ONERA and the SME ANDHEO have received an award for the design and implementation of an aerothermal simulation method for the hot parts of aircraft engines. Its outstanding performance enables analysis by calculating thermal phenomena throughout the entire flight, thereby attracting great industrial interest.
Tristan Soubrié (2nd), associate director of ANDHEO, and Marc Errera (3rd), technical manager of the "Transient Aerothermal Coupling" project at ONERA, receive the “Collaboration" prize of the Numerical Simulation Trophies. 28 June 2016, Ecole Polytechnique - ©TERATEC
Multi-physics and coupling
This work was carried out at the request of Safran Aircraft Engines and was funded by the French Civil Aviation Authority (DGAC, Direction Générale de l’Aviation Civile). The idea was to enable the almost real-time simulation of the thermal transient in the metal structures of an aircraft engine over the entire duration of a flight (several hours), from takeoff to landing.
This problem was a veritable challenge, since it was necessary to establish original methods, both accurate and efficient, for the coupling of heat transfer modes between fluid and solid media. The challenge faced by the ONERA-ANDHEO collaboration was to overcome all numerical problems and to develop a workable strategy as soon as possible in the design offices.
Fluid-structure thermal simulation for the high-pressure turbine disc (CFM 56 type engine). In the center, the disc (cross-section) whose temperatures can reach 1500°C at the combustion chamber outlet (in red). In blue, against the disc, the air-cooling system whose temperature still reaches 7 to 800°C. Simulation in two hours of a 7600 second flight.
The project originated from ONERA research work, funded internally, on innovating aerothermal coupling techniques between structures and fluids. The promising results obtained by ONERA researchers have resulted in a contract with Safran Aircraft Engines: the progress made seemed indeed mature enough to move on to the demonstration stage for an industrial case.
The coupled state stabilized at each point of the cycle is obtained by an iterative process, considered as converged when the maximum temperature difference between the fluid and the solid reaches 0.001°C. The cooling system in contact with the disc is shown here.
Outstanding performance in terms of computing time
ANDHEO engineers, in association with ONERA's researchers, initially set up a coupled platform between the Fluent software (fluid mechanics) and the Zset-Zebulon software (co-developed by ONERA) for the structure part and heat transfers in solids. The tool enabling this strong coupling is the OpenPalm library, an open source tool co-developed by Cerfacs* and ONERA for highly customized couplings. The coupling methods were then tested systematically at ONERA.
Then, at the end, the SME ANDHEO, ONERA’s longtime partner, carried out an industrial calculation showing the effectiveness of the numerical procedures developed at ONERA. "Today, two hours of simulation are enough, with this Fluent-OpenPalm-Zset-Zebulon approach, to analyses the thermal load throughout an entire flight; that is to say, 300 times less than what would have been the case with the Fluent internal coupling solution" says Tristan Soubrié.
The success of this operation lies, in particular, in the innovative nature of the stationary aerothermal coupling numerical approaches (2013), which were adapted by ONERA to the transient mode. It thus became possible to analyze a transient in the structures over very long periods. The efficiency of the coupling strategy comes from fluid calculations at successive chosen times, according to the flight program, coupled with continuously calculated solid heat transfers. All heat transfer modes (convection, conduction, radiation) are taken into account.
The upper end of the disc is in contact with the turbine blade and the test section, and therefore with the hot gases at the combustion chamber outlet. Throughout this flight example, it is subjected to temperature cycles, prescribed in the calculations and shown schematically in this figure.
Transfert à l'industrie et poursuite des recherches à l'ONERA
In general, aerothermal coupling is only used in industry to seek a fluid-solid stationary state. However, a flight lasts for several hours and includes various stages that must absolutely be taken into account (takeoff, cruising, altitude change, etc.). The solution proposed by ONERA and ANDHEO to Safran Aircraft Engines enables the thermal load to be analyzed throughout a long flight as from now, as well as enabling life duration problems to be tackled under the best conditions.
"In the future, we will continue to develop increasingly powerful aerothermal methods. In addition, two theses will begin at ONERA in the month of October on this topic, dealing with the elsA*-Zset-Zebulon coupling. ONERA and ANDHEO are also already scheduled to contribute to the transfer of the coupling methods to Safran tools." concludes Marc Errera.
Notes
- * Cerfacs : French Centre for Research and Advanced Training in Scientific Computing
- * elsA : aerodynamic simulation software package co-developed mainly by ONERA, Airbus, and Safran
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