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.

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.

scholarly journals Suppression of Performance Curve Instability of an Axial-Flow Pump by Using a Double-Inlet-Nozzle

2008 ◽  
Vol 2008 ◽  
pp. 1-7 ◽  
Author(s):  
P. Pérez Flores ◽  
G. Kosyna ◽  
D. Wulff
Keyword(s):  
Axial Flow ◽  
Performance Curve ◽  
Improved Method ◽  
Flow Rates ◽  
Piv Measurements ◽  
Casing Treatment ◽  
Pump Head ◽  
Axial Flow Pump ◽  
Sudden Decrease ◽  
Flow Pump

It has been shown that the sudden decrease of pump head in an axial flow pump caused by stall can be overcome by means of casing treatment. Flat axial grooves in front of the impeller break the swirl of the near-casing backflow. The disadvantage of this method is strong cavitation at the inlet of the grooves for flow rates below the stall point. In this paper another improved method to stabilize the performance curve will be presented, using a double-inlet-nozzle. At the onset of stall the initial near-casing backflow with its high swirl is lead off into the gap between both nozzles. At design conditions this double-inlet-nozzle is working as an injector, supporting the near-casing-inflow. The function of the double-inlet-nozzle is demonstrated by PIV-measurements.

scholarly journals Axial Flow Compressor Stability Enhancement: Circumferential T-Shape Grooves Performance Investigation

Aerospace ◽  
2021 ◽  
Vol 8 (1) ◽  
pp. 12
Author(s):  
Marco Porro ◽  
Richard Jefferson-Loveday ◽  
Ernesto Benini
Keyword(s):  
Vortex Breakdown ◽  
Pressure Ratio ◽  
Axial Flow ◽  
Suction Side ◽  
Treatment Technique ◽  
Tip Leakage Flow ◽  
Stall Inception ◽  
Stall Margin ◽  
Casing Treatment ◽  
Stall Margin Improvement

This work focuses its attention on possibilities to enhance the stability of an axial compressor using a casing treatment technique. Circumferential grooves machined into the case are considered and their performances evaluated using three-dimensional steady state computational simulations. The effects of rectangular and new T-shape grooves on NASA Rotor 37 performances are investigated, resolving in detail the flow field near the blade tip in order to understand the stall inception delay mechanism produced by the casing treatment. First, a validation of the computational model was carried out analysing a smooth wall case without grooves. The comparisons of the total pressure ratio, total temperature ratio and adiabatic efficiency profiles with experimental data highlighted the accuracy and validity of the model. Then, the results for a rectangular groove chosen as the baseline case demonstrated that the groove interacts with the tip leakage flow, weakening the vortex breakdown and reducing the separation at the blade suction side. These effects delay stall inception, improving compressor stability. New T-shape grooves were designed keeping the volume as a constant parameter and their performances were evaluated in terms of stall margin improvement and efficiency variation. All the configurations showed a common efficiency loss near the peak condition and some of them revealed a stall margin improvement with respect to the baseline. Due to their reduced depth, these new configurations are interesting because they enable the use of a thinner light-weight compressor case as is desirable in aerospace applications.

scholarly journals Study on the Performance Improvement of Axial Flow Pump’s Saddle Zone by Using a Double Inlet Nozzle

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1493
Author(s):  
Weidong Cao ◽  
Wei Li
Keyword(s):  
Flow Rate ◽  
Three Dimensional ◽  
Axial Flow ◽  
Rotating Stall ◽  
Stable Operation ◽  
Inlet Section ◽  
Pump Impeller ◽  
Rate Condition ◽  
Axial Flow Pump ◽  
Flow Pump

The operating range of axial flow pumps is often constrained by the onset of rotating stall. An improved method using a double inlet nozzle to stabilize the performance curve is presented in the current study; a single inlet nozzle and three kinds of double inlet nozzle with different rib gap widths at the inlet of axial flow pump impeller were designed. Three dimensional (3D) incompressible flow fields were simulated, and the distributions of turbulence kinetic energy and velocity at different flow rates located at the inlet section, as well as the pressure and streamline in the impeller, were obtained at the same time. The single inlet nozzle scheme and a double inlet nozzle scheme were studied; the experimental and numerical performance results show that although the cross section is partly blocked in the double inlet nozzle, the head and efficiency do not decline at stable operation flow rate. On small flow rate condition, the double inlet nozzle scheme effectively stabilized the head-flow performance, whereby the block induced by the backflow before the impeller was markedly improved by using a double inlet nozzle. It has also been found that the rib gap width impacts the efficiency curve of the axial flow pump.

scholarly journals Study on cavitation influence for pump head in an axial flow pump

2015 ◽  
Vol 656 ◽  
pp. 012062 ◽  
Author(s):  
K Hosono ◽  
Y Kajie ◽  
S Saito ◽  
K Miyagawa
Keyword(s):  
Axial Flow ◽  
Pump Head ◽  
Axial Flow Pump ◽  
Flow Pump

scholarly journals Effects of an Inlet Vortex on the Performance of an Axial-Flow Pump

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2854
Author(s):  
Wenpeng Zhang ◽  
Fangping Tang ◽  
Lijian Shi ◽  
Qiujin Hu ◽  
Ying Zhou
Keyword(s):  
Pressure Fluctuation ◽  
Axial Velocity ◽  
Guide Vane ◽  
Shape Change ◽  
Axial Flow ◽  
Weighted Average ◽  
Stable Operation ◽  
Hydraulic Loss ◽  
Axial Flow Pump ◽  
Flow Pump

The formation of an inlet vortex seriously restricts axial-flow pump device performance and poses a great threat to the safe and stable operation of the entire system. In this study, the change trends of an inlet vortex and its influence on an axial-flow pump are investigated numerically and experimentally in a vertical axial-flow pump device. Four groups of fixed vortex generators (VGs) are installed in front of the impeller to create stable vortices at the impeller inlet. The vortex influence on the performance of pump device is qualitatively and quantitatively analyzed. The vortex patterns at different positions and moments in the pump device are explored to reveal the vortex shape change trend in the impeller and the pressure fluctuation induced by the vortex. The reliability and accuracy of steady and unsteady numerical results are verified by external characteristics and pressure fluctuation experimental results. Results show that it is feasible to install VGs before the impeller inlet to generate stable vortices. The vortex disturbs the inlet flow fields of the impeller, resulting in significant reductions of the axial velocity weighted average angle and the axial velocity uniformity. The vortex increases the inlet passage hydraulic loss and reduces the impeller efficiency, while it only slightly affects the guide vane and outlet passage performance. The vortex causes a low-frequency pressure pulsation and interacts with the impeller. The closer the vortex is to the impeller inlet, the more significant the impeller influence on the vortex. The blade cuts off the vortex in the impeller; afterwards, the vortex follows the blade rotation, and its strength weakens.

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.

scholarly journals Numerical Simulation and Experiment of the Effects of Blade Angle Deviation on the Hydraulic Characteristics and Pressure Pulsation of an Axial-Flow Pump

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Lijian Shi ◽  
Jun Zhu ◽  
Yao Yuan ◽  
Fangping Tang ◽  
Penglan Huang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Pressure Pulsation ◽  
Low Frequency ◽  
Axial Flow ◽  
Stable Operation ◽  
Blade Angle ◽  
Angle Deviation ◽  
Axial Flow Pump ◽  
Pump Stations ◽  
Flow Pump

Inadequate blade angle adjustment or manufacturing errors will cause inconsistencies in the blade angle of an axial-flow pump. In this study, the hydrodynamic characteristics of an axial-flow pump with inconsistent blade angle are investigated by analyzing hydraulic performance and pressure pulsation. The analysis is conducted by performing a numerical simulation combined with a model test. Results show that, relative to the case without blade angle deviation, the case with blade angle deviation exhibits changes in the periodicity of the flow field in the impeller. Such changes result in uneven pressure changes in the impeller passage. The pressure pulsation induced by the blade angle deviation is mainly low-frequency pulsation; that is, it is twice the rotation frequency. The amplitude of the main frequency pulsation is 1.5–3 times that of the blade without angle deviation. This low frequency that dominates the whole pump device easily causes the vibration and weakens the safety and stability of the pump. The blade angle deviation exerts great influence on the unsteady characteristics. Hence, blade angle deviation seriously affects the safe and stable operation of axial-flow pumps and pump stations.

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.

Flow Measurement at Partial Flow Rate With LDV Around Rear Rotor of Contra-Rotating Axial Flow Pump

2007 ◽  
Author(s):  
Shuichi Yamashita ◽  
Satoshi Watanabe ◽  
Kusuo Okuma ◽  
Kyota Shirasawa ◽  
Akinori Furukawa
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Flow Measurement ◽  
Axial Flow ◽  
Internal Flow ◽  
Stable Operation ◽  
Pressure Measurements ◽  
Specific Speed ◽  
Axial Flow Pump ◽  
Flow Pump

An application of contra-rotating rotors, in which a rear rotor is employed in tandem with a front one and these rotors rotate in the opposite direction each other, has been proposed against a demand for developing higher specific speed axial flow pump. The internal flow field of pump should be considered in the design for higher performance and more stable operation. The flow field in contra-rotating axial flow pump was measured with LDV and wall pressure measurements. In the present paper, the experimental results are shown and the flow behaviors would be discussed.

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