Effect of Nozzle Outlet Type On the Flow Field Velocity and Impact Pressure of High Pressure Water Jet Peening

Water jet peening can effectively improve the fatigue strength of metal materials, and the outlet shape of nozzle greatly affects the effect of water jet peening. In this paper, the effects of nozzle outlet shape on water jet velocity and impact pressure is studied by numerical simulation, and the jet velocity and dynamic pressure for different standoff distances are also discussed. The results show that the water jets of square, circular and triangular nozzles are highly concentrated, and the water jet of elliptical nozzles is the most divergent. The axial velocity attenuation of the square nozzle along the axis is slower than that of the other three nozzles. The water axial velocity of the elliptical nozzle attenuates fastest and the length of the core segment of the water jet is the smallest. Within a certain axial distance, the dynamic pressure area in the central area of the elliptical water jet is obviously larger than that of the other three nozzles, and the effective treatment range is large, which is more suitable for the welding surface strengthening operation.

Numerical Study on Effects of Geometric Parameters on the Release Characteristics of Straight Sudden Expansion Gas Extinguishing Nozzles

In order to guide the optimization design of the nozzle of the aircraft-fixed gas fire extinguishing system, we studied the influence of nozzle geometric parameters including outlet–inlet area ratio, length–diameter aspect ratio, and wall roughness on the distribution of pressure and velocity in the nozzle on the basis of CFD simulations. Although the structure of the nozzle is axisymmetric, the spatial distribution of the pressure and velocity during the flow and release of gas extinguishing agent is not completely symmetric. It was found that both of the outlet–inlet area ratio (δ) and the length–diameter aspect ratio (ξ) had a significant impact on the distribution characteristics of the pressure and axial velocity in the nozzle. With the increase of δ, the average pressure at the outlet cross-section of the nozzle decreased monotonically, while the average axial velocity at the outlet increased approximately linearly. When ξ≥2, the uniformity of the pressure and velocity distribution at the nozzle outlet was significantly improved. Moreover, with the increase of ξ, the average pressure and the average axial velocity of the outlet both showed a non-monotonic change trend, and the optimal value of ξ should be about 3.0. Compared with δ and ξ, the influence of the nozzle wall roughness (εN) on the flow and release characteristics of the extinguishing agent was weak. With the increase of εN, the average pressure of the nozzle outlet increased slightly, while the average axial velocity at the nozzle outlet decreased slightly.

Experimental Study of the Velocity of the Electrovortex Flow of In-Ga-Sn in Hemispherical Geometry

The paper describes the application of the thermocorrelation method for measuring the velocity in a current-carrying liquid. An electrovortex flow occurs when the current passing through a conducting medium interacts with its own magnetic field. Measurements of the velocity of the turbulent electrovortex flow of the liquid metal (eutectic alloy In-Ga-Sn) were carried out in a hemispherical container in the range of currents of 100–450 amperes in the presence and absence of compensation of the Earth’s magnetic field. The efficiency of the thermocorrelation method in a current-carrying liquid has been demonstrated. The dependences of the axial velocity on the current and the velocity profiles along the axis were obtained. It was found that the presence of the Earth’s magnetic field leads to a significant decrease in the average value of the axial velocity in the entire range of currents.

Some effects of flow expansion on the aerodynamics of horizontal-axis wind turbines

The flow upwind of an energy-extracting horizontal-axis wind turbine expands as it approaches the rotor, and the expansion continues in the vorticity-bearing wake behind the rotor. The upwind expansion has long been known to influence the axial momentum equation through the axial component of the pressure, although the extent of the influence has not been quantified. Starting with the impulse analysis of Limacher and Wood (2020), but making no further use of impulse techniques, we derive its exact expression when the rotor is a circumferentially uniform disc. This expression, which depends on the radial velocity and the axial induction factor, is added to the thrust equation containing the pressure on the back of the disc. Removing the pressure to obtain a practically useful equation shows the axial induction in the far wake is twice the value at the rotor only at high tip speed ratio and only if the relationship between vortex pitch and axial induction in non-expanding flow carries over to the expanding case. At high tip speed ratio, we assume that the expanding wake approaches the Joukowsky model of a hub vortex on the axis of rotation and tip vortices originating from each blade. The additional assumption that the helical tip vortices have constant pitch allows a semi-analytic treatment of their effect on the rotor flow. Expansion modifies the relation between the pitch and induced axial velocity so that the far-wake area and induction are significantly less than twice the values at the rotor. There is a moderate decrease – about 6 % – in the power production, and a similar size error occurs in the familiar axial momentum equation involving the axial velocity.

Effects of axial motion and couple stress on lubrication performances of ship stern shaft

Increasingly prominent marine oil pollution problems highlight the importance of environmentally friendly lubricants in a ship. According to the actual navigation environment, the couple stress effect of environmentally friendly lubricants and axial motion of stern shaft is considered to establish a new hydrodynamic lubrication model, and finite difference method and Simpson integral method have been utilized to solve film pressure and bearing carrying capacity, respectively. Various performance characteristics were obtained for a range of couple stress parameters, misalignment angles and rotation speeds. The results show that axial motion and couple stress have opposite effects on film distribution, the minimum film thickness decreases with the increasing of axial velocity while the maximum film pressure significant reduce as couple stress parameter grows. The axial position corresponding to the maximum pressure is reduced from 0.51 to 0.49 m as axial velocity enhances from 0 to 0.8 m/s while couple stress parameter is 0, but nearly remains the place while couple stress is considered. Meanwhile, couple stress lubricants effectively restrain friction of journal caused by hydrodynamic effect, and the decreasing amplitude is nearly independent of axial velocity.

Cattaneo–Christov heat flux effect on MHD peristaltic transport of Bingham Al2O3 nanofluid through a non-Darcy porous medium

The present investigation analyzes the influence of Cattaneo–Christov heat and mass fluxes on peristaltic transport of an incompressible flow. The fluid is obeying Bingham alumina nanofluid. The fluid flows between two co-axial vertical tubes. The system is expressed by a varying radially magnetic field with respect to the space. Soret effect and non-Darcy porous medium are taken into account. The governing system of equations is tackled by utilizing the approximations of long wavelength with low Reynolds number and with the help of homotopy perturbation method (HPM). It is noticed that the axial velocity magnifies with an increase in the value of Bingham parameter. Meanwhile, the value of the axial velocity reduces with the elevation in the value of the magnetic field parameter. On the other hand, the elevation in the value of thermal relaxation time leads to a reduction in the value of fluid temperature. Furthermore, increasing in the value of mass relaxation time parameter makes an enhancement in the value of nanoparticles concentration. It is noticed also that the size of the trapped bolus enhances with the increment in the value of Bingham parameter. The current study has many accomplishments in several scientific areas like medical industry, medicine, and others. Therefore, it represents the depiction of the gastric juice motion in the small intestine when an endoscope is inserted through it.

Numerical Analysis of Stratified and Slug Flows

The main purpose of this study is to compare two-dimensional (2D) and three-dimensional (3D) two-phase models for both stratified and slug flows. These two flow regimes interest mainly the petroleum and chemical industries. The volume of fluid (VOF) approach is used to predict the interface between the two-phase flows. The stratified turbulent flow corresponds to the oil-water phases through a cylindrical pipe. To simulate the turbulent stratified flow, the k − ω turbulence model is used. The slug laminar flow concerns the kerosene-water phases through a rectangular microchannel. The simulated results are validated using the previous experimental results available in the literature. For the stratified flow, the axial velocity and the water volume fraction profiles obtained by 2D and 3D models approximate the measurement profiles at the same test section. Also, the T-junction in a 2D model affects only the inlet vicinity. For downstream, the 2D and 3D models lead to the same axial velocity and water volume distribution. For the slug flow, the simulated results show that the 3D model predicts the thin film wall contrary to the 2D model. Moreover, the 2D model underestimates the slug length.

Investigation On Swirl Instability in a Vane-Type Separator with Tomographic PIV

The separation efficiency of a vane-type separator is greatly affected by swirl instability. The separator consists of a swirling vane, a recovery vane and a main pipe. Driven by centrifugal force, the bubbly flow tends to develop into stratified flow with a continuous gas core floating in the central axis of the separator and facilitating the separation. Yet, the straight gas core can turn into a double helix under some circumstances for example if the pressure difference across the orifices of recovery vane falls below the critical value, and swirl instability occurs. In order to reveal the underlying mechanism, a device with adjustable operating pres-sure was introduced to reproduce the dynamic process of gas core transform between stable and unstable. With the increase of pressure difference, the gas core morphology near the recovery vane will turn from double-helix to straight-line within several seconds. The whole process was investigated further by using the tomographic particle image velocimetry. Results show that the development of vorticity structures in the swirl flow gives rise to the evolution of gas core morphology and keeps it stable. Furthermore, the direction of axial velocity, which becomes negative by low pressure differences, is found to be crucial in controlling the formation of inner forced vortex and hence leading to the occurrence of swirl instability. In addition, the magnitude of positive axial velocity is identified to be of great significance in vorticity enhancement.

The Behavior of Supersonic Jets Generated by Combination Gas in the Steelmaking Process

In the duplex steelmaking process, the oxygen flow rate is suppressed to reduce the increasing rate of the temperature in the molten bath, resulting in severe dynamic conditions. To improve the mixing effect of the molten bath, a Laval nozzle structure designed for combination gas has been proposed. In this research, five types of Laval nozzle structure have been built based on the combination gas content, and both numerical simulations and experiments are performed to analyze the flow field of the supersonic jet. The axial velocity and oxygen concentration were measured in the experiment, which agreed well with the numerically simulated data. The results show that both initial axial velocity and potential core length increase with the flow rate of combination gas. Further, applying a higher N2 flow rate could improve the oxygen utilization rate at different ambient temperatures, but this issue increases the oxygen utilization rate; however, the latter can be reduced at higher ambient temperatures.