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In this paper, the super-cavitating phenomenon under the effect of two vehicles' encounter motion processes is numerically studied. Particular attention is given to the influence of the vertical gaps between the vehicle, the cavitation number, and the slenderness ratio on the cavity profile and radial force of the object. Several numerical models are built to study the cavity evolution process and the force acting on the vehicle to explore the influence mechanism of two vehicles' encounter motion on supercavitating flow. The study shows that the cavity around the vehicle is primarily affected by the vertical gaps and cavitation number, but is relatively weakly affected by the slenderness ratio. Several impact laws are acquired in the paper. The relationship between cavity fracture time and vertical gaps is approximately a power function and obeys the law of t = 5.433h0.3688. The concept of the time of the maximum radial force occurrence and the cavitation number follows the formula of t = 4.86e0.3688σ. The relationship between the maximum radial force occurrence position and the cavitation number is a function of Ln and consistent with the law n = −0.799ln(σ) + 8.427. [ABSTRACT FROM AUTHOR]

The separator is a key component of coal pneumatic conveying systems, which plays an important role in improving particle collection efficiency and reducing dust pollution. In this paper, a combined rotary separator was designed. Based on the traditional cyclone separator, the rotor blades were installed and matched with the guide vanes to increase the material separation and collection performance. The influence of rotor speed on the characteristics of the separator was studied by computational fluid dynamics simulation, and the flow field velocity and pressure distribution and the particle trajectory and separation degree were obtained. The results showed that the flow field tangential velocity plays a dominant role in the separation process and is approximately symmetrically distributed with the rotor axis as the center. The velocity of the flow field in the inner rotor is approximately positively correlated with the rotor speed, and the tangential velocity gradually decreases with the increase in the flow field height. The static pressure of the flow field is approximately axisymmetric along the rotor axis, and there is a pressure gradient from the outer separation cone to the rotor axis. The particles in the separator show a separation phenomenon based on the different sizes, and the change trend of the separation degree under different rotor speeds is similar. When the rotor speed is 160 rpm, the particles maintain the highest integrity. The rotor speed of 320 rpm has a protective effect on coarse particles above 1000 µm. [ABSTRACT FROM AUTHOR]

The high-speed water-entry phenomenon of vehicles with a free and constant speed is numerically studied. The different behaviors of the cavities created by the vertical water entry of projectiles with different nose shapes, tail shapes, and impact speeds are investigated. The drag characteristics of the projectiles with a free or constant impact speed are compared. The flow characteristics of the flow field are compared and analyzed. Unlike the cavity induced by free-speed water entry, that induced by constant-speed water entry is more stable and is maintained for a longer time. The expansion of the projectile tail can weaken the effect of the re-jet flow, generated by the cavity seal, on the head of the cavity and prolong the attachment time of the cavity. The shape of the projectile tail can cause drag disturbance, but the key factor determining the drag of the projectile mainly depends on the water entering speed and the nose shape of the projectile. [ABSTRACT FROM AUTHOR]

In the paper, the air cavity created by vertical water entry of cylinders with different slenderness ratio (defined as “s=L/D”) is investigated experimentally, theoretically, and computationally. The study is focused on the range of Froude numbers, Fr = V/(gr) 0.5, (12< Fr< 30). Particular attention is given to the effect of slenderness ratios on the surface seal time, the evolution process of the cavities. To understand the water entry physical processes, we conduct several experiments of water entry of different length cylinders. A theory model considering the added mass (induced by the water motion), buoyancy force, gravity, and water-resisting force is developed to predict the relationship between the falling distance and evolution time. Studies show that for the same size bullet the surface seal time of the cavity decreases with the increase of impact speed. Under the identical impact speed, the cavity seal time decreases with the increase of the slenderness ratio. For the consistent impact speed, with the value of “s” increase, the falling distance increase (the same moment). The falling distance captured by the developed theoretical model match with the experimental and numerical data.

We conducted an experimental study on the formation of cavity and splash crown during the impact of superhydrophobic and hydrophilic spheres on water and polyethylene oxide solution (non-Newtonian liquid). We investigated the influences of falling speed of spheres on splash crown and cavity formation. In particular, we focused on the evolution time of splash and cavity when spheres with different contact angles fall into different liquids under various speeds and the different behavior of splash curtain. Results show that sphere contact angle and liquid viscosity have a great effect on cavity formation. The increase in contact angle and liquid viscosity induces cavity formation. However, viscosity has a certain inhibitory effect on crown evolution. The faster the falling speed is, the shorter the splash crown's evolution time, but the greater the volume will be. A pinch-off model of cavity has a great impact on the formation of "Worthington jet." [ABSTRACT FROM AUTHOR]