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.

Predicting Two Phase Flow Pressure Drop With CFD and ANN

2010 ◽  
Author(s):  
I˙smail Teke ◽  
O¨zden Ag˘ra ◽  
Hakan Demir ◽  
S¸. O¨zgu¨r Atayılmaz
Keyword(s):  
Pressure Drop ◽  
Flow Model ◽  
Two Phase Flow ◽  
Saturation Temperature ◽  
Smooth Tube ◽  
Phase Flow ◽  
Two Phase ◽  
Analytical Formulas ◽  
Flow Pressure ◽  
Good Agreement

In this study, the several well known two-phase viscosity models were used for predicting two-phase flow pressure drop in a smooth tube using Computational Fluid Dynamics (CFD) software at homogenous flow conditions. Pressure drop for two different mass flux values (300 and 650 kg/m2s) for R134a with a saturation temperature of 45 °C in a smooth tube has been modeled according to the homogenous flow model and the results have been compared with the analytical formulas and experimental data from the literature. Three different average viscosity correlations were used. It is seen that the numerical results are in a good agreement with the homogenous flow model and fall in ± 30% band. Also, the results derived from the average viscosity expression are in a good agreement with the results calculated using separated two-phase flow correlations. In addition to this, Artificial Neural Networks (ANNs) were employed for predicting the pressure drop in a horizontal smooth pipe. The trained network gives the best values over the correlations with less than 1% mean relative error.

3D Cavitations Turbulent Transient Calculation in the Francis Turbine Model

2012 ◽  
Vol 479-481 ◽  
pp. 2466-2470
Author(s):  
Dun Zhang ◽  
Yuan Zheng
Keyword(s):  
Model Experiment ◽  
Flow Model ◽  
Three Dimensional ◽  
Francis Turbine ◽  
Two Phase ◽  
Mixture Flow ◽  
Phase Mixture ◽  
Simulation Results ◽  
Accurate Numerical Solution ◽  
Turbine Model

Analysis had been carried out, based on the three-dimensional transient viscous turbulent calculation of a Francis turbine full flow field, the complete cavitations model and the two-phase mixture flow model were combined during the calculation, more accurate numerical solution had been obtained. According to the simulation results, the site and extent of cavitations in the turbine flow were reflected within the specific conditions, and were more consistent with the cavitations phenomenon observed in the model experiment, also provided a reference for the more in-depth research.

Hydraulic turbines—basic principles and state-of-the-art computational fluid dynamics applications

1999 ◽  
Vol 213 (1) ◽  
pp. 85-102 ◽  
Author(s):  
P Drtina ◽  
M Sallaberger
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
State Of The Art ◽  
Three Dimensional ◽  
Hydraulic Turbine ◽  
Francis Turbine ◽  
Basic Principles ◽  
Vast Number ◽  
Basic Fluid ◽  
Hydraulic Turbines

The present paper discusses the basic principles of hydraulic turbines, with special emphasis on the use of computational fluid dynamics (CFD) as a tool which is being increasingly applied to gain insight into the complex three-dimensional (3D) phenomena occurring in these types of fluid machinery. The basic fluid mechanics is briefly treated for the three main types of hydraulic turbine: Pelton, Francis and axial turbines. From the vast number of applications where CFD has proven to be an important help to the design engineer, two examples have been chosen for a detailed discussion. The first example gives a comparison of experimental data and 3D Euler and 3D Navier-Stokes results for the flow in a Francis runner. The second example highlights the state-of-the-art of predicting the performance of an entire Francis turbine by means of numerical simulation.

Numerical Investigations of Solid-Liquid Two-Phase Turbulent Flows through Francis Turbine

2012 ◽  
Vol 548 ◽  
pp. 853-859
Author(s):  
Xue Lin Tang ◽  
Shang Yu Yang ◽  
Fu Jun Wang ◽  
Yu Lin Wu
Keyword(s):  
Turbulent Flows ◽  
Turbine Unit ◽  
Solid Phase ◽  
Turbulent Viscosity ◽  
Hydraulic Turbine ◽  
Algebraic Model ◽  
Francis Turbine ◽  
Two Phase ◽  
Calculated Velocity ◽  
Solid Liquid

This work is to investigate solid-liquid flows inside entire passage of a large Francis turbine unit and a modified algebraic model is proposed to take the solid-phase turbulent viscosity into consideration based on realizable turbulence model for the liquid phase and further development of the commercial CFD software. The energy conversion between the pressure and velocity, and the sedimentation distribution characteristics around all the hydraulic parts are simulated. The calculated velocity and sedimentation concentration distributions inside the runner are not uniform due to the effect of the centrifugal and Coriolis force. In addition, the calculated eccentric vortex rope in the draft tube causes vortex cavitation and vibration to the turbine unit, which leads to the eccentric sedimentation distribution. The simulation results (i.e., the mixture pressure, velocity and sedimentation distributions) are in good agreement with the natural rule, suggesting that the simulation strategies are capable to handle two-phase flows over complex geometries. The computational results can provide the useful information for hydraulic turbine designs. Future work will focus on the optimizations of hydraulic impeller designs using simulated results.

Numerical Study of Cavitating Flow in Two-Phase LNG Expander

2016 ◽  
Author(s):  
Peng Song ◽  
Jinju Sun ◽  
Kaiqiang Li ◽  
Ke Wang ◽  
Changjiang Huo
Keyword(s):  
Design Optimization ◽  
Numerical Study ◽  
Temperature Drop ◽  
Flow Analysis ◽  
Flow Characteristics ◽  
Cavitating Flow ◽  
Cavitation Model ◽  
Two Phase ◽  
Hydraulic Turbines ◽  
Liquefaction Process

LNG expander is developed and used as a replacement of a J-T valve in liquefaction process of natural gas to reduce significantly the energy consumption in the LNG plant. Similar to conventional hydraulic turbines, the unexpected cavitation also occurs in the LNG expander. In the present study, cavitating flow in two-phase LNG expander is investigated. With the justified Rayleigh-Plesset cavitation model, cavitating flow characteristics is investigated for the LNG expander in the entire stage environment including an annular bend, nozzle ring, and radial inflow impeller. On the basis of cavitating flow analysis, a coaxial rotating exducer is developed and fitted downstream to the impeller, so as to reduce the cavitation in impeller and subsequently prevent impeller damage. The following are demonstrated: (1) without exducer, significant cavitating flow is encountered at the impeller trailing edge and also in half streamline-wise region, and they are resulted from the viscous dissipation and flow separation; (3) with exducer, the impeller cavitation has diminished entirely but it has occurred in the successive exducer; (3) a use of exducer enhances the energy conversion capability of the rotors, but reduces the overall temperature drop and efficiency of the expander; (4) the design optimization of exducer is required to suppress the exducer cavitation, which also needs to be incorporated with the impeller design to achieve a better match between rotor/stator, so as to maximize the design optimization benefits.

A Prediction of the Leakage Through Cracks for Leak Before Break

2014 ◽  
Author(s):  
Jing Zhang ◽  
Yingwei Wu ◽  
Lei Ding ◽  
Hongwei Qiao ◽  
Pengzhou Li ◽  
...  
Keyword(s):  
Flow Model ◽  
Crack Open Displacement ◽  
Two Phase ◽  
Crack Open ◽  
Naturally Occurring ◽  
Open Displacement ◽  
Leak Before Break ◽  
Phase Fluid ◽  
New Phase ◽  
Good Agreement

A code was developed in this study to predict the leakage of the leak before break (LBB). Various stagnation conditions were considered, including the subcooled water, the two-phase fluid and the overheated steam. Moreover, both the critical and noncritical flow was studied. The Henry-Fauske critical flow model was revised by a new phase transition point and the pressure drop due to friction and turns were modified. The code was verified by the comparison with the experimental data on the leakage of conventional pipes, artificial cracks and naturally occurring cracks, which shows a good agreement and this code has a higher precision than the existing codes. The influence of crack morphologies on LBB leakage was discussed, including the local roughness, the global roughness, the crack open displacement (COD) and the number of the corners. Besides, the dependence of the LBB leakage on stagnation enthalpy and back pressure was also investigated.

Study on Analytical Prediction of Forced Convective CHF in the Wide Range of Quality

2002 ◽  
Author(s):  
S. Kodama ◽  
I. Kataoka
Keyword(s):  
Fluid Model ◽  
Flow Analysis ◽  
Prediction Method ◽  
Flow Transition ◽  
Analytical Prediction ◽  
High Quality ◽  
Two Phase ◽  
Wide Range ◽  
Mist Flow ◽  
Transition Criterion

For the purpose of predicting CHF for a wide range in quality, we developed the analytical CHF prediction method. Two-phase flow analysis code based on multi-fluid model was developed and, by using typical dryout model and DNB model, CHF predictions for a wide range in quality were carried out, firstly. The dryout model and DNB model gave good predictions for high quality conditions and low quality conditions respectively. The boundary between high quality and low quality seemed to be about 0.1 to 0.2, which corresponds to the annular mist flow transition criterion. Based on this result, secondly, we carried out CHF predictions by using dryout model or DNB model selectively depending on the flow regime and got agreement to some extent with CHF data for a wide range in quality.

Numerical Simulation of Two Phase Flows in a Bath With Top-Blowing Lance Injection

1999 ◽  
Author(s):  
J. L. Xia ◽  
T. Ahokainen ◽  
L. Holappa
Keyword(s):  
Numerical Simulation ◽  
Flow Model ◽  
Turbulent Dispersion ◽  
Dispersion Forces ◽  
Two Phase Flows ◽  
Two Phase ◽  
Operational Conditions ◽  
Plume Region ◽  
Insight Into ◽  
Good Agreement

Abstract Numerical simulation of two phase flows in a bath agitated by top blowing lance injection is carried out using the CFX code. An Eulerian-Eulerian two phase flow model is used. The drag, lift and turbulent dispersion forces are taken into account for the interface interactions. Calculations show that there exist different flow patterns with changing the operational conditions (Q, dn, and hn/H). The gas-liquid plume spreads radially, gradually in most of the plume region and extensively near the free surface. For the cases considered, bubbles in the central plume (r = 0.006 m) accelerate up to their terminal rising velocity, then move at this rising velocity, and thereafter decelerate when they approach the surface. A similar behaviour is demonstrated for the liquid rising velocity. Numerical results are compared with available experimental data, and a good agreement is achieved. Predictions provide insight into the flow behaviour and useful information for engineering design.

scholarly journals Simulations of Steady Cavitating Flow in a Small Francis Turbine

2016 ◽  
Vol 2016 ◽  
pp. 1-15 ◽  
Author(s):  
Ahmed Laouari ◽  
Adel Ghenaiet
Keyword(s):  
Draft Tube ◽  
Safety Margin ◽  
Hydraulic Turbine ◽  
Cavitation Number ◽  
Hydrodynamic Performance ◽  
Francis Turbine ◽  
Two Phase ◽  
Ansys Cfx ◽  
Flow Through

The turbulent flow through a small horizontal Francis turbine is solved by means of Ansys-CFX at different operating points, with the determination of the hydrodynamic performance and the best efficiency point. The flow structures at different regimes reveal a large flow eddy in the runner and a swirl in the draft tube. The use of the mixture model for the cavity/liquid two-phase flow allowed studying the influence of cavitation on the hydrodynamic performance and revealed cavitation pockets near the trailing edge of the runner and a cavitation vortex rope in the draft tube. By maintaining a constant dimensionless head and a distributor vane opening while gradually increasing the cavitation number, the output power and efficiency reached a critical point and then had begun to stabilize. The cavitation number corresponding to the safety margin of cavitation is also predicted for this hydraulic turbine.

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