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Advanced Modelling Methodology for Bearing Chamber in Hot Environment

Periodic Reporting for period 3 - AMBEC (Advanced Modelling Methodology for Bearing Chamber in Hot Environment)

Reporting period: 2019-08-01 to 2020-04-30

The goal of AMBEC project is to achieve a complete understanding of the physical phenomena in the bearing chamber of the gas-turbine engine and to create a reliable methodology able to calculate the heat transfer coefficient and the fluid flows for different zones of the bearing chamber depending on the key engine operating parameters.

The challenge of this task is in a multiphase fluid in the bearing chamber, which is a mixture of the injected oil and air. Getting through the nozzle, the oil spreads over the bearing surface forming the oil film. The film is moving because of aerodynamic forces, gravity and viscosity. In parallel, it is influenced by the oil droplets, which fall on it from the bearing, as well as by the air flow, which can generate and carry out the droplets from the surface of the film. Because of this complex interaction, the oil film has a variable thickness along the circumference of the bearing chamber. This fact affects the process of heat exchange between the chamber walls and the air / oil mixture. Other facts that influence the heat-exchange processes are the shaft rotational speed, the pressure in the bearing chamber, the oil and air flow rates, bearing chamber design and roughness of its walls, etc.

The AMBEC team will combine an advanced CFD simulation and in-depth experimental research to study the heat exchange processes between air, oil drops, non-uniform oil film and bearing chamber walls in a multiphase ever-changing environment. It will help to create a versatile, accurate and user-friendly methodology, which will be an efficient instrument for the industrial design of compact bearing chambers operating in a hot environment.

Application of AMBEC methodology will help engine developers to cut time and efforts required for design and development of innovative compact bearing chambers and to ensure reliable operation of bearings in a hot environment at lower oil and secondary air flow rates.
AMBEC is a multidisciplinary project based on a combination of extensive experimental studies and advanced numerical simulation. Therefore, the AMBEC team is particularly focused on the planning and implementation of these 2 key technical activities.

Under the supervision of the Topic Manager, the consortium has defined a test matrix for experimental studies of flow distribution and heat transfer phenomena in the bearing chamber in a hot environment as well as formulated a set of parameters to be measured and their accuracy applicable for research purposes. Test matrix involves such parameters as oil and air flow rates and temperature, rotation speed, roughness of the chamber walls, etc. and foresees 100+ measurement points. Such an extensive experimental programme is required to generate a sufficient amount of data to validate numerical simulation and fine-tune the AMBEC methodology.

Another challenging task the AMBEC team is working on is the design and manufacturing of the test vehicle and test bench applicable for the realization of all planned multi-parametric studies. Firstly, the conceptual design was developed and agreed with the Topic Manager. Then, the strength and dynamic calculation were performed to required safety factors and avoid critical rotor speeds and resonance frequencies within the test vehicle operation range [0…25,000 rpm]; the hydraulic calculations were performed to develop the test vehicle geometry and areas of the inner channels and seals for air and oil cavities; the concept of the bearing chamber outer case external cooling was selected to improve the accuracy of experimental internal heat transfer coefficient determination. Specific attention was paid to the selection of proper instrumentation for measurement of temperatures, oil-air mixture flow rate and oil film thickness, which are the key parameters for understanding of multiphase process in the bearing chamber and calculation of heat transfer coefficient and the fluid flows. Manufacturing of the test vehicle and test bench components was started in October 2019. It is expected that the AMBEC test bench will be commissioned in September 2020.

In parallel, the state-of-the-art in the research of multiphase flow characteristics and heat transfer phenomena in the bearing chamber was analysed to gain from the experience accumulated by the research community and to identify the key challenges to be overcome by the AMBEC project. Experimental data available in the literature were used to launch preliminary two-phase modelling of fluid and heat flows in the bearing chamber of simplified geometry. In the frame of this preliminary modelling, the specific attention was paid to CFD model improvement and grid adaptation to optimize calculation speed and accuracy and maximize the efficiency of further simulation activities. This exercise also helps to understand process parameters to be controlled during the test campaign and locate properly the sensors in the experimental bearing chamber.

As soon as the AMBEC bearing chamber geometry and arrangement of the oil supply nozzles were agreed, three-dimensional CFD simulations were launched starting from the analysis of isothermal bearing chamber and evolving to the analysis of multiphase flow distribution and heat transfer modelling in the real bearing chamber with averaged phase parameters. Performed simulations helped to develop the methodology for calculation of the working process in the bearing chamber, which will be one of the key outcomes of the AMBEC project. At the moment of this report preparation, the methodology was validated on the basis of experimental data of Kurz et al (presented at ASME Turbo Expo 2012) and simulation results of Bristot et al (presented at ASME Turbo Expo 2016). The comparative analysis gave positive results. Further validation will be performed on the basis of the AMBEC experimental campaign data.
The key output of the project will be the AMBEC methodology, which will combine advanced numerical simulation of multiphase flows and heat transfer effects in the bearing chamber. It will be much more advanced than the state-of-the-art approaches and methodologies thanks to the simulation of the oil film generation and motion with account for (i) combined effect of interphase interaction, gravity and centrifugal forces as well as (ii) possibility of the liquid film rupture onto the droplets with their further crushing and coagulation. Such a complex and innovative approach will ensure the high accuracy of the calculation results.

Application of AMBEC methodology for the design of the bearing chambers of the next-generation aircraft gas turbine engines will help to optimize the oil flow rate, thus will result in less intensive operation of oil pumps, lower engine fuel consumption rate and less environmental impact in terms of СО2 and NOx emissions. On the other hand, the methodology application will make a positive influence on overall engine development costs and lead time, thus contributing to strengthening European engine manufacturers’ competitiveness at the global market.

Altogether, the AMBEC project outputs will contribute to the greening of EU aviation and more affordable mobility for European citizens and EU businesses.
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