Clarification of Performance Curve Instability Mechanism Using Large Eddy Simulation of Internal Flow of a Mixed-Flow Pump

2015 ◽  
Author(s):  
Isao Hagiya ◽  
Chisachi Kato ◽  
Yoshinobu Yamade ◽  
Takahide Nagahara ◽  
Masashi Fukaya
Keyword(s):  
Flow Rate ◽  
Leading Edge ◽  
Low Flow ◽  
Performance Curve ◽  
Instability Mechanism ◽  
Positive Slope ◽  
Mixed Flow ◽  
Flow Rates ◽  
Direction Opposite ◽  
Flow Pump

We analyzed the internal flows of a test mixed-flow pump exhibiting performance curve instability at low flow rates by using LES to clarify the performance curve instability mechanism. The LES was conducted using the open source software FrontFlow/blue [1]. In particular, we investigated in detail the flows at the flow rates, where the head curve had a positive slope under low flow rate condition. We clarified that Euler’s head drop caused by a stall near the tip of the rotor-blades is a dominant factor at the instability of the test pump. At the bottom point of the positive slope of the head curve, stall regions covered all the rotor-blade passages on the tip side. The drop of the angular momentum in the impeller caused by the stall on the leading edge side exceeds the increment caused by the decrease in the flow rate on the trailing edge at the bottom point of the positive slope. At the middle point of the positive slope of the head curve we also found regions with low-velocities in some blade passages. Such regions, namely stall cells, rotated around the impeller for one revolution while the impeller rotated almost about 20 revolutions in the direction opposite to the impeller’s rotation. The region with low-velocity first appears at the trailing edge and expands toward the leading edge. The angle of attack of the neighbouring blade in the direction opposite to the rotation of the blade increases and that blade pitch begins to stall. When that blade pitch is fully stalled, it is no longer loaded and the positive pressure gradient in that blade pitch decreases. The blade pitch is most likely to accept the excess flow. It recovers from the stalled state.

scholarly journals Numerical and experimental investigation of the pressure fluctuation in a mixed-flow pump under low flow conditions

2019 ◽  
Vol 234 (1) ◽  
pp. 46-57 ◽  
Author(s):  
Xi Shen ◽  
Desheng Zhang ◽  
Bin Xu ◽  
Ruijie Zhao ◽  
Yongxin Jin ◽  
...  
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Flow Separation ◽  
Pressure Fluctuation ◽  
Static Pressure ◽  
Leading Edge ◽  
Low Flow ◽  
Flow Conditions ◽  
Mixed Flow ◽  
Flow Pump

In this paper, the large eddy simulation is utilized to simulate the flow field in a mixed-flow pump based on the standard Smagorinsky subgrid scale model, which is combined with the experiments to investigate pressure fluctuations under low flow conditions. The experimental results indicated that the amplitude of fluctuation at the impeller inlet is the highest, and increases with the reduction of the flow rate. The main frequencies of pressure fluctuation at the impeller inlet, impeller outlet, and vane inlet are blades passing frequency, while the main frequency at the vane outlet changes with the flow rate. The results of the simulation showed that the axial plane velocity at impeller inlet undergoes little change under 0.8 Qopt. In case of 0.4 Qopt, however, the flow field at impeller inlet becomes complicated with the axial plane velocity changing significantly. The flow separation is generated at the leading edge of the suction surface at t* = 0.0416 under 0.4 Qopt, which is caused by the increase of the incidence angle and the influence of the tip leakage flow. When the impeller rotates from t* = 0.0416 to t* = 0.1249, the flow separation intensified and the swirling strength of the separation vortex is gradually increased, leading to the reduction of the static pressure, the rise of adverse pressure gradient, and the generation of backflow. The static pressure at the leading edge of the impeller recovers gradually until the backflow is reached. In addition, the flow separation is the main reason for the intensification of the pressure fluctuation.

Experimental Study on Unstable Characteristics of Mixed-Flow Pump at Low Flow-Rates

2003 ◽  
Author(s):  
Hiroshi Funakoshi ◽  
Hiroshi Tsukamoto ◽  
Koji Miyazaki ◽  
Kazuyoshi Miyagawa
Keyword(s):  
Unsteady Flow ◽  
Flow Rate ◽  
Dynamic Characteristics ◽  
Fast Response ◽  
Low Flow ◽  
Positive Slope ◽  
Mixed Flow ◽  
Flow Measurements ◽  
Pressure Transducers ◽  
Flow Pump

Static and dynamic characteristics of a mixed flow pump were measured at low flow rate, where the steady characteristic curves show a positive slope. Unsteady flow was measured at upstream and downstream of impeller, as well as on the casing wall of diffuser passage by using a fast response five-hole pitot tube and semi-conductor type pressure transducers. Dynamic response of the pump to the sinusoidal change in flow rate was measured under constant rotational speed. As a result of the unsteady flow measurements, the positive slope of steady characteristic was found to be caused by the impeller tip separation, inlet backflow, and pre-rotation. Moreover, the dynamic characteristics of the pump were found to become unstable with the increased frequency of flow rate.

Effect of Tip Clearance on Suction Performance at Different Flow Rates in a Mixed Flow Pump

2014 ◽  
Author(s):  
Yo Han Jung ◽  
Young Uk Min ◽  
Jin Young Kim
Keyword(s):  
Performance Test ◽  
Stokes Equations ◽  
Flow Characteristics ◽  
Tip Clearance ◽  
Low Flow ◽  
Tip Leakage Flow ◽  
Mixed Flow ◽  
Flow Rates ◽  
Suction Performance ◽  
Flow Pump

This paper presents a numerical investigation of the effect of tip clearance on the suction performance and flow characteristics at different flow rates in a vertical mixed-flow pump. Numerical analyses were carried out by solving three-dimensional Reynolds-averaged Navier-Stokes equations. Steady computations were performed for three different tip clearances under noncavitating and cavitating conditions at design and off-design conditions. The pump performance test was performed for the mixed-flow pump and numerical results were validated by comparing the experimental data for a system characterized by the original tip clearance. It was shown that for large tip clearance, the head breakdown occurred earlier at the design and high flow rates. However, the head breakdown was quite delayed at low flow rate. This resulted from the cavitation structure caused by the tip leakage flow at different flow rates.

LES of Internal Flows in a Mixed-Flow Pump With Performance Instability

2002 ◽  
Author(s):  
Chisachi Kato ◽  
Hiroshi Mukai ◽  
Akira Manabe
Keyword(s):  
Flow Rate ◽  
Moving Boundary ◽  
Tangential Velocity ◽  
Design Tool ◽  
Low Flow ◽  
Flow Rate Ratio ◽  
Internal Flows ◽  
Mixed Flow ◽  
Specific Speed ◽  
Flow Pump

This paper describes large eddy simulation (LES) of the internal flows of a high-specific-speed mixed-flow pump at low flow-rate ratios over which measured head-flow characteristics exhibits weak instability. In order to deal with a moving boundary interface in the flow field, a form of the finite-element method in which overset grids are applied from multiple dynamic frames of reference has been developed. The method is implemented as a parallel program by applying a domain-decomposition programming model. The predicted pump heads reproduce the instability and agree quantitatively well with their measured equivalents although the predicted stall takes place at somewhat lower flow-rate ratio than in the measurements. The phase-averaged distributions of the meridional- and tangential-velocity components at the impeller’s inlet and exit cross-sections were also compared with those measured by a Laser-Doppler velocimetry (LDV). Reasonably good agreements have been obtained between the computed and measured profiles. The developed LES program thus seems to be a promising design tool for a high specific-speed mixed-flow pump particularly for off-design evaluations.

Blade Interaction Forces in a Mixed-Flow Pump With Vaned Diffuser

2009 ◽  
Author(s):  
Cheng Li ◽  
B. P. M. van Esch
Keyword(s):  
Flow Rate ◽  
Mixed Flow ◽  
Interaction Forces ◽  
Vaned Diffuser ◽  
Shaft System ◽  
High Head ◽  
The Many ◽  
Direction Opposite ◽  
Flow Pump ◽  
Good Agreement

Hydrodynamic forces in turbomachinery can cause problems ranging from excessive wear to vibrations. Of the many different causes of fluid-induced forces, their source attributed to blade interaction is perhaps best studied. Most studies, however, focus on high head pumps. This paper presents a study of blade interaction forces in a mixed-flow pump with vaned diffuser. It covers both experimental and numerical results. A mixed-flow pump is built into a closed-loop test rig. In order to measure the instantaneous forces and bending moments on the impeller, a co-rotating dynamometer is used, which is built in-between the impeller and the shaft of the pump. Extensive calibration proved necessary to determine the dynamic behavior of the shaft system. Measurements of forces at blade passing frequency show an unexpected dependency on flow rate. Another important observation is that blade excitation forces cause the impeller to whirl in a direction opposite to shaft rotation. Results of measurements are compared with unsteady CFD calculations using FLUENT®. Computed global characteristics show a good agreement with measurements. Also the magnitude of blade interaction forces shows a good qualitative agreement. Over a large range of flow rates, the dependency of magnitude on flow rate agrees well with the trend found in the measurements. Deviations are explained.

Suppression of Performance Curve Instability of a Mixed Flow Pump by Use of J-groove

2000 ◽  
Vol 122 (3) ◽  
pp. 592-597 ◽  
Author(s):  
Sankar L. Saha ◽  
Junichi Kurokawa ◽  
Jun Matsui ◽  
Hiroshi Imamura
Keyword(s):  
Angular Momentum ◽  
Pressure Gradient ◽  
Reverse Flow ◽  
Swirl Flow ◽  
Maximum Efficiency ◽  
Performance Curve ◽  
Positive Slope ◽  
Mixed Flow ◽  
Remarkable Effect ◽  
Flow Pump

In order to control and suppress performance curve instability characterized by the positive slope of head-capacity curve of a mixed flow pump, a very simple passive method utilizing shallow grooves mounted on a casing wall parallel to the pressure gradient (J-groove) is proposed. The optimum groove dimension and location for suppressing such an instability are determined experimentally. Results show that shallow grooves of adequate dimension and proper location can suppress such instability perfectly without decreasing the pump maximum efficiency. The remarkable effect of shallow grooves is to decrease both the swirl strength and the propagation of reverse flow at the impeller inlet region, through angular momentum absorption owing to mixing of groove reverse flow and swirl flow, yielding recovery of impeller theoretical head. [S0098-2202(00)02603-1]

scholarly journals Large-Eddy Simulation of Unsteady Flow in a Mixed-Flow Pump

2003 ◽  
Vol 9 (5) ◽  
pp. 345-351 ◽  
Author(s):  
Chisachi Kato ◽  
Hiroshi Mukai ◽  
Akira Manabe
Keyword(s):  
Large Eddy Simulation ◽  
Flow Rate ◽  
Tangential Velocity ◽  
Low Flow ◽  
Flow Rate Ratio ◽  
Mixed Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Specific Speed ◽  
Flow Pump

This article describes the large-eddy simulation (LES) of the internal flows of a high–specific-speed, mixed-flow pump at low flow-rate ratios over which measured head-flow characteristics exhibit weak instability. In order to deal with a moving boundary interface in the flow field, a form of the finite-element method in which overset grids are applied from multiple dynamic frames of reference has been developed. The method is implemented as a parallel program by applying a domain-decomposition programming model.The predicted pump heads reproduce the instability and agree fairly well with their measured equivalents, although the predicted stall takes place at a flow-rate ratio that is a few percentage points lower than the measurements. The phase-averaged distributions of the meridional- and tangential velocity components at the impeller's inlet and exit cross sections were also compared with those measured by laser-Doppler velocimetry. Reasonably good agreements have been obtained between the computed and measured profiles. The developed LES program thus seems to be a promising design tool for a high–specific-speed, mixed-flow pump, particularly for off-design evaluations.

Prediction of Stress on Pump Blade by One-Way Coupled Method of Fluid and Structure Simulation

2007 ◽  
Author(s):  
Katsutoshi Kobayashi ◽  
Shigeyoshi Ono ◽  
Ichiro Harada ◽  
Yoshimasa Chiba
Keyword(s):  
Flow Rate ◽  
Flow Separation ◽  
Leading Edge ◽  
Numerical Results ◽  
Stream Line ◽  
Suction Surface ◽  
Flow Rates ◽  
Total Head ◽  
Shaft Power ◽  
Flow Pump

The stress of a mixed flow pump with open type blades was measured and predicted by a one-way coupled simulation to evaluate the reliability of pump strength. The mechanism generating a large stress was investigated by numerical results. The stress became maximum at 70%Q flow rate of the off design point in both experimental and numerical results. Although the shaft power and total head became maximum at 0%Q flow rate of the shut off point, these did not relate to cause the largest stress. The pressure distribution on the surface of blade was investigated by simulated flow field. The flow separation at 0%Q flow rate occurred near the hub side on the suction surface of blade and loads became largest on the stream line of hub side among the all flow rates. On the other hand, the flow separation at 70%Q flow rate occurred over the whole area through the leading edge and loads became largest on the stream line of tip side among the all flow rates. It was found that the stress could be determined from the location where the flow separation was generated and the area size of it.

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