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In spite of extensive research on macroscopic solid movements in the dense granular system of a moving bed air reactor, research on the evolution characteristics of the mesoscale inter-particle contact force network is still lacking. In this work, discrete element simulations are conducted to investigate the force chain structure properties in a moving bed air reactor. The results show that during the particle discharging process, the force chain network exhibits great anisotropy, and force chain contacts account for only about 13–14% of all inter-particle contacts, while the strong particle–particle contacts account for about 37–41% of all the particle–particle interactions. The collimation coefficients of force chains are more stable at the early stages and then decrease sharply over time. Both particle–particle and particle–wall friction coefficients affect the number, strength, collimation coefficient, and direction of force chains but have little influence on the length distribution of force chains. An in-depth analysis of the evolution of the force network provides new insights for further understanding dense granular flow in a moving bed air reactor for chemical looping combustion.

In this study, a novel gas burner combining air swirl and an inverse diffusion flame (IDF) is designed for industrial applications. Numerical simulations using the Reynolds-averaged Navier–Stokes (RANS) method and simplified reaction mechanisms are conducted to predict the turbulent flow and combustion performance of the burner. Detailed flow structures, flame structures and effects of burner configurations are examined. The simulation results indicate that the swirl action of the burner creates a central recirculation zone and two external recirculation zones at the burner head, which stabilize combustion. The tangential velocity is minimal at the center of the burner and decreases with increasing distance from the outlet. As the distance from the exit increases, the maximum tangential velocity gradually decreases, and the peak value shifts towards the wall. This decrease in tangential velocity with axial distance signifies the gradual dissipation of the swirl effect, which disappears near the chamber outlet. The comparisons reveal that altering the number of burner fuel nozzles is more effective in reducing NO emissions than changing the inclination angle of the fuel nozzles, in the given conditions. Favorable combustion conditions are achieved when there are 16 fuel nozzles and the nozzle inclination angle is 60°, resulting in a 28.5% reduction in NO emissions at the outlet, compared to the reference condition.

Based on CFD analysis technology, this paper studies the cavitation performance of an LNG submerged pump and the pressure pulsation characteristics under cavitation excitation. The variation laws of the waveform, amplitude and frequency of the pressure pulsation in the impeller of the LNG submerged pump under different flow rates and NPSHa are also analysed. By calculating the root mean square of the pressure coefficient of the low-frequency pulsation, the influence of the aggravation process of cavitation on the low-frequency pulsation in the LNG submerged pump is quantitatively analysed, and the characteristics of the pressure pulsation in the LNG submerged pump under the cavitation condition are revealed. The results show that with the increase in flow rate, the pressure pulsation in the impeller becomes stronger, periodically, and the amplitude decreases. The influence of cavitation on the pressure pulsation in the primary impeller is greater than that in the secondary impeller. When critical cavitation occurs, the low-frequency signal amplitude of pressure pulsation in the primary impeller increases and exceeds the blade frequency, becoming the main frequency.

The goal of this paper is to study numerically the flow physics of a fountain formed by twin-jet impingement on ground. The incompressible Reynolds-Averaged Navier-Stokes (RANS) equations with realizable k-ε and WA (Wray-Agarwal) turbulence model are employed in the numerical simulations with ANSYS Fluent. A series of numerical simulations for straight and inclined fountain formations are conducted by changing the geometric and flow parameters of twin jets and distance between them. The changes in parameters include variations in the jet Reynolds number from 2 × 104 to 8 × 104, impingement height, distance between the centerlines of the two jets from 1.4D to 16D where D is the jet diameter, and ratio of the Reynolds number of the two jets from 1 to 4. It is shown that different Reynolds numbers of the two jets can result in a fountain that inclines towards the jet with smaller Reynolds number. Detailed flow field simulations for a large number of cases are presented, and the flow physics of fountain formation is analyzed for the first time in the literature.

The wind energy pump system is a new green energy technology. The wide high efficiency region of pump is of great significance for energy conservation of wind power pumping system. In this study, factorial experiment design (FED) and computational fluid dynamics (CFD) are employed to optimize the hydraulic design of wind energy centrifugal pump (WECP). The blade outlet width b2, blade outlet angle β2, and blade wrap angle ψ are chosen as factors of FED. The effect of the factors on the efficiency under the conditions of 0.6Qdes, 0.8Qdes, 1.0Qdes, and 1.4Qdes is systematically analyzed. The matching feature of various volute tongue angle with the optimized impeller is also investigated numerically and experimentally. After the optimization, the pump head changes smoothly during full range of flow condition and the high efficiency region is effectively improved. The weighted average efficiency of four conditions increases by 2.55%, which broadens the high efficiency region of WECP globally. Besides, the highest efficiency point moves towards the large flow conditions. The research results provide references for expanding the efficient operation region of WECP.

Hypersonic flows about space vehicles produce flowfields in thermodynamic non-equilibrium with the local Knudsen numbers Kn which may lie in all the three regimes: continuum, transition and rarefied. Continuum flows can be modeled accurately by solving the Navier–Stokes (NS) equations; however, the flows in transition and rarefied regimes require a kinetic approach such as the direct simulation Monte Carlo (DSMC) method or the solution of the Boltzmann equation. The Boltzmann equation and the general solution approach, using the splitting method, will be introduced in this paper. Details of the method used for solving both the classical Boltzmann equation (CBE) and the generalized Boltzmann equation (GBE) are also provided. The gas mixture discussed in this paper may consist of both monoatomic and diatomic gases. In particular, the method is applied to simulate two of the three primary constituents of air (N2, O2, and Ar) in a binary mixture at 1:1 density ratio at Mach 2 and 5, with gases in translational, rotational and vibrational non-equilibrium.

The goal of this paper is to employ a multiobjective genetic algorithm (MOGA) to optimize the shape of a well-known wind turbine airfoil S809 to improve its lift and drag characteristics, in particular to achieve two objectives, that is, to increase its lift and its lift to drag ratio. The commercially available software FLUENT is employed to calculate the flow field on an adaptive structured mesh using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a two-equation k-ω SST turbulence model. The results show significant improvement in both lift coefficient and lift to drag ratio of the optimized airfoil compared to the original S809 airfoil. In addition, MOGA results are in close agreement with those obtained by the adjoint-based optimization technique.