CFD studie proudění v difuzoru vírového generátoru s využitím Large Eddy Simulation

Computational Fluid Dynamic Study of the Flow Downstream of the Swirl Generator Using Large Eddy Simulation

abstract

en

Computational study of swirl generator apparatus is carried out commercial software Ansys Fluent v.14. employing Large Eddy Simulation (LES) model for turbulence modelling. Computational domain of swirl generator includes approximately 13 million of cells, consists of straight inlet pipe, swirl generator, conical diffuser with extended outlet and corresponds with real part of test rig situated in laboratory of V. Kaplan Dept. of Fluid Engineering, Faculty of Mechanical Engineering, Brno University of Technology. Swirl generator (see fig. 1) is device with ten shaped blades fixed around inner spike and situated in front of connected straight conical diffuser so that generates swirling flow similar to one occurring in draft tube (outlet diffuser) of Francis turbine operated at partial load (flow rate lower than optimal). This flow configuration is related to formation of so called vortex rope. Vortex rope is spiral-shaped, sometimes cavitating structure (water evaporated due to low pressure) which rotates in draft tube and produces high pressure pulsation in whole turbo machine, thus restricts wider operation conditions of hydraulic power plant. Simplification of this complex flow by swirl generator is effort to fully understand mechanism of vortex rope formation and find out how mitigate undesirable effects.

Výpočtová studie vírového generátoru s využitím software Ansys Fluent v.14. a Large eddy simulation modelu. Výpočtová doména se sestává z 13 mil. buňek a tvoří ji přímé vtokové potrubí, vírový generátor a válcový difuzor s rozšířenou výtokovou oblastí. Model je kopií úseku experimentálního okruhu v laboratoři OFI V. Kaplana VUT Brno.

Computational study of swirl generator apparatus is carried out commercial software Ansys Fluent v.14. employing Large Eddy Simulation (LES) model for turbulence modelling. Computational domain of swirl generator includes approximately 13 million of cells, consists of straight inlet pipe, swirl generator, conical diffuser with extended outlet and corresponds with real part of test rig situated in laboratory of V. Kaplan Dept. of Fluid Engineering, Faculty of Mechanical Engineering, Brno University of Technology. Swirl generator (see fig. 1) is device with ten shaped blades fixed around inner spike and situated in front of connected straight conical diffuser so that generates swirling flow similar to one occurring in draft tube (outlet diffuser) of Francis turbine operated at partial load (flow rate lower than optimal). This flow configuration is related to formation of so called vortex rope. Vortex rope is spiral-shaped, sometimes cavitating structure (water evaporated due to low pressure) which rotates in draft tube and produces high pressure pulsation in whole turbo machine, thus restricts wider operation conditions of hydraulic power plant. Simplification of this complex flow by swirl generator is effort to fully understand mechanism of vortex rope formation and find out how mitigate undesirable effects.

LES, vířivé proudění, vírový cop, vírový generátor

LES, swirling flow, vortex rope, swirl generator

12.03.2013

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