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

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).

Download Full-text

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

Volume 1: Symposia ◽

10.1115/ajkfluids2015-33010 ◽

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.

Download Full-text

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

Volume 1B, Symposia: Fluid Machinery; Fluid Power; Fluid-Structure Interaction and Flow-Induced Noise in Industrial Applications; Flow Applications in Aerospace; Flow Manipulation and Active Control: Theory, Experiments and Implementation; Fundamental Issues and Perspectives in Fluid Mechanics ◽

10.1115/fedsm2013-16058 ◽

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.

Download Full-text

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

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650918812541 ◽

2018 ◽

Vol 233 (4) ◽

pp. 476-488 ◽

Cited By ~ 4

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.

Download Full-text

Experimental and Numerical Investigation on the Tip Leakage Vortex Cavitation in an Axial Flow Pump with Different Tip Clearances

Processes ◽

10.3390/pr7120935 ◽

2019 ◽

Vol 7 (12) ◽

pp. 935 ◽

Cited By ~ 2

Author(s):

Bin Xu ◽

Xi Shen ◽

Desheng Zhang ◽

Weibin Zhang

Keyword(s):

Axial Flow ◽

Tip Clearance ◽

Water Diversion ◽

Tip Leakage Flow ◽

Unstable Flow ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Viscous Loss ◽

Axial Flow Pump ◽

Flow Pump

The tip gap existing between the blade tip and casing can give rise to tip leakage flow and interfere with the main flow, which causes unstable flow characteristics and intricate vortex in the passage. Investigation on the tip clearance effect is of great important due to its extensive applications in the rotating component of pumps. In this study, a scaling axial flow pump used in a south-north water diversion project with different sizes of tip clearances was employed to study the tip clearance effect on tip leakage vortex (TLV) characteristics. This analysis is based on a modified turbulence model. Validations were carried out using a high-speed photography technique. The tip clearance effect on the generation and evolution of TLV was investigated through the mean velocity, pressure, and vorticity fields. Results show that there are two kinds of TLV structures in the tip region. Accompanied by tip clearance increasing, the viscous loss in the tip area of the axial flow pump increases. Furthermore, the tip clearance effect on pressure distribution in the blade passage is discussed. Beyond that, the tip clearance effect on vortex core pressure and cavitation is studied.

Download Full-text

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

Processes ◽

10.3390/pr9091653 ◽

2021 ◽

Vol 9 (9) ◽

pp. 1653

Author(s):

Nengqi Kan ◽

Zongku Liu ◽

Guangtai Shi ◽

Xiaobing Liu

Keyword(s):

Optimization Design ◽

Flow Characteristics ◽

Axial Flow ◽

Leading Edge ◽

Tip Clearance ◽

Hydraulic Loss ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Axial Flow Pump ◽

Flow Pump

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.

Download Full-text

Experimental and numerical investigation on the effect of tip leakage vortex induced cavitating flow on pressure fluctuation in an axial flow pump

Renewable Energy ◽

10.1016/j.renene.2020.09.004 ◽

2021 ◽

Vol 163 ◽

pp. 1195-1209

Author(s):

Shen Xi ◽

Zhang Desheng ◽

Xu Bin ◽

Shi Weidong ◽

B.P.M. (Bart) van Esch

Keyword(s):

Numerical Investigation ◽

Pressure Fluctuation ◽

Axial Flow ◽

Cavitating Flow ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Axial Flow Pump ◽

Flow Pump

Download Full-text

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

Fluid Dynamics Research ◽

10.1088/1873-7005/aa6637 ◽

2017 ◽

Vol 49 (3) ◽

pp. 035504 ◽

Cited By ~ 7

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

Download Full-text

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

Computers & Fluids ◽

10.1016/j.compfluid.2015.01.010 ◽

2015 ◽

Vol 112 ◽

pp. 61-71 ◽

Cited By ~ 69

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

Download Full-text

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

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/09544062211032989 ◽

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.

Download Full-text