and surface pressures are quantified as a function of the pressure ratio driving the collapse and of the initial bubble stand-off distance from the wall; these quantities are compared to the available theory and experiments and show good agreement with the data for both the bubble dynamics and the propagation of the shock emitted upon the collapse. Non-spherical collapse involves the formation of a re-entrant jet directed towards the wall or in the direction of propagation of the incoming shock. In shock-induced collapse, very high jet velocities can be achieved, and the finite time for shock propagation through the bubble may be non-negligible compared to the collapse time for the pressure ratios of interest. Several types of shock waves are generated during the collapse, including precursor and water-hammer shocks that arise from the re-entrant jet formation and its impact upon the distal side of the bubble, respectively. The water-hammer shock can generate very high pressures on the wall, far exceeding those from the incident shock. The potential damage to the neighbouring surface is quantified by measuring the wall pressure. The range of stand-off distances and the surface area for which amplification of the incident shock due to bubble collapse occurs is determined.