Tip Clearance and Tip Vortex Cavitation in an Axial Flow Pump

1997 ◽  
Vol 119 (3) ◽  
pp. 680-685 ◽  
Author(s):  
R. Laborde ◽  
P. Chantrel ◽  
M. Mory
Keyword(s):  
Axial Flow ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Rotating Machine ◽  
Axial Flow Pump ◽  
Gap Height ◽  
Flow Pump

A combined study of tip clearance and tip vortex cavitations in a pump-type rotating machine is presented. Cavitation patterns are observed and cavitation inception is determined for various gap heights, clearance and blade geometries, and rotor operating conditions. An optimum clearance geometry is seen to eliminate clearance cavitation when the clearance edge is rounded on the blade pressure side. The gap height has a strong effect on clearance cavitation inception, but the trends vary considerably when other parameters are also modified. The gap height and clearance geometry have less influence on tip vortex cavitation but forward and backward blade skew is observed to reduce and increase tip vortex cavitation, respectively, as compared to a blade with no skew.

Stall inception phenomena in a single-stage axial-flow pump

2003 ◽  
Vol 217 (4) ◽  
pp. 471-479 ◽  
Author(s):  
I Goltz ◽  
G Kosyna ◽  
U Stark ◽  
H Saathoff ◽  
S Bross
Keyword(s):  
Axial Flow ◽  
Wall Pressure ◽  
Operating Conditions ◽  
Single Stage ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Stall Inception ◽  
Oil Flow ◽  
Axial Flow Pump ◽  
Flow Pump

The paper describes an experimental investigation on stall inception phenomena in a single-stage axial-flow pump, utilizing an oil flow technique and two different photo techniques. Moreover, the unsteady casing wall pressure was measured. Representative results are shown and discussed: the pump characteristic for two different NPSH values, selected oil flow pictures of the casing wall and the rotor blades, the wall pressure distribution at design, selected pictures of the cavitating core of the tip clearance vortex at stable and unstable operating conditions and the visualization of a cross-passage vortex as a deep stall phenomenon. These results allow a number of key features of the stall inception process to be identified and to be followed along the unstable part of the pump characteristic.

scholarly journals Research on the Influence of Tip Clearance of Axial-Flow Pump on Energy Characteristics under Pump and Turbine Conditions

Machines ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 56
Author(s):  
Yanjun Li ◽  
Qixu Lin ◽  
Fan Meng ◽  
Yunhao Zheng ◽  
Xiaotian Xu
Keyword(s):  
Flow Rate ◽  
Dissipation Rate ◽  
Great Influence ◽  
Axial Flow ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Blade Tip ◽  
Axial Flow Pump ◽  
Flow Pump ◽  
Blade Tip Clearance

In order to study the influence of tip clearance on the performance and energy dissipation of the axial-flow pump and the axial-flow pump as a turbine, and find the location of high dissipation rate, this study took an axial-flow pump model as its research object and designed four tip radial clearance schemes (0, 0.2, 1 and 2 mm). The unsteady calculation simulation of each tip clearance scheme was carried out based on CFD technology. The calculated results were compared with the experimental results, and the simulation results were analyzed using entropy production analysis theory. The results showed that, under both an axial-flow pump and axial-flow pump as turbine operating conditions, increasing the blade tip clearance led to a decrease in hydraulic performance. Compared with the 0 mm clearance, the maximum decreases in pump efficiency, head and shaft power under 2 mm tip clearance were 15.3%, 25.7% and 12.3% under the pump condition, and 12.7%, 18.5% and 28.8% under the turbine condition, respectively. Under the axial-flow pump operating condition, the change in blade tip clearance had a great influence on the total dissipation of the impeller, guide vane and outlet passage, and the maximum variation under the flow rate of 1.0 was 53.9%, 32.1% and 54.2%, respectively. Under the axial-flow pump as a turbine operating condition, the change in blade tip clearance had a great influence on the total dissipation of the impeller and outlet passage, the maximum variation under the flow rate of 1.0 was 22.7% and 17.4%, respectively. Under the design flow rate condition, with the increase in tip clearance, the dissipation rate of the blade surface showed an increasing trend under both the axial-flow pump and axial-flow pump as turbine operating conditions, and areas of high dissipation rate were generated at the rim and clearance.

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.

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

Processes ◽  
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.

scholarly journals Improvement of the Efficiency of the Axial-Flow Pump at Part Loads due to Installing Outlet Guide Vanes Mechanism

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Fan Yang ◽  
Hao-ru Zhao ◽  
Chao Liu
Keyword(s):  
Prediction Model ◽  
Flow Rate ◽  
High Efficiency ◽  
Guide Vane ◽  
Axial Flow ◽  
Hydraulic Performance ◽  
Operating Conditions ◽  
Ann Model ◽  
Axial Flow Pump ◽  
Flow Pump

In order to investigate the influence of adjustable outlet guide vane on the hydraulic performance of axial-flow pump at part loads, the axial-flow pump with 7 different outlet guide vane adjustable angles was simulated based on the RNG k-ε turbulent model and Reynolds time-averaged equations. The Vector graphs of airfoil flow were analyzed in the different operating conditions for different adjustable angles of guide vane. BP-ANN prediction model was established about the effect of adjustable outlet guide vane on the hydraulic performance of axial-flow pump based on the numerical results. The effectiveness of prediction model was verified by theoretical analysis and numerical simulation. The results show that, with the adjustable angle of guide vane increasing along clockwise, the high efficiency area moves to the large flow rate direction; otherwise, that moves to the small flow rate direction. The internal flow field of guide vane is improved by adjusting angle, and the flow separation of tail and guide vane inlet ledge are decreased or eliminated, so that the hydraulic efficiency of pumping system will be improved. The prediction accuracy of BP-ANN model is 1%, which can meet the requirement of practical engineering.

Influence of tip clearance on pressure fluctuations in an axial flow pump

2016 ◽  
Vol 30 (4) ◽  
pp. 1603-1610 ◽  
Author(s):  
Jianjun Feng ◽  
Xingqi Luo ◽  
Pengcheng Guo ◽  
Guangkuan Wu
Keyword(s):  
Pressure Fluctuations ◽  
Axial Flow ◽  
Tip Clearance ◽  
Axial Flow Pump ◽  
Flow Pump

PIV Measurements and CFD Analysis in an Axial-Flow Pump

2007 ◽  
Author(s):  
Fang-Ping Tang ◽  
Chao Liu ◽  
Ji-Ren Zhou ◽  
Hua Yang ◽  
Li Cheng
Keyword(s):  
Flow Rate ◽  
Outer Part ◽  
Axial Flow ◽  
Operating Conditions ◽  
Design Flow ◽  
Separation Flow ◽  
Mean Velocity ◽  
Piv Measurements ◽  
Axial Flow Pump ◽  
Flow Pump

In this study, an axial flow pump impeller without guide vanes is experimentally investigated. The impeller used in the experiments consists of four blades. The particle image velocimetry technique and a five-hole probe have been used. Measurements of flow velocities in the outer part of the impeller have been made. PIV measurements have been realized in 12 meridian planes between blade-to-blade for design and off-design operating conditions. The meridian velocity is obtained with phase averaged method and the total circumferential mean velocity is obtained with an arithmetical average over the 12 circumferential data. The calculation is based on the CFX-TASC flow CFD code solving the three-dimensional Reynolds-averaged Navier-Stokes equation with RNG k–ε model of turbulence. The paper focuses on the comparisons of the results. Difference for the flow field between numerical and experimental results is small at large and design flow rate, while big difference occurs at small flow rate. It indicates that the numerical model is not suitable for separation flow.

An experimental insight into the effect of confinement on tip vortex cavitation of an elliptical hydrofoil

1999 ◽  
Vol 390 ◽  
pp. 1-23 ◽  
Author(s):  
OLIVIER BOULON ◽  
MATHIEU CALLENAERE ◽  
JEAN-PIERRE FRANC ◽  
JEAN-MARIE MICHEL
Keyword(s):  
Boundary Layer ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Velocity Profiles ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Flat Plates ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception

The present paper is devoted to an analysis of tip vortex cavitation under confined situations. The tip vortex is generated by a three-dimensional foil of elliptical planform, and the confinement is achieved by flat plates set perpendicular to the span, at an adjustable distance from the tip. In the range of variation of the boundary-layer thickness investigated, no significant interaction was observed between the tip vortex and the boundary layer which develops on the confinement plate. In particular, the cavitation inception index for tip vortex cavitation does not depend significantly upon the length of the plate upstream of the foil. On the contrary, tip clearance has a strong influence on the non-cavitating structure of the tip vortex and consequently on the inception of cavitation in its core. The tangential velocity profiles measured by a laser-Doppler velocimetry (LDV) technique through the vortex, between the suction and the pressure sides of the foil, are strongly asymmetric near the tip. They become more and more symmetric downstream and the confinement speeds up the symmetrization process. When the tip clearance is reduced to a few millimetres, the two extrema of the velocity profiles increase. This increase results in a decrease of the minimum pressure in the vortex centre and accounts for the smaller resistance to cavitation observed when tip clearance is reduced. For smaller values of tip clearance, a reduction of tip clearance induces on the contrary a significant reduction in the maxima of the tangential velocity together with a significant increase in the size of the vortex core estimated along the confinement plate. Hence, the resistance to cavitation is much higher for such small values of tip clearance and in practice, no tip vortex cavitation is observed for tip clearances below 1.5 mm. The cavitation number for the inception of tip vortex cavitation does not correlate satisfactorily with the lift coefficient, contrary to classical results obtained without any confinement. Owing to the specificity introduced by the confinement, the usual procedure developed in an infinite medium to estimate the vortex strength from LDV measurements is not applicable here. Hence, a new quantity homogeneous to a circulation had to be defined on the basis of the maximum tangential velocity and the core size, which proved to be better correlated to the cavitation inception data.

Structure of the Rotor Tip Flow in a Highly Loaded Single-Stage Axial-Flow Pump Approaching Stall: Part II — Stall Inception — Understanding the Mechanism and Overcoming Its Negative Impacts

Volume 3 ◽  
2004 ◽  
Author(s):  
I. Goltz ◽  
G. Kosyna ◽  
D. Wulff ◽  
H. Schrapp ◽  
U. Stark ◽  
...  
Keyword(s):  
Axial Flow ◽  
Tip Clearance ◽  
Simple Type ◽  
Stall Inception ◽  
Pump Head ◽  
Flow Phenomena ◽  
Axial Flow Pump ◽  
Tip Clearance Vortex ◽  
Highly Loaded ◽  
Flow Pump

When reaching the stall point of an axial-flow pump, the pump head characteristic becomes unstable and the pump head suddenly drops. Before this happens however, at even higher flow rates the NPSH3 and the pump body and shaft vibrations increase dramatically. For effectively increasing the available operating range, it is essential to find a solution for all three problems without reducing the pump efficiency at design. The paper describes an experimental investigation on the outlined subject that gives insight into the flow phenomena leading to stall. Based on this knowledge a very simple type of casing treatment was chosen and investigated. It was found to satisfy all mentioned requirements. Subject to the investigations is a highly loaded axial-flow pump having a nq of 150 (SI units). The overall pump performance was investigated measuring pump head, efficiency, NPSH3, and casing as well as shaft vibrations. Further-more, oil flow pictures taken at the pump casing and at the rotor blades, and video captures of the cavitating core of the tip clearance vortex were analyzed for understanding the flow phenomena leading to stall (see also related paper Part I, Schrapp et al. (2004)). From the video captures it was realized that the behavior of the tip clearance vortex which was found to perform so-called spiral-type vortex breakdown is triggering stall inception in this machine.

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