scholarly journals Investigation of the Pressure Fluctuation Alleviation in a Hydraulic Turbine by Runner Modification

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1332 ◽  
Author(s):  
An Yu ◽  
Qinghong Tang ◽  
Xincheng Wang ◽  
Daqing Zhou ◽  
Jintao Liu
Keyword(s):  
Power Systems ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Flow Simulation ◽  
Hydraulic Turbine ◽  
Pressure Oscillations ◽  
Two Phase ◽  
Vortex Rope ◽  
Part Load ◽  
Load Conditions

Cavitation and system instability are the most common problems occurring in hydraulic power systems, especially operated under part-load conditions. Previous research show that when the hydraulic turbine operates apart from designed conditions, such as part-load conditions, a helical vortex rope occurs from the runner exit, and usually generates severe pressure oscillations. Cavitation usually appears and turns the rope to become a two-phase cavitation rope. The occurrence of cavitation rope is believed to be the main reason of the severe pressure oscillations. Based on a new multiphase flow simulation method re-developed in ANSYS CFX, this paper did the runner modification by using grooves and made the investigation of pressure fluctuation alleviation in a hydraulic turbine at different cavitation numbers. The behavior of cavitation rope and the pressure fluctuations induced by cavitation under typical part load conditions with modified runner were analyzed in present research. The results show that besides the pressure fluctuation induced by the rope rotating, cavitation induced a new pressure fluctuation with a lower frequency. For the embedded analysis the results show that the modified runner can decrease the vortex rope eccentricity and increase the vortex core pressure and finally alleviate the two types of pressure fluctuations. Also, the turbine efficiency has a little rise when equipped with the modified runner.

Unsteady vortical flow simulation in a Francis turbine with special emphasis on vortex rope behavior and pressure fluctuation alleviation

2017 ◽  
Vol 231 (3) ◽  
pp. 215-226 ◽  
Author(s):  
Xianwu Luo ◽  
An Yu ◽  
Bin Ji ◽  
Yulin Wu ◽  
Yoshinobu Tsujimoto
Keyword(s):  
Pressure Fluctuation ◽  
Swirling Flow ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Flow Simulation ◽  
Vortical Flow ◽  
Francis Turbine ◽  
Vortex Rope ◽  
Spiral Vortex ◽  
Baroclinic Torque

Hydro turbines operating at partial flow conditions usually have vortex ropes in the draft tube that generate large pressure fluctuations. This unsteady flow phenomenon is harmful to the safe operation of hydropower stations. This paper presents numerical simulations of the internal flow in the draft tube of a Francis turbine with particular emphasis on understanding the unsteady characteristics of the vortex rope structure and the underlying mechanisms for the interactions between the air and the vortices. The pressure fluctuations induced by the vortex rope are alleviated by air admission from the main shaft center, with the water-air two phase flow in the entire flow passage of a model turbine simulated based on the homogeneous flow assumption. The results show that aeration with suitable air flow rate can alleviate the pressure fluctuations in the draft tube, and the mechanism improving the flow stability in the draft tube is due to the change of vortex rope structure and distribution by aeration, i.e. a helical vortex rope at a small aeration volume while a cylindrical vortex rope with a large amount of aeration. The preferable vortex rope distribution can suppress the swirl at the smaller flow rates, and is helpful to alleviate the pressure fluctuation in the draft tube. The analysis based on the vorticity transport equation indicates that the vortex has strong stretching and dilation in the vortex rope evolution. The baroclinic torque term does not play a major role in the vortex evolution most of the time, but will much increase for some specific aeration volumes. The present study also depicts that vortex rope is mainly associated with a pair of spiral vortex stretching and dilation sources, and its swirling flow is alleviated little by the baroclinic torque term, whose effect region is only near the draft tube inlet.

Generation of Twin Vortex Rope in the Draft-Tube Elbow of a Francis Turbine During Deep Part-Load Operation

2021 ◽  
Author(s):  
Mohammad Hossein Khozaei ◽  
Arthur Favrel ◽  
Toshitake Masuko ◽  
Naoki Yamaguchi ◽  
Kazuyoshi Miyagawa
Keyword(s):  
Linear Correlation ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Model Tests ◽  
Francis Turbine ◽  
Deep Part ◽  
Swirl Number ◽  
Vortex Rope ◽  
Part Load

Abstract This paper focuses on the generation of twin vortex rope in the draft-tube elbow of a Francis turbine at deep part-load operation through analyzing the results of model tests along with numerical simulations. Model tests, including pressure fluctuations measurements, are conducted over 10 speed factors. By considering the frequency of the pressure fluctuations with respect to the swirl intensity at the runner outlet, the part-load operating range is divided into three regimes, with two clear transitions between each occurring at swirl numbers 0.4 and 1.7. For operating conditions with a swirl number S>0.4, a linear correlation between the frequency of the precessing vortex core and the swirl number is established. During deep part-load regime (S>1.7), low-frequency pressure fluctuations appear. Their frequency feature another linear correlation with the swirl number. Unsteady CFD simulation of the full domain is performed to elucidate the generation mechanisms of the low-frequency fluctuations. By tracking the center of the vortical structures along the draft-tube, generation of three vortices in the elbow responsible for the pressure fluctuations at the lowest frequency is highlighted: the main PVC hits the draft-tube wall in the elbow resulting in its break down into three vortices rotating with half the rotational speed of the PVC. Two of the vortices rotate with opposite angular position, constituting a structure of twin vortices. The periodic rotation of these three vortices in the elbow induces the low-frequency pressure fluctuations.

scholarly journals Design of Experiments Applied to Francis Turbine Draft Tube to Minimize Pressure Pulsations and Energy Losses in Off-Design Conditions

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3894
Author(s):  
Arthur Favrel ◽  
Nak-Joong Lee ◽  
Tatsuya Irie ◽  
Kazuyoshi Miyagawa
Keyword(s):  
Draft Tube ◽  
Pressure Fluctuations ◽  
Internal Flow ◽  
Francis Turbine ◽  
Energy Losses ◽  
Geometrical Parameters ◽  
Cfd Simulations ◽  
Part Load ◽  
Full Load ◽  
Load Conditions

This paper proposes an original approach to investigate the influence of the geometry of Francis turbines draft tube on pressure fluctuations and energy losses in off-design conditions. It is based on Design of Experiments (DOE) of the draft tube geometry and steady/unsteady Computational Fluid Dynamics (CFD) simulations of the draft tube internal flow. The test case is a Francis turbine unit of specific speed Ns=120 m-kW which is required to operate continuously in off-design conditions, either with 45% (part-load) or 110% (full-load) of the design flow rate. Nine different draft tube geometries featuring a different set of geometrical parameters are first defined by an orthogonal array-based DOE approach. For each of them, unsteady and steady CFD simulations of the internal flow from guide vane to draft tube outlet are performed at part-load and full-load conditions, respectively. The influence of each geometrical parameter on both the flow instability and resulting pressure pulsations, as well as on energy losses in the draft tube, are investigated by applying an Analysis of Means (ANOM) to the numerical results. The whole methodology enables the identification of a set of geometrical parameters minimizing the pressure fluctuations occurring in part-load conditions as well as the energy losses in both full-load and part-load conditions while maintaining the requested pressure recovery. Finally, the results of the CFD simulations with the final draft tube geometry are compared with the results estimated by the ANOM, which demonstrates that the proposed methodology also enables a rough preliminary estimation of the draft tube losses and pressure fluctuations amplitude.

Simulations and Measurements of Pressure Oscillations Caused by Vortex Ropes

2006 ◽  
Vol 128 (4) ◽  
pp. 649-655 ◽  
Author(s):  
Zhengwei Wang ◽  
Lingjiu Zhou
Keyword(s):  
Stokes Equations ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Suction Side ◽  
Rotational Frequency ◽  
Francis Turbine ◽  
Pressure Oscillations ◽  
Hydraulic Unit ◽  
Load Conditions

Pressure oscillations caused by vortex rope were measured in the draft tube of a prototype Francis turbine. The three-dimensional, unsteady Reynolds-averaged Navier-Stokes equations with the RNG κ−ϵ turbulence model were solved to model the flow within the entire flow path of the prototype hydraulic unit including the guide vanes, the runner, and the draft tube. The model was able to predict the pressure fluctuations that occur when operating at 67–83% of the optimum opening. The calculated frequencies and amplitudes of the oscillation show reasonable agreement with the experiment data. However, the results at 50% opening were not satisfactory. Pressure oscillations on the runner blades were found to be related to the precession of vortex ropes which caused pressure on the blades to fluctuate with frequencies of −fn+fd (fn is the rotational frequency and fd is vortex procession frequency). The peak-to-peak amplitudes of the pressure oscillations on the blades at the lower load conditions (67% opening) were higher than at higher load conditions (83% opening). Fluctuations on the suction side tended to be stronger than on the pressure side.

Investigation on Complex Pressure Fluctuations in a Gas-Solids Circulating Fluidized Bed Rieser

2012 ◽  
Vol 538-541 ◽  
pp. 610-615
Author(s):  
Jun Xu ◽  
Xing Xing Chen ◽  
Gui Lei Wang ◽  
Yao Dong Wei
Keyword(s):  
Fluidized Bed ◽  
Pressure Fluctuation ◽  
Circulating Fluidized Bed ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Axial Direction ◽  
High Amplitude ◽  
Solid Mass ◽  
Two Phase ◽  
Mass Fluxes

The experiment is carried out in a 13-meter-high circulating fluidized bed(CFB) to investigate gas-solid two-phase flow by pressure sensor. The axial pressure and pressure fluctuation are measured in different solid mass fluxes. With the solid mass flux increasing, pressure gradually increases, and pressure gradually decreases along the riser upwards. The characteristic of pressure fluctuation in the riser is analyzed, which indicates that pressure fluctuation in the riser originates from the inlet. The intensity of the pressure fluctuation decreases along the riser upwards. This pressure fluctuation is composed of two types: one is of low frequency and high amplitude, which is resulted from unstable feeding to the riser and keeps coherent along the axial direction. And the other is of high frequency and low amplitude, which is the result of a variety of factors, such as cluster movement, gas-solid interaction and gas velocity fluctuation.

Experimental Evidence of Hydroacoustic Pressure Waves in a Francis Turbine Elbow Draft Tube for Low Discharge Conditions

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Jorge Arpe ◽  
Christophe Nicolet ◽  
François Avellan
Keyword(s):  
Pressure Fluctuation ◽  
Swirling Flow ◽  
Draft Tube ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Hydropower Plant ◽  
Francis Turbine ◽  
Scale Model ◽  
Vortex Rope

The complex three-dimensional unsteady flow developing in the draft tube of a Francis turbine is responsible for pressure fluctuations, which could prevent the whole hydropower plant from operating safely. Indeed, the Francis draft tube is subjected to inlet swirling flow, divergent cross section, and the change of flow direction. As a result, in low discharge off-design operating conditions, a cavitation helical vortex, so-called the vortex rope develops in the draft tube and induces pressure fluctuations in the range of 0.2–0.4 times the runner frequency. This paper presents the extensive unsteady wall pressure measurements performed in the elbow draft tube of a high specific speed Francis turbine scale model at low discharge and at usual plant value of the Thoma cavitation number. The investigation is undertaken for operating conditions corresponding to low discharge, i.e., 0.65–0.85 times the design discharge, which exhibits pressure fluctuations at surprisingly high frequency value, between 2 and 4 times the runner rotation frequency. The pressure fluctuation measurements performed with 104 pressure transducers distributed on the draft tube wall, make apparent in the whole draft tube a fundamental frequency value at 2.5 times the runner frequency. Moreover, the modulations between this frequency with the vortex rope precession frequency are pointed out. The phase shift analysis performed for 2.5 times the runner frequency enables the identification of a pressure wave propagation phenomenon and indicates the location of the corresponding pressure fluctuation excitation source in the elbow; hydroacoustic waves propagate from this source both upstream and downstream the draft tube.

Influence of Blade Pitch and Number of Blades of a Pump Inducer on Single and Two-Phase Flow Performance

2020 ◽  
Author(s):  
Michael Mansour ◽  
Trupen Parikh ◽  
Dominque Thévenin
Keyword(s):  
High Performance ◽  
Two Phase Flow ◽  
Low Flow ◽  
Phase Flow ◽  
Flow Conditions ◽  
Two Phase ◽  
Phase Mixing ◽  
Part Load ◽  
Two Phases ◽  
Load Conditions

Abstract This study investigates the influence of various inducer configurations upstream of a pump impeller on the single and two-phase flow performance. Three pitch values (P = 0.151, 0.251, and 0.351 m), as well as three different numbers of blades (N = 2, 3, and 4 blades), were studied, leading to a total of 9 different inducer geometries. The main objective of the present study is to analyze and compare the corresponding performances and the two-phase mixing behavior, which is necessary for improving the two-phase pumping ability. 3D steady-state simulations using the Moving Reference Frame (MRF) approach were applied for single-phase flow, while a transient setup using a moving-mesh approach was employed for two-phase simulations. Turbulence was modeled by the Reynolds Stress Model (RSM), whereas the Volume of Fluid (VOF) method was applied to model air-water interactions. The results show that the increase in the number of blades leads to a high performance drop at overload (high-flow) conditions, but only to a slight performance enhancement at part-load (low-flow) conditions. Additionally, the effective flow range of the inducer corresponding to high efficiency becomes narrower for a higher number of blades. Concerning the inducer pitch, at part-load conditions, a lower pitch is slightly beneficial to smoothly suck the flow and damp the low-flow vortices; employing a high pitch at these conditions results in intensified flow vortices, reducing slightly the performance. On the other hand, the blade pitch is very influential for the performance at optimal and overload conditions, where a lower pitch causes flow blockage, leading to significant performance deterioration and a very limited range of applications. Generally, it was found that a modification of the inducer configuration affects the performance much more at overload compared to part-load conditions. Concerning two-phase mixing performance, the highest pitch provides the best mixing since the inducer is able to effectively churn the two phases. Similarly, an increase in the number of blades amplifies the turbulence between the two phases, thus improving mixing. Overall, a higher inducer pitch and a low to moderate number of inducer blades best ensure high performance, wide working range, and efficient two-phase mixing.

Sign in / Sign up

Export Citation Format

Share Document