Study on Unsteady Tip Leakage Vortex Cloud Cavitation in an Axial Flow Pump Using an Improved Numerical Method

2015 ◽  
Author(s):  
Desheng Zhang ◽  
Weidong Shi
Keyword(s):  
Shear Layer ◽  
Numerical Method ◽  
Three Dimensional ◽  
Axial Flow ◽  
Cloud Cavitation ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Sheet Cavitation ◽  
Axial Flow Pump ◽  
Flow Pump

The aim of the present investigation is to simulate and analyze the formation of three-dimensional tip leakage vortex (TLV) cloud cavitation and the periodic collapse of TLV-induced vortices cavitation. The improved SST k-ω turbulence model and the homogeneous cavitation model were validated by the simulation of unsteady cavitation shedding flow around the NACA66-mod hydrofoil, and then the unsteady TLV cloud cavitation and unstable vortices cavitation in an axial flow pump were predicted by using the improved numerical method. The predicted three-dimensional cavitation structure of TLV and vortices as well as the collapse features show a qualitative agreement with the high speed photography results. Numerical results show that the TLV cavitation cloud in the axial flow pump mainly includes tip clearance cavitation, shear layer cavitation and TLV cavitation, and TLV-induced vortices cavitation occurs in the downstream of blade trailing edge (TE). TLV cavitation cloud is relatively steady before about 80% blade chord with the high vapor volume fraction inside the TLV core. The unsteady TLV cavitation cloud occurs near the TE of blade where the transient cavity shapes of sheet cavitation and TLV cavitation all fluctuate, which results in the decrease of the axial velocity in the tip region. It is found that the unstable vortices cavitation in shear layer in the downstream of TE collapses periodically. The correlation analysis shows that TLV cavitation cloud and vortices cavitation collapse are significantly associated with the interaction between TLV breakdown and boundary layer in the downstream of blade TE.

Numerical and Experimental Investigation of Tip Leakage Vortex Cavitation Patterns and Mechanisms in an Axial Flow Pump

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Desheng Zhang ◽  
Weidong Shi ◽  
Dazhi Pan ◽  
Michel Dubuisson
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Axial Flow ◽  
Tip Clearance ◽  
Cloud Cavitation ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Flow Pump ◽  
Corner Vortex

The tip leakage vortex (TLV) cavitating flow in an axial flow pump was simulated based on an improved shear stress transport (SST) k-ω turbulence model and the homogeneous cavitation model. The generation and dynamics of the TLV cavitation throughout the blade cascades at different cavitation numbers were investigated by the numerical and experimental visualizations. The investigation results show that the corner vortex cavitation in the tip clearance is correlated with the reversed flow at the pressure side (PS) corner of blade, and TLV shear layer cavitation is caused by the interaction between the wall jet flow in the tip and the main flow in the impeller. The TLV cavitation patterns including TLV cavitation, tip corner vortex cavitation, shear layer cavitation, and blowing cavitation are merged into the unstable large-scale TLV cloud cavitation at critical cavitation conditions, which grows and collapses periodically near trailing edge (TE).

Experimental and numerical investigation of tip leakage vortex cavitation in an axial flow pump under design and off-design conditions

2020 ◽  
pp. 095765092090629
Author(s):  
Xi Shen ◽  
Desheng Zhang ◽  
Bin Xu ◽  
Changliang Ye ◽  
Weidong Shi
Keyword(s):  
Shear Stress ◽  
Turbulence Model ◽  
Axial Velocity ◽  
Axial Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Sheet Cavitation ◽  
Shear Stress Transport ◽  
Axial Flow Pump ◽  
Flow Pump

The interaction of tip leakage flow and main flow in an axial flow pump can induce the tip leakage vortex, which causes the unstable flow and complex cavitation structures. In the present research, the modified shear stress transport k–ω turbulence model was utilized to predict the cavitating flow of the model pump under design and off-design conditions. Validations were carried out using high-speed photography techniques. Results show that the simulation results about cavitation performance based on the modified shear stress transport k–ω turbulence model agree well with the experimental results. Cavitation inception occurs more possible at part-load conditions, and with the increase of the flow rate, the starting point of tip leakage vortex gradually moves to the back edge of the blade chord. Both the sheet cavitation and the triangular cavitation cloud that formed in the blade tip grow in size and intensity gradually with the decrease of cavitation number. Distributions of the cavity area fraction and axial velocity show that the tip leakage vortex cavitation locates at the radial coefficient r* = 0.95–1.0 with peaks at about r* = 0.97, while the sheet cavitation is found at r* = 0.5–0.9 on the suction side (SS). The cavitation structures lead to a significant decrease in the axial velocity, especially in the tip region of the blade.

Numerical and Experimental Investigation of Tip Leakage Vortex Trajectory in an Axial Flow Pump

2013 ◽  
Author(s):  
Desheng Zhang ◽  
Weidong Shi ◽  
Suqing Wu ◽  
Dazhi Pan ◽  
Peipei Shao ◽  
...  
Keyword(s):  
Flow Rate ◽  
Axial Flow ◽  
Tip Clearance ◽  
High Speed Photography ◽  
Rate Condition ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Starting Point ◽  
Axial Flow Pump ◽  
Flow Pump

In this paper, the tip leakage vortex (TLV) structures in an axial flow pump were investigated by numerical and experimental methods. Based on the comparisons of different blade tip clearance size (i.e., 0.5 mm, 1mm and 1.5mm) and different flow rate conditions, TLV trajectories were obtained by Swirling Strength method, and simulated by modified SST k-ω turbulence model with refined high-quality structured grids. A high-speed photography test was carried out to capture the tip leakage vortex cavitation in an axial flow pump with transparent casing. Numerical results were compared with the experimental leakage vortex trajectories, and a good agreement is presented. The detailed trajectories show that the start point of tip leakage vortex appears near the leading edge at small flow rate, and it moves from trailing edge to about 30% chord span at rated flow rate. At the larger flow rate condition, the starting point of TLV shifts to the middle of chord, and the direction of TLV moves parallel to the blade hydrofoil. As the increasing of the tip size, the start point of TLV trajectories moves to the central of chord and the minimum pressure in vortex core is gradually reduced.

A study on tip leakage vortex dynamics and cavitation in axial-flow pump

2017 ◽  
Vol 49 (3) ◽  
pp. 035504 ◽  
Author(s):  
Lei Shi ◽  
Desheng Zhang ◽  
Yongxin Jin ◽  
Weidong Shi ◽  
B P M (Bart) van Esch
Keyword(s):  
Vortex Dynamics ◽  
Axial Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Flow Pump

Numerical and experimental investigation of tip leakage vortex trajectory and dynamics in an axial flow pump

2015 ◽  
Vol 112 ◽  
pp. 61-71 ◽  
Author(s):  
Desheng Zhang ◽  
Weidong Shi ◽  
B.P.M. (Bart) van Esch ◽  
Lei Shi ◽  
Michel Dubuisson
Keyword(s):  
Experimental Investigation ◽  
Axial Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Flow Pump

Numerical simulation on hydraulic performance and tip leakage vortex of a slanted axial-flow pump with different blade angles

2021 ◽  
pp. 095440622110329
Author(s):  
Zhaodan Fei ◽  
Hui Xu ◽  
Rui Zhang ◽  
Yuan Zheng ◽  
Tong Mu ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Strain Tensor ◽  
Axial Flow ◽  
Hydraulic Performance ◽  
Tip Leakage Flow ◽  
Blade Angle ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Flow Pump

The blade angle has a great effect on hydraulic performance and internal flow field for axial-flow pumps. This research investigated the effect of the blade angle on hydraulic performance and tip leakage vortex (TLV) of a slanted axial-flow pump. The hydraulic performance and the TLV are compared with different setting angles. The dimensionless turbulence kinetic energy (TKE) is used to investigate the TLV. A novel variable fv is utilized to analyze the relation among the TLV, strain tensor and vorticity tensor. The proper orthogonal decomposition (POD) method is used to analyze TLV structure. The results show that with the increase of the blade angle, the pump head is getting larger, the flow rate of the best efficiency moves to be larger, and both the primary TLV (P-TLV) and the secondary TLV (S-TLV) are getting stronger. The P-TLV often exists in the outer edge of TKE distribution and S-TLVs often exist in the largest value area of TKE. This phenomenon is more evident with blade angle increasing. Through POD method, it shows that the first six modes contain more than 90% of TKE. The reason why the TKE value near the region of S-TLV is high is that the tip leakage flow is a kind of jet-like flow with high kinetic energy. The main structure of the P-TLV is shown in modes 4−6, resulting in a reflux zone but not with the highest TKE.

Study on unsteady tip leakage vortex cavitation in an axial-flow pump using an improved filter-based model

2017 ◽  
Vol 31 (2) ◽  
pp. 659-667 ◽  
Author(s):  
Desheng Zhang ◽  
Lei Shi ◽  
Ruijie Zhao ◽  
Weidong Shi ◽  
Qiang Pan ◽  
...  
Keyword(s):  
Axial Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Flow Pump

scholarly journals Numerical Analysis of the Effect of Cavitation on the Tip Leakage Vortex in an Axial-Flow Pump

2021 ◽  
Vol 9 (7) ◽  
pp. 775
Author(s):  
Hu Zhang ◽  
Jun Wang ◽  
Desheng Zhang ◽  
Weidong Shi ◽  
Jianbo Zang
Keyword(s):  
Axial Flow ◽  
Strength Distribution ◽  
Cavitating Flows ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Clearance Flow ◽  
Axial Flow Pump ◽  
Vorticity Transport ◽  
Flow Pump

To understand the effect of cavitation on the tip leakage vortex (TLV), turbulent cavitating flows were numerically investigated using the shear-stress transport (SST) k–ω turbulence model and the Zwart–Gerber–Belamri cavitation model. In this work, two computations were performed—one without cavitation and the other with cavitation—by changing the inlet pressure of the pump. The results showed that cavitation had little effect on the pressure difference between the blade surfaces for a certain cavitation number. Instead, it changed the clearance flow and TLV vortex structure. Cavitation caused the TLV core trajectory to be farther from the suction surface and closer to the endwall upstream of the blade. Cavitation also changed the vortex strength distribution, making the vortex more dispersed. The vortex flow velocity and turbulent kinetic energy were lower, and the pressure pulsation was more intense in the cavitating case. The vorticity transport equation was used to further analyze the influence of cavitation on the evolution of vortices. Cavitation could change the vortex stretching term and delay the vortex bending term. In addition, the vortex dilation term was drastically changed at the vapor–liquid interface.

Numerical investigation of tip flow dynamics and main flow characteristics with varying tip clearance widths for an axial-flow pump

2018 ◽  
Vol 233 (4) ◽  
pp. 476-488 ◽  
Author(s):  
Simin Shen ◽  
Zhongdong Qian ◽  
Bin Ji ◽  
Ramesh K Agarwal
Keyword(s):  
Flow Rate ◽  
Axial Flow ◽  
Tip Clearance ◽  
Main Stream ◽  
Specific Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Tip Separation Vortex ◽  
Flow Pump

The effects of varying tip clearance widths on tip flows dynamics and main flows characteristics for an axial-flow pump are studied employing computational fluid dynamics method. An analysis is presented for the distributions of turbulent kinetic energy, mean axial velocity, and mean vorticity magnitude at the specific flow rate of 0.7 Q BEP , focusing on flow patterns in the tip region with different tip clearance widths and associated flows. From the simulation results we find that the flow structure of tip vortex and its transportation strongly depend on the tip clearance width, especially for the extension of tip leakage vortex, appearance of induced vortex and the area of tip separation vortex. For a small clearance of 0.15 mm at 0.7 Q BEP, there is no tip separation vortex at the tip. When tip clearance width becomes larger, a tip separation vortex attaches more on the surface of blade tip as well as vortex intensity of tip flows increases. For tip clearances of 0.9 and 1.2 mm, there is a small part of induced vortex near the blade leading edge. Meanwhile, no induced vortex can be captured for tip clearances of 0.15 and 0.45 mm. The relative angle between the blade chord and tip leakage vortex trajectory reduces gradually when tip clearance width increases from 0.45 to 1.2 mm. Additionally, the radial position of tip leakage vortex core moves inwards as tip clearance width increases. Furthermore, a larger tip clearance width has greater effects on the main-stream characteristics especially near the shroud, which is due to more energy being exchanged between tip flows and main flows. At the flow rate 0.7 Q BEP, both the efficiency and head of the pump reduce with an increasing tip clearance because of greater energy loss.

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