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CaFE Report Summary

Project ID: 642536
Funded under: H2020-EU.1.3.1.

Periodic Reporting for period 1 - CaFE (Development and experimental validation of computational models for cavitating flows, surface erosion damage and material loss)

Reporting period: 2015-01-01 to 2016-12-31

Summary of the context and overall objectives of the project

CaFE is the acronym of the project “Development and experimental validation of computational models for Cavitating Flows, surface Erosion damage and material loss”. It has started on 1st January 2015 and ends on 31st December 2018.
The CaFE project aims to develop and experimentally validate state-of-the-art computational model for cavitation erosion, addressing issues from the macroscopic flow development, which is of interest to engineering practice (industrial, biomedical etc) down to fundamental physics of bubble dynamics and material sciences.
What is cavitation erosion?
Cavitation, described as the formation of vapour/gas bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure. Understanding and controlling cavitation has been a major challenge in engineering for many years.
How will the CaFE project help?
The research topics of the CaFE project can be divided into two major categories: experiments and simulations. The research aims to:
• Conduct new advanced quantitative experiments (PIV, X-ray densitometry, pressure and material loss) that will guide the development of computational models and serve as validation data
• Develop models using computational fluid dynamics and material loss simulating cavitation and its interaction with the material.
Once developed and validated, the computational tools will be applied to resolve the complex flow in a wide range of industrial application where cavitation and erosion can be realised. These include high pressure Diesel fuel injectors, high pressure pumps, hydraulic turbines, marine propellers and mechanical heart valves
CaFE has designed 16 topically complementary research projects covering four core research areas:
Work Package 1: Direct numerical simulations, fluid-structure interaction and material loss
Work Package 2: Quantitative measurements in cavitating flows
Work Package 3: Macroscopic flow development and surface erosion indicators
Work Package 4: Industrial applications
Additionally, CaFE aims:
1. To perform all required training activities for all Marie Curie fellows (Work Package 5)
2. To coordinate the project and disseminate the results (Work Package 6)

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Until mid - term the CAFÉ consortium:
• Has recruited 15 Research Fellows (ESRs) that are funded by the programme and 1 Research Fellow that is funded directly by EPFL. (The CaFE Research Fellows: )
• Has submitted 17 deliverables (Summaries of technical deliverables: )
• Has successfully provided a range of scientific and general skills training to the recruited ESRs ( ), which is part of an ongoing procedure.
• Has been disseminating the outcome of the work performed ( ) and has engaged the ESRs to outreach activities. ( )

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Until mid - term CAFÉ has made the following contribution and impact relative to the state-of-the-art:
D1.1: Interface tracking
Investigations performed as part of this deliverable represent fundamental work on numerical techniques and can have an impact on upcoming simulation techniques for bubbly flows with phase change. More specifically, the collapse of a collapsing vapor bubble has been investigated using a new interface capturing method. Although the new method includes information not able to deduce from the single-fluid models, it verifies that the latter ones can serve as a useful engineering tool due to their relative cheap computational costs and efficient implementation. Moreover, the new method enables capturing of bubble rebound processes without additional nucleation models.
D1.7: Bubble dynamics model including heat and mass transfer
An explicit density-based solver of the compressible Euler equations suitable for cavitation simulations has been developed, using the full Helmholtz energy equation of state (EoS) for n-Dodecane. Tabulated data have been derived from this EoS in order to calculate the thermodynamic properties of the liquid, vapour and mixture composition during cavitation using a finite element approximation; this results to significantly reduced computational cost despite the complex thermodynamics model incorporated. The latter is able to predict the temperature variation of both the liquid and the vapour phases. The developed model is new in the literature for the particular fuel. It allows calculation of temperature increase during the collapse of bubbles, which can be linked to fuel pyrolysis in injector nozzles.
D2.2: MHV test rig
Patients with heart valve malfunction are often cured with implantation of mechanical heart valve. A test rig to investigate cavitation has been designed and tested. The rig can be utilized to test independently the effects under flow or static pressure waves. The test section consists of a venture nozzle, made up of Plexiglas. The test section of the rig can be easily replaced or modified with a different geometry to further investigate cavitation. New results have been already obtained using high speed imaging. A more in depth research regarding different cavitation regimes is/can be done in the test rig using different visual investigation techniques i.e. high-speed imaging, X-rays and particle image velocimetry.
D3.1: Barotropic LES in cavitating flows
An LES methodology was extended to handle cavitating flows including full thermodynamics that can predict temperature changes. This advances previous barotropic models (with water as working media) that omit such effects. In order to allow calculations at realistic simulation times, a tree-structured adaptive look-up table generator was developed in order to allow for efficient and accurate representation of thermodynamic states. In addition, a pre-existing dynamic mode decomposition (DMD) tools has been developed to handle block-structured data as provided by the LES code. Therefore, data management and data conversion programs had to be developed. This DMD tool allows analysis of complicated 3D-flows; in particularly it has been extended to extract coherent structures, like periodic vapour clouds or turbulent structures developing in cavitating flows.

D4.4: Nozzle tip cavitation
In this deliverable, an initial experimental and computational investigation into cavitation in a Diesel fuel injector has been performed. The geometry used, though similar to other geometries, is new. The results enable further understanding of the fluid mechanics and cavitation characteristics at work when comparing the CFD simulations to the experimental large scale model results. The results presented are steps towards reducing product development time. This, in turn, can lead to reducing the final cost of products by identifying potential problematic areas earlier in the design and development phase.

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