scholarly journals Experiments and numerical simulations of a flow instability in a low-specific-speed pump-turbine

2019 ◽  
Vol 240 ◽  
pp. 072042
Author(s):  
Koichiro Matsumura ◽  
Kazuhiko Yokota ◽  
Wakana Tsuru ◽  
Donghyuk Kang ◽  
Hayate Sugiyama
Keyword(s):  
Numerical Simulations ◽  
Flow Instability ◽  
Pump Turbine ◽  
Low Specific Speed ◽  
Specific Speed

Investigation of the Flow Instabilities of a Low Specific Speed Pump-Turbine: Part 2 — Flow Control With Fluid Injection

2020 ◽  
Author(s):  
Sabri Deniz ◽  
Martin von Burg ◽  
Manuel Tiefenthaler
Keyword(s):  
Flow Control ◽  
Flow Instability ◽  
Guide Vane ◽  
Water Injection ◽  
Rotating Stall ◽  
Flow Instabilities ◽  
Fluid Injection ◽  
Pump Turbine ◽  
Low Specific Speed ◽  
Specific Speed

Abstract This the second part of a two-part paper focusing on the flow instabilities of low-specific pump turbines. In this part, results of the flow control application with fluid injection (using both water and air) in the vaneless space in order to suppress the flow instabilities of a low specific speed model pump-turbine in turbine mode operation at HSLU (Lucerne University of Applied Sciences) Switzerland are presented. Based on the analysis of the experimental data, flow visualization, and CFD results focusing especially on the flow features in the vaneless space and at the runner inlet, the onset and development of the flow instabilities are explored as presented in the first part of this paper. Based on these analyses, the flow control technology by injecting air and water as well as suction of the fluid in the vaneless space of the model pump-turbine is implemented for suppressing the flow instabilities and thus extending the operating range of the pump-turbine. Both air- and water-injection are applied by using an external energy source (compressor and pump) and discrete nozzles circumferentially distributed in the vaneless space. The S-shaped pump-turbine characteristics in turbine operating mode are modified so that the slope at speed no load conditions is no more positive meaning an improvement in the stability behavior. To the best of our knowledge, this is the first successful application of flow control with fluid injection in the vaneless space of pump-turbines. Fluid injection is applied at two different guide vane openings, i.e. at 6° and 18°. The analysis of the unsteady pressure data indicates the suppression of flow instability such as rotating stall with fluid injection in the vaneless space. The water injection is more effective than the air injection for modifying the slope of the pump-turbine characteristics.

scholarly journals On the Rotor Stator Interaction Effects of Low Specific Speed Francis Turbines

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Einar Agnalt ◽  
Igor Iliev ◽  
Bjørn W. Solemslie ◽  
Ole G. Dahlhaug
Keyword(s):  
Guide Vane ◽  
Pressure Fluctuations ◽  
Angular Position ◽  
Pressure Sensors ◽  
Pump Turbine ◽  
Blade Loading ◽  
Loading Case ◽  
Rotor Stator Interaction ◽  
Low Specific Speed ◽  
Specific Speed

The rotor stator interaction in a low specific speed Francis model turbine and a pump-turbine is analyzed utilizing pressure sensors in the vaneless space and in the guide vane cascade. The measurements are analyzed relative to the runner angular position by utilizing an absolute encoder mounted on the shaft end. From the literature, the pressure in the analyzed area is known to be a combination of two effects: the rotating runner pressure and the throttling of the guide vane channels. The measured pressure is fitted to a mathematical pressure model to separate the two effects for two different runners. One turbine with 15+15 splitter blades and full-length blades and one pump-turbine with six blades are investigated. The blade loading on the two runners is different, giving different input for the pressure model. The main findings show that the pressure fluctuations in the guide vane cascade are mainly controlled by throttling for the low blade loading case and the rotating runner pressure for the higher blade loading case.

scholarly journals Measuring the Dynamic Characteristics of a Low Specific Speed Pump—Turbine Model

Energies ◽  
2016 ◽  
Vol 9 (3) ◽  
pp. 199 ◽  
Author(s):  
Eve Walseth ◽  
Torbjørn Nielsen ◽  
Bjørnar Svingen
Keyword(s):  
Dynamic Characteristics ◽  
Pump Turbine ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Turbine Model

Investigation of the Flow Instabilities of a Low Specific Speed Pump-Turbine: Part 1 — Experimental and Numerical Analysis

2020 ◽  
Author(s):  
Sabri Deniz ◽  
Armando Del Rio ◽  
Martin von Burg ◽  
Manuel Tiefenthaler
Keyword(s):  
Experimental Data ◽  
Guide Vane ◽  
Turbulence Models ◽  
Operating Mode ◽  
Rotating Stall ◽  
Flow Instabilities ◽  
Pump Turbine ◽  
Flow Features ◽  
Low Specific Speed ◽  
Specific Speed

Abstract This is the first part of a two-part paper focusing on the flow instabilities of low-specific pump turbines. In this part, results of the CFD simulations and experiments of the research carried out on a low specific speed model pump-turbine at HSLU (Lucerne University of Applied Sciences) Switzerland are presented. The requirements of a stable and reliable pump-turbine operation under continuously expanding operating ranges, challenges the hydraulic design and requires new developments. Previous research at the HSLU [1] analyzed the instabilities of a medium specific speed (i.e. nq = 45) pump turbine. This paper presents the results of experimental (model pump-turbine at the test rig) and numerical (CFD) investigations of the pump-turbine instabilities of a low specific speed (nq = 25) pump-turbine in the turbine operating mode in the region of S-shaped characteristics (that is where the pump-turbine is synchronized and oscillations may occur during load rejection). The four-quadrant characteristics of a low specific speed model pump-turbine with two similar runners differentiating in the size (diameter) are measured. Testing of both runners with the same guide vane system provided information about the effects of the increased vaneless space (the distance between the guide vanes and runner) on the pump-turbine performance and stability both in turbine- and pump operating modes. A CFD methodology by using different numerical approaches and applying several turbulence models is developed in order to accurately predicting the characteristics of the reversible pump-turbines in the S-shaped region (speed no load conditions) as well as analyzing the flow features especially at off-design conditions. This CFD model is validated against the experimental data at 6° and 18° guide vane openings in turbine operating mode. With the measured data of the unsteady pressure measurements and detailed investigation of unstable ranges on the pump-turbine characteristics, flow instabilities in the low-specific speed model pump-turbine are analyzed. Relevant frequencies such as rotating stall, steady and unsteady vortex formations are determined. Based on the analysis of the experimental data and CFD results focusing especially on the flow features in the vaneless space and at the runner inlet, the onset and development of the flow instabilities are explored.

Experimental evidence of cavitation influences on the positive slope on the pump performance curve of a low specific speed model pump-turbine

2017 ◽  
Vol 113 ◽  
pp. 1539-1550 ◽  
Author(s):  
Guocheng Lu ◽  
Zhigang Zuo ◽  
Yuekun Sun ◽  
Demin Liu ◽  
Yoshinobu Tsujimoto ◽  
...  
Keyword(s):  
Experimental Evidence ◽  
Performance Curve ◽  
Positive Slope ◽  
Pump Turbine ◽  
Pump Performance ◽  
Low Specific Speed ◽  
Specific Speed

scholarly journals Analysis of the influence of a stator type modification on the performance of a pump with a hole impeller

2019 ◽  
Vol 9 (1) ◽  
pp. 218-228
Author(s):  
Bartłomiej Chomiuk ◽  
Janusz Skrzypacz
Keyword(s):  
Numerical Simulations ◽  
Experimental Research ◽  
Liquid Flow ◽  
Centrifugal Pumps ◽  
Pump Unit ◽  
Manufacturing Costs ◽  
Flow Through ◽  
Low Specific Speed ◽  
Specific Speed ◽  
The Impact

AbstractThe article presents the results of numerical analyses and experimental research of the influence of various types of stators on a liquid flow through a centrifugal pump with a hole impeller. It is a continuation of authors research of cooperation pump stators with alternative types of impellers which work in ultra low specific speed. Hole impellers have become a significant alternative to classical ones in a range of extremely low specific speed nq<10. The aim of the research is to verify the quality as well as quantity of computer modeling results, and to estimate accuracy by examining the impact of a grid and a turbulence model with which the numerical simulations reflect the actual flow.Knowledge concerning construction of hydraulic elements of centrifugal pumps working in the range of parameters corresponding specific speed (nq<10) is insufficient. The outlet elements were tested in various configurations of constructional features. The complexity of the construction of the stator can significantly affect the manufacturing costs of pump unit.

Applicability of Wall-Function Approach in Simulations of Turbomachines

2015 ◽  
Author(s):  
Kay Juckelandt ◽  
Frank-Hendrik Wurm
Keyword(s):  
Boundary Layer ◽  
Numerical Simulations ◽  
Function Method ◽  
Design Flow ◽  
Centrifugal Pumps ◽  
Wall Function ◽  
Modeling Error ◽  
Local Modeling ◽  
Low Specific Speed ◽  
Specific Speed

Numerical simulations of centrifugal pumps with low specific speed show significant differences in calculated efficiency from experiments. This causes designers to refrain from CFD methods and stick to prototyping. Investigations regarding the applicability of numerical simulations on these pumps are carried out. Unsteady simulations of a low specific speed pump are performed. The focus of this paper is boundary layer treatment, as losses due to boundary layer flow are dominant in low specific speed pumps. The wall-function as well as the low-Reynolds-number method is applied for boundary layer treatment. A method to calculate the local modeling error of the wall-function method is introduced. Experiments on a test pump are conducted to validate the simulations. Performance curves, locally highly resolved pressure distributions and velocity profiles are obtained. Simulations with resolved boundary layers match experimental data very good. It is shown that simulated efficiency is sensitive to the boundary layer treatment. The wall-function simulations deviate significantly at off-design flow rate, particularly at overload. The analysis reveals that modeling errors of the wall-function method mainly contribute to incorrect loss prediction. A local modeling error distribution is calculated and a meshing guideline for low specific speed pumps is derived.

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