Investigation of Unsteady Pressure Pulsation in New Type Dishwasher Pump with Special Double Tongue Volute

Through numerical simulations, this work analyzes the unsteady pressure pulsation characteristics in new type of dishwasher pump with double tongue volute and single tongue volute, under volute static and rotation conditions. Likewise, the performance tests were also carried out to verify the numerical results. Multiple monitoring points were set at the various positions of new type dishwasher pump to collect the pressure pulsation signals, and the relevant frequency signals were obtained via Fast Fourier Transform, to analyze the influence of volute tongue and its passive speed on the pump performance. The results reveal that when the double tongue volute is stationary, the pressure pulsation amplitudes increase from the impeller inlet to the impeller outlet. Under the influence of shedding vortex, the pressure pulsation in the lateral region of tongue becomes disorganized, and the main frequency of pressure pulsation changes from blade frequency to shaft frequency. In addition, compared with the static volute, double tongue volute can effectively guide the water flow out of the tongue during the rotation process, thus ensuring good periodicity for pressure pulsation in the tongue region. Accordingly, a volute reference scheme with passive rotation speed is proposed in this study, which can effectively improve the pressure pulsation at tongue position, and provides a new idea for rotor-stator interference to guide the innovation of dishwasher.

Influence of grooved volute casing parameters on pressure pulsation and erosion wear characteristics in a centrifugal pump

Previous work has shown that performance and internal flow characteristics of a centrifugal pump can be significantly improved with grooved volute casing (GVC). However, it has been found that the selection of the design parameters of the groove structure also has a direct impact on the performance output, internal flow pressure pulsation and erosion wear characteristics of the overflow components of centrifugal pump, so it is necessary to further analyze the design rules of the groove structure parameters. In this study, we first investigated the influence of the number of grooves on the head, efficiency and unsteady pressure pulsation characteristics of the internal flow field of the centrifugal pump, and on this basis, the correlation between different particle parameters and the erosion wear of key overflow components under the conditions of solid–liquid two-phase flow were also studied, and the erosion wear characteristics of the inner wall of the volute casing of centrifugal pump with GVC and original volute casing (OVC) structures were compared. This research leads to the conclusion that when the number of grooves is 3, the groove structure has the least influence on the performance of the centrifugal pump, and the overall change of the performance curve is more stable. Additionally, the pressure pulsation at each monitoring point of the GVC under the same flow condition is smaller, and when the number of grooves increases, the pressure pulsation amplitude also decreases. When the number of grooves is 3, the GVC shows a more significant flow improvement effect under all flow conditions. Based on the improvement of the groove structure on the flow stability, the particle motion behavior can be affected at the same time, so that the pump with GVC can mitigate the erosion wear of the inner wall of the volute casing under the solid–liquid two-phase flow conditions, which improves the critical performance and service life of the key overflow components of the pump.

Investigation on Unsteady Cavitation Flow and Excited Pressure Fluctuations in Regulating Valve

A multi-field synchronous measurement system for the cavitation flow in a regulating valve was established. The system combines a high-speed full-flow field display system with a pressure measurement system to realize the simultaneous acquisition of cavitation shapes and pressure pulsations. Cavitation flow occurs near the throttle orifice, which is obviously a quasi-periodic behavior. The unsteady cavitation flow mainly includes three stages: the growth of the attached cavity, the fracture and shedding of the attached cavity and the growth and collapse of the free cavity. The time evolution of the cavitation behaviors is highly related with excited pressure fluctuations. With the increasing attached cavity area, the corresponding pressure in the flow field decreases slowly. When the attached cavity falls off and develops downstream, the cavity area decreases gradually, and the pressure increases gradually. When the free cavity shrinks and collapses, the pressure in the flow field reaches the peak value. The pressure pulsation and the change of cavity area have the same dominant frequency, around 2000 Hz, at the monitoring point in the upstream, throat and expansion monitoring points. Furthermore, with increasing inlet pressure, the mean and variance values of cavitation area become larger, and the excited pressure fluctuation at each measuring point becomes more intense. The mean value of pulsating pressure at the throat gradually increases, while the pressure in the expansion section presents a downward trend. The variance of pressure pulsation and the maximum pressure also increase gradually with the increase in inlet pressure. The change of cavitation area and the pressure pulsation in the regulating valve complement each other. The results in this paper could provide experimental guidance on optimizing the structure of the valve, inhibiting cavitation occurrence and prolonging the service life of the valve.

Comparative analysis of air and water flows in simplified hydraulic turbine models

This article presents a comparative analysis of flow characteristics behind a hydraulic turbine runner in air and water. Swirling flow with a precessing vortex core (PVC) was investigated using a laser Doppler anemometer and pressure pulsation sensors. The experiments were conducted on aerodynamic and hydrodynamic test rigs over a wide range of hydraulic turbine operating conditions. Part-load modes of hydraulic turbine operation were investigated using the Fourier transform of pressure pulsations obtained from acoustic sensors. The features of the swirling flow were shown for the range of operating conditions from deep partl-load to overload.

Influence of non-uniform inflow on unsteady internal flow characteristics of waterjet pump

Waterjet propulsion has many advantages when operating at high-speed conditions. As a special way of navigation, it is mostly used in high-speed ships and shallow draft ships. In this paper, a mixed-flow waterjet pump was taken as the research object. For the two cases of non-uniform inflow and uniform inflow, a modified RANS/LES method was adopted for unsteady calculation of the whole channel, aiming at investigating the influence mechanism of the non-uniform inflow on the energy performance and pressure pulsation characteristics of the waterjet pump. The hydrodynamic characteristics of the waterjet pump were comprehensively analyzed such as head, efficiency, axial-force, internal flow and pressure pulsation. It is found that the non-uniform inflow will reduce the external characteristics of the waterjet pump and lead to the huge fluctuation of energy performance with time. Low-speed swirls occur locally in the intake duct for non-uniform inflow, in which condition the vorticity is much higher than that for uniform inflow. In terms of the low-speed area, [Formula: see text] and [Formula: see text], the values under non-uniform inflow condition are generally larger than those under uniform flow condition when in the impeller and guide vane zone. The dominant frequencies of pressure pulsation are, respectively, [Formula: see text], 7[Formula: see text] and 4[Formula: see text] in the intake duct, impeller and diffuser, which are almost consitent for the two cases. However, the frequency features are more diverse, and the amplitudes corresponding to the same frequencies are more intense for non-uniform inflow.

A Study on the Cavitation and Pressure Pulsation Characteristics in the Impeller of an LNG Submerged Pump

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.

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.