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🎓PhD Defense : ClĂ©ment MOCQUARD : “Large Eddy Simulations of afterburner in fighter aircraft engines”

  Monday 22 January 2024 at 14h00

  Conference Room - CERFACS - Toulouse       Organized by Nathalie BROUSSET    

link you tube:https://youtube.com/live/hDQ6mSMSr8o?feature=share  

Abstract :

Afterburners – also called reheat, augmentor or sequential burners – are found both in the gas turbine industry and aircraft engines. This work focuses on aircraft engines afterburners which are located downstream of the low-pressure turbines. Aircraft’s afterburners have a significantly lower efficiency than the primary burners because they release heat at a lower pressure part of the Brayton cycle. However, they become attractive when the thrust to provide to the aircraft varies a lot during the flight, and when trying to improve maximum thrust. It is mainly the case for high-speed/supersonic flights, short distance take-off, or tactical maneuvers. To meet such requirements, the propulsion engine has to be more versatile, and the extra thrust provided by an afterburner can prove useful. While supersonic aircrafts are almost exclusively encountered in military applications, an exception was the supersonic Concorde commercial jet which needed an afterburner to meet its thrust requirements. On modern aircrafts, the specifications concerning the global engine efficiency, lifetime, maximum thrust, emissions etc. have led to more and more constraints on the augmentor design. The architectures and design methods which have been developed in the past decades are now unable to satisfy today’s constraints and new designs are being investigated. In the industry, engineers nowadays rely on numerical tools to find the best solutions to their problems. In particular, for propulsion systems, unsteady fluid dynamic and combustion studies, Large Eddy Simulations (LES), which used to be prohibitively expensive in the past, is becoming increasingly used by industrial design offices. Despite the increase in computational power, LES of real-scale complex 3D geometries are still extremely expensive, and the present work aims at providing models allowing to find a good compromise between cost and accuracy of LES. Moreover, most of the research efforts so far focused mainly on the modelling of combustion phenomenon in primary combustion chambers, where a fuel/air mixture is burnt at relatively low temperature. In an afterburner, the fuel (kerosene) is injected in very hot burnt gas coming from the primary combustion chamber, and the models usually used from primary chambers can not be used directly to compute afterburners. In a first part, a new 2-step chemical scheme was developed for kerosene combustion at the conditions encountered in afterburners. Secondly, an extension of Thickened Flame model is proposed in order to better reproduce auto-ignition events which are likely to occur in afterburners. A Euler-Lagrange approach was used to model the liquid fuel injection, atomization, and evaporation. Then, the models developed during this thesis are used to compute a real scale lab experiment as well as a simplified geometry representative of the Safran M88 aircraft engine afterburner. Those last simulations highlight the complexity of the reactive flow inside afterburners and the usefulness of LES in the design of afterburning aircraft engines.

Jury :

Denis VEYNANTECentrale – SupĂ©lec – ParisReferee
Nicolas NOIRAY ETHZ – ZurichReferee
Benedetta FRANZELLI  Centrale – SupĂ©lec – ParisMember
 Yoann MERYSafran GroupInvited member
Davide LAERACERFACSCo-director