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.
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.
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.
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.
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.