Experimental investigation of heat and mass transfer of an annular impinging jet

This work presents an experimental study of a turbulent flow and heat transfer of an annular impinging jet for organizing effective surface cooling. Heat and mass transfer of the impinging annular jet was studied at Re = 5500. At that, a distance from the nozzle to the wall was varied. The focus was made on configurations with small nozzle-to-wall distances. It is shown that, depending on the indicated distance, fundamentally different flow regimes with characteristic features of heat transfer distribution are observed.

Proper orthogonal decomposition analysis of coherent motions in a turbulent annular jet

A three-dimensional incompressible annular jet is simulated by the large eddy simulation (LES) method at a Reynolds number Re = 8 500. The time-averaged velocity field shows an asymmetric wake behind the central bluff-body although the flow geometry is symmetric. The proper orthogonal decomposition (POD) analysis of the velocity fluctuation vectors is conducted to study the flow dynamics of the wake flow. The distribution of turbulent kinetic energy across the three-dimensional POD modes shows that the first four eigenmodes each capture more than 1% of the turbulent kinetic energy, and hence their impact on the wake dynamics is studied. The results demonstrate that the asymmetric mean flow in the near-field of the annular jet is related to the first two POD modes which correspond to a radial shift of the stagnation point. The modes 3 and 4 involve the stretching or squeezing effects of the recirculation region in the radial direction. In addition, the spatial structure of these four POD eigenmodes also shows the counter-rotating vortices in the streamwise direction downstream of the flow reversal region.

Effect of Closure Characteristics of Annular Jet Mixed Zone on Inspiratory Performance and Bubble System

In the flotation process, gas-liquid properties and the bubble system greatly influence bubble mineralization. In order to clarify how the mechanism applies to the closure characteristics of an annular jet mixed flow zone on the inspiratory performance and the bubble system, different degrees of closure on the velocity field and gas-liquid ratio in the mixed flow zone were investigated using numerical simulation. The variations in the characteristics of bubble size distribution, rising velocity, and gas content under different closure levels were measured with a high-speed dynamic camera technology. The results confirmed that when the closure degrees of the mixed flow zone improved, the inlet jet could gradually overcome the static pressure outside the nozzle effectively. It formed a gas-liquid mixing zone with high turbulence first, and a large pressure difference at the gas-liquid junction second. This helped to increase the inspiratory capacity. At the same time, the gas-liquid ratio rose gradually under conditions of constant flow. When the nozzle outlet was completely closed, the gas-liquid ratio gradually stabilized. For the bubble distribution system, an enhancement in the closure degrees can effectively reduce the bubble size, and subsequently, the bubble size distribution became more uniform. Due to the improved gas-liquid shear mixing, the aspect ratio of the bubbles can be effectively changed, consequently reducing the bubble rising speed and increasing the gas content and bubble surface area flux of the liquid.

Formation and Penetration Capability of an Annular-Shaped Charge

Shaped charges are widely used in the field of national defense because of their high energy density and strong directivity; however, one of their limitations is that the penetration diameter is small. Compared with a traditional shaped charge, an annular-shaped charge can create a larger penetration aperture at the target, thereby causing more damage to underwater targets. To enhance the damage effect of a shaped charge on an underwater structure, we designed an annular-shaped charge structure. To end this, we first established a velocity calculation model of the liner and analyzed its formation process. The hydrocode software Autodyn was used to simulate the jet formation process. Second, two parameters of the annular liner height and thickness of the bottom and their effect on the annular jet formation were analyzed. Finally, an experiment was conducted to validate the penetration capability of this charge. The experimental results indicate that the annular-shaped charge can penetrate a typical underwater structure and form a large penetration aperture with a diameter of 420 mm, which is 1.4 times the charge diameter. Furthermore, the numerical results show good agreement with the experimental data; only a 1.67% deviation was observed.

Multi-Objective Optimization of Jet Pump Based on RBF Neural Network Model

In this study, an annular jet pump optimization method is proposed based on an RBF (Radial Basis Function) neural network model and NSGA-II (Non-Dominated Sorting Genetic Algorithm) optimization algorithm to improve the hydraulic performance of the annular jet pump applied in submarine trenching and dredging. Suction angle, diffusion angle, area ratio and flow ratio were selected as design variables. The computational fluid dynamics (CFD) model was used for numerical simulation to obtain the corresponding performance, and an accurate RBF neural network approximate model was established. Finally, the NSGA-II algorithm was selected to carry out multi-objective optimization and obtain the optimal design variable combination. The results show that the determination coefficient R2 of the two objective functions (jet pump efficiency and head ratio) of the approximate model of the RBF neural network were greater than 0.97. Compared with the original model, the optimized model’s suction angle increased, and the diffusion angle, flow ratio and area ratio decreased. In terms of performance, the head ratio increased by 30.46% after the optimization of the jet pump, and efficiency increased slightly. The proposed jet pump performance optimization method provides a reference for improving the performance of other pumps.