Jet Impact Pressure Research Articles

Pressure reduction in plunge pools by triangular wedges at high-head overfall spillways

Overfall spillways are important hydraulic structures for the release of overtopping water flows downstream of a dam. To reduce the effects of the impact of falling water in plunge pools, an overfall spillway outlet design that produces a longitudinally spreading jet is required. This study examined the effects of a triangular wedge placed at the end of an overfall spillway to deflect the water flow in the lateral direction, making the jet longitudinally diffuse before reaching the plunge pool. Laboratory data on the mean pressure coefficient were used to analyse the effects of various design parameters. An increase in the deflection ratio and a decrease in the weir crest length reduced the jet impact pressure. Compared with the impact of a rectangular jet falling into a plunge pool, an appropriate triangular wedge structure was found to improve the spreading of the impingement jet and reduce the mean dynamic pressure coefficient. By optimising the geometric design to accomplish jet impact control, the results of the present investigation may help engineers to design overfall spillways in high-head dam projects.

A new 3-D multi-fluid model with the application in bubble dynamics using the adaptive mesh refinement

Violent pulsating bubbles behave diversely in different circumstances. It is a multi-scale problem in both space and time. In 3-D problems, the numerical simulation is usually too expensive to implement in practice with a fixed grid. In this paper, a 3-D multi-fluid model is established based on the Eulerian finite element method and the adaptive mesh refinement technique to investigate the bubble evolution and its toroidal motion near a solid vertical wall. The mixture formula for compressible multi-fluid flow is adopted to ensure conservativeness. By means of the block-based adaptive mesh refinement, the accuracy and the efficiency of the simulation are well balanced. The present model is validated by comparing the results with an underwater explosion experiment and the existing numerical results. The results agree well and a fast convergence is observed. Then, several cases with different buoyancy parameters are simulated, and the toroidal bubble motion and their pressure load on the solid wall are analyzed. The bubble’s motion exhibits complex physics, such as the formation of the crescent-shaped bubble, the air cushion effect during the jet penetration, and the nonlinear relationship between the jet impact pressure and the angle between the jet and the opposite bubble surface.

Fluid-solid-thermal coupling analysis of rock failure under the joint action of cutting and jet impingement

Mechanical cutting assisted by high-pressure jet is a common and efficient drilling method in the exploration of hot dry rock (HDR). The drilling efficiency can be further improved with an in-depth understanding in the rock-breaking mechanism, which is a complex process involving the coupling of thermal stress, jet impact pressure and cutting force. To address such a multi-physics coupling issue, a loosely coupling method was adopted in this work to accomplish the exchange of data, including temperature, heat flux, nodes deformation and impinging pressure of jet in every time increment. In the fluid subdomain, the liquid nitrogen (LN2) jet and water jet were modeled and compared to demonstrate the potential of the novel jet in improving the drilling rate. In the solid subdomain, cutting force monitored in the experiment was loaded, and the concrete damage plastic model was employed to evaluate damage behaviors of the rock. Relative experiments were conducted to validate the reliability of simulation results. Results indicate that a great temperature difference develops on the coupling surface under the impingement of LN2 jet due to its cryogenic feature and lower heat transfer efficiency. Thereby, irreversible damage of the rock can be induced even at room temperature (298 K). As for the water jet, tensile damage is not observed until the rock temperature increases to 473 K. The assistance of jet impact on rock breaking is mainly reflected in two aspects: (1) the occurrence of tensile damage on the coupling surface facilitates the subsequent rock cutting; (2) the enhancement of tensile damage around the cutter promotes the initiation of cracks. Higher rock temperatures significantly improve the heat transfer rate and enhance the advantage of jet assistance. The present study can provide a new sight for the exploration of HDR.

Theoretical Analysis of the Mechanical Effects of Water Jet

The mechanical characteristics and stress state caused by water jet loading are influenced by many factors that have restricted studies on the jet mechanism. Using the basic theory of elasticity and fluid dynamics, the mechanical effects of water jet loading are analyzed. Based on the simplified jet distribution pressure, the elastic analytical solution of the stress distribution in a semi-infinite plane under the jet distribution pressure is derived, and the stress distribution characteristics are discussed. In addition, the Mohr–Coulomb yield criterion served as a fracture criterion, enabling establishment of the relationship between jet pressure and rock strength. The results indicate that the compressive stress is symmetrically distributed around the jet axis with the maximum at the center. Conversely, the shear stress is Anti-symmetrically distributed around the jet axis with the maximum at the point (0.5r, ± 0.65r). The initial fracture of rock under the impact of water jet is mainly shear compression failure. The Mohr–Coulomb yield criterion is useful for estimating the relationships between the rock failure zone diameter with the water jet impact pressure.

THE MECHANISM OF JETTING BEHAVIORS OF AN OSCILLATING BUBBLE

The dynamic behaviors of an oscillating bubble (e.g., underwater explosion bubble, cavitation bubble and air-gun bubble) are well known to be strongly dependent on the nature of boundary conditions. Many experiments demonstrated that a high-speed liquid jet is formed away from a free surface or towards a nearby rigid wall. The violent jet impact is believed to be one of the most important mechanisms of cavitation erosion and damages by an underwater explosion. In the previously published literature, the Kelvin impulse based on spherical bubble theory is adopted to determine the gross migration and jet direction of bubbles. However, the underlying mechanisms of jet inception and development are not fully understood and the characteristics of the jet impact still lack exploration. In the present work, both experimental and numerical methods are adopted to do some fundamental studies on bubble dynamics beneath a free surface and near a rigid wall. The electric discharge method is used to generate a bubble and the bubble motion is captured by a high-speed camera. Meanwhile, the boundary integral method is adopted to conduct numerical simulation. The presence of a nearby boundary alters the pressure gradient surrounding the bubble, which has a significant influence on the jet inception. Additionally, a local high-pressure region is generated near the bubble bottom, and it results in a positive feedback mechanism that further accelerates the jet. This mechanism reveals the fact that the jet can speed up to a hundred meters per second within a relatively short time. A localized high-pressure region is caused by the jet impact around the jet tip and the maximum pressure decreases gradually as the rebound of the toroidal bubble. At last, the effect of the dimensionless standoff parameter (defined as $\gamma = d / R_{m}$, where $d$ is the distance between the initial bubble center and the rigid wall and $R_{m}$ is the maximum bubble radius) on the jet impact pressure is discussed.

Nonlinear interaction between a gas bubble and a suspended sphere

The fully nonlinear interaction between a gas bubble and a suspended sphere is studied using boundary integral method. The violently expanding and collapsing bubble would cause the sphere to move, in reverse, the sphere response can strongly affect the bubble dynamics. Differing from previous studies, we use the auxiliary function method to decouple the mutual dependence between the force and the sphere motion. To validate our model, two experiments are carried out for a spark-generated bubble interacting with a suspended sphere, captured by using a high speed camera. Our numerical results agree well with the experimental data for both cases, in terms of bubble shapes and sphere displacement. We further conduct convergence and sensitivity studies, in which consistent results have been achieved. Then, the effects of two parameters are investigated, i.e., the stand-off parameter (defined as γ=d/Rm, where d is the minimum distance between initial bubble center and the sphere surface, Rm is the maximum equivalent bubble radius) and the size ratio (defined as θ=Rs/Rm, where Rs is the sphere radius). The sphere is pushed away by the expanding bubble and gets attracted towards the collapsing bubble. Bubble motion varies greatly with different parameters. We found the maximum jet impact pressure on the sphere is realized when θ is around 2.

EXPERIMENTAL STUDY ON THE EFFECTS OF HYDRAULIC CONFINING PRESSURE ON IMPACTING CHARACTERISTICS OF JETS

Original Manuscript Submitted: 4/6/2012; Final Draft Received: 6/15/2012 The high hydraulic confining pressure exhibited in oil-well downholes and deep water conditions affects jet dynamic characteristics remarkably. A set of devices and equipment were developed to study the influence of confining pressure on jet impact pressure and rock-breaking efficiency. The three most popular jet types—a conical water jet, a cavitating jet, and an abrasive jet—were studied with a maximum nozzle pressure drop of 25.0 MPa and maximum confining pressure of 20.0 MPa. Results clearly reveal the close relationship among confining pressure and jet impact pressure and rock-breaking efficiency. The axial jet impact pressure and rock removal volume decrease while as confining pressure increases, and the decreasing curve becomes flattened at a certain point. Under the same conditions, the rock-breaking efficiency of the cavitating nozzle jet is higher than the conical nozzle jet, and cavitating erosion and pressure fluctuation are the important factors affecting jet rock-breaking efficiency. Furthermore, under confining pressure conditions, pure water jets have an optimal standoff distance about 3 to 5 times that of the nozzle outlet diameter, at which the highest rock removal volume is achieved. According to the study, a drop of jet impact pressure with growth of confining pressure may be the main reason for the decreasing rock-breaking capability. The study could be used as a reference for setting and optimizing jet application conditions, and also could be adopted for developing working parameter selections as well as guiding the nozzle structure designs.

COMPARISON OF 20-, 23-, AND 25-GAUGE AIR INFUSION FORCES

To determine and compare 20-, 23-, and 25-gauge retinal infusion air jet impact pressure (force per unit area) in an experimental setting. Experimental laboratory investigation. Infusion cannulas were connected to a compressed air system. A controlled valve mechanism was used to obtain increasing levels of infusion pressure. Each infusion tube was positioned in front of a manual transducer to measure force. Impact pressure was calculated using known formulas in fluid dynamics. The 20-gauge infusion jet showed similar impact pressure values compared with the 23-gauge infusion jet. Both showed higher levels than the 25-gauge infusion jet. This was because of the smaller jet force for the 25-gauge system. In this experimental study, both the 23- and the 20-gauge air infusion jet showed higher impact pressure values compared with the 25-gauge air infusion jet. This could be of concern regarding air infusion during 23-gauge vitrectomy since retinal damage has been shown in standard-gauge surgeries.

Structure of Emulsion Cavitation Jet and Jet Peening Impact on the Fatigue of Plan Carbon Steel Q235A

Due to developing the strengthening effect of liquid jet peening on the surface modification for metallic materials, in this study, an emulsion jet peening is produced by injecting a high-speed emulsion jet into an emulsion filled tank. The test system and fixed emulsion of cavitation jet was developed. High speed photography technique was used to observe and analysis the structure of emulsion cavitation jet at various upstream pressures . The results indicate that the structure of emulsion cavitation jet in terms of jet impact pressure, intensive degree and uniformity is better than that water jet. The jet structure depends on the jet pressure. The cavitation jet length increases rapidly at the initial stage and then it stabilizes after few milliseconds. The stabilized length of jet increases and the diverges angle decreases with increasing pressures. Specimens made of plan carbon steel (Q235A, China standard) were exposed to emulsion jet peening at the stand-off distances of 20 mm with a constant upstream pressure, 20 MPa for 60 s. The fatigue test shows that the crack initiation life by treatment of emulsion jet peening increases about 12.5% and 20.2% compared to water jet and unpeened specimen respectively.

An Auto-Switched Chaos System Design and Experimental Study of Pulsed Cavitating Multihole Nozzle

In order to improve the rock breaking ability of jet nozzle in radial drilling technique, pulsed cavitating multihole nozzle was designed on the basis of multihole nozzle. And its modulation mechanism of pulsed cavitating jet was analyzed. Rock breaking test was carried out to compare the rock breaking results of pulsed cavitating multihole nozzle and multihole nozzle. The results indicated that the rock breaking result of pulsed cavitating multihole nozzle is better than that of multihole nozzle. The rock breaking volume is 1.23∼2.35 times. To guarantee the minimum hole diameter is bigger than nozzle diameter, jet impact pressure should not be lower than 30MPa in the experiment. The experimental optimal standoff distance is 12mm. The findings in this paper can increase the extension of horizontal holes and improve drilling rate in radial drilling technique.

Focussed Hydraulic Energy - A New Look At Two-Nozzle Drilling

Abstract Drilling with a tri-cone bit equipped with two equal-sized nozzles and one blank nozzle has previously been used in an attempt to increase penetration rates through improved bottom-hole cleaning. A new concept uses two unequal-sized nozzles and higher bit hydraulic power to create maximum hydraulic energy at the bit and to transmit a larger fraction of that energy to the hole bottom in a pattern more conducive to bottom-hole cleaning. Applications of this technology in the Valhalla Field of Alberta have increased the average rate of penetration by 42% and reduced drilling cost by 27%. Introduction The rate of penetration (ROP) achieved in conventional rotary drilling with a tri-cone bit is controlled by a dynamic equilibrium between the generation of cuttings and the removal of cuttings from the drilling surface, Ineffective cuttings removal often limits the actual ROP to much less than what would be mathematically expected if perfect bottom-hole cleaning conditions had xisted. In such cases, improved bottom-hole cleaning results in increased ROP. When drilling with three equal-sized nozzles each jet impacts on the drilling surface and lifts drill cuttings off of the rock face by turbulent scouring. The fluid then reverses against itself in the confined area between the cones to transport the cuttings up the hole. There is no fluid flow underneath the cones where cuttings generation takes place. Cuttings removal can only take place after the cones have rolled over them and they have been lifted off of the rock surface sufficiently to be entrained in the returning fluid flow. The original two equal-sized nozzle hydraulics design attempted, with varying degrees of success, to improve cuttings removal by initiating crossflow under the bit and providing a flow path for the returning fluid unhampered by a downward jet, This design failed to relate the effect of nozzle diameter and jet impact pressure distribution on the cuttings removal process. A new two-nozzle design was proposed which incorporates unequal nozzle diameters to focus hydraulic energy on the hole bottom in a pattern which improves bottom-hole cleaning, It has been field-tested with consistent success in hundreds of bit runs in northern, central and eastern Alberta, and in over 100 bit runs in the Australian Outback. The field test summarized in this paper was conducted in the Valhalla Field of Alberta, 50 km northwest of Grande Prairie (Fig. 1). The reader should be cautioned that the study population is small, and that the tests were conducted to minimize, but could not eliminate all the variables which could impact on the findings. These constraints prevent the author from establishing conclusive proof of the effectiveness of focussed hydraulic energy. The author intends only to provide sufficient evidence to encourage thoughtful discussion. Discussion Literature Review Laboratory bottom-hole pressure surveys by Sutko and Myers(1) demonstrated that as the number of nozzles on a tri-cone bit is progressively reduced from three to two to one, the maximum impact pressure under the remaining jets is increased. Concurrently, the minimum bottom-hole pessure is reduced.