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Saturated Open-pore Foams for Innovative Tribology in Turbomachines – SOFITT

Saturated Open-pore Foams for Innovative Tribology in Turbomachines

The projetct addresses an emerging activity dealing with a biomimetically inspired mechanism consisting of self-sustained fluid films generated within saturated compressible porous layers. It aims to design a new, reliable, highly efficient and low ecological solution for guidance and supporting systems in turbomachinery.

Find innovative and efficient technical solutions that break with current practices

The performance of many industrial applications is largely based on the quality and reliability of the guidance and support systems (high rotational speeds, low friction torque, damping capability, etc.). In the TRIBOLUB team (Tribology of lubricated interfaces), one of the main objectives is to consolidate the understanding of the physical phenomena that condition the behavior of the fluid supporting elements. <br />This project was born from the need to find innovative technical solutions that break with current practices and provide high-performance support systems in terms of load capacity and damping. It aims to develop an emerging activity in the TRIBOLUB team which deals with a new lubrication mechanism of biomimetic inspiration. It consists of self-sustained fluid films generated within compressible porous layers (CPL) imbibed with liquids, and subjected to external normal or tangential forces. It must be stressed out that, even if the subject can be included in the large family of mechanics of fluid flows through a porous medium, the originality comes from creating stiffness and damping by dynamically modifying the geometry of an imbibed porous layer.

In order to achieve the proposed objectives, the project is divided into three scientific WorkPackages conducted through three PhDs with three connected aspects: understanding the mechanical properties of the porous complex structures, modelling the fluid-structure interaction, and finally applying the findings to design and test new supporting elements. Two additional WorkPackages are devoted to the management and respectively to the capitalization and dissemination of the project findings.
The WorkPackage 1 (Project management and coordination) runs over the 57 months of the project and until all the work is completed. The leader will be responsible for coordinating the project. He will:
- organize and animate meetings and follow-up of the various studies (one meeting per trimester)
- collect and disseminate progress reports within the project scope
- provide funders with the scientific, technical and financial reports that will be requested
The main objective of WorkPackage 2 (Understanding the mechanical properties of porous complex structures) is to understand the mechanical behavior of the porous complex structures, linked to microstructural properties of the solid material and interactions with the fluid. The work will be led in two steps. First, the material will be studied in 3D by using X-ray microtomography and volume digital correlation. Secondly, an original dynamic loading setup will be designed to apply the similar loading conditions as the ones applied in the real bearing systems.
The third WorkPackage (Numerical modelling of fluid/structure interaction in the porous layer) is dedicated to the development of two predictive models to study the response to external stresses of liquid-soaked compressible materials, in particular by estimating their load and damping capacities. Firstly, at the microscopic scale, the development of a flow model will permit to simulate the flow inside the porous structure. Secondly, at a larger scale, a mechanical behavior model will be developed to predict the macroscale response, in particular the deformations.
The forth WorkPackage (Design and test of new supporting elements) aims to design two lubricated elements: a thrust bearing and a squeeze damper and it is divided into three tasks. The first task proposes experimental studies on guidance systems supporting static axial load. The second task still deals with experimental aspects testing the damping capacity of XPHD solutions in the presence of an unbalance. The third task concerns the development of numerical simulation models on the scale of XPHD components.
The fifth WorkPackage mainly concerns the publication of scientific articles and participation in international conferences

The main results of the first 18 months of project are linked with WP 2 and 3:
Material candidates: Two main composites are on the focus of this study, elastomeric and metal foams imbibed with fluid and polymer respectively. Polyurethane foams offer high open – poreness making it preferable for XPHD lubrication. Different foam samples were gathered and tested. It was concluded that higher density foam with high PPI offer superior performance. Imbibition tests were also conducted and as a result higher than 90% imbibition ratios were found in all cases, eliminating the risk of unsaturated foam.
Testing devices and experimental procedures: three devices have been developed, for X – ray in situ testing of imbibed polymer foams, for dynamical characterization of metal-foam polymer composites as well as a real bearing system for global characterization of soaked PU foam. A special device had to be designed, capable of testing imbibed foams with a target resolution of less than 6 µm. For the metal-polymer IPC a simple device, dynamical shaker based on a single degree-of-freedom spring-damper model with base excitation has been developed. A real bearing system has also been designed and mounted.
Determining the global dynamic properties of the metal foam matrix, polymer and their combination: The vibration transfer function from the base to the mass is used to quantify the damping capacity of the materials used. Different frequencies are achieved by using four different masses (200 to 500 gram). Significant change was observed for the loss factor while the increase in the dynamic modulus is less important. The NiCr and Cu foam have higher PPI than the aluminum foam and as a result more surface area, contributing to an increased lost energy by the interfacial damping mechanisms. The smaller pore size also constraints more the polymer inside the structure, thus achieving better elastic properties.
Identifying the morphology and deformation mechanisms of PU foams using image analysis tools: From the X-Ray Tomography we directly obtain a 3D gray-scaled image, so the method chosen for this purpose is that of image analysis and processing. The software ImageJ was used for the implementation of the mathematical morphological operations. We have extended and optimized the use of specific techniques to created new methods to precisely identify and trace evolution during different compression stages, making it possible to identify the local deformation of every cell.
In the framework of WP3, we have created a numerical «production« chain, starting from the images obtained by X-ray tomography, passing by the generation of a numerical discretization of the medium and ending by CFD simulations allowing us to determine the essential parameters to simulate the flow (permeability, tortuosity, Forchheimmer coefficient) Moreover, we are able to numerically generate porous media from stochastic parameters using Voronoi type algorithms

The project is at the interface of several scientific fields: solid mechanics, fluid mechanics and thermal engineering. It calls on multidisciplinary skills in experimental mechanics and numerical analysis. Each member of the project team has a strong foundation in his areas of expertise but this joint work will certainly bring them new skills following the complementary approaches foreseen in the proposal. The knowledge acquired in this project can not only be used to find innovative technical solutions in turbomachinery but, in the longer term, can also be applied to studies dedicated to biological tissues or to human joints where the behavior of soaked porous materials (human cartilage) is also a key point.
At the level of the Pprime Institute, the project brings together three different teams, which will help to strengthen the Institute's cohesion.

As we have already said, the main objective of this proposal is to find high-performance support systems in terms of friction, load and damping capacities. This is a permanent concern of the TRIBOLUB team and the achievement of this objective could have a very important impact in the fields of transportation and energy production. Indeed, a previous study estimates that 23% of the total energy consumption in the world comes from tribological contacts. Of this total, 20% is used to overcome friction and 3% is used to remanufacture worn parts and replacement equipment due to wear and tear related failures. The greatest short-term energy savings are expected in transportation (25%) and power generation (20%), the main industrial applications targeted by the presented project.

A.E. Ennazii, A. Beaudoin, A. Fatu, P. Doumalin, Y. Henry, J. Bouyer, E. Lacaj and P. Jolly, Toolchain from the creation of the mesh to the CFD simulations, InterPore2021, 13th Annual Meeting, 31 May – 4 june 2021

A.E. Ennazii, A. Beaudoin, A. Fatu, P. Doumalin, Y. Henry, J. Bouyer, E. Lacaj and P. Jolly, Toolchain from the creation of the mesh to the CFD simulations, JMECA2021, poster

The present proposal addresses an emerging activity dealing with a new lubrication mechanism of biomimetic inspiration, called eX-Poro-HydroDynamic (XPHD) lubrication. It consists of self-sustained fluid films generated within compressible porous layers imbibed with liquids and subjected to external normal or tangential forces. The objective is to find innovative technical solutions that break with current practices, offering efficient turbomachinery guidance and support systems in terms of load capacity, damping, reliability, friction and environmental impact. The project aims to demonstrate industrial applications and to develop numerical tools capable of predicting the operating behavior of these new technologies.
The scientific target deals with challenges stem from the coupling of multiple mechanisms being intrinsically inter- and multi-disciplinary. The project is at the interface of several scientific fields: solid mechanics, fluid mechanics and thermal engineering. It calls on multidisciplinary skills in experimental mechanics and numerical analysis. The knowledge acquired in this project can be used not only to find innovative technical solutions in turbomachinery but, in the longer term, can also be applied to studies dedicated to biological tissues or to human joints where the behavior of soaked porous materials (human cartilage) is also a key point.
To achieve the objective, the project relies on the scientific and experimental expertise of three research teams covering the fields of tribology, photomechanics and modelling of fluid-structure interaction. It is organized into three scientific WorkPackages.
The main objective of the first scientific WorkPackage is to understand the mechanical behavior of the porous complex structures (combination of a solid deformable structure with a high porosity, soaked with fluid), linked to microstructural properties of the solid material and interactions with the fluid. The work will be carried out in three steps intended to decouple the physical effects in order to facilitate the understanding of physical phenomena: quasi-static 3D investigation, dynamic investigation on 2D simplified sample and global dynamic characterization in terms of rigidity and damping.
The experimental data acquired will serve as input parameters for the second scientific WorkPackage, dedicated to the development of two numerical models aiming to study the response to external stresses of liquid-soaked porous materials, in particular by estimating their elastic response and damping capacity. A first task will be dedicated to the simulation at the microscopic scale of the flow through the structure of porous compressible materials. A second task proposes, on a larger scale, the development of a mechanical behavior model to predict the macroscale response, in particular the fluid/structure interaction.
The third scientific WorkPackage will use the experimental and numerical results obtained in the first two WorkPackages to design two lubricated elements: a thrust bearing and a squeeze damper. The work will be divided into three tasks. A first task proposes experimental studies on guidance systems supporting static axial load. A second task also deals with experimental aspects by testing the damping capacity of XPHD solutions in the presence of an unbalance. The third task concerns the development of numerical simulation models on the scale of XPHD components.
Two additional WorkPackages will be respectively devoted to the management and to the capitalization and dissemination of the project findings.

Project coordination

Aurelian Fatu (Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Pprime - HYDEE Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique
Pprime - PEM Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique
Pprime - TRIBOLUB Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique

Help of the ANR 446,472 euros
Beginning and duration of the scientific project: March 2020 - 48 Months

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