Abstract
Impulse turbine casings play a very important role and experience dictates that the efficiency of a Pelton turbine is closely dependent on the success of keeping vagrant spray water away from the turbine runner and the water jet. Despite this overarching purpose, there is no standard design guidelines and casing styles vary from manufacturer to manufacturer, often incorporating a considerable number of shrouds and baffles to direct the flow of water into the tailrace with minimal interference with the aforementioned. Secondly, the success of a casing design is dependent on its ability to maintain this objective across a wide range of operating conditions that vary as a consequence of fluctuations in speed and load, resulting in considerable differences in spray leaving the runner. Conventionally, the baffle plates are designed to be most effective at the best efficiency, or duty, point and have been shown to be ineffective at extremes of speed and load. Therefore, efforts to design a casing with minimal amount of shrouding to reduce manufacturing costs is the objective of the project sponsors. The present work incorporates the Reynolds-averaged Navier Stokes (RANS) k-ε turbulence model and a two-phase Volume of Fluid (VOF) model, using the ANSYS® FLUENT® code to simulate the casing flow in a 2-jet horizontal axis Pelton turbine. The results of the simulation of two casing configurations are compared against flow visualisations and measurements obtained from a model established at the National Technical University of Athens. The CFD simulation also informs the design of new casing inserts to see their influence on the flow. Therefore, the outcome of this investigation provides further insight into guidelines for improved Pelton turbine casing design.
Highlights
The casing of a Pelton turbine is an important component as it collects the water leaving the runner
Impulse turbine casings play a very important role and experience dictates that the efficiency of a Pelton turbine is closely dependent on the success of keeping vagrant spray water away from the turbine runner and the water jet
The design of the casing as a means to reduce this impact is of interest to manufactures [1]. Numerical tools such as Computational Fluid Dynamics (CFD) have been applied to the development of Pelton turbines, the individual components are treated in isolation and the resulting high fidelity models offer a good prediction of the reasonable gains in efficiency from the optimisation of each component
Summary
The casing of a Pelton turbine is an important component as it collects the water leaving the runner. On the basis of the above considerations, this paper will demonstrate how the Reynolds-averaged Navier Stokes (RANS) k-ɛ turbulence model and a two-phase Volume of Fluid (VOF) model within the ANSYS® FLUENT® code can be employed as a visualisation tool to investigate casing flows and improve the design of a 2-jet horizontal axis Pelton turbine.
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