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.

Structure of the Rotor Tip Flow in a Highly-Loaded Single-Stage Axial-Flow Pump Approaching Stall: Part I — Breakdown of the Tip-Clearance Vortex

Volume 3 ◽  
2004 ◽  
Author(s):  
H. Schrapp ◽  
U. Stark ◽  
I. Goltz ◽  
G. Kosyna ◽  
S. Bross
Keyword(s):  
Vortex Breakdown ◽  
Axial Flow ◽  
Single Stage ◽  
Tip Clearance ◽  
Flow Rates ◽  
Axial Flow Pump ◽  
Tip Clearance Vortex ◽  
Spiral Type ◽  
Highly Loaded ◽  
Flow Pump

Moderate cavitation was used to visualize the tip clearance vortex in a highly-loaded single-stage axial-flow pump. Two different techniques were utilized to produce photographs and videos. From these it was found that for flow rates lower than design an initially well defined clearance vortex undergoes spiral-type vortex breakdown. This result was theoretically confirmed in an approximate manner by solving the Bragg and Hawthorne equation for an isolated vortex with a measured casingwall pressure distribution as a prescribed boundary condition.

Flow Structure of an Axial-Flow Pump From Stable Operation to Deep Stall

2005 ◽  
Author(s):  
G. Kosyna ◽  
I. Goltz ◽  
U. Stark
Keyword(s):  
Vortex Breakdown ◽  
Axial Flow ◽  
Rapid Expansion ◽  
Stable Operation ◽  
Stall Inception ◽  
Casing Treatment ◽  
Passage Vortex ◽  
Pump Head ◽  
Axial Flow Pump ◽  
Flow Pump

Different experimental techniques were used to investigate the structure of the rotor tip flow in a highly-loaded single-stage axial-flow pump. Probably the most important result of this investigation is the first-time visualization of a spiral-type vortex breakdown in an axial-flow turbomachine. The occurrence of the breakdown leads to a rapid expansion of the clearance vortex in stream wise, span wise and pitch wise direction and this has a major impact on stall inception. In deep stall the rotor tip flow is dominated by the well-known part load recirculation vortex as well as by a lesser-known cross passage vortex. Furthermore, the paper presents a simple but very effective type of casing treatment, which stabilizes the pump head characteristic completely.

The Effects of Variable-Inlet Guide Vanes on Performance of an Axial Flow Pump With Tip Clearance

2015 ◽  
Author(s):  
Wei-Min Feng ◽  
Jing-Ye Pan ◽  
Zhi-Wei Guo ◽  
Qian Cheng
Keyword(s):  
Reverse Flow ◽  
Guide Vane ◽  
Axial Flow ◽  
Tip Clearance ◽  
Inlet Guide Vane ◽  
Guide Vanes ◽  
Inlet Guide Vanes ◽  
Pump Head ◽  
Axial Flow Pump ◽  
Flow Pump

The effects of variable-inlet guide vanes on the performance of an axial flow pump considering tip clearance are investigated. The performance and the main flow field of the whole passage with five different angles of inlet guide vanes ( −10°, −5°, 0°, 5°, 10°) and with two tip clearance sizes (1‰ and 2‰) are presented. The results show that when the angle of inlet guide vane increases from negative values to positive values, the pump head reduces for two tip clearance sizes. This is mainly caused by the change of inlet velocity triangle of blade. Moreover, as tip clearance size increases from 1‰ to 2‰, both the pump head and efficiency decrease because of increasing of the strength of tip clearance leakage vortex and reverse flow.

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.

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.

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

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.

Simulation Research on Cavitation Flow in Tip Clearance of Axial-Flow Pump

2012 ◽  
Vol 588-589 ◽  
pp. 1255-1258
Author(s):  
Zhong Li ◽  
Ning Zhang ◽  
Bo Hong ◽  
Qing Li
Keyword(s):  
Development Process ◽  
Axial Flow ◽  
Leading Edge ◽  
Tip Clearance ◽  
Cavitation Flow ◽  
Simulation Research ◽  
Cavitation Region ◽  
Axial Flow Pump ◽  
Rng Turbulence Model ◽  
Flow Pump

Based on external characteristic test, the performance of designed axial-flow model pump was determined. Combingmixture N-S equations with RNG turbulence model and full cavitation model, the cavitation flow in tip clearance of axial-flow pump at flow rate of best efficiency point is simulated. The results show that the incipient cavitation region is located in the leading edge of tip airfoil. With the decrease of cavitation number, the cavitation region at tip airfoil moves gradually from leading edge to trailing edge. The development process of cavitation can be divided into three different stages and the typical characteristics of each stage are given

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