scholarly journals Numerical investigation of the flow phenomena around a low specific speed Francis turbine's guide vane cascade

2016 ◽  
Vol 49 ◽  
pp. 062016 ◽  
Author(s):  
Sailesh Chitrakar ◽  
Biraj Singh Thapa ◽  
Ole Gunnar Dahlhaug ◽  
Hari Prasad Neopane
Keyword(s):  
Numerical Investigation ◽  
Guide Vane ◽  
Flow Phenomena ◽  
Low Specific Speed ◽  
Specific Speed

scholarly journals Numerical investigation on the effects of leakage flow from Guide vane-clearance gaps in low specific speed Francis turbines

2020 ◽  
Vol 1608 ◽  
pp. 012016
Author(s):  
Saroj Gautam ◽  
Ram Lama ◽  
Sailesh Chitrakar ◽  
Hari Prasad Neopane ◽  
Biraj Singh Thapa ◽  
...  
Keyword(s):  
Numerical Investigation ◽  
Guide Vane ◽  
Leakage Flow ◽  
Low Specific Speed ◽  
Specific Speed

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.

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.

scholarly journals Experimental Study of a Low-Specific Speed Francis Model Runner during Resonance

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Einar Agnalt ◽  
Petter Østby ◽  
Bjørn W. Solemslie ◽  
Ole G. Dahlhaug
Keyword(s):  
Acoustic Pressure ◽  
Pressure Field ◽  
Second Harmonic ◽  
Guide Vane ◽  
Excitation Frequency ◽  
Pressure Sensors ◽  
At Resonance ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Developed Pressure

An analysis of the pressure in a runner channel of a low-specific speed Francis model runner during resonance is presented, which includes experiments and the development of a pressure model to estimate both the convective and acoustic pressure field from the measurements. The pressure was measured with four pressure sensors mounted in the runner hub along one runner channel. The mechanical excitation of the runner corresponded to the forced excitation from rotor-stator interaction. The rotational speed was used to control the excitation frequency. The measurements found a clear resonance peak in the pressure field excited by the second harmonic of the guide vane passing frequency. From the developed pressure model, the eigenfrequency and damping were estimated. The convective pressure field seems to diminish almost linearly from the inlet to outlet of the runner, while the acoustic pressure field had the highest amplitudes in the middle of the runner channel. At resonance, the acoustic pressure clearly dominated over the convective pressure. As the turbine geometry is available to the public, it provides an opportunity for the researchers to verify their codes at resonance conditions.

Sign in / Sign up

Export Citation Format

Share Document