Pressure fluctuation and flow instability in S-shaped region of a reversible pump-turbine

2020 ◽  
Vol 154 ◽  
pp. 826-840 ◽  
Author(s):  
Wenwu Zhang ◽  
Zhenmu Chen ◽  
Baoshan Zhu ◽  
Fei Zhang
Keyword(s):  
Pressure Fluctuation ◽  
Flow Instability ◽  
Pump Turbine

scholarly journals Research of Pressure Fluctuation with Experiment and Numerical Simulation for Dredging Pump

2021 ◽  
Vol 2097 (1) ◽  
pp. 012028
Author(s):  
Mingming Liu ◽  
Haifei Zhuang ◽  
Lei Cao
Keyword(s):  
Numerical Simulation ◽  
Pressure Fluctuation ◽  
Flow Instability ◽  
Simulation Method ◽  
Design Flow ◽  
Low Flow ◽  
Pressure Amplitude ◽  
Main Frequency ◽  
Simulation And Experiment ◽  
Fluctuation Amplitude

Abstract In order to reveal the dredge pump flow instability characteristics, the cavitation and pressure fluctuation in experimental study are carried out, the pressure fluctuation frequency domain and time domain characteristics of three different position inside the volute are analyzed. The results showed that, before cavitation, the main frequency at different positions at different flow rates is 1 times the main frequency of the blade. The fluctuation amplitude near the volute tongue and diffusion section is slightly larger than that at other positions. Before cavitation, the fluctuation amplitude at the same position off design flow is slightly higher than that near the design flow. Cavitation has little influence on the main frequency of the pressure fluctuation. After cavitation, the pressure fluctuation amplitude in the low flow point and the position of the volute tongue under each condition has little change, but cavitation aggravates the pressure fluctuation in the other conditions. Besides, the comparison between simulation and experiment results shows the dredge pump performance curve is in good agreement with the simulation curve, and the simulation results of pressure amplitude at different positions are basically consistent with the experiment results, which verifies the reliability of the numerical simulation method.

Pressure fluctuation characteristics of a model pump-turbine during runaway transient

2021 ◽  
Vol 163 ◽  
pp. 517-529
Author(s):  
Wen-Tao Su ◽  
Xiao-Bin Li ◽  
Yu-Xing Xia ◽  
Quan-Zhong Liu ◽  
Maxime Binama ◽  
...  
Keyword(s):  
Pressure Fluctuation ◽  
Pump Turbine

Suppression of flow instability in draft tube of Pump Turbine using J-Groove

2019 ◽  
Vol 22 (6) ◽  
pp. 5-13
Author(s):  
Ujjwal Shrestha ◽  
Patrick Mark Singh ◽  
Young Do Choi
Keyword(s):  
Flow Instability ◽  
Draft Tube ◽  
Pump Turbine

scholarly journals Flow instability transferability characteristics within a reversible pump turbine (RPT) under large guide vane opening (GVO)

2021 ◽  
Author(s):  
Maxime Binama ◽  
Kan Kan ◽  
Hui-Xiang Chen ◽  
Yuan Zheng ◽  
Daqing Zhou ◽  
...  
Keyword(s):  
Flow Instability ◽  
Guide Vane ◽  
Pump Turbine

Unstable Characteristics and Rotating Stall in Turbine Brake Operation of Pump-Turbines

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Christian Widmer ◽  
Thomas Staubli ◽  
Nathan Ledergerber
Keyword(s):  
Electricity Market ◽  
Flow Instability ◽  
Guide Vane ◽  
Pressure Fluctuations ◽  
Vortex Formation ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Momentum Exchange ◽  
Pump Turbine ◽  
Stationary Vortex

Reversible pump-turbines are versatile in the electricity market since they can be switched between pump and turbine operation within a few minutes. The emphasis on the design of the more sensitive pump flow however often leads to stability problems in no load or turbine brake operation. Unstable characteristics can be responsible for hydraulic system oscillations in these operating points. The cause of the unstable characteristics can be found in the blocking effect of either stationary vortex formation or rotating stall. The so-called unstable characteristic in turbine brake operation is defined by the change of sign of the slope of the head curve. This change of sign or “S-shape” can be traced back to flow recirculation and vortex formation within the runner and the vaneless space between runner and guide vanes. When approaching part load from sound turbine flow the vortices initially develop and collapse again. This unsteady vortex formation induces periodical pressure fluctuations. In the turbine brake operation at small guide vane openings the vortices increase in intensity, stabilize and circumferentially block the flow passages. This stationary vortex formation is associated with a total pressure rise over the machine and leads to the slope change of the characteristic. Rotating stall is a flow instability which extends from the runner, the vaneless space to the guide and the stay vane channels at large guide vane openings. A certain number of channels is blocked (rotating stall cell) while the other channels comprise sound flow. Due to a momentum exchange between rotor and stator at the front and the rear cell boundary, the cell is rotating with subsynchronous frequency of about 60 percent of the rotational speed for the investigated pump-turbine (nq = 45). The enforced rotating pressure distributions in the vaneless space lead to large dynamic radial forces on the runner. The mechanisms leading to stationary vortex formation and rotating stall were analyzed with a pump-turbine model by the means of numerical simulations and test rig measurements. It was found that stationary vortex formation and rotating stall have initially the same physical cause, but it depends on the mean convective acceleration within the guide vane channels, whether the vortex formations will rotate or not. Both phenomena lead to an unstable characteristic.

Numerical Simulation of Flow Instability in Vortex Diodes

2017 ◽  
Author(s):  
Junrong Wang ◽  
Qi Xiao ◽  
Hanbing Ke ◽  
Xu Hu ◽  
Shaodan Li ◽  
...  
Keyword(s):  
Pressure Fluctuation ◽  
Flow Resistance ◽  
Flow Instability ◽  
Reverse Flow ◽  
Experimental Studies ◽  
Low Flow ◽  
Flow Mode ◽  
Geometrical Parameters ◽  
Typical Structure ◽  
Transient Simulations

A vortex diode is used as a highly reliable check-valve in nuclear applications, where it mainly benefits from the intrinsic properties of no moving parts and no leakage. Its basic principle is similar to the diode in an electric circuit. The typical structure of a vortex diode consists of a chamber with axial and tangential ports. When the fluid is injected through the axial port, a simple radial flow in the chamber leads to a relatively low flow resistance. On the other hand, in the reverse flow mode, a strongly swirling vortex can be set up in the chamber, resulting in a very high flow resistance. Several experimental studies found vortex-induced vibration of a vortex diode in the reverse flow mode, where it indicated that the flow was unstable in the vortex diode. This phenomenon may affect the reliability of the vortex diode. However, the mechanism has not been investigated systematically and profoundly. In this paper, 3-D simulations are carried out to help understand the related flow characteristics in the vortex diode. Standard k-ε model was selected for forward flow, while Reynolds stress model was selected for reverse flow. We have found that the results from transient simulations are in good agreement with experimental data. The transient simulations also capture the periodic pressure fluctuation in the vortex diode. Vortex diodes with different structures and geometrical parameters are simulated at different Reynolds number conditions. It is found that the characteristics of the pressure fluctuation are determined by the structure parameters and working conditions of the vortex diode. The flow instability is mainly caused by the asymmetry of the vortex diode. The work presented in this paper will be useful to give better understanding of flows in vortex diodes and to provide some guidance for optimizing the vortex diode.

Pressure fluctuation propagation of a pump turbine at pump mode under low head condition

2014 ◽  
Vol 57 (4) ◽  
pp. 811-818 ◽  
Author(s):  
Lei Guo ◽  
JinTao Liu ◽  
LeQin Wang ◽  
DaQing Qin ◽  
XianZhu Wei
Keyword(s):  
Pressure Fluctuation ◽  
Pump Mode ◽  
Pump Turbine ◽  
Low Head

Study on the Influence of Centrifugal Pump Inlet Flow Field Instability and Methods of Adjustment

2019 ◽  
Author(s):  
Bo Qian ◽  
Jinping Chen ◽  
Peng Wu ◽  
Bin Huang ◽  
Dazhuan Wu
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Pressure Fluctuation ◽  
Flow Instability ◽  
Wake Flow ◽  
Experimental Investigations ◽  
Inlet Flow ◽  
Inlet Tube ◽  
Fluctuation Amplitude ◽  
Pump Inlet

Abstract The quality of centrifugal pump inlet flow field is an important factor that affecting the performance of pump. Studies have proved that the vortex in the inlet area can also bring an extra flow instability to pump, which results in a hydro-induced vibration. This phenomenon is more common and significant in the pumps with an elbow tube, which is often applied to minimize installation size, before pump inlet. Therefore, it is necessary to look into the influence of inlet flow field instability on pump performance especially the vibration performance. The methods of adjusting pump inlet flow field is also worthy of being studied in the meantime. In this study, the influence of inlet vortex on the performance of centrifugal pump with an elbow inlet tube is investigated by means of CFD analysis. The flow is significantly affected when going through the elbow tube inlet and then turbulence is generated as a result, which enters the impeller at the next moment. The turbulence brings an asymmetrical flow condition at the impeller suction area, which can intensify pressure pulsation and hydro-induced vibration. In order to reduce the turbulence, two modifications on the elbow inlet tube are investigated in this study. A specially designed vane is deployed inside the inlet tube in the MOD1, and the MOD2 is added with two splitter vanes on the basis of the MOD1. The turbulent flow in the elbow inlet tube can be reordered as it is controlled by the vanes. The difference on pump performances that the inlet vane has made is specifically simulated and compared. The flow fields of the inlet tube influenced by the vane is also investigated on the vortex distribution and velocity vector distribution. The MOD1 has a generally smaller pressure fluctuation amplitude than the prototype in the impeller inlet area while the pressure fluctuation amplitude of the MOD2 in the impeller inlet area is stronger than the prototype. It is considered as a consequence of multiple effects, which are, the rise of velocity because of flow area replacement by the vanes making the flow field less stable as well as the wake flow induced by the vanes increasing the instability of the flow field. Therefore, although the flat vanes can help adjusting the flow field, their negative influences also act in the opposite way. It is worthwhile to find the balance between the benefits and the costs in flow field stability of installing adjusting vanes. The selection of parameter, number and installation position needs to be further investigated. The numerical results of the MOD1 are also validated through experimental investigations.

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