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2017

Poster

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Poster présenté au Forum Teratec de juin 2017


2018

Articles


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Low order modeling method for assessing the temperature of multi-perforated plates
Romain Bizzari a,, Dorian Lahbib a,b, Antoine Dauptain a, Florent Duchaine a, Stephane Richard b, Franck Nicoud c

a CERFACS - 42, Av. Gaspard Coriolis, 31057 Toulouse cedex 1, France
b Safran Helicopter Engines - Avenue Joseph Szydlowski, 64510 Bordes, France c IMAG, Univ. Montpellier, CNRS, Montpellier, France

A low-order model is proposed to predict the temperature of a multi-perforated plate from an unresolved adiabatic computation. Its development relies on the analysis of both an adiabatic and a conjugate heat transfer wall resolved large eddy simulation of an academic multi-perforated liner representative of the cooling systems used in combustion chambers of actual aero-engines. These two simulations show that the time averaged velocity field is marginally modified by the coupling with the heat diffusion in the per- forated plate when compared to the adiabatic case. This gives rise to a methodology to assess the wall temperature from an unresolved adiabatic computation. It relies on heat transfer coefficients from refer- enced correlations as well as a mixing temperature relevant to the flow in the injection region where the cold micro-jets mix with the hot outer flow. In this approach, a coarse mesh simulation using an homo- geneous adiabatic model for the aerodynamics of the flow with effusion is post-processed to provide a low cost alternative to conjugate heat transfer computations based on hole resolved meshes. The model is validated on an academic test case and successfully applied to a real industrial combustion chamber.


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Abstract In aero-engines, mutiperforation cooling systems are often used to shield the combustor wall and ensure durability of the engine. Fresh air coming from the casing goes through thousands of angled perforations and forms a film which protects the liner. When performing Large Eddy Simulations (LES) of a real engine, the number of sub-millimetric holes is far too large to allow a complete and accurate description of each aperture. Homoge- neous models allow to simulate multiperforated plates with a mesh size bigger than the hole but fail in representing the jet penetration and mixing. A heterogeneous approach is pro- posed in this study, where the apertures are thickened if necessary so that the jet-crossflow interaction is properly represented. Simulations using homogeneous and thickened-hole models are compared to a fully resolved computation for various grid resolutions in order to illustrate the potential of the method.


Conférences internationales


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ASSESSMENT OF A COOLANT INJECTION MODEL ON COOLED HIGH-PRESSURE VANES IN LARGE EDDY SIMULATION

M. Harnieh, M. Thomas, R. Bizzari, L. Gicquel and F. Duchaine CERFACS CFD Team

Combustion temperatures in modern gas turbine engines reach levels well above the thermal stress limit of materials applied in chamber and high-pressure tur- bines. Being the most critical component of the en- gine, the high-pressure turbine blades are therefore equipped with cooling systems to ensure safe and longterm operation. To predict the flow in such con- figurations, Reynolds Average Navier Stokes (RANS) simulations are usually used in the industrial con- text but are limited by its steady formalism. Poten- tial improvement is foreseen with Large Eddy Sim- ulation (LES) which resolves the most energetic tur- bulent structures while modeling the small ones and has been found to be well suited to predict turbulent and fully unsteady flows. However, assessing the im- pact of a cooling system on the flow field of the high- pressure turbine using high fidelity simulations still re- mains prohibitively expensive. This work investigates the applicability of a recently proposed effusion cool- ing model, designed for modeling cooling of the com- bustion chamber liners on cooled turbine blades. This model was specifically designed to mimic the impact of coolant jets and does not require to solve the flow in the liners which leads to a dramatic reduction of the CPU cost.
To assess the applicability of the model on turbine blades, the cooled Nozzle Guide Vanes (NGV) of the FACTOR configuration are chosen. A modeled LES using the hole model is carried out and compared to a hole-resolved LES on the same configuration. Results show that both simulations give very close results. The time averaged skin temperature of the modeled LES is slightly lower than the resolved one. Indeed, the coolant film around the NGVs is colder and thinner with the model. Futhermore, investigation of the RMS fields also shows that the turbulent mixing is less im- portant if applied the model to blades.



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Mesh local refinement to enhance effusion cooling models

R. Bizzaria · M. F ́eranda · A. Dauptaina · G. Staffelbacha · S. Richardb · J.-D. Mullerc · T. Ogierb · G. Exilardb · F. Nicoudd

In aeronautical combustors, effusion cooling is the preferred technique used to shield walls from the hot gases. Jets from thousands of sub-millimeter angled perforations form a film isolating the liner. When performing a Large Eddy Simulation (LES) of a real engine, including effects of the effusion cooling is a challenge. A modeling technique [1] has been developed recently to address this issue. However in that work, the precision is still relative to the mesh. The present study proposes an automatic adaptive method which increases the mesh resolution in key areas allowing to achieve more accurate results at moderate additional cost.

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Conférences nationales


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A short overview of the models developed during my PhD forSafran Helicopter Engine
12 December 2018
INCA, Bordes
Romain Bizzaria,, Antoine Dauptaina, Franck Nicoudb aCERFACS - 42, Av. Gaspard Coriolis, 31057 Toulouse cedex 1 - France
bIMAG, Univ. Montpellier, CNRS, Montpellier - France

Numerical simulation is progressively taking importance in the design of an aeronau- tical engine. However, concerning the particular case of cooling devices, the high number of sub-millimetric cooling holes is an obstacle for computational simulations. A classical approach goes through the modelling of the effusion cooling by homogenisation. It allows to simulate a full combustor but fails in representing the jet penetration and mixing. A new approach named thickened-hole model was developed during my thesis to overcome this issue. A work on improving the mesh resolution on key areas thanks to an automatic adaptive method is also presented, leading to a clear breakthrough.
In parallel, as the flame tube temperature is a cornerstone for the combustor durability, a low-cost approach is proposed to predict it. To meet the time-constraints of design, it is based on thermal modelling instead of a direct thermal resolution.

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Heterogeneous modelling of multiperforated plates in LES
Romain Bizzaria,, Antoine Dauptaina, Laurent Gicquela, Franck Nicoudb

aCERFACS - 42, Av. Gaspard Coriolis, 31057 Toulouse cedex 1 - France
bInstitut Montpellierain Alexander Grothendieck, CNRS, Univ. Montpellier -

In aero-engines, hot gases issued by combustion are close to 2400K where liners can only sustain 1300K before melting. Mutiperforation cooling systems are thus often used. Fresh air coming from the casing goes through thousands of angled perforations and form a film which protect the liner. When computing a real engine, the number of sub- millimetric holes is far too large to allow a complete description of each aperture and appropriate models are thus needed. The homogeneous model of Mendez and Nicoud [1] allows to simulate multiperforated plates with a mesh size bigger than the hole but fails representing the jet penetration and mixing. An heterogeneous model which repre- sents the jet dynamics is presented in this paper. If the mesh is too coarse, this model automatically thickens the apertures to properly represent the jet in crossflow using the modeling ideas from [1] which ensure the proper mass and momentum flux. Fully resolved simulation, homogeneous and heterogeneous models simulations are compared with ex- perimental results to validate the present model.

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SFT

Romain Bizzaria,, Dorian Lahbiba, Antoine Dauptaina, Florent Duchainea, Stephane Richarda, Franck Nicoudb

aCERFACS - 42, Av. Gaspard Coriolis, 31057 Toulouse cedex 1 - France bIMAG, Univ. Montpellier, CNRS, Montpellier

A low-order model is proposed to predict the temperature of a multi-perforated plate from an unresolved adiabatic computation. Its development relies on the analysis of both an adiabatic and a conjugate heat transfer wall resolved large eddy simulation of an aca- demic multi-perforated liner representative of the cooling systems used in combustion chambers of actual aero-engines. These two simulations show that the time averaged velocity field is marginally modified by the coupling with the heat diffusion in the per- forated plate when compared to the adiabatic case. This gives rise to a methodology to assess the wall temperature from an unresolved adiabatic computation. It relies on heat transfer coefficients from referenced correlations as well as a mixing temperature relevant to the flow in the injection region where the cold micro-jets mix with the hot outer flow. In this approach, a coarse mesh simulation using an homogeneous adiabatic model for the aerodynamics of the flow with effusion is post-processed to provide a low cost al- ternative to conjugate heat transfer computations based on hole resolved meshes. The model is validated on an academic test case and successfully applied to a real industrial combustion chamber.

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