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This paper aims to apply experimental methods to investigate the effect of the thickness of gas layers on the wall on the collapse direction of spark-induced bubbles. In the experiment, two high-speed cameras synchronously record the time evolution of the bubbles and the corresponding parameters such as the normalized collapse position and bubble collapse time. Experiments yielded results for individual bubbles over a range of normalized distances from 0 to 4.0 for different air layer thicknesses. Based on the morphology of the bubbles, the experimental jets were visualized into six different modes, namely, forward jet (FJ), merging jet (MJ), bidirectional jet (BJ), reversing jet (RJ), forward followed by reversing jet (FRJ), and non-directional jet (NDJ). The height of the air layer on the wall is affected by the fluctuation of the bubble volume and shows the opposite trend to the change of the bubble volume. The air film reaches its maximum height when the bubble collapses, which affects the final jet pattern. In addition, as the thickness of the air layer increases, the center of the bubble gradually migrates away from the wall. The different collapse modes and the migration of the bubble centers have positive significance for reducing cavitation erosion in engineering.

We analyse VLBI and optical images of AGNs and their host galaxies and look for statistical correlations between the shape and orientation of the galaxy and the direction of the jet. We utilise the Astrogeo catalogue, which has over 9000 VLBI sources, many of those with a clear core-jet like structure that allows for the jet position angle to be reliably determined. We then use the VLBI source positions to search for optical counterparts within various optical surveys. In order to parameterise the orientation and shape of the host galaxy, we fitted a Gaussian elliptical model to the optical image, taking the PSF into account. We check our own shape parameters from this fit against the ones provided by the optical surveys. As of yet, no clear correlation between the galaxy morphology and the jet direction is seen. [ABSTRACT FROM AUTHOR]

The flow stability induced by the impingement of gas jets exiting from the intake manifold affects the in-cylinder flow characteristics of internal combustion engine. Using high-speed planar particle image velocimetry (PIV) with proper orthogonal decomposition (POD) analysis, an investigation was conducted to reveal the spatio-temporal characteristics of annular gas jets impinging in a region between the exits of two intake valves. Unique flow behaviors are identified where strong initial interaction of impinging jets appears near the valve exit as a result of fierce flow vorticity competition in both clockwise and counter-clockwise directions. This mixing zone exhibits strong fluctuations in the angle of the merged gas jet. Flow vorticity and merged jet angle are highly correlated with each other, and the quasi-periodical behavior of the jet impingement is linked to the kinetic energy dissipation. In addition, using POD, the underlying flow structures show large-scale rotating structures with translation which are responsible for the quasi-periodical behavior. In summary, three types of flow stability can be identified resulting from different levels of induced impingement: one-way interaction of single jet flow case, two-way interaction of dual impinging jets with equal flow magnitude, and transitional one-way interaction of dual impinging jets with unequal flow magnitude. [ABSTRACT FROM AUTHOR]

High temperature smoke caused by fire is a major cause of casualties. In order to ensure the safety of personnel, it is very important to control the spread of smoke and enable personnel to quickly withdraw from the fire scene. While traditional hard isolation, such as fire doors, may hinder the safe evacuation of people, the use of an air curtain as a flexible isolation has received more and more attention from researchers. In this paper, the influence of jet direction of compound air curtain on the smoke control effect was studied, and six working conditions were designed. The temperature and smoke isolation of the compound air curtain were numerically simulated by using ANSYS FLUENT software. The parameters such as temperature, velocity pressure and velocity streamline were analyzed, and the smoke control effects of six different jet directions were discussed. The simulation results were verified by Pyrosim fire simulation software simulation software. The results show that the direction of jet flow has a significant influence on the smoke control effect, and the fire smoke control effect under working conditions 4 and 5 is better. The working condition 5 (both air curtain A and air curtain B have outward jet direction) has the best smoke prevention effect, which is suitable for a situation that is close to the fire source. Working condition 4 (outward direction of air curtain A and inward direction of air curtain B) has the second-best effect of smoke prevention, which is suitable for situations far from the fire source.

• Bubbles exhibit various jet modes under conditions of different thicknesses of air film. • The reverse jetting mode can reduce the material damage caused by bubble collapse. • The interaction between bubbles and gas films influences the jetting modes. • The thickness of the gas film affects the migration of bubbles. This paper aims to apply experimental methods to investigate the effect of the thickness of gas layers on the wall on the collapse direction of spark-induced bubbles. In the experiment, two high-speed cameras synchronously record the time evolution of the bubbles and the corresponding parameters such as the normalized collapse position and bubble collapse time. Experiments yielded results for individual bubbles over a range of normalized distances from 0 to 4.0 for different air layer thicknesses. Based on the morphology of the bubbles, the experimental jets were visualized into six different modes, namely, forward jet (FJ), merging jet (MJ), bidirectional jet (BJ), reversing jet (RJ), forward followed by reversing jet (FRJ), and non-directional jet (NDJ). The height of the air layer on the wall is affected by the fluctuation of the bubble volume and shows the opposite trend to the change of the bubble volume. The air film reaches its maximum height when the bubble collapses, which affects the final jet pattern. In addition, as the thickness of the air layer increases, the center of the bubble gradually migrates away from the wall. The different collapse modes and the migration of the bubble centers have positive significance for reducing cavitation erosion in engineering. [ABSTRACT FROM AUTHOR]

The authors investigate the effects of the direction of the gas jet on the solid residence time distribution in a CFB riser. Tracer technique was employed to calculate the RTD of solids. A Eulerian–Eulerian model with kinetic theory of granular flow and species transport was used to simulate the motion of tracer particles in a CFB riser. For a comparative analysis of the direction of the gas jet, simulations of vertical, horizontal and hybrid jets were carried out. The direction of the gas jet significantly influenced the axial and radial structure of bed, and hence affected the RTD for solid particles. The mean residence time of solids was changed, and the results showed that 16.3 s, 14.8 s, and 11.4 s with vertical, horizontal and hybrid jets nozzles, respectively. [ABSTRACT FROM AUTHOR]

The oblique water entry of hollow cylinders with four different apertures is investigated experimentally at low velocities. The evolution characteristics of cavities, jets and splashes with different initial conditions and apertures are disclosed and discussed. The results show that the transition of cavity closure patterns with increasing water-entry velocities is postponed due to the existing water-entry angle. A curved through-hole jet is discovered and its upward ejecting direction can be altered from right to left by different guidance of the inner wall. The cylinder velocities usually increase first, decrease second and recover gradually again. But the final recovery degrees are different with various apertures, water-entry angles and velocities. Under the clockwise moments in the early cavity evolution, hollow cylinders rotate clockwise continuously underwater. • The closure pattern transition can be postponed by the existing water-entry angle. • The cavity closure time is approximately the same at a small aperture. • A curved through-hole jet is discovered and its upward ejecting direction can be altered. • Various apertures and entry conditions affect the final recovery degree of cylinder velocities. [ABSTRACT FROM AUTHOR]

High temperature smoke caused by fire is a major cause of casualties. In order to ensure the safety of personnel, it is very important to control the spread of smoke and enable personnel to quickly withdraw from the fire scene. While traditional hard isolation, such as fire doors, may hinder the safe evacuation of people, the use of an air curtain as a flexible isolation has received more and more attention from researchers. In this paper, the influence of jet direction of compound air curtain on the smoke control effect was studied, and six working conditions were designed. The temperature and smoke isolation of the compound air curtain were numerically simulated by using ANSYS FLUENT software. The parameters such as temperature, velocity pressure and velocity streamline were analyzed, and the smoke control effects of six different jet directions were discussed. The simulation results were verified by Pyrosim fire simulation software simulation software. The results show that the direction of jet flow has a significant influence on the smoke control effect, and the fire smoke control effect under working conditions 4 and 5 is better. The working condition 5 (both air curtain A and air curtain B have outward jet direction) has the best smoke prevention effect, which is suitable for a situation that is close to the fire source. Working condition 4 (outward direction of air curtain A and inward direction of air curtain B) has the second-best effect of smoke prevention, which is suitable for situations far from the fire source. [ABSTRACT FROM AUTHOR]

Introducing jet for drag reduction and thermal protection in hypersonic flows has attained worldwide attentions due to its giant potential, and this paper focused on the drag and heat reduction efficiency of unit mass flow rate for different jet directions in hypersonic flows. The developed code employed conjugate heat transfer approach to solve unsteady Reynolds-averaged Navier-Stokes equations and Fourier's heat conduction equation simultaneously, and then it was thoroughly validated by two classical experiments. Based on that, the flow field characteristics induced by different jet directions under the constant mass flow rate of jet were numerically investigated. Besides, two parameters were introduced to quantitatively evaluate the drag and heat reduction efficiency of different jet directions. The obtained results show that though the total mass flow rate of jet is constant, jet direction still has a decisive influence in manipulating the flow structures, and the rear jet would result in more complicated shock waves due to the interaction between the rear jet flow and spike. The force produced by the jet is the key role in determining the total drag, and the variation of pressure distribution along the blunt body is not the direct presentation of drag reduction performance. The opposing jet has the highest drag reduction efficiency, and lateral jet has the highest heat flux reduction. However, compared with the lateral and rear jets, the opposing jet has better thermal protection performance from the overall perspective as it can also protect the aerodome head from severe aerodynamic heating. [ABSTRACT FROM AUTHOR]