The gas film characteristics of bidirectional dry gas seals with trapezoidal grooves were studied by comparing with the traditional spiral grooved gas seals. The two-dimensional compressible Reynolds equation was solved by finite difference method. The typical performance parameters including gas film force, leakage, gas film stiffness, and torque were compared under different parametrical conditions. The pattern of trapezoidal grooves wasted part of groove area in bidirectional operation; though the grooves were designed by overlapping trapezoids to make up for the performance loss, the resulting decrease in gas film stiffness was notable. The resisting disturbance ability of trapezoidal grooved seals was poorer than that of spiral grooved seals, while the load-carrying capacity, sealing ability, and power consumption of trapezoidal grooved seals differed slightly from those of spiral grooved seals. The trapezoidal grooved seals are not recommended in unidirectional rotational compressors due to the decreasing stability.

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Gravitation vortex-type water turbines use gravitational vortex generated when water is guided into the tank and drained from the hole at the bottom of the tank. When a circular tank is used, a runner inlet flow becomes uneven circumferentially, resulting in poor performance. To control the flow in the tank and make it uniform in the circumferential direction, we used a volute tank to elucidate the impact of tank geometry on the performance and flow field of the gravitation vortex-type water turbines. We further investigated the performance and flow field of the water turbine using volute and circular tanks through experiments and free surface flow analysis. We compare the performance and flow field of the volute tank to those of the circular tank. We found that the effective head and turbine output of the volute tank decreased more than those of the circular tank, whereas the water turbine efficiency of the volute tank improved more than that of the circular tank at low to medium rotational speeds. This is because the theoretical head of the volute tank was smaller than that of the circular tank, but the runner inlet flow was uniform in the circumferential direction, and the loss in the tank, which is the dominant loss in the circular tank, was greatly reduced.

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A pump as turbine is optimized firstly, then the distribution of gas, the vortex structure evolution, the force characteristic and energy conversion characteristic are analyzed under pure liquid and gas-liquid two-phase conditions. The result manifests that because of the existence of gas, the pressure gradient decreased and the normal flow of high-pressure fluid in the turbine is inhibited by gas. The radial force vector, the time domain value and the main frequency amplitude are all smaller than that of pure liquid condition, and hydraulic vibration is more likely to be caused by the flow uncertainty of gas. The energy conversion performance of the unit is worse.

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Based on the pressure parameters of the turbine, the operation condition of the turbine is determined. Based on the input data, the operation condition of the turbine is predicted by the long short-term memory network. Firstly, the identification model of BP neural network method is established to identify the specific working conditions by using the historical values obtained in the practical engineering application. Then, according to the correlation between the measuring points, the multiple time series long short-term memory network prediction model (LSTM) is constructed, and the state trend of the hydraulic turbine unit under this condition is predicted. The corresponding punishment factors are calculated by using the prediction data of each measuring point and the threshold value of the prediction band, which are mapped into the radar chart. Finally, an anomaly early warning system with flexible early warning rules based on equipment deviation index is proposed. Through the experimental analysis, the validity of the long short-term memory network prediction model and the radar graph model for calculating the deviation degree of the equipment is verified, and the advanced warning for the abnormal state of different acquisition points under different working conditions is realized, which provides a new method for the abnormal prediction and fault diagnosis of the hydraulic turbine.

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Pump efficiency correction equations for converting from water to viscous liquids have been established for the turbulent-flow and laminar-flow regions. However, the two equations are discontinuous in the transient-flow region. This paper proposes a new equation for the transient-flow region that is based on fluid-dynamical considerations. Moreover, an alternative equation is examined for the turbulent-flow region that avoids an underestimate caused by the current efficiency correction equation that was adopted in ISO/TR 17766.

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A computational model is formulated to investigate the unsteady flow characteristics of a circular cylinder behind an impinging airfoil near-wake at Re=200. The distance between the airfoil trailing edge and the downstream cylinder axis is fixed at 1.5D where D is the diameter of circular cylinder and the lateral spacing is varied from –5 to 5 so as to numerically investigate the effect of lateral spacing on the flow characteristics. The present work is concerned on the following aspects: the general flow patterns, the vortex shedding frequency, force fluctuations and spectra, as well as the effect of lateral spacing on the flow features at low Reynolds number and small axial spacing. The calculated flow pattern and its comparison with the visualization by Laser-Induced Fluorescence (LIF) technique are conducted. It is determined that three regimes can be defined in terms of H/D, where H is the distance between the cylinder center and the line extended from the airfoil leading edge to trailing edge. And four kinds of typical flow pattern associated with the three regimes can be identified accordingly. It is interesting to find that both the fluctuations of lift and drag forces on the circular cylinder exhibit symmetric features centered at H/D=0 and the dump distribution of is found as well.

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In this study, the cavitation flow field of a centrifugal pump with four different positions of balance holes was studied by experiment and simulation. The results show that: the critical cavitation number decreases first and then increases with the position, the critical cavitation numbers of positions 2, 3 and 4 are smaller than the original model, and the effect of improving cavitation performance is obvious. The input of the high-pressure liquid from the balance cavity increases the absolute pressure of the cavitation area, and changes the pressure gradient in the cavitation area, then the cavitation suppressed. The position of the balance hole has obvious influence on the axial force, positions 2 and 3 reduce the axial force and improve the stress condition of the centrifugal pump, while positions 1 and 4 increase the axial force. It can be concluded that the positions o 2, 3 and 4 can improve the cavitation performance, so the cavitation performance of the centrifugal pump can be significantly improved by setting balance holes along the 2, 3 and 4 lines, also the balance hole should be avoided at position 1.

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The rice flow characteristics in pneumatic conveying determined the performance of pneumatic metering device for rice seed. The non-spherical rice seed motion in pneumatic conveying with bend was investigated by CFD-DEM simulation. The rice seed particle model was established by multi-sphere method, and a typical pneumatic conveying horizontal-vertical pipe with bend was selected. The applicability of three drag force models on non-spherical particle was compared. The particle flow characteristics in different pipes including the vertical-horizontal pipe and the horizontal-horizontal pipe were investigated. The non-spherical particle formed a particle rope at the outlet of bend, and the particle rope dispersed at downstream of the vertical pipe. The effect of particle shape on gas-solid flow characteristics was obtained. The gas velocity value in the bend for non-spherical rice particle was higher than that for spherical particle. The non-spherical rice particle rope dispersed more slowly than the spherical particle rope. The particle velocity profile of non-spherical and spherical particles was similar. The differences of the gas-solid flow predicted by Free stream model, Ergun and Wen & Yu model, and De Filice model were limited. The particle rope can also be formed in vertical-horizontal pipe and horizontal-horizontal pipe, but its dispersion represented different features. The results showed that particle shape and structure of pipe can influence the gas-solid flow characteristics, and a suitable particle model was important for the gas-solid flow simulation by CFD-DEM.

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To improve the airflow distribution consistency of each branch in the pneumatic fertilizer transportation system, so as to reduce the influence of airflow instability on the uniformity and stability of fertilizer transportation, as well as the energy waste in the process of pneumatic fertilizer transportation, a centralized pneumatic fertilizer transportation system for deep fertilization device was designed. Through theoretical calculation, the needed air flow rate, airflow speed and fertilizer pipe diameter of the system were obtained, and the fan was selected. Based on the Fluent simulation and bench tests, the influence of three air distribution method of placing fan at the end of main duct, placing fan in the middle of main duct and centralized air distribution on the airflow velocity and consistency of each branch was analyzed. The results showed that the airflow consistency of each branch in the centralized air distribution method was the best. Taking the air velocity at the outlet of each branch and its variation coefficient as the evaluation index, single factor and orthogonal simulation tests was carried out to optimize the structural parameters of centralized air distribution device. The simulation results showed that the primary and secondary factors affecting the air distribution consistency were: A (sidewall inclination angle), B (branch diameter), C (branch distance), A×B (interaction between A and B), B×C (interaction between B and C), A×C (interaction between A and C), and all the factors and their interactions had significant effects. The best parameter combination was sidewall inclination angle 15°, branch diameter 32 mm, branch distance 43 mm. With the combination, the variation coefficient of airflow velocity was 0.27% in simulation test and 1.23% in bench test. This research optimized the structure and parameters of pneumatic fertilizer transporting system, and provided references for the design and optimization of pneumatic fertilization and seeding device.

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The corresponding author in the original paper is corrected to Junhu Yang and the corresponding email is lzyangjh@lut.cn.

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