Výpočtové modelování kavitace jv jednoduchých geometriích, ale komlexních prouděních

Computational modelling of cavitation in simple geometries, but complex flows

článek ve sborníku ve WoS nebo Scopus

en

Cavitation occurs when local pressure in flowing liquid drops below saturated vapor pressure. If the resulting vapor bubbles are transported to regions of higher pressure then sudden condensation follows, which is accompanied by emission of pressure and acoustic waves. Above described process leads to cavitation erosion and consequently to shorter service time of the hydraulic machines. Cavitation can be modeled by current CFD tools with simplified cavitation models. Computational simulations revealed that proper capturing of the underlying one-phase flow field is crucial to obtain correct vorticity distribution. Clouds filled with vapor are born from regions of concentrated vorticity and shed downstream. Only advanced turbulence models (Reynolds Stress Model, Scale Adaptive Simulation) are able to predict vorticity field and development of the unsteady swirling flow. Increased vorticity generation in two-phase flows is caused by additional term in vorticity equation – baroclinic torque. Present paper dicusses relative magnitude of vorticity generation terms for cases of concentrated vortical structure and separated boundary layer over hydrofoil.

Při poklesu tlaku v kapalině na úroveň tlaku nasycených par dochází ke vzniku kavitace (kavitačních bublin), které při dalším transportu do oblasti vyššího tlaku zpětně kondenzují. Tento jev je provázen šířením tlakových vln a akustickou emisí, důsledkem je kavitační eroze obtékaného povrchu. Kavitaci lze výpočtově modelovat prostředky CFD s vyižitím zjednodušených kavitačních modelů. Článek ukazuje, že pro korektní výpočet kavitujícího proudění je nutné určit správnou hodnotu vířivosti, ktereá je generována na rozhraní fází v důsledku tzv. baroklinického členu. Hodnota tohoto členu je dokumentována u dvou typů proudění: kavitující koncentrovaný vír, odtržené proudění na hydraulickém profilu.

Cavitation occurs when local pressure in flowing liquid drops below saturated vapor pressure. If the resulting vapor bubbles are transported to regions of higher pressure then sudden condensation follows, which is accompanied by emission of pressure and acoustic waves. Above described process leads to cavitation erosion and consequently to shorter service time of the hydraulic machines. Cavitation can be modeled by current CFD tools with simplified cavitation models. Computational simulations revealed that proper capturing of the underlying one-phase flow field is crucial to obtain correct vorticity distribution. Clouds filled with vapor are born from regions of concentrated vorticity and shed downstream. Only advanced turbulence models (Reynolds Stress Model, Scale Adaptive Simulation) are able to predict vorticity field and development of the unsteady swirling flow. Increased vorticity generation in two-phase flows is caused by additional term in vorticity equation – baroclinic torque. Present paper dicusses relative magnitude of vorticity generation terms for cases of concentrated vortical structure and separated boundary layer over hydrofoil.

kavitace, vířivost, baroklinický člen

cavitation, vorticity, baroclinic torque

2014

03.11.2014

FAV ZČU Plzeň

Plzeň

978-80-261-0429-2

Computational mechanics 2014; book of extended abstracts

1–2

2