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inveSTigation of an ultrA compact Reverse flow combusTor

Periodic Reporting for period 3 - START (inveSTigation of an ultrA compact Reverse flow combusTor)

Reporting period: 2020-11-01 to 2021-03-31

The main objective of START project is to carry out a series of advanced investigations on a prototypical reverse flow, ultra-compact, combustor designed and manufactured by GE-Avio for turboprop engine as a part of the SAT ITD MAESTRO. The aim is to support the validation of the developed technologies and design rules by means of full annular combustion tests and high fidelity numerical simulations.
Targeted objectives of START can be summarized as follows:
• Verify a full additive combustor at real engine conditions in terms of combustor performance, by the measurement of emissions, gas exit temperature and liner metal temperature, through extensive full annular tests. Data will also permit validation of numerical modelling results.
• Improve the knowledge of combustor metal temperature and validation of aero-thermal predictions by gathering 2D temperature maps using InfraRed techniques across dedicated optical access on the full annular rig.
• Improve and further validate existent aero-thermal CFD modelling based on a two-step approach: RANS based CHT calculations for metal temperature and flow split predictions and LES (or Hybrid RANS-LES) calculations of the flame domain for combustor performance evaluation.
• Development of an innovative CFD approach based on unsteady CHT based on Hybrid RANS-LES, to allow direct calculation of aero-thermal and combustion performance behavior of the combustor. The methodology will also exploit and further validate dedicated strategy to model multi-hole liners.
Most part of the work carried out in the 1st period of the START project deals with the development and assessment of a multiphysics tool, named U-THERM3D, for high-fidelity predictions of metal temperature using the code ANSYS Fluent in the context of Scale Resolving Simulations. Such activity is in charge to UNIFI. In the past years, a 3D coupled approach for the thermal design of combustor liners was developed by UNIFI and has been used as starting point for the the new U-THERM3D approach. The basic idea is a desynchronisation of time steps in the solution of the involved phenomena, that can be summarized in convection (including several sub-phenomena as combustion, spray evolution etc.), conduction in the solid and radiation. Each of them is solved in a dedicated simulation, running with a parallel coupling strategy. The procedure used in U-THERM3D is depicted in Figure 1. As far as radiation is concerned a steady solver is exploited because of the extremely small time scales. Convective and radiative wall heat fluxes are manipulated before sending them to the conduction solver. In addition to the three solvers, a dedicated tool for the calculation of effusion holes is coupled, relying on the imprinted technique as sketched in Figure 2.
Before testing the new methodology on the START full additive combustor, it was decided to prove and assess the U-THERM3D tool on two test cases: the AvioAero LEMCOTEC combustor and the DLR model combustor FIRST. Some details about LEMCOTEC combustor and its injection system are reported in Figure 3. An example of the results obtained by the investigation of an Approach operating condition is reported in Figures 4 and 5.
Central task of the project was the execution of the full annular test of the START combustor developed by AvioAero. Tests were carried out at the Sesta-Lab facilities of COSVIG. Besides the standard sensors installed on the test article by the Topic Manager, including a rotating probe for the exhaust gas analysis, UNIFI managed the adoption of an innovative type of thermal paints for metal temperature measurement. The Thermal History Coating THC paint developed by Sensor Coating System Ltd (SCS) was considered for the outer liner. The innovative THC provided by SCS permits a much higher accuracy in the measurement (below 2°C), with a pointwise description of the temperature over the painting. The use of a plasma sprayed coating also allow to have a higher resistance in the harsh environment of the full-scale combustion tests. Figure 6 reports a picture of the combustor liner painted the innovative THC and with the standard thermal paints.
Once raw data of the tests have been delivered to the Topic Manager, including the post-processing of the metal temperature carried out by SCS on the THC, activity of data analysis and further post-processing by UNIFI (Task 3.1) was carried out. As an example of the obtained results in terms of metal temperature, Figure 7 reports a picture of the sampled 300 points over combustor outer liner.
In Task 3.2 the developed U-THERM3D methodology has been applied to investigate the START combustor. In figure 8 a comparison of the predicted outlet temperature distribution with the measured data is reported, pointing out an excellent agreement. Figure 9 shows a comparison of the predicted and measured metal temperature. Also in this case a very good agreement is observed.
Concerning the dissemination, activities performed during the START project have been presented at some international workshops and conferences. The restrictions introduce worldwide due to the COVID-19 pandemic have greatly affected further contributions to public events such as the participations to Airshows as planned in the Annex I.
Three publications have been prepared and published by UNIFI regarding the development and validation steps of the U-THERM3D methodology.
Regarding the exploitation of the obtained results and knowledge, the following items can be summarized for the two partners. UNIFI: The most relevant outcome of UNIFI in the START project is the development of the U-THERM3D methodology and its validation. Currently, a License Agreement is under definition between UNIFI and AvioAero for the official release of the U-THERM3D methodology. The developed methodology will be used and further improved and validated in a new research program started on March 1st 2021 (project ACROSS, Euro-HPC). COSVIG: Concerning COSVIG, the main outcome from the START project is the further update of the test cell #2 at Sesta-Lab premises. The tests carried out during START project have permitted to define operations and control strategies optimized for small size combustors fed by liquid fuels which were not commonly investigated in the past at Sesta-Lab premises.
MAESTRO goals concerning the thermal efficiency of turboprop engine aim at reducing SFC of -11% with respect to a 2014 reference engine. The final outcome will be a set of TRL6 technologies that could also potentially used in other applications. Besides the reduction of SFC, MAESTRO is also working at significantly reducing the total operating cost of the engine (up to -10%). Combined achievement of SFC and costs targets is pushing towards the introduction of Additive Manufacturing (AM) for some parts of the engine.
The innovation and knowledge improvement brought by START project in the development of technologies for a mature and reliable application of AM hot gas parts, will greatly impact on the competitiveness of European aeronautic industry, especially in the sector of small aircraft, where reduction of size, weight and costs is a cutting-edge aspect.
Figure 7: Pointwise metal temperature distribution over the THC paint
Figure 4: Temperature maps computed with U-THERM3D approach
Figure 6: Combustor with Thermal paints
Figure 8: Temperature maps comparison
Figure 3: AvioAero LEMCOTEC combustor prototype
Figure 9: Cold side outer liner temperature comparison
Figure 1: U-THERM3D parallel coupling strategy
Figure 2: Sketch of the effusion holes modelling
Figure 5: Comparison of the centerline temperature between experiments, THERM3D and U-THERM3D on the