scholarly journals The Influence of Transient Regimes on Unsteady Vortex Phenomena in the Model of the Draft Tube of the Hydraulic Turbine

2019 ◽  
Vol 14 (4) ◽  
pp. 55-68
Author(s):  
D. A. Suslov ◽  
I. V. Litvinov ◽  
S. I. Shtork ◽  
E. U. Gorelikov
Keyword(s):  
Flow Rate ◽  
Swirling Flow ◽  
Draft Tube ◽  
Maximum Level ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Rotor Speed ◽  
Precessing Vortex Core ◽  
Transient Regimes ◽  
Partial Load

This article is devoted to study the swirling flow with the formation of the precessing vortex core (PVC) in the cone of the model of the draft tube of the hydraulic turbine. The experiments were carried out on the aerodynamic set-up both in stationary and in transient regimes of operation of the hydraulic turbine. The hydraulic turbine operating conditions were varied by continuously changing the flow rate at a constant rotor speed. The formation of the PVC in the flow and the maximum level of pressure pulsations in the regime modeling the partial load regime of a turbine are revealed. The boundaries of the occurrence of the PVC effect are determined with varying rotor speed and air flow rate. It was found that the dependence of the PVC lifetime in transition regimes correlate with the transition time. It was shown that the velocity profiles in transient conditions change quasistatically between the operation regime with partial loading of the turbine and the regime of the highest efficiency of the turbine.

scholarly journals Experimental Study of Transient Flow Regimes in a Model Hydroturbine Draft Tube

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1240
Author(s):  
Ivan Litvinov ◽  
Daniil Suslov ◽  
Evgeny Gorelikov ◽  
Sergey Shtork
Keyword(s):  
Vortex Core ◽  
Transient Flow ◽  
Swirling Flow ◽  
Draft Tube ◽  
Transient Regime ◽  
Operating Conditions ◽  
Transient Time ◽  
Precessing Vortex Core ◽  
Transient Regimes ◽  
Partial Load

Swirling flow with the formation of a precessing vortex core (PVC) in the draft tube model of a hydroturbine was studied. Experiments were performed on an aerodynamic setup under transient operating conditions of the hydroturbine. The turbine operating conditions were varied by continuously changing the flow rate at a constant runner speed. The transition from the partial load regime, when a precessing vortex core is formed, to the best efficiency point without a core is considered. Applied to this task, a comparison of the windowed Fourier transform with wavelet analysis is given. The dependence of the PVC lifetime in the transient regime correlates with the transient time. It is shown that the velocity profiles and the spectrum of pressure pulsations in transient regimes change quasistatically between part-load operation and the best efficiency point of the turbine. The phase-averaged velocity distributions in the transient regimes show that a transient regime is a sequence of quasisteady regimes.

scholarly journals Manipulation of the swirling flow instability in hydraulic turbine diffuser by different methods of water injection

2018 ◽  
Vol 180 ◽  
pp. 02090 ◽  
Author(s):  
Pavel Rudolf ◽  
Jiří Litera ◽  
Germán Alejandro Ibarra Bolanos ◽  
David Štefan
Keyword(s):  
Swirling Flow ◽  
Flow Instability ◽  
Draft Tube ◽  
Water Injection ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Necessary Condition ◽  
Vortex Rope ◽  
Wide Range

Vortex rope, which induces substantial pressure pulsations, arises in the draft tube (diffuser) of Francis turbine for off-design operating conditions. Present paper focuses on mitigation of those pulsations using active water jet injection control. Several modifications of the original Susan-Resiga’s idea were proposed. All modifications are driven by manipulation of the shear layer region, which is believed to play important role in swirling flow instability. While some of the methods provide results close to the original one, none of them works in such a wide range. Series of numerical experiments support the idea that the necessary condition for vortex rope pulsation mitigation is increasing the fluid momentum along the draft tube axis.

scholarly journals Comparative analysis of air and water flows in simplified hydraulic turbine models

2022 ◽  
Vol 2150 (1) ◽  
pp. 012001
Author(s):  
S G Skripkin ◽  
D A Suslov ◽  
I V Litvinov ◽  
E U Gorelikov ◽  
M A Tsoy ◽  
...  
Keyword(s):  
Comparative Analysis ◽  
Pressure Pulsation ◽  
Swirling Flow ◽  
Flow Characteristics ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Precessing Vortex Core ◽  
Wide Range ◽  
Turbine Runner ◽  
The Fourier Transform

Abstract This article presents a comparative analysis of flow characteristics behind a hydraulic turbine runner in air and water. Swirling flow with a precessing vortex core (PVC) was investigated using a laser Doppler anemometer and pressure pulsation sensors. The experiments were conducted on aerodynamic and hydrodynamic test rigs over a wide range of hydraulic turbine operating conditions. Part-load modes of hydraulic turbine operation were investigated using the Fourier transform of pressure pulsations obtained from acoustic sensors. The features of the swirling flow were shown for the range of operating conditions from deep partl-load to overload.

Detection of Unsteady Flow in a Kaplan Hydraulic Turbine Using Machine Mechanical Model and Rotor Measured Vibrations

2012 ◽  
Author(s):  
Paolo Pennacchi ◽  
Andrea Vania ◽  
Steven Chatterton ◽  
Ezio Tanzi
Keyword(s):  
Unsteady Flow ◽  
Flow Rate ◽  
Mechanical Model ◽  
Turbine Unit ◽  
Draft Tube ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Design Stage ◽  
System Response ◽  
Model Based

Hydraulic stability is one of the key problems during the design stage of hydraulic turbines. Despite of modern computational tools that help to define dangerous operating conditions and optimize runner design, hydraulic instabilities may fortuitously arise during the turbine life, as a consequence of variable and different operating conditions at which a hydraulic turbine can be subject. In general, the presence of unsteady flow reveals itself in two different ways: at small flow rate, the swirling flow in the draft tube conical inlet occupies a large portion of the inlet and causes a strong helical vortex rope; at large flow rate conditions the unsteady flow starts midway and causes a breakdownlike vortex bubble, followed by weak helical waves. In any case, hydraulic instability causes mechanical effects on the runner, on the whole turbine and on the draft tube, which may eventually produce severe damages on the turbine unit and whose most evident symptoms are vibrations. This notwithstanding, condition monitoring systems seldom are installed on this purpose in hydraulic power plants and no examples are reported in literature about the use of model-based methods to detect hydraulic instability onset. In this paper, by taking the advantage of a testing campaign performed during the commissioning of a 23 MW Kaplan hydraulic turbine unit, a rotordynamic model-based method is proposed. The turbine was equipped by proximity and vibration velocity probes, that allowed measuring lateral and axial vibrations of the shaft-line, under many different operating conditions, including also some off-design ones. The turbine mechanical model, realized by means of finite beam elements and considering lateral and axial degrees of freedom, is used to predict turbine unit response to the unsteady flow. Mechanical system response is then compared to the measured one and the possibility to detect instability onset, especially in real-time, is discussed.

scholarly journals Numerical and experimental investigation of the effect of baffles on flow instabilities in a Francis turbine draft tube under partial load conditions

2019 ◽  
Vol 11 (1) ◽  
pp. 168781401882446 ◽  
Author(s):  
Xing Zhou ◽  
He-gao Wu ◽  
Chang-zheng Shi
Keyword(s):  
Swirling Flow ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Tangential Velocity ◽  
Operating Conditions ◽  
Dynamics Simulation ◽  
Flow Instabilities ◽  
Francis Turbine ◽  
Vortex Rope ◽  
Partial Load

An improved method for preventing vortex rope formation and alleviating the associated pressure fluctuations in turbine draft tubes is investigated using baffles in the draft tube to hinder the swirling flow emerging from a Francis turbine runner. A strong swirl produces flow instabilities and pressure fluctuations. Partial load operating conditions at the rated water head and three flow rates are taken into consideration. It is demonstrated using a computational fluid dynamics simulation that this method effectively eliminates the vortex rope, particularly when using four baffles. The amplitude of the pressure pulsation in the draft tube modified with four baffles was 0.42 times that in a traditional draft tube. The baffles were found to reduce the tangential velocity of the flow in the draft tube and consequently hinder the development of the fierce swirling flow. This type of decrease is more significant compared to the gradual decay due to viscous effects of the solid wall in a traditional draft tube. The conclusion was verified by the results of experiments conducted using a novel device. The measured increase in turbine efficiency exceeded 3% at the evaluated partial loading point, indicating improved economic performance of the turbine.

Hydraulic Instability Onset Detection in Kaplan Turbines by Monitoring Shaft Vibrations

2012 ◽  
Author(s):  
P. Pennacchi ◽  
P. Borghesani ◽  
S. Chatterton ◽  
A. Vania
Keyword(s):  
Experimental Test ◽  
Turbine Unit ◽  
Swirling Flow ◽  
Draft Tube ◽  
Operating Conditions ◽  
Low Flow ◽  
Operating Life ◽  
Vortex Rope ◽  
Power Load ◽  
Helical Vortex

Design of hydraulic turbines has often to deal with hydraulic instability. It is well-known that Francis and Kaplan types present hydraulic instability in their design power range. Even if modern CFD tools may help to define these dangerous operating conditions and optimize runner design, hydraulic instabilities may fortuitously arise during the turbine life and should be timely detected in order to assure a long-lasting operating life. In a previous paper, the authors have considered the phenomenon of helical vortex rope, which happens at low flow rates when a swirling flow, in the draft tube conical inlet, occupies a large portion of the inlet. In this condition, a strong helical vortex rope appears. The vortex rope causes mechanical effects on the runner, on the whole turbine and on the draft tube, which may eventually produce severe damages on the turbine unit and whose most evident symptoms are vibrations. The authors have already shown that vibration analysis is suitable for detecting vortex rope onset, thanks to an experimental test campaign performed during the commissioning of a 23 MW Kaplan hydraulic turbine unit. In this paper, the authors propose a sophisticated data driven approach to detect vortex rope onset at different power load, based on the analysis of the vibration signals in the order domain and introducing the so-called “residual order spectrogram”, i.e. an order-rotation representation of the vibration signal. Some experimental test runs are presented and the possibility to detect instability onset, especially in real-time, is discussed.

Performance of Francis Turbine Operating at Excess Load Condition

2020 ◽  
Author(s):  
Muhannad Altimemy ◽  
Justin Caspar ◽  
Alparslan Oztekin
Keyword(s):  
Flow Field ◽  
Draft Tube ◽  
Turbine Blades ◽  
Pressure Fluctuations ◽  
Load Condition ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Partial Load ◽  
Dynamics Simulations ◽  
Excess Load

Abstract Computational fluid dynamics simulations are conducted to characterize the spatial and temporal characteristics of the flow field inside a Francis turbine operating in the excess load regime. A high-fidelity Large Eddy Simulation (LES) turbulence model is applied to investigate the flow-induced pressure fluctuations in the draft tube of a Francis Turbine. Probes placed alongside the wall and in the center of the draft tube measure the pressure signal in the draft tube, the pressure over the turbine blades, and the power generated to compare against previous studies featuring design point and partial load operating conditions. The excess load is seen during Francis turbines in order to satisfy a spike in the electrical demand. By characterizing the flow field during these conditions, we can find potential problems with running the turbine at excess load and inspire future studies regarding mitigation methods. Our studies found a robust low-pressure region on the edges of turbine blades, which could cause cavitation in the runner region, which would extend through the draft tube, and high magnitude of pressure fluctuations were observed in the center of the draft tube.

Air Injection by Self-Aspirating Impeller in Aerobic Fermentation

1975 ◽  
Vol 38 (2) ◽  
pp. 94-99 ◽  
Author(s):  
F. A. AZI ◽  
A. G. MEIERING ◽  
C. L. DUITSCHAEVER ◽  
A. E. READE
Keyword(s):  
Flow Pattern ◽  
Flow Rate ◽  
Oxygen Transfer ◽  
Draft Tube ◽  
Air Flow ◽  
Air Injection ◽  
Vertical Flow ◽  
Rotor Speed ◽  
Air Flow Rate ◽  
Biological Tests

A novel fermentor is described in which aeration is achieved by air induction through a hollow impeller system: no air pump is required. Air flow into the vessel increased with rotor speed, impeller diameter and height of liquid above the impeller. Although longer impellers increased the air flow rate. oxygen transfer was favored by shorter impellers. The presence of a draft tube in the vessel creates a vertical flow pattern in the medium which increases gas hold-up and, therefore, oxygen transfer. Biological tests on the system using a mold and a yeast showed that performance compared favorably to conventional fermentor systems using separate aerators and agitators.

Flow in the Simplified Draft Tube of a Francis Turbine Operating at Partial Load—Part I: Simulation of the Vortex Rope

2014 ◽  
Vol 81 (6) ◽  
Author(s):  
Hosein Foroutan ◽  
Savas Yavuzkurt
Keyword(s):  
Experimental Data ◽  
Axial Velocity ◽  
Draft Tube ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Turbulence Closure ◽  
Francis Turbine ◽  
Outer Flow ◽  
Vortex Rope ◽  
Partial Load

Numerical simulations and analysis of the vortex rope formation in a simplified draft tube of a model Francis turbine are carried out in this paper, which is the first part of a two-paper series. The emphasis of this part is on the simulation and investigation of flow using different turbulence closure models. Two part-load operating conditions with same head and different flow rates (91% and 70% of the best efficiency point (BEP) flow rate) are considered. Steady and unsteady simulations are carried out for axisymmetric and three-dimensional grid in a simplified axisymmetric geometry, and results are compared with experimental data. It is seen that steady simulations with Reynolds-averaged Navier–Stokes (RANS) models cannot resolve the vortex rope and give identical symmetric results for both the axisymmetric and three-dimensional flow geometries. These RANS simulations underpredict the axial velocity (by at least 14%) and turbulent kinetic energy (by at least 40%) near the center of the draft tube, even quite close to the design condition. Moving farther from the design point, models fail in predicting the correct levels of the axial velocity in the draft tube. Unsteady simulations are performed using unsteady RANS (URANS) and detached eddy simulation (DES) turbulence closure approaches. URANS models cannot capture the self-induced unsteadiness of the vortex rope and give steady solutions while DES model gives sufficient unsteady results. Using the proper unsteady model, i.e., DES, the overall shape of the vortex rope is correctly predicted and the calculated vortex rope frequency differs only 6% from experimental data. It is confirmed that the vortex rope is formed due to the roll-up of the shear layer at the interface between the low-velocity inner region created by the wake of the crown cone and highly swirling outer flow.

Computational Study of Pump Turbine: Partial Load Operations

2020 ◽  
Author(s):  
Muhannad Altimemy ◽  
Justin Caspar ◽  
Alparslan Oztekin
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Computational Study ◽  
Pressure Fluctuations ◽  
System Stability ◽  
Pump Turbine ◽  
Vortex Rope ◽  
Signal Velocity ◽  
Partial Load ◽  
Les Model

Abstract The performance of a pump-turbine under partial flow rates, 85%, 75%, and 65%, is studied using the LES model. The power signal, velocity, vorticity, and pressure field is presented over the blades and throughout the draft tube. Pressure fluctuations are probed at various locations over the wall of the draft tube. Examining the flow field in the blade region can provide further insights into the system performance. Flow-induced pressure fluctuations can disrupt system stability. For this turbine, a strong swirling region is observed around the draft tube walls, causing pressure fluctuations. The size and intensity of this region decrease with the flow rate. A vortex rope is present in all cases. At the design point, the strength is constant throughout the draft tube. However, at partial load, the rope is weakened along the draft tube. Between the region dominated by the vortex rope and the wall, there is a swirling shear layer, which moves closer to the wall as the flow rate decreases. Both the magnitude of pressure fluctuations at the wall and the pressure difference over the blade decrease with the flow rate. The decreased pressure differences over the blade represent less power produced, and the decline in fluctuation magnitude at the wall represents more system stability. For this turbine, there appears to be a trade-off between power and strength of pressure fluctuations.

Sign in / Sign up

Export Citation Format

Share Document