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Activity title

Assessments of Numerical Simulation Methods for Turbulent Cavitating Flows

Activity Reference

AVT-320

Panel

Applied Vehicle Technology

Security Classification

NATO UNCLASSIFIED

Status

Planning

Activity type

RTG

Start date

2019

End date

2021

Keywords

Bubbly flows, Cavitation, Erosion, Noise, Turbulence

Background

Turbulent cavitating flows impact the operation of military ships in several significant ways. Physics-based, high-fidelity simulation of these flows faces several challenges. The main challenge faced in tackling turbulent multiphase flows of naval interest stems from the inherently complex physics of the flows occurring at high Reynolds numbers of O(107 - 109). Presence of multiple phases alone poses fundamental difficulties mainly due to distinctive multiple regimes of interfacial morphology ranging from dilute gas-bubble flows to churning bubbly flows to stratified flows. The physics of cavitating flows is further complicated, inasmuch as cavitation involves phase change, namely vaporization and condensation, that is influenced by non-condensable gases, gas nuclei and thermodynamics. In addition, turbulence greatly affects the interfacial dynamics of multiphase flows and the dynamics of cavitating bubbles throughout their lifetime across a wide range of length- and time-scales. Recent developments in the measurement techniques for turbulent multiphase flows using state-of-the-art optical techniques, high-speed video and X-rays have enabled us to look into the flow-fields and phase distributions of multiphase flows with unprecedented precision. The experimental data with such details not only give a new insight into the fundamental physics of the flows but also offer great opportunities to validate numerical simulations in a systematic and comprehensive manner. Although challenges still remain for high-fidelity numerical simulations, today’s high-performance computing with peta-flop processors and massive parallelism allows us to pursue a paradigm where the salient physics of turbulent multiphase flows can be predicted using advanced computational algorithms and physical models based on first principles with acceptable numerical uncertainty. In view of the strategic importance of the subject flows to the Navy, it is timely that the NATO AVT community initiates a collaborative effort to assess current technologies, develop best practices and identify areas needing improvements.

Objectives

• Review and select candidate experiments for case studies • Review numerical approaches to high-fidelity simulation of turbulent cavitating flows • Conduct benchmark computations for the selected cases of turbulent cavitating flows • Identify shortfalls of the numerical methods for simulating turbulent cavitating flows • Develop best practices for high-fidelity numerical simulation of turbulent cavitating flows • Recommend future efforts in computations and experiments We hope first to gain a sound understanding of the fundamental physics of turbulent cavitating flows using a combined numerical and experimental campaign. The end goal of this cooperative research is to enable high-fidelity numerical prediction of not only global quantities such as forces and moments but also the phenomenological details of turbulent cavitating flows. With the help of high-performance computing, we will take physics-based numerical simulation one-level up to demonstrate its utility in building a digital twin of a selected marine propulsion system (e.g., waterjet pump). Reports and papers will also be among the deliverables.

Topics

• State-of-the-art experiments for turbulent cavitating flows • Mathematical frameworks to describe multiphase flows (e.g., Eulerian, Lagrangian) • Scale-resolving simulation of turbulent flows • Mass-transfer (vaporization and condensation) modelling • Effects of turbulence on the life cycle of cavitating bubbles • Numerical algorithms for solutions of turbulent multiphase flow equations One critically important aspect of cavitation from S & T standpoint we hope to shed light on is the role played by turbulent flow-fields such as fluctuating pressure in driving cavitation (e.g., cavitation inception, shedding and collapse of cloud cavity) that has not been properly addressed in previous numerical simulations.

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