scholarly journals COMPARATIVE ANALYSIS OF PRESSURE PULSATIONS CAUSED BY SPIRAL-VORTEX STRUCTURES IN THE FLOW PART OF THE HYDRAULIC TURBINE MODEL

2021 ◽  
Vol 21 (3) ◽  
pp. 49-56
Author(s):  
D. Suslov ◽  
◽  
I. Litvinov ◽  
E. Gorelikov ◽  
Keyword(s):  
Draft Tube ◽  
Hydraulic Turbine ◽  
Vortex Structures ◽  
Flow Section ◽  
Pressure Pulsations ◽  
Spiral Vortex ◽  
Flow Part ◽  
Hydraulic Turbines ◽  
Draft Tubes ◽  
Turbine Model

The paper studies the pressure pulsations in the hydraulic turbines flow section arise as a result of vortex structures in non-optimal hydraulic turbine operation regimes. The authors directly compare the approaches to the extraction of synchronous and asynchronous components in pressure pulsation signals, as well as using the decomposition into azimuthal modes. Pressure pulsations were measured using four acoustic sensors while varying the operating regimes of the hydraulic turbine model. The pressure pulsations were compared for the shallow draft tube and the deep draft tube of the hydraulic turbine. It is shown that the level of pressure pul-sations is the same for two types of draft tubes. There is no methodological difference in the application of the two approaches to the extraction of pressure pulsations in the flow. The results shall be applicable in the de-velopment of new methods for suppressing spiral-vortex structures in non-optimal regimes of operation of hydraulic turbines in order to increase their overall efficiency.

Investigations Of Pressure Pulsations In A Model Of Draft Tube Of Hydraulic Turbine Caused By Vortex Rings

2016 ◽  
Vol 11 (4) ◽  
pp. 25-32
Author(s):  
Sergey Skripkin ◽  
Mikhail Tsoy ◽  
Sergey Shtork ◽  
Pavel Kuibin
Keyword(s):  
Vortex Ring ◽  
High Speed ◽  
Draft Tube ◽  
Hydraulic Turbine ◽  
Vortex Rings ◽  
Experimental Investigations ◽  
Visualization Technique ◽  
Vortex Rope ◽  
Hydro Turbine ◽  
Hydraulic Turbines

Current work is devoted to experimental investigations of behavior of precessing vortex rope in a draft tube model of hydraulic turbine. We used combination of stationary and freely rotating swirlers as a hydro turbine model. Such construction provides velocity distribution on the draft tube inlet close to distribution in natural hydraulic turbines operated at non-optimal conditions. The phenomenon of precessing vortex rope reconnection with further formation of vortex ring was founded in this experimental research using high-speed visualization technique. Synchronization of highspeed visualization and pressure measurements allowed us to relate pressure shock on the draft tube wall with vortex ring moving along wall.

scholarly journals On the Evaluation of Mesh Resolution for Large-Eddy Simulation of Internal Flows Using Openfoam

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 24
Author(s):  
Zahra Seifollahi Moghadam ◽  
François Guibault ◽  
André Garon
Keyword(s):  
Draft Tube ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Sudden Expansion ◽  
Test Cases ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Mesh Resolution ◽  
Hydraulic Turbines ◽  
Academic Test

The central aim of this paper is to use OpenFOAM for the assessment of mesh resolution requirements for large-eddy simulation (LES) of flows similar to the ones which occur inside the draft-tube of hydraulic turbines at off-design operating conditions. The importance of this study is related to the fact that hydraulic turbines often need to be operated over an extended range of operating conditions, which makes the investigation of fluctuating stresses crucial. Scale-resolving simulation (SRS) approaches, such as LES and detached-eddy simulation (DES), have received more interests in the recent decade for understanding and mitigating unsteady operational behavior of hydro turbines. This interest is due to their ability to resolve a larger part of turbulent flows. However, verification studies in LES are very challenging, since errors in numerical discretization, but also subgrid-scale (SGS) models, are both influenced by grid resolution. A comprehensive examination of the literature shows that SRS for different operating conditions of hydraulic turbines is still quite limited and that there is no consensus on mesh resolution requirement for SRS studies. Therefore, the goal of this research is to develop a reliable framework for the validation and verification of SRS, especially LES, so that it can be applied for the investigation of flow phenomena inside hydraulic turbine draft-tube and runner at their off-design operating conditions. Two academic test cases are considered in this research, a turbulent channel flow and a case of sudden expansion. The sudden expansion test case resembles the flow inside the draft-tube of hydraulic turbines at part load. In this study, we concentrate on these academic test cases, but it is expected that hydraulic turbine flow simulations will eventually benefit from the results of the current research. The results show that two-point autocorrelation is more sensitive to mesh resolution than energy spectra. In addition, for the case of sudden expansion, the mesh resolution has a tremendous effect on the results, and, so far, we have not capture an asymptotic converging behavior in the results of Root Mean Square (RMS) of velocity fluctuations and two-point autocorrelation. This case, which represents complex flow behavior, needs further mesh resolution studies.

scholarly journals Numerical Investigation of the Influence of Special Structures On Suppression of Pressure Pulsations in The Draft Tube of a High-Head Hydraulic Turbine

2019 ◽  
Vol 92 (6) ◽  
pp. 1489-1500
Author(s):  
A. V. Sentyabov ◽  
A. V. Minakov ◽  
D. V. Platonov ◽  
D. A. Dekterev ◽  
A. V. Zakharov ◽  
...  
Keyword(s):  
Numerical Investigation ◽  
Draft Tube ◽  
Hydraulic Turbine ◽  
Pressure Pulsations ◽  
High Head

Hydraulic Turbine Setting Criteria

1965 ◽  
Vol 87 (3) ◽  
pp. 295-298
Author(s):  
F. O. Ruud
Keyword(s):  
Draft Tube ◽  
Hydraulic Turbine ◽  
Cavitation Damage ◽  
Hydraulic Turbines

Higher settings of hydraulic turbines are proposed which will result in lower relative tailwater levels with associated operational improvements. Present selling criteria may lead to unsatisfactory operation at higher tailwater levels. Cavitation damage is not necessarily prevented by low settings, and draft-tube surges may occur under high tailwater conditions.

Experimental Investigation Of Double Precessing Vortex Rope Forming In Draft Tube Models

2015 ◽  
Vol 10 (2) ◽  
pp. 73-82
Author(s):  
Sergey Skripkin ◽  
Mikhail Tsoy ◽  
Sergey Shtork
Keyword(s):  
High Speed ◽  
Draft Tube ◽  
Hydraulic Turbine ◽  
Reynolds Numbers ◽  
Pressure Pulsations ◽  
Vortex Rope ◽  
Precessing Vortex Core ◽  
Turbine Equipment ◽  
Hydro Turbines ◽  
Design Pressure

This work is devoted to the experimental research of the flow structure in draft tube models of hydro turbines. Precessing vortex core was formed using fixed swirler in a flow such as observed in natural hydro turbines under off-design conditions. In laboratory conditions it has been able to find the effect of the transition between single- and double- vortex rope. Their frequency characteristics have been measured in the range of Reynolds numbers 5·104 –5·105 . Based on the analysis of data high-speed shooting the mechanism of complete transition between single and double vortex modes was investigated in detail. The investigation of this phenomenon is of particular interest for the design and operation of hydraulic turbine equipment due to off-design pressure pulsations with sudden changes in frequency and amplitude in a flow occurring.

The numerical simulation of draft tube cavitation in Francis turbine at off-design conditions

2016 ◽  
Vol 33 (1) ◽  
pp. 139-155 ◽  
Author(s):  
Jing Yang ◽  
Lingjiu Zhou ◽  
Zhengwei Wang
Keyword(s):  
Draft Tube ◽  
Francis Turbine ◽  
Pressure Pulsations ◽  
Cavitation Flow ◽  
Vortex Rope ◽  
Content Type ◽  
Columnar Vortex ◽  
Spiral Vortex ◽  
Mesh Density ◽  
Load Conditions

Purpose – The vortex ropes in draft tube of Francis turbine always cause fluctuation and vibration, which consequently threaten the safety and stability of hydro turbines. The purpose of this paper is to use a cavitation flow computational method to simulate spiral vortex ropes under part load conditions and columnar vortex ropes under high-load conditions in draft tube. The unsteady cavitating flow characteristics in draft tube and its interaction with runner cavitation were analyzed. Design/methodology/approach – The calculation method was verified by cavitation simulation around a 3D hydrofoil. The results show that the Large Eddy Simulation (LES) turbulence model with the Zwart-Gerber-Blemari cavitation model have comparative advantage in cavitation simulations whether from capture of cavity shape or prediction of pressure changes. So it was chosen to simulate the two-phase cavitation flow in Francis turbine. The boundary conditions for inlet and outlet were set to inlet total pressure and outlet static pressure. The finite volume method with the central difference was adopted to discretize the equations. Findings – The calculated Thoma number agreed well with the experimental data. The vortex rope diameter and length increased with the cavitation development for both of the two types of vortex ropes conditions. The maximum peak-to-peak values of pressure pulsations located in the draft tube elbow part under all of the Thoma numbers conditions. Under spiral vortex rope conditions, the pressure pulsation in the same section of draft tube cone show obviously phase shift. The vortex rope affects the development of runner cavitation, which induces the symmetric and axisymmetric cavitation region in the suction side of blades for spiral and columnar vortex rope condition, respectively. Research limitations/implications – The mesh independence had been checked only in non-cavitation flow; in addition, the mesh density did not well satisfy the requirements of LES due to the limitations of computing power. The higher mesh density on a simplified model with one blade flow path and the entire draft tube may be helpful for obtaining more precise results. Originality/value – The spiral and columnar vortex ropes in a Francis turbine were compared and analyzed. The annular hydraulic jump appeared in the columnar vortex rope conditions has little effects on the pressure pulsations. The uneven flow field caused by spiral vortex led to the asymmetric cavitation development.

Numerical Prediction of Critical Cavitation Performance in Hydraulic Turbines

2003 ◽  
Author(s):  
Sadao Kurosawa ◽  
Kiyoshi Matsumoto
Keyword(s):  
Flow Model ◽  
Flow Analysis ◽  
Prediction Method ◽  
Hydraulic Turbine ◽  
Francis Turbine ◽  
Two Phase ◽  
Cavitation Performance ◽  
Hydraulic Turbines ◽  
Critical Cavitation ◽  
Good Agreement

In this paper, numerical method for predicting critical cavitation performance in a hydraulic turbine is presented. The prediction method is based on unsteady cavitation flow analysis to use bubble two-phase flow model. The prediction of the critical cavitation performance was carried out for the aixal hydraulic turbine and the francis turbine as a typical examples. Results compared to the experiment showed a good agreement for the volume of cavity and the performance drop off and it was recognized that this method could be used as an engineering tool of a hydraulic turbine development.

scholarly journals CFD Analysis of The Hydraulic Turbine Draft Tube to Improve System Efficiency

2016 ◽  
Vol 40 ◽  
pp. 02003 ◽  
Author(s):  
Spandan Chakrabarty ◽  
Bikash Kr. Sarkar ◽  
Subhendu Maity
Keyword(s):  
Draft Tube ◽  
Hydraulic Turbine ◽  
Cfd Analysis ◽  
System Efficiency ◽  
Hydraulic Turbine Draft Tube

scholarly journals Effect of Sediment Size in Hydraulic Turbine Material: A Case Study of Roshi Khola in Nepal

2013 ◽  
Vol 13 (2) ◽  
pp. 129-132
Author(s):  
Laxman Poudel
Keyword(s):  
Weight Loss ◽  
High Velocity ◽  
Hydraulic Turbine ◽  
Direct Impact ◽  
Test Rig ◽  
Reservoir Capacity ◽  
Sediment Size ◽  
Micron Size ◽  
Hydraulic Turbines

Siltation problem in Nepal is major and challenging in hydropower development. It degrades the reservoir capacity and hydraulic turbines’ efficiency. Many researches have been carried out in this field and have proven sand as major substance that erodes the turbine material, but only few researches have accounted every parameters of sand on degradation of hydraulic turbines. This paper accounts size of sediments important parameter that has direct impact on turbine material. Sediment size impact has been studied firstly by characterizing size into six layered using sieve analyzer and testing its impact using high velocity test rig at Kathmandu University. Sand samples from 20 different stations of Roshi river were collected and tested on turbine material 18Cr4Ni. It found that greater micron sizes of sediments have great impact was than relatively smaller ones. It is depicted that 300-400 micron size sediment, have highest impact with weight loss of 0.022 milligram, 212-300 micron size has 0.013 milligram weight loss, 90-212 micron size has 0.012 and below 90 micron sizes have 0.0075 milligram of weight loss. Nepal Journal of Science and Technology Vol. 13, No. 2 (2012) 129-132 DOI: http://dx.doi.org/10.3126/njst.v13i2.7725

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