Petley, Sean and Aggidis, George Athanasios (2018) Transient CFD and experimental analysis for improved Pelton turbine casing designs. In: 29th IAHR Symposium on Hydraulic Machinery and Systems, 2018-09-17 - 2018-09-21.
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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-ɛ 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.