On Pelton Efficiency and Cavitation (original) (raw)
Related papers
Numerical prediction of efficiency and cavitation for a Pelton turbine
IOP conference series, 2019
The first part of the paper illustrates the setup and the methodologies adopted for the numerical analysis of the flow in a 6-jet Pelton turbine with vertical axis. At first, steady state simulations of flow in a distributor for three positions of needle stroke were performed. The results were used for the calculation of flow energy losses, analysis of jet quality and setting inlet boundary conditions for runner analysis. Runner analysis was done only for the maximal opening. The purpose of runner analysis for the model size was efficiency prediction. Numerical results were validated with the results from the test rig. Simulations for the prototype were done in order to check whether water sheets evacuating from the buckets impact the previous bucket and whether there is any interaction between the evacuating water sheets and the incoming jets. Analysis was done also for one nozzle operation. In the second part of the paper cavitation prediction for the prototype of a 2-jet Pelton turbine is presented. The problem, because of computational cost, was reduced to five runner buckets and one jet. A multiphase flow consists of water, air and water vapour. For cavitation pitting the vapour has to stick to the buckets and mass transfer from vapour to water has to happen in a very short time without the presence of air. With detailed analysis of numerical results it was concluded that in this case no cavitation pitting is expected.
Jet quality and Pelton efficiency
The paper gives a short overview on contents and goals of a research project on jets of Pelton turbines performed by the Hochschule Lucerne and the Ecole Centrale de Lyon in collaboration with ANDRITZ Hydro. Effects governing the quality of jets in Pelton plants are discussed, such as: the jet dispersion, which is defined by the widening of the jet with distance from the nozzle and includes the air water mixture on the jet's surface, the jet deviation, which is defined by the deviation of the jets centerline from the theoretical axis, deformation described by the out of roundness of the jet, rotation of the jet, the turbulence level, secondary flows leading to streaks on the jet, entrapped air bubbles causing sudden expansions on the jet surface and finally droplets or splashing water impinging on the free jet in the housing of the turbine. With case studies in power plants the potential for improvement of efficiency is pointed out. The combination of thermodynamic efficiency measurement, flow visualization and CFD simulations allowed in the investigated cases good interpretation. The images taken of the jet in the power plants allowed quantitative evaluation of the jet diameter and its dispersion and eventually deviation. A clear relationship of increased jet dispersion and decreased efficiency could be found. Furthermore, a direct correlation of upstream bends and jet dispersion was found. This effect is induced by secondary flows.
Detailed Analysis of Flow in Two Pelton Turbines with Efficiency and Cavitation Prediction
International Journal of Fluid Machinery and Systems, 2019
This paper presents results of the numerical analysis of two Pelton turbines: a 6-jet turbine for middle head and a 2jet turbine for high head. For the 6-jet turbine losses in manifold, quality of the jets and turbine efficiency were predicted and validated with the experimental data. Additional improvement of accuracy of efficiency prediction was obtained with cavitation modelling. It was also checked that there was no interaction between the evacuating water sheets and the incoming jets. For a 2-jet turbine cavitation prediction was done. Small vapour cavity at the inner side and a larger one at the back side of the bucket were observed. Detailed analysis of cavitation and condensation processes showed that the conditions for cavitation pitting were not fulfilled.
Numerical Analyses of Cavitating Flow in a Pelton Turbine
Journal of Fluids Engineering, 2014
ABSTRACT Erosion and wear of hydraulic surfaces are frequent problems in hydraulic turbines, which lead to a decrease of the performance in time and/or in extreme cases to the rotor mechanical failure. These circumstances have negative repercussions on the annual produced power due to the decay of the efficiency, the delivered power, and to the off line periods as result of ordinary and extraordinary hydraulic profiles maintenances. Consistently, the study of this wearing process is an important step to improve the impeller design, and to avoid or minimize the rise of extraordinary maintenance. While mechanical damages are well documented and studied, little information can be found on cavitation in Pelton turbines. In this paper, a CFD model was applied to study the cavitation mechanics on a Pelton turbine. A Pelton runner affected by pitting cavitation was taken as a test case. The bucket geometry was modeled and analyzed using unsteady Reynolds averaged Navier-Stokes (RANS) multiphase analyses. Numerical results allowed us to highlight the different vapor productions during the cut-in water jet processes by the bucket. Furthermore, a simple procedure to identify the locations of higher damage risk was presented and verified in the test case runner
Effect of Jet Length on the Performance of Pelton Turbine : Distance Between Nozzle Exit and Runner
2016
Pelton turbine is the most commonly used high head impulse turbine with low discharge. For obtaining highest power output from runner one of the most important parameter is quality of jet which strikes bucket tangentially. The quality of jet and its impact work depends on the distance between the nozzle exit and runner along with its angle of strike. In the present paper, the effect of distance between the nozzle outlet and the runner on performance of Pelton turbine is discussed with the help of numerical technique. It is found that that axial flow of water is more for least (100 mm) distance while the radially inward and outward flow is more for larger (150 mm) distance between nozzle and runner.
In the course of refurbishment of the HPP Rothenbrunnen with three horizontal twin Pelton turbines the injectors were replaced and the internals within the casing were modified. The runners were not replaced. Thermodynamic efficiency measurements before and after refurbishment provided proof of an efficiency increase of up to 1.4 percent, an excellent result for such minimal modifications. In addition to efficiency measurements also flow visualizations were performed installing a camera and lightening system within the casing of the turbine. The visualizations clearly showed a reduction of the splashing water in the casing of the turbine and less jet dispersion.
Effect of Discharge Coefficient on Performance of Multi Jet Pelton Turbine Model
The conversion of hydraulic energy into mechanical energy takes place in hydraulic turbines. Further this energy is converted to electrical energy with the help of generators and then supplied to consumer. With increasing demand, efficiency of every machine plays vital role. When water is stored at very high head, hydraulic energy can be converted efficiently into mechanical energy with the help of Pelton turbine. The performance of Pelton turbine at designed and off-design points is important. Performance of turbo-machines is generally evaluated before installation with the help of model testing at designed and off design regimes. Now-a-days with advanced computers and numerical techniques, Computational Fluid Dynamics (CFD) has emerged as boon for optimisation of turbo-machines. In present work, performance analysis of existing six jet Pelton turbine at design and off design discharge has been numerically carried out using Ansys-CFX. The efficiency results are compared with available model test result and found to have close comparison. The variation in pressure distribution, water velocity and water distribution have also been obtained and discussed.
Effect of Jet Shape on Flow and Torque Characteristics of Pelton Turbine Runner
2014
In Pelton turbine, the energy carried by water is converted into kinetic energy by providing nozzle at the end of penstock. The shape of jet affects the force and torque on the bucket and runner of turbine. The nozzle of circular cross section is commonly used. In this paper attempt has been made to study the effect of four different jet shapes on the flow and torque characteristics of Pelton turbine runner through numerical simulation.
Numerical investigation of the interaction between jet and bucket in a Pelton turbine
This article presents the numerical investigation of the interaction between the jet and the bucket in a Pelton turbine. Unsteady numerical analyses were carried out on a single jet Pelton turbine installed in the north of Italy. A two-phase inhomogeneous model was used. Two different jet configurations were analysed and compared. In the first configuration, the interaction between the runner and an axial-symmetric jet characterized by a given velocity jet profile was investigated, whereas in the second configuration the runner was coupled with the needle nozzle and the final part of the penstock and the interaction between the jet and the bucket was analysed. A detailed analysis of the torque highlighted the influence of the shape of the water jet on the turbine losses and the influence of the stator on the efficiency of this type of hydraulic machines was shown. The numerical results were compared with the experimental data derived from the installation test of the turbine in order to validate the numerical analysis.
Advances in Fluid Mechanics VI, 2006
Free-jet turbines working under backpressure conditions represent an economical alternative to conventional hydroelectric plant configurations. However, the air introduced into the tailwater generates an air/water mixture. Its reaction to a rising ambient pressure is at present being studied at the above Institute. This report deals with the effect an increase in ambient pressure has on the volume and consistency of the two-phase mixture and the rise velocity of air bubble swarms. In addition, a test setup is described which was used to study the physical reaction of the water/air mixture to a change in ambient pressure conditions. The results and their effects on the configuration of free-jet turbines working under backpressure are discussed.