Study on the Comparison of the Hydraulic Performance and Pressure Pulsation Characteristics of a Shaft Front-Positioned and a Shaft Rear-Positioned Tubular Pump Devices

The shaft front-positioned tubular pump device has been widely used in practical engineering, but the shaft rear-positioned pump device is rarely used due to its low efficiency. To investigate the effect of the shaft position on the performance of a tubular pump device, the optimized shaft front-positioned and shaft rear-positioned pump devices were compared and studied. Both tubular pump devices adopt a TJ04-ZL-06 pump model. Three dimensional steady and unsteady numerical simulations combined with model tests were used to compare the difference of two pump devices. Meanwhile, three groups of pressure monitoring points were set at different positions of the pump device to collect pressure information and pressure pulsation was analyzed. The results show that, the highest efficiency of the shaft front and rear positioned pump device are 81.78% and 80.26%, respectively. The hydraulic performance of the two inlet passages is excellent, and the hydraulic loss is close to each other. Therefore, the hydraulic performance of the pump device depends mainly on the hydraulic performance of the outlet passage. The shaft is set in the outlet passage, which will increase the hydraulic loss and reduce efficiency. Under design conditions, the pressure pulsation amplitude at the impeller inlet is the largest, and the pressure pulsation amplitude increases from the hub to the shroud. The pressure pulsation amplitude of the shaft rear-positioned pump device is larger than that of the shaft front-positioned pump device. The pressure pulsation at the impeller inlet and outlet is greatly affected by the number of blades, and the main frequency is three times the RF. This study can provide practical and effective guidance for the design and optimization of the shaft front-positioned and rear-positioned tubular pump devices, which has theoretical value and application value.

Analysis of the Influence of Inlet Guide Vanes on the Performance of Shaft Tubular Pumps

To study the influence of inlet guide vanes (IGVs) on the pressure pulsation of a shaft tubular pump, this paper first conducts an experiment to study IGVs. Then, numerical calculations of the shaft tubular pump with and without IGVs are performed to analyze the hydraulic performance and pressure fluctuation characteristics. Finally, the reliability and accuracy of the data are verified by a model test. Numerical simulation results show that with additional IGVs, the pressure pulsation amplitude at the impeller inlet first decreases and then increases under small-flow and design conditions but gradually increases under large-flow conditions. When the IGVs are added to the impeller inlet of the shaft tubular pump, the hydraulic loss in front of the impeller inlet increases, resulting in a significant drop in the head and efficiency of the pump device when the flow rate is less than 1.12 Qd; when the flow rate is greater than 1.12Qd, the head and efficiency of the pump device do not change significantly. IGVs can improve the condition of impeller water inflow and reduce pressure fluctuation on the blade surface.

Numerical Simulation and Experiment of Hydraulic Loss of Two-Stage Flap Valves

As a type of flap valve evolved from integral flap valve, two-stage flap valve has the advantages of large opening angle, small hydraulic loss and small impact force on the flap valve seat when the flap valve is closed. In order to analyze and study the hydraulic loss characteristics of the two-stage flap valve, this paper takes a pump station as an example. Based on theoretical analysis, combined with numerical simulation and model test, the hydraulic loss of two-stage flap valve is studied, and the relationship between hydraulic loss and pump station flow is obtained. According to the test results, the hydraulic loss of two-stage flap valve increases with the increase of flow rate under the same opening angle of flap valve. Under the same flow condition, the larger the opening angle of the flap valve is, the smaller the hydraulic loss of the two-stage flap valve is. When the opening angle of the upper flap valve is greater than 46° and the opening angle of the lower flap valve is greater than 64°, the hydraulic loss is less than 70mm and tends to be stable. The influence of hydraulic loss on the performance of pump device is gradually weakened. The relationship between hydraulic loss and flow of two-stage flap valve no longer satisfies the relationship of square under the constant opening angle. Moreover, the larger the opening angle of the two-stage flap valve is, the greater the relationship between hydraulic loss and flow is. Compared with the integral flap valve, the two-stage flap valve has better structural form and hydraulic characteristics, and has little influence on the performance of the pump device, which can provide reference for the application of the two-stage flap valve in the pump station.

Investigation of Complex Characteristics of Waterjet Propulsion Device with Intake Grid

The intake grid is always installed technically to protect the impeller at the entrance of the waterjet propulsion device’s inlet duct affecting its performance. Therefore, this study discussed the complex features of the circular, rectangular, and streamlined intake grid. Consistent geometry size of the intake grid mentioned above is to be maintained to guarantee the identical flow capacity at the entrance of inlet duct. Using experimental and simulated method, the outcomes are drawn as below. Rather than the circular and rectangular intake grid, the streamlined intake grid can improve the hydraulic performance of the waterjet propulsion device. The numerical method is proved to be correct as the consistence of the hydraulic characteristic between the test and simulated results. The causes of hydraulic loss in the contraction segment and straight pipe segment are the intake grid and the inflow velocity, respectively; meanwhile, the loss in the belt pipe segment owes to the vortex, flow separation, and impact on the back. The intake grid has a positive effect on the depth of the inlet velocity profile, but a negative effect on the width of it. The intake grid installation results in thrust reduction, the progress of velocity-weighted average angle, and the regress of axial velocity uniformity. The performance of waterjet propulsion device is complex and evaluated by the hydraulic performance index (HPI), thrust performance index (TPI), and characteristic of flow pattern index (CFPI). Based on the three evaluation indexes, the streamlined scheme is raised to be the recommended scheme.

RANS CFD Analysis of Hump Formation Mechanism in Double-Suction Centrifugal Pump under Part Load Condition

The RANS (Reynolds-averaged Navier–Stokes equations) with CFD (Computational Fluid Dynamics) simulation method is used to analyze the head hump formation mechanism in the double-suction centrifugal pump under a part load condition. The purpose is to establish a clear connection between the head hump and the microcosmic flow field structure, and reveal the influence mechanism between them. It is found that the diffuser stall causes a change in the impeller capacity for work, and this is the most critical reason for hump formation. The change in the hydraulic loss of volute is also a reason for hump, and it is analyzed using the energy balance equation. The hump formation mechanism has not been fully revealed so far. This paper found the most critical flow structure inducing hump and revealed its inducing mechanism, and greatly promoted the understanding of hump formation. The impeller capacity for work is analyzed using torque and rotational speed directly, avoiding large error caused by the Euler head formula, greatly enhancing the accuracy of establishing the connection between the impeller capacity for work and the coherent structure in the flow field under a part load condition. When a pump is running in the hump area, a strong vibration and noise are prone to occur, endangering the pump safety and reliability, and even the pump start and the transition of different working conditions may be interrupted. Revealing the hump formation mechanism provides a key theoretical basis for suppressing hump. Hump problems are widespread in many kinds of pumps, causing a series of troubles and hazards. The analysis method in this paper also provides a reference for other pumps.

Investigation on Clocking Effect of Diffuser in a Multi-Stage Centrifugal Pump

The clocking effect is an important phenomenon in the multi-stage Rotating machinery. In order to master the rules and mechanism of diffuser clocking effect on the performance of multi-stage centrifugal pump, the orthogonal tests were applied to design the test scheme. The energy performance and outlet pressure pulsation of a multi-stage centrifugal pump with different diffuser clocking positions were synchronously measured. It was found that the diffuser clocking position had little influence on the energy performance, but had an obvious effect on the outlet pressure pulsation. When the diffuser clocking positions were 0°, 30°, 30° and 30° (CL4), the effective value of outlet pressure pulsation and its amplitude at the main frequency (Impeller Rotation Frequency) were decreased the most, approximately 27.2 % and 38.5 % ,respectively. The CFD method was used to simulate the unsteady flow in the pump with the optimal diffuser clocking position (CL4) and without diffuser clocking position (CL1) respectively to reveal the mechanism of diffuser clocking effect. The simulation results showed that the change of diffuser clocking position can improve the inlet and outlet velocity distribution and reduce the area of high turbulent kinetic energy and the number of cores in the outlet flow passage, which is beneficial to the operation stability of the pump. Compared with the CL1, the hydraulic loss in the four diffusers was reduced by 2.43 %, 12.15 %, 11.43 % and 13.19 % respectively under the optimal diffuser clocking scheme (CL4), and the total reduction of hydraulic loss is about 1.11 % of the pump head.

Effect of Tip Clearance on Helico-Axial Flow Pump Performance at Off-Design Case

To reveal the effect of tip clearance on the flow behaviors and pressurization performance of a helico-axial flow pump, the standard k-ε turbulence model is employed to simulate the flow characteristics in the self-developed helico-axial flow pump. The pressure, streamlines and turbulent kinetic energy in a helico-axial flow pump are analyzed. Results show that the tip leakage flow (TLF) forms a tip-separation vortex (TSV) when it enters the tip clearance and forms a tip-leakage vortex (TLV) when it leaves the tip clearance. As the blade tip clearance increases, the TLV moves along the blade from the leading edge (LE) to trailing edge (TE). At the same time, the entrainment between the TLV and the main flow deteriorates the flow pattern in the pump and causes great hydraulic loss. In addition, the existence of tip clearance also increases the possibility of TLV cavitation and has a great effect on the pressurization performance of the helico-axial flow pump. The research results provide the theoretical basis for the structural optimization design of the helico-axial flow pump.

Numerical Simulation on the Influence of Rotating Speed on the Hydraulic Loss Characteristics of Desalination Energy Recovery Turbine

The performance of energy recovery turbine (ERT) directly determines the cost and energy consumption of reverse osmosis desalination. In order to study the performance and loss mechanisms of ERT under different conditions, the external characteristics and the losses of different components were quantitatively analyzed. The loss mechanisms of each component in the turbine were revealed through the comparative analysis of the internal flow field. The results show that the efficiency is 2.2% higher than that at the design speed when turbine runs at n = 22000 r/min. The impeller losses account for more than 67% of the total losses. The impeller loss is mainly observed at the leading edge. The vortex on the pressure side of the leading edge is caused by the impact effect, while the vortex on the suction side of the leading edge is caused by the flow separation. With the increase in the rotating speed, the loss caused by flow separation in impeller decreases obviously. The volute loss is mainly observed near the tongue, which is caused by the flow separation at the tongue. The design of the tongue is very important to the performance of the volute. The turbulent kinetic energy (TKE) and loss decrease with the increase in the rotating speed. The loss in the draft tube is mainly observed at the inlet core. With the increase in the rotating speed, the turbulence pulsation and the radial pressure fluctuation amplitude reduce. Therefore, the turbine can be operated at the design or slightly higher than the design rotating speed under the condition that both the hydraulic condition and the intensity are satisfied, which are conducive to the efficient utilization of energy.