Long-Period Pressure Pulsation Estimated in Numerical Simulations for Excessive Flow Rate Condition of Francis Turbine

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Kenji Shingai ◽  
Nobuaki Okamoto ◽  
Yuta Tamura ◽  
Kiyohito Tani
Keyword(s):  
Numerical Simulations ◽  
Flow Rate ◽  
Draft Tube ◽  
Homogeneous Model ◽  
Francis Turbine ◽  
Computational Time ◽  
Condensation Process ◽  
Rate Condition ◽  
Long Period ◽  
Rotor Stator Interaction

A series of numerical simulations for a Francis turbine were carried out to estimate the unsteady motion of the cavity in the draft tube of the turbine under a much larger flow rate condition than the swirl-free flow rate. The evaporation and condensation process was described by using a simplified Rayleigh–Plesset equation. A two-phase homogeneous model was adopted to calculate the mixture of gas and liquid phases. Instantaneous pressure monitored at a point on the draft tube formed long-period pulsations. Detailed analysis of the simulation results clarified the occurrence of a uniquely shaped cavity and the corresponding flow pattern in every period of the pressure pulsations. The existence of a uniquely shaped cavity was verified with an experimental approach. A simulation without rotor-stator interaction also obtained long-period pulsations after an extremely long computational time. This result shows that the rotor-stator interaction does not contribute to the excitation of long-period pulsations.

scholarly journals Effect of Air Injection on the Internal Flow Characteristics in the Draft Tube of a Francis Turbine Model

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1182
Author(s):  
Seung-Jun Kim ◽  
Yong Cho ◽  
Jin-Hyuk Kim
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Air Injection ◽  
Low Flow ◽  
Francis Turbine ◽  
Navier Stokes ◽  
Vortex Rope

Under low flow-rate conditions, a Francis turbine exhibits precession of a vortex rope with pressure fluctuations in the draft tube. These undesirable flow phenomena can lead to deterioration of the turbine performance as manifested by torque and power output fluctuations. In order to suppress the rope with precession and a swirl component in the tube, the use of anti-swirl fins was investigated in a previous study. However, vortex rope generation still occurred near the cone of the tube. In this study, unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted with a scale-adaptive simulation shear stress transport turbulence model. This model was used to observe the effects of the injection in the draft tube on the unsteady internal flow and pressure phenomena considering both active and passive suppression methods. The air injection affected the generation and suppression of the vortex rope and swirl component depending on the flow rate of the air. In addition, an injection level of 0.5%Q led to a reduction in the maximum unsteady pressure characteristics.

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

2014 ◽  
Vol 81 (6) ◽  
Author(s):  
Hosein Foroutan ◽  
Savas Yavuzkurt
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Companion Paper ◽  
Francis Turbine ◽  
Control Technique ◽  
Outer Flow ◽  
Vortex Rope ◽  
Stagnant Region ◽  
Partial Load

Numerical simulations and investigation of a method for controlling the vortex rope formation in draft tubes are carried out in this paper, which is the second part of a two-paper series. As shown in the companion paper, formation of the vortex rope is associated with a large stagnant region at the center of the draft tube. Therefore, it is concluded that a successful control technique should focus on the elimination of this region. In practice, this can be performed by axially injecting a small fraction (a few percent of the total flow rate) of water into the draft tube. Water jet is supplied from the high-pressure flow upstream of the turbine spiral case by a bypass line; thus, no extra pump is needed in this method. It is shown that this method is very effective in elimination of the stagnant region in a simplified draft tube operating at two part-load conditions, i.e., at 91% and 70% of the best efficiency point (BEP) flow rate. This results in improvement of the draft tube performance and reduction of hydraulic losses. The loss coefficient is reduced by as much as 50% for the case with 91% of BEP flow rate and 14% for the case with 70% of BEP flow rate. Unsteady, three-dimensional simulations show that the jet increases the axial momentum of flow at the center of the draft tube and decreases the wake of the crown cone and thereby decreases the shear at the interface of the stagnant region and high velocity outer flow, which ultimately results in elimination of the vortex rope. Furthermore, reduction (by about 1/3 in the case with 70% of BEP flow rate) of strong pressure fluctuations leads to reliable operation of the turbine.

scholarly journals Numerical and experimental study of variable speed automobile engine cooling water pump

2020 ◽  
Vol 103 (2) ◽  
pp. 003685042092522 ◽  
Author(s):  
Wei Li ◽  
Leilei Ji ◽  
Lingling Ma ◽  
Yongfei Yang ◽  
Ling Zhou ◽  
...  
Keyword(s):  
Flow Rate ◽  
Cooling Water ◽  
Internal Flow ◽  
Water Pump ◽  
Tip Leakage Flow ◽  
Rate Condition ◽  
Rotating Speed ◽  
Engine Cooling ◽  
Cavitation Performance ◽  
Rotor Stator Interaction

To investigate the performance of engine cooling water pump in automobile with variable rotating speed, experimental tests and numerical simulation are carried out on an engine cooling water pump under the rotating speed of 2650, 2960, 3700, and 4300 r/min. The hydraulic performance under 3700 r/min rotating speed and the cavitation performance under 340 L/min flow rate are tested and analyzed. The predicted results agree well with the experimental results, indicating that the simulation has high accuracy. The results show that the head of engine cooling water pump increases gradually and the best-effective region moves toward high flow rate condition with the increase in rotating speed. The augment of rotating speed would deteriorate the internal flow fields and causes more energy losses, which is due to the increase in tip leakage flow and enhancement of rotor–stator interaction effects. And, the rotor–stator interaction effect is sensitive to the temperature under various rotating speeds. Furthermore, the required net positive suction head increases with the increase in rotational speed and anti-cavitation performance is weakened during cavitation conditions.

Investigations of Compressible Turbulent Flow in a High-Head Francis Turbine

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Chirag Trivedi
Keyword(s):  
Compressible Flow ◽  
Incompressible Flow ◽  
Draft Tube ◽  
Francis Turbine ◽  
Accurate Estimation ◽  
Compressibility Effect ◽  
Numerical Errors ◽  
Rotor Stator Interaction ◽  
High Head ◽  
Runner Design

Dynamic stability of the high-head Francis turbines is one of the challenging problems. Unsteady rotor–stator interaction (RSI) develops dynamic stresses and leads to crack in the blades. In a high-head turbine, vaneless space is small and the amplitudes of RSI frequencies are very high. Credible estimation of the amplitudes is vital for the runner design. The current study is aimed to investigate the amplitudes of RSI frequencies considering a compressible flow. The hydro-acoustic phenomenon is dominating the turbines, and the compressibility effect should be accounted for accurate estimation of the pressure amplitudes. Unsteady pressure measurements were performed in the turbine during the best efficiency point (BEP) and part load (PL) operations. The pressure data were used to validate the numerical model. The compressible flow simulations showed 0.5–3% improvement in the time-averaged pressure and the amplitudes over incompressible flow. The maximum numerical errors in the vaneless space and runner were 6% and 10%, respectively. Numerical errors in the instantaneous pressure amplitudes at the vaneless space, runner, and draft tube were ±1.6%, ±0.9%, and ±1.8%, respectively. In the draft tube, the incompressible flow study showed the pressure amplitudes up to eight times smaller than those of the compressible. Unexpectedly, the strong effect of RSI was seen in the upper and lower labyrinth seals, which was absent for the incompressible flow.

Francis Turbine Operation at Excess Flow Rate Using Large Eddy Simulation: The Effect of Water Injection

2020 ◽  
Author(s):  
Muhannad Altimemy ◽  
Justin Caspar ◽  
Saif Watheq ◽  
Alparslan Oztekin
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Tube Wall ◽  
Temporal Structure ◽  
Pressure Fluctuations ◽  
Water Injection ◽  
Design Flow ◽  
Francis Turbine ◽  
Reduced Pressure ◽  
Large Eddy

Abstract High-fidelity Large Eddy Simulations (LES) were conducted to characterize the spatial and temporal structure of turbulent flows in an industrial-sized Francis turbine running at 120% of the design flow rate. Injection at a 4% and 8% flow rate is applied and investigated as a mitigation method for pressure-induced fluctuations along the draft tube. Contours of velocity and vorticity in the draft tube are presented to examine the effects of water injection. Probes placed alongside the draft tube measure the pressure signal and compare both operational regimes to characterize the pressure fluctuations. The intensity of pressure fluctuations along the draft tube wall is an order of magnitude smaller compared to that at the center. As the injection is applied, the intensity of the pressure fluctuations along the draft tube wall is increased while the intensity of pressure fluctuations in the center of the draft tube is reduced. Pressure probes in the center of the draft tube measure an 86% to 57% reduction in amplitude for 4% to 8% flow rate injection, respectively. There is a 30% to 40% increase in fluctuations along the wall for 4% to 8% flow rate injection, respectively. These changes in flow structure are due to the dissipation of the vortex rope as the injection is applied.

Investigation on Combined Air and Water Injection in Francis Turbine Draft Tube to Reduce Vortex Rope Effects

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Moona Mohammadi ◽  
Ebrahim Hajidavalloo ◽  
Morteza Behbahani-Nejad
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Water Injection ◽  
Total Loss ◽  
Design Flow ◽  
Air Injection ◽  
Francis Turbine ◽  
Two Phase ◽  
Operating Range ◽  
Two Fluids

In this paper, the effect of water, air, and their combined injection from two different injection points is studied in order to reduce vorticity effects in a draft tube of prototype turbine working at three operating points. The flow from spiral case to the end of draft tube is simulated using the shear stress transport k–ω turbulence and two-phase models. Using an appropriate validation method, acceptable results were obtained under the noninjection condition. To determine suitable number of points and inlet flow rate for air injection as well as the appropriate nozzle diameter for air and water injection, a new method which considers the ratio of total loss to the pressure recovery factor is used, in addition to using the traditional method which calculates the total loss in the draft tube. Comparing results of the three types of injections shows air injection in the operating range greater than 70% of turbine design flow rate, is much more effective than water injection or the combination of air and water injection. However, in the operating range below 70%, either water or air injections are not suitable, but combination of these two fluids can improve system performance.

scholarly journals Effect of Fins on the Internal Flow Characteristics in the Draft Tube of a Francis Turbine Model

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2806 ◽  
Author(s):  
Seung-Jun Kim ◽  
Young-Seok Choi ◽  
Yong Cho ◽  
Jong-Woong Choi ◽  
Jung-Jae Hyun ◽  
...  
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Low Flow ◽  
Francis Turbine ◽  
Vortex Rope ◽  
Turbine Model ◽  
Low Flow Rate

Undesirable flow phenomena in Francis turbines are caused by pressure fluctuations induced under conditions of low flow rate; the resulting vortex ropes with precession in the draft tube (DT) can degrade performance and increase the instability of turbine operations. To suppress these DT flow instabilities, flow deflectors, grooves, or other structures are often added to the DT into which air or water is injected. This preliminary study investigates the effects of anti-cavity fins on the suppression of vortex ropes in DTs without air injection. Unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted using a scale-adaptive simulation shear stress transport turbulence model to observe the unsteady internal flow and pressure characteristics by applying anti-cavity fins in the DT of a Francis turbine model. A vortex rope with precession was observed in the DT under conditions of low flow rate, and the anti-cavity fins were confirmed to affect the mitigation of the vortex rope. Moreover, at the low flow rate conditions under which the vortex rope developed, the application of anti-cavity fins was confirmed to reduce the maximum unsteady pressure.

3D PIV and LDV Measurements at the Outlet of a Francis Turbine Draft Tube

2002 ◽  
Author(s):  
Monica Sanda Iliescu ◽  
Gabriel Dan Ciocan ◽  
Franc¸ois Avellan
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Small Variation ◽  
Hydraulic Turbine ◽  
Field Analysis ◽  
Francis Turbine ◽  
Outlet Section ◽  
Recovery Coefficient ◽  
Transversal Section ◽  
Operating Points

For certain geometries of elbow draft tubes of a hydraulic turbine, a drop in the pressure recovery coefficient is observed for a small variation of the flow rate. In order to determine the possible causes of this characteristics shape, the flow field analysis for 4 nearby operating points have been investigated. For velocity and turbulence fields investigation in the outlet section of the studied draft tube, LDV measurements were performed in a transversal section and the 3D-PIV system was qualified for global velocity measurements in longitudinal sections, with an accuracy of less than 3%. By correlating the LDV and PIV results, the quantification of the flow rate through each channel, related to the operating points, and the description of the secondary flow in the outlet zone are possible.

Detection of Draft Tube Surge and Erosive Blade Cavitation in a Full-Scale Francis Turbine

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Xavier Escaler ◽  
Jarle V. Ekanger ◽  
Håkon H. Francke ◽  
Morten Kjeldsen ◽  
Torbjørn K. Nielsen
Keyword(s):  
Draft Tube ◽  
Guide Vane ◽  
Full Range ◽  
Pressure Fluctuations ◽  
Acoustic Emissions ◽  
Suction Side ◽  
Full Scale ◽  
Francis Turbine ◽  
Complete Measurement ◽  
Rotor Stator Interaction

A full-scale Francis turbine has been experimentally investigated over its full range of operation to detect draft tube swirling flows and cavitation. The unit is of interest due to the presence of severe pressure fluctuations at part load and of advanced blade suction-side cavitation erosion. Moreover, the turbine has a particular combination of guide vanes (20) to runner blades (15) that makes it prone to significant rotor-stator interaction (RSI). For that, a complete measurement system of dynamic pressures, temperatures, vibrations, and acoustic emissions has been setup with the corresponding transducers mounted at selected sensitive locations. The experiments have comprised an efficiency measurement, a signal transmissibility evaluation, and the recording of the raw signals at high sampling rates. Signal processing methods for demodulation, peak power estimation, and cross correlation have also been applied. As a result, draft tube pressure fluctuations have been detected around the Rheingans frequency for low loads and at 4% of the rotating frequency for high loads. Moreover, maximum turbine guide bearing acoustic emissions have been measured at full load with amplitude modulations at both the guide vane passing frequency and the draft tube surge frequency.

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