Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - CaFE (Development and experimental validation of computational models for cavitating flows, surface erosion damage and material loss)

Teaser

The CaFE ITN network has developed novel state-of-the-art computational model for cavitation erosion, validated against new and unique experimental data. These models have included aspects of bubble dynamics, real-fluid thermodynamics, advanced numerical methods and material...

Summary

The CaFE ITN network has developed novel state-of-the-art computational model for cavitation erosion, validated against new and unique experimental data. These models have included aspects of bubble dynamics, real-fluid thermodynamics, advanced numerical methods and material sciences, which have been linked to methodologies for industrial flow problems.

The work has been completed according to the Grant Agreement, fully respecting the overall project aim. The scientific outcomes of CaFE have been published in numerous peer-reviewed and highly esteemed journal papers and 34 conference proceedings.

In addition to the conducted research, the CaFE network has trained the ESRs on a range of unique scientific modules, that have broadened their perspectives in both research and classical engineering skills. Equally important, ESRs have been trained on a range of transferable skills. Last but not least, the ESRs have been engaged in a total of 23 outreach activities, disseminating their work to relevant non-specialised communities that made the EU funding and the impact of the performed research visible to the general public.

CaFE has successfully addressed the following scientific objectives:

1. Developed models suitable for simulating bubble collapse processes, including real-fluid thermodynamics and tackling their interaction with solid surfaces, thus allowing prediction of the induced erosion/material loss.

2. Performed and provided new and unique experimental data in a range of geometries and using a variety of techniques.

3. Developed cavitation erosion indicators that have been implemented in both existing and newly developed LES and URANS numerical codes.

4. Developed new and applied the above models to cases of interest to the industrial beneficiaries and partners.

In addition, the CaFE team developed a training programme for the ESRs, which covered: (a) specialised training courses offered by the participating institutions; (b) network-wide training activities in the format of seminar, workshop, conference and summer school; (c) knowledge exchange with the members of the network through activities such as secondments and open events.

Work performed

The research work performed in four designated Work Packages is summarised as follows:

1. In WP1 (ESR1-ESR4), simulation of fundamental aspects of bubble dynamics and induced erosion from ‘first principles’ has been performed. Four areas of research have been addressed: (a) development of a DNS methodology for bubble cluster collapses near a solid surface; (b) coupled fluid-structure and material deformation simulations induced by the collapse of cavitation bubbles; (b) FEM simulations of material fatigue when exposed to successive bubble collapses; (d) real-fluid thermodynamic closure between the collapsing bubble and the surrounding fluid as well as non-condensable gas content inside the bubble.
2. In WP2 (ESR5,6 and 16), quantitative flow measurements that link the cavitating fluid flow field with the erosion sites have been obtained. Three experiments have been performed: (a) XPCI at the high energy X-ray Advanced Photon Source of Argonne National Labs (US) accompanied by PIV measurements in flows in orifices; (b) Shadowgraphs, PIV and X-ray densitometry in venture nozzles; (c) High speed visualisation and PIV during the nucleation and development of cavitating vortices in hydrofoils.
3. In WP3 (ESR7-ESR10), LES and URANS methodologies have been developed, applicable to simulation of cavitating flows and surface erosion indication at macroscopic scales. More specifically, four models/codes have been developed: (a) a barotropic Equation of State for a diesel-like test-fluid, which was utilized to obtain tabulated thermodynamic data and applied to the simulation of flows in Diesel injectors; (b) a hybrid Eulerian-Lagrangian solver in which the larger cavities are considered in the Eulerian framework and the small (sub-grid) structures are tracked as Lagrangian bubbles; (c) a surface erosion model based on the energy balance between the energy of collapsing cavities and erosion damage; (d) a cavitation-BEM model for simulating compressible cavitating flows with moving objects, such as projectiles and mechanical heart valves.
4. In WP4 (ESR11-ESR15), the validated models have been applied to cases of industrial interest as specified by the non-academic beneficiaries and partners; these have included: (a) cavitating vortices in hydrofoils utilised by hydraulic turbines; (b) full-scale rotating marine propellers and interaction with hull; (c) control valves and metering valves of fuel injectors; (d) automotive diesel injector orifices, examining the effects of eroded injectors on spray development; (e) fuel gear pumps utilised by the aviation industry.

Final results

The CaFE project has advanced state-of-the-art in the following ways:

• Provided new and unique experimental data in cavitating flows, including PIV, X-ray densitometry, X-ray phase contrast imaging, pressure measurements and material loss in flow orifices, venture nozzles and hydrofoils.
• Developed new closure models for real-fluid thermodynamics and relevant equations of state that included the effects of non-condensable gases, developed new sub-grid scale models for bubble dynamics utilising new mass transfer models and accounting for induced surface erosion during bubble collapse; these have been implemented into existing as well as newly developed LES and URANS computational fluid dynamics that have been fully coupled for the first time with solid (elastic, plastic) deformation and material loss numerical codes.
• Applied the developed models to a wide range of industrial applications; simulations performed for the first time with the new models have provided physical inside leading to erosion-free design guidelines for high pressure Diesel fuel injectors, gear pumps, hydrofoils and marine propellers.

Impact can be foreseen on: (a) the career of the ESRs, (b) scientific/technological advances, (c) institutional level and (d) general public well-being.
(a) Career of ESRs: the training by research that lead to their PhDs, the transferable skill training, their interaction and exposure to industrial practice and new cultures will inevitably shape their future careers.
(b) Scientific/technological advances: the novel areas of research addressed have provided new physical insight into cavitation erosion and resulted to new computational tools adopted by a wide range of industries; this is expected to pave the way towards the design of more energy/environmentally efficient products for the automotive, marine, energy and aviation industries involved in CaFE.
(c) Institutional level: the academic beneficiaries and partners have greatly benefited from CaFE through the new publications in highly esteemed journals, dissemination of their research to the wider community during conference and workshops and the formation of new partnerships that have resulted to new funded projects. The non-academic beneficiaries and partners have also greatly benefited from the new design tools available, which can assist in their future businesses.
(d) General public: the new technology/designs obtained as a result of CaFE, will have an impact to the general public well-being, as more efficient Diesel fuel injectors, marine propellers and hydraulic turbines can result to enormous savings in greenhouse gases.

Website & more info

More info: http://www.cafe-project.eu.