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Engineering Edge

Multi-physics takes off at Avio

A Flowmaster-NASTRAN Approach for Reducing Fuel Consumption in Aero Engines

By A. Deponti (EnginSoft), D. Coutandin (AVIO Group), M. Pavan (AVIO Group)

Modern aero-engine development is driven by a number of factors and requirements, but probably none greater than the requirement to increase overall efficiency. This is largely due to environmental concerns and the ever more stringent emission targets that result, as well as a desire to insulate operators from rises in fuel costs through reduced consumption.

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Figure 1. Gas turbine

High turbine efficiency is a critical factor in ensuring these demands are met, yet the turbine is a component which must operate reliably at extremely high rotational speeds at a range of ambient temperatures (40⁰C on the tarmac to -60⁰C at cruising altitude isn’t unlikely) and velocities during a complete flight mission-profile. The exhaust flowing through the turbine will itself likely be at several hundred degrees Celsius. This is significant as an important consideration in the design of an efficient turbine is the clearance between the fixed and rotational sections. Specifically, this clearance should be minimized. What makes this a particular challenge is the fact that, if not actively controlled, the clearance would change during a flight profile with the expansion of components due to the operating temperatures noted above. An effective cooling strategy is therefore critical in order that efficient operation is possible throughout the entire operating range. To put this in perspective, the diameter of an aerospace turbine is often greater than 1 meter, while the required clearance might be less than 0.5mm.

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Figure 2. Integrated multi-physics approach

This extreme design challenge can only be accurately and reliably met when the engineer is in a position to consider the entire system and its physics; fluid dynamics, thermal effects and structural deformations must be considered together in a multi-physics approach that gives the designer access to the entire picture.

The Multi-Physics Approach

The numerical multi-physics approach described here is an automatic procedure developed by AVIO with the help of EnginSoft. This approach is capable of managing the operation and data transfer of three different commercial softwares:

  • MSC.P-thermal: Thermal solver used for the computation of the temperature distribution in the solid structure;
  • MSC.Marc: Deformation analysis tool used for the computation of solid structure deformation;
  • Flowmaster®: System level fluid-dynamic solver used for the computation of the flow field through the gas turbine.

The multi-physics simulation is driven by a specific FORTRAN library implemented into MSC.P-thermal. The FORTRAN library manages the co-simulation by invoking the fluid-dynamic solver (Flowmaster) and the deformation analysis software (MSC.Marc) when required. In particular, the call to Flowmaster is managed by a coupling interface procedure implemented ad hoc in Visual Basic. The coupling interface manages the data transfer between the two codes and manages the fluid-dynamic simulation in all its parts by setting simulation and component data, running the simulation and exporting the results.

System Level Simulations

To guarantee the required design accuracy, the entire system needs to be modeled, integrating rotor and static systems of the entire turbine. In particular, all secondary air systems, cooling circuits, active clearance control devices and the main flow path are to be considered in a system level analysis.

A simulation of the entire engine mission considers idle, take off, cruise, approach and landing phases. A complete simulation lasts about one week and requires about 5000 Flowmaster simulations and about 3000 deformation analyses. All simulations and data transfer are automatically controlled and managed by the thermal solver through of the automatic interface procedure as described above.

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Figure 3. Results of an integrated multi-physics simulation of the entire engine mission: clearance (%)

Conclusions

The implemented numerical multi-physics approach is able to achieve a better understanding of the thermal behavior of the turbine during the entire engine mission early in the design phase. This, in turn, allowed us to define the optimal geometries, materials and cooling mass flows for active clearance control. In the final analysis, the implemented multi-physics integrated approach, when used early in the design phase, allows the definition of the optimal clearances capable of achieving high efficiency and, as a consequence, a reduction in fuel consumption. A fundamental consideration with respect to meeting future emission limits.

Avio

Avio is a world leader in the design, development and manufacturing of aerospace propulsion components and systems for both civil and military aircraft. Avio works through the whole lifecycle of the products - from design to maintenance, repair and operations services.
Avio is headquartered in Rivalta di Torino, Turin, Italy, and operates across four continents. It employs over 5,200 staff, 4,500 of whom are based in Italy.

Avio was founded in 1908 and has played a crucial role in tackling the technological and business challenges of our time. Through continuous investment in R&D, and thanks to its relationships with the top Italian and international universities and research centers, Avio has developed leadership in technology and manufacturing.

 
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