scholarly journals Study on Unsteady Cavitation Flow and Pressure Pulsation Characteristics in the Regulating Valve

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Liu Xiumei ◽  
He Jie ◽  
Li Beibei ◽  
Zhang Chi ◽  
Xu Huawen ◽  
...  
Keyword(s):  
Velocity Distribution ◽  
Pressure Pulsation ◽  
Oscillation Period ◽  
Diameter Ratio ◽  
Radius Ratio ◽  
Peak Time ◽  
Periodic Flow ◽  
Cavitation Flow ◽  
Cavitation Bubbles ◽  
Initial Stage

A combined numerical-experiment investigation on the unsteady cavitation flow and pressure fluctuation characteristics in the regulating valves is conducted in this paper. The cavitation flow in the regulating valve is an unsteady and periodic flow which could be divided into fixed and travelling cavitation bubbles. The fixed cavitation bubbles are formed in the gap in the initial stage and then fell off and formed the travelling cavitation bubbles because of the re-entrant jet. The travelling cavitation bubbles move downstream, oscillate, and break up into several smaller bubbles. Changes in the length/radius ratio (L/R0) of the valve spool is an important factor affecting unsteady cavitation flow and pressure pulsation characteristics in the regulating valve. The length of travelling cavitation bubbles increases firstly and then decreases with increasing time. With the increase of the length/radius ratio (L/R0), the oscillation period of cavitation bubbles also increases. In the initial stage of cavitation bubbles, the velocity distribution inside the regulating valve is relatively stable, and no re-entrant jet could be found although L/R0 is different. In the collapse stage of cavitation bubbles, the velocity distribution becomes extremely unstable because the collapsing cavitation bubbles affect the pressure drop and velocity field in the flow channel. Furthermore, the amplitude of pressure pulsation increases gradually, and the peak time of the pressure pulsation is gradually delayed while increasing the length/diameter ratio.

scholarly journals Investigation into the Influence of Division Pier on the Internal Flow and Pulsation in the Outlet Conduit of an Axial-Flow Pump

2021 ◽  
Vol 11 (15) ◽  
pp. 6774
Author(s):  
Fan Yang ◽  
Dongjin Jiang ◽  
Tieli Wang ◽  
Pengcheng Chang ◽  
Chao Liu ◽  
...  
Keyword(s):  
Velocity Distribution ◽  
Pressure Pulsation ◽  
Axial Flow ◽  
Hydraulic Loss ◽  
Main Frequency ◽  
Starting Position ◽  
The Difference ◽  
Axial Flow Pump ◽  
Outlet Conduit ◽  
Flow Pump

The outlet conduit is an important construction connecting the outlet of the pump guide vane and the outlet pool; in order to study the hydraulic performance of the straight outlet conduit of the axial-flow pump device, this paper adopts the method of numerical simulation and analyzes the influence of the division pier on the pressure and velocity distribution inside and near the wall of the straight outlet conduit based on three design schemes. Four pressure pulsation measuring points were arranged in the straight outlet conduit, and the low-frequency pulsation characteristic information inside the straight outlet conduit with and without the division pier was extracted by wavelet packet reconstruction. The results show that the addition of a division pier has an effect on the hydraulic loss, near-wall pressure and velocity distribution in the straight outlet conduit. A small high-pressure zone is formed near the wall at the starting position of the division pier, and a large high-speed zone is formed on the left side at the starting position of the division pier. The length of the division pier has no significant effect on the flow distribution of the straight outlet conduit and the pressure and velocity distribution near the wall. Under different working conditions, each monitoring point has the maximum energy in the sub-band (0~31.25 Hz). With the increase of the flow rate, the total pressure energy of the straight outlet conduit decreases gradually. Under each condition, the difference of the energy proportion of the horizontal monitoring points of the straight outlet conduit is small, and the difference of the energy proportion of the two monitoring points at the top and bottom of the outlet channel is relatively large. The energy of the two monitoring points in the straight outlet conduit with a division pier is smaller than that of the two monitoring points in the straight outlet conduit without a division pier. There are differences in the main frequency and the power spectrum corresponding to the main frequency of the monitoring points in the straight outlet conduit, and the reasonable setting of the division pier is conducive to reducing the pressure pulsation of the flow in the straight outlet conduit and is beneficial to the safe and stable operation of the pump device.

Effects of Trailing Edge Position of Splitter Blade on the Pressure Pulsation in a Low Specific Centrifugal Pump

2019 ◽  
Author(s):  
Jinfeng Zhang
Keyword(s):  
Velocity Distribution ◽  
Turbulence Intensity ◽  
Pressure Fluctuation ◽  
Relative Velocity ◽  
Pressure Pulsation ◽  
Suction Side ◽  
Maximum Pressure ◽  
Trailing Edge ◽  
Flow Rates ◽  
Pulsation Amplitude

Abstract A combination of experimental and numerical simulation was carried out to analyze influence of trailing edge position of splitter blade on the pressure fluctuation in low specific pumps with and without splitter blades under different flow rates. Performance experiments and PIV tests were performed to verify the results of numerical calculation. Several monitor points were placed in the calculation model pump to collect the pressure fluctuation signals, which were processed by Fast Fourier Transform to obtain the frequency results for further analysis. Besides, turbulence intensity and relative velocity distribution were also analyzed in regions of impeller and volute. The results showed that compared with prototype without splitter blade and the splitter blade schemes, when the trailing edge of splitter blade deviates to the suction side of main blade, the maximum pressure pulsation amplitudes are the lowest at different monitoring points of model pump. And the variation of pressure pulsation amplitude in this scheme is relatively stable with the change of flow rates compared with other schemes. Furthermore, the splitter blade scheme with an appropriate trailing edge position has the lowest average turbulence intensity and optimal relative velocity distribution in main flow passage component. Therefore, this paper proposes a reference scheme of the trailing edge position of the splitter blade to effectively decrease predominate pressure pulsation amplitude.

The stability of viscous axial flow in an annulus with a rotating inner cylinder

1977 ◽  
Vol 352 (1670) ◽  
pp. 351-380 ◽  
Keyword(s):  
Velocity Distribution ◽  
Tangential Velocity ◽  
Axial Flow ◽  
Radius Ratio ◽  
Neutral Stability ◽  
Axial Distribution ◽  
Critical Wavelength ◽  
Explicit Finite Difference ◽  
The Stability ◽  
The Galerkin Method

Predictions by two methods are presented of the onset of instability in developed tangential flow in a concentric annulus due to inner cylinder rotation. The first formulation is as an initial-value problem in which the time evolution of initially-distributed small random vorticity perturbations of given axial wavelength is monitored by numerically integrating the unsteady perturbation equations by explicit finite-difference procedure. The second method is the Galerkin approach where an eigenvalue problem is formulated in which the linearized disturbance equations are solved to predict the neutral stability condition. Comparisons for a radius ratio N of 0.9 and Re up to 350 show that an averaged axial velocity distribution and the exact axial distribution yield similar predictions of Ta c and the corresponding critical wavelength; these however, differ markedly from previous narrow-gap predictions based on a parabolic approximation to the axial distribution. The current use of the exact developed tangential velocity distribution permits investigation by the Galerkin method for 0.9≽ N ≽ 0.1 and Re up to 2000. Computations of Ta c are in satisfactory agreement with earlier measurements for N of 0.95, 0.82 and 0.81 and accord well with current measurements over the range 50 ≼ Re ≼ 400 in an annulus of radius ratio 0.9.

Numerical Simulation of the Transient Flow in a Pump-Turbine During the Load Rejection Process With Special Emphasis on the Cavitation Effect

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Xiaolong Fu ◽  
Deyou Li ◽  
Hongjie Wang ◽  
Guanghui Zhang ◽  
Zhenggui Li ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Single Phase ◽  
Pressure Pulsation ◽  
Phase Flow ◽  
Cavitation Flow ◽  
Single Phase Flow ◽  
Pump Turbine ◽  
Cavitation Effect ◽  
Simulation Results ◽  
Load Rejection Process

Abstract At present, pumped-storage power technology is the only available and effective way for the load balancing and energy storage in the grid network scale. During the frequent switch back and forth conditions, there are severe pressure pulsation and cavitation in pump-turbines. However, their generation mechanism has not been determined yet. This work contributes to the numerical simulation of the transient behaviors in a prototype pump-turbine during the load rejection process with special emphasis on cavitation effect. In this study, the two-dimensional dynamic remesh and variable speed slide mesh methodologies were employed to perform the simulation of the transient single-phase flow and cavitation flow in a pump-turbine. The simulation results of single-phase flow and cavitation flow were both consistent with the experimental data except in local regions based on the experimental validation of prototype tests. However, the numerical results considering cavitation effects have a better behavior than those of single-phase flow in the predictions of pressure pulsation and rotational speed. Then, the cavitation flow simulation results were analyzed deeply, especially in pressure pulsation and cavitation flow field. Analysis revealed that three typical complex frequency components of pressure were captured in the cavitation flow, which significantly affect the axial hydraulic thrust on the runner. And it is validated that they are primarily induced by the cavity collapse near the trailing edges of the runner blades in reverse pump mode and the interaction between cavitation and vortex rope in draft-tube in turbine mode.

Numerical investigation of the effects of splitter blade deflection on the pressure pulsation in a low specific speed centrifugal pump

2019 ◽  
Vol 234 (4) ◽  
pp. 420-432 ◽  
Author(s):  
Jinfeng Zhang ◽  
Guidong Li ◽  
Jieyun Mao ◽  
Shouqi Yuan ◽  
Yefei Qu ◽  
...  
Keyword(s):  
Velocity Distribution ◽  
Turbulence Intensity ◽  
Pressure Fluctuation ◽  
Relative Velocity ◽  
Pressure Pulsation ◽  
Maximum Pressure ◽  
Flow Rates ◽  
Pulsation Amplitude ◽  
Low Specific Speed ◽  
Specific Speed

A combination of experimental and numerical simulation was carried out to analyze the influences of the splitter blade deflection on the performance and pressure fluctuation in low specific speed pumps with and without splitter blades under different flow rates. Performance experiments and particle image velocimetry (PIV) tests were performed to verify the results of the numerical calculation. Several monitoring points were placed in the calculation model pump to collect the pressure fluctuation signals, which were processed by Fast Fourier Transform to obtain the frequency results for further analysis. In addition, turbulence intensity and relative velocity distribution were also analyzed in the regions of the impeller and volute. The results showed that compared with a prototype without a splitter blade and the splitter blade schemes, the maximum pressure pulsation amplitudes are the lowest at different monitoring points of the model pump when the splitter blade deflects to the suction side of the main blade. The variation of pressure pulsation amplitude in this scheme is relatively stable with the change of flow rates compared with other schemes. Furthermore, the impeller scheme with an appropriate deflection of the splitter blade has the lowest turbulence intensity and optimal relative velocity distribution in the main flow passage. Therefore, this paper proposes a reference scheme of the impeller with the splitter blade to effectively decrease the predominate pressure pulsation amplitude.

Effects of Blade Pressure Side Modification On Unsteady Pressure Pulsation and Flow Structures in a Centrifugal Pump

2021 ◽  
Author(s):  
Chengshuo Wu ◽  
Wenqi Zhang ◽  
Peng Wu ◽  
Jiale Yi ◽  
Haojie Ye ◽  
...  
Keyword(s):  
Velocity Distribution ◽  
Centrifugal Pump ◽  
Pressure Pulsation ◽  
Internal Flow ◽  
Flow Structures ◽  
Pressure Side ◽  
Unsteady Pressure ◽  
Operation Conditions ◽  
Impeller Outlet ◽  
Steady State Simulation

Abstract In this paper, the effects of modifying the blade pressure side on unsteady pressure pulsation and flow structures in a low specific speed centrifugal pump are carried out by experimental and CFD. Seven monitor points are arranged in the circumferential direction of the impeller outlet to capture the pressure signals in the volute at the flow rate of 0.2-1.6Qd. Results show that blade PS modification introduced here can significantly alleviate the amplitude of pressure pulsation at blade passing frequency in all concerned operation conditions. The volute domain is replaced by an even outlet region for CFD analysis to study the effects on internal flow field. The SST turbulence model is adopted for steady-state simulation while the DDES based on the SST approach is adopted for transient simulation. Results show that local velocity fluctuation is the dominant reason for pressure pulsation in the volute. After PS modification, the relative velocity distribution at impeller outlet is more uniform and the intensity of shedding vortex at the blade trailing edge decreases significantly. The change of internal flow structure improves the uniformity of circumferential velocity distribution at downstream of impeller outlet, which leads to the decrease of pressure fluctuation amplitude in the volute. Meanwhile, the Local Euler Head distribution and the blade loading of PS are presented and compared. Results show that the reduction of pressure pulsation attributes to the more uniform energy distribution at impeller outlet which is achieved by actively unloading the PS of the modified blades.

Research on Cavitation Induced Noise in a Centrifugal Pump

2011 ◽  
Author(s):  
Bo Gao ◽  
Minguan Yang ◽  
Zhong Li ◽  
Can Kang
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
High Frequency ◽  
Noise Level ◽  
Volume Fraction ◽  
Operating Conditions ◽  
Frequency Noise ◽  
Cavitation Flow ◽  
Cavitation Noise ◽  
Cavitation Bubbles

To study the cavitation flow field and cavitation induced noise features in a centrifugal pump, a model pump is chosen as the research object. Cavitation flow field at design and off-design operating conditions is visualized by high speed camera. The cavitation bubbles spatial distribution changing with pump net positive suction head (NPSH) value have been captured. Meanwhile, cavitation noise signals from the pump at the corresponding operating conditions have been acquired in the frequency band from 10 up to 8kHz. Noise levels at broadband frequency and discrete frequency, such as rotating frequency (RF) and blade pass frequency (BPF), are discussed. It is of help to recognize the relationship between cavitation bubbles and emitted noise spectrum characteristics. Experimental results indicate that the total noise level is unlikely to raise before and in the cavitation inception period. But sound pressure level (SPL) over high frequency broadband increases obviously, as well as SPL at BPF and half of that. It is hard to change at RF. When the NPSH goes down until to the onset of cavitation damage, cavitation cloud appears. The volume fraction of bubbles in every impeller passage is different. The total and high frequency noise level reach peak values near the NPSH critical point. The discrete tone at half of BPF also raises steeply. Cavitation bubbles are filled both on suction and pressure side of the blades in fully developed cavitation stage. Emitted noise energy fluctuates due to the unsteady features of internal flow in the pump.

scholarly journals Experimental and numerical investigation of geometric effect on cavitation flow through orifice

2021 ◽  
Vol 22 ◽  
pp. 31
Author(s):  
Mohammad Reza Davoudi ◽  
Miralam Mahdi
Keyword(s):  
Numerical Solutions ◽  
Great Influence ◽  
Finite Volume Methods ◽  
Diameter Ratio ◽  
Cavitation Flow ◽  
Cavitation Model ◽  
Geometric Effect ◽  
Single Hole ◽  
Cavitation Phenomenon ◽  
Flow Through

Due to the set of factors and conditions, the stream pressure through the orifice decreases, which can lead to the occurrence of the cavitation phenomenon. The most important factor in this regard is the geometry of orifice. In the first part of this study, the flow through two types of single-hole orifice and a multi-hole orifice were experimentally studied. The results showed that the single hole orifice with a two-sided sloped edge caused less pressure drop, which in order to control the cavitation phenomenon is more efficient compared to the single-hole and multi-hole orifices with one-sided sloped edges and the same equal diameter ratio. Additionally, all experiments were simulated in the second part of this research using finite volume methods. Considering the complexity of the problem, several numerical solutions were investigated to approach the experimental results. Finally, it was determined that the type of gridding, turbulence method, and cavitation model have a great influence on the accuracy of the obtained numerical results.

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

Machines ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 32
Author(s):  
Xiumei Liu ◽  
Jie He ◽  
Yongwei Xie ◽  
Beibei Li ◽  
Yujia Zhang ◽  
...  
Keyword(s):  
Flow Field ◽  
Measurement System ◽  
High Speed ◽  
Pressure Pulsation ◽  
Pressure Fluctuations ◽  
Inlet Pressure ◽  
Maximum Pressure ◽  
Cavitation Flow ◽  
Measuring Point ◽  
The Mean

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.

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