Redukovný model proudění v sací troubě

Reduced order model of draft tube flow

conference paper

en

Swirling flow with compact coherent structures is very good candidate for proper orthogonal decomposition (POD), i.e. for decomposition into eigenmodes, which are the cornerstones of the flow field. Present paper focuses on POD of steady flows, which correspond to different operating points of Francis turbine draft tube flow. Set of eigenmodes is built using a limited number of snapshots from computational simulations. Resulting reduced order model (ROM) describes whole operating range of the draft tube. ROM enables to interpolate in between the operating points exploiting the knowledge about significance of particular eigenmodes and thus reconstruct the velocity field in any operating point within the given range. Practical example, which employs axisymmetric simulations of the draft tube flow, illustrates accuracy of ROM in regions without vortex breakdown together with need for higher resolution of the snapshot database close to location of sudden flow changes (e.g. vortex breakdown). ROM based on POD interpolation is very suitable tool for insight into flow physics of the draft tube flows (especially energy transfers in between different operating points), for supply of data for subsequent stability analysis or as an initialization database for advanced flow simulations.

Vírové proudění se silnými koherentními strukturami je velmi vhodné pro popis pomocí vlastní ortogonální dekompozice (POD). Článek je zaměřen na popis osověsymetrického proudění v sací troubě pro řadu provozních bodů pomocí POD. Vlastní tvary proudění jsou sestaveny ze "snímků" získaných z CFD simulace. Výsledný redukovaný model popisuje chování stacionárního osověsymetrického proudění pro celý provozní rozsah turbíny. ROM umožňuje interepolaci mezi provozními body a rekonstrukci rychlostních nebo tlakových polí pro vybraný provozní bod. Praktický příklad ilustruje použití ROM a ukazuje, že ROM funguje velmi dobře pokud nejde o interpolaci v blízkosti provozního bodu zahrnujícícho vortex breakdown (tj. vznik vírového copu). V tom případě je nutné databázi pro tvorbu POD zpřesnit přidáním dodatečných vstupních dat. Výsledný ROM lze také využít např. jako inicializační data pro CFD výpočty.

Swirling flow with compact coherent structures is very good candidate for proper orthogonal decomposition (POD), i.e. for decomposition into eigenmodes, which are the cornerstones of the flow field. Present paper focuses on POD of steady flows, which correspond to different operating points of Francis turbine draft tube flow. Set of eigenmodes is built using a limited number of snapshots from computational simulations. Resulting reduced order model (ROM) describes whole operating range of the draft tube. ROM enables to interpolate in between the operating points exploiting the knowledge about significance of particular eigenmodes and thus reconstruct the velocity field in any operating point within the given range. Practical example, which employs axisymmetric simulations of the draft tube flow, illustrates accuracy of ROM in regions without vortex breakdown together with need for higher resolution of the snapshot database close to location of sudden flow changes (e.g. vortex breakdown). ROM based on POD interpolation is very suitable tool for insight into flow physics of the draft tube flows (especially energy transfers in between different operating points), for supply of data for subsequent stability analysis or as an initialization database for advanced flow simulations.

draft tube, proper orthogonal decomposition, POD, reduced order model, vortex rope

2014

01.12.2014

IOP Science

1755-1315

IOP Conference Series-Earth and Environmental Science

22

1

1–10

10