Fundamental and Applied Energetics
ONERA and micro energy sources : the micro gas turbine engine
DecaWATT : development of a demonstrator of a micro gas turbine engine
In a second step, ONERA has undertaken the development and realization of a demonstrator of micro gas turbine engine, through a PRF (Federating Research Project), which lasts 4 years and is to end in the end of 2010. Even if this type of internal project is mostly financed by ONERA, this project benefited from the support of the ANR (National Research Agency) thanks to the ISA Carnot institute. In this case, all the aspects of the development of a micro gas turbine engine must be studied, from the global energetic study, through the fabrication and integration of the parts, to the experimental tests of the complete prototype. This global project gathers a few ONERA departments: DEFA (Fundamental and Experimental Energetics), DMSC (Composite Materials and Structures), DMSM (Metallic Materials and Structures) and DAAP (Applied Aerodynamics).
During this ongoing project, various works have been achived, some of which are illustrated below:
- Structures of micro gas turbine engine developed by ONERA
Structure of ONERA current micro gas turbine engine (one stage).
Structure of ONERA double stage micro gas turbine engine: “thermodynamic cocoon” (patented structure).
Performances of the ONERA gas turbine engines are estimated through a global energetic study. For that matter, a system-approach code has been developed to simulate a micro gas turbine engine, taking account of the thermal fluxes. Hence, the various structures can be compared in terms of efficiency and output power.
First micro combustion chamber under operation (volume: 850 mm3): premixed C3H8-air combustion.
Second micro combustion chamber under operation (volume: 1 cm3): non premixed combustion.
Experimental studies have been carried on: two micro combustion chambers have been tested. Unlike the first chamber, the second one (called “volume chamber”), corresponds to the ONERA micro gas turbine engine structure. Air and fuel are injected separately in this chamber: combustion is not premixed.
Moreover, other fuels, which are easily stockable under liquid phase, are under study, and more particularly propane (C3H8). This considerably helps to reduce the mass and the volume of the fuel tank.
Numerical simulation of C3H8-air combustion in the second combustion chamber. Left: H2O mass fraction; right: temperature.
A theoretical study has also been led, through 3D numerical simulation calculations carried out with the internally developed code: CEDRE. On the one hand, some simulations are realized on existing combustion chambers, to get a better understanding of the flow and combustion structure; on the other hand, some simulations are led on new configurations, to prospect on new concepts and new shapes of chamber.
- Design of compressor and turbine:
Left: micro turbine (10 mm in diameter) + inlet guide vanes. Right: micro compressor (10 mm in diameter) + radial-axial diffuser.
Examples of calculations for an 8 mm diameter compressor. Left: aerodynamics simulation, Mach field (ElsA). Right: mechanics simulation, axial deformations.
The design of the compressor and the turbine is one of the key-points of this project. 3D numerical simulation calculations have been led, thanks to the ONERA specific code: ELSA (Aerodynamic Simulation). Currently, diameter of the impellers equals 10 mm, air mass flow rate equals 1 g/s and pressure ratios are in the range of 3.
To verify the feasibility of the obtained aerodynamic designs, thermo mechanical calculations have been carried out (centrifugal forces and high temperatures). Hence, iterations have been led between aerodynamics and mechanics, to achieve the final design of the impellers.
On an experimental point of view, these impellers will soon be tested on a test rig, which is currently under conception. The aim is to make the following parts: (compressor + turbine linked by a shaft) rotate at nominal speed. Thus, compressor, turbine, journal bearing and thrust bearing will be tested.
3D view of the test rig dedicated to the test of the rotating parts and aerodynamic guiding system (under conception).
- Materials and fabrication methods:
Examples of fabricated parts of the micro gas turbine engine.
Selection of the materials and the fabrication methods is a crucial point for our project. Indeed, the constraints are actually demanding:
- gap between rotating parts and static parts in the range of the micrometer: very high machining precision;
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temperatures over 1000 Kelvin: mechanical resistance at high temperatures, thermal expansion, oxidation;
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rotating speed in the range of 900 000 rpm: mechanical resistance, even at high temperatures;
This study led, for each part of the micro gas turbine engine, to the selection of one or two materials, and an associated fabrication method.
Concerning the electric generator, prospecting has been led. Solutions adapted to small scales and high rotating speeds appear to exist.
