News Releases

July 2006

ESTEC calls on ONERA for FEEP characterisation

To fulfil its aim of testing the Equivalence Principle to within 10^-15, a principle which let us recall is the basis of our concept of gravity, the satellite on the joint Cnes/ESA Microsope mission (Micro Satellite with Drag Control for the Observation of the Equivalence Principle), due to be launched in 2009, will have on board two ultra-sensitive accelerometers designed by ONERA. They constitute the core of the scientific payload. The satellite will also be equipped with twelve caesium FEEP (Field Emission Electric Propulsion) thrusters, a type of electric motor that has not yet been put into orbit. The ESTEC, ESA's R&T centre, has recently entrusted ONERA with the characterisation of these caesium thrusters manufactured by the Italian company Alta. According to Denis Packan, a research engineer in the department handling this ten-month study, "Uncertainties remain concerning the life time, consumption and more generally the physics of this type of thruster, in particular the number of caesium atoms that it emits. "

Thus ONERA engineers will pay close attention not to the caesium ions involved in the thrust but to the "neutral" elements, i.e. the caesium atoms. The latter might indeed contaminate the satellite by depositing in particular on the solar panels, resulting in possible short circuits. This is why it is necessary to ascertain what quantity of caesium atoms is emitted by a FEEP thruster. Denis Packan and Jean Bonnet, also a research engineer in the same unit, will employ a whole set of optical diagnostics for this unusual experiment, interview all optical and mechanical devices will be installed in a vacuum chamber and subjected to caesium. "It's a kind of challenge that will require setting up certain devices for the first time, and furthermore on a flight model ", notes the Palaiseau engineer.

License transfer on the horizon for the "MONOPASTILLE" accelerometer

ONERA researchers have just presented French manufacturers in the avionics sector with the "MONOPASTILLE" accelerometer patent they filed in May 2004. It is in fact a new version, flat and in a single unit, of the quartz Vibrating Inertial Accelerometer (VIA) developed and transferred in 1997 to manufacturers. Let us recall that accelerometers of this type, chemically etched onto quartz wafers, contain a small crystal blade that vibrates in the manner of a guitar string. " The entire accelerometer is made up of two quartz discs put together in a case with differential configuration. This case reduces the influence of interfering physical magnitudes acting together on the two discs, such as the temperature and pressure inside the case " explains Olivier Le Traon, a research engineer .

In the new version, the two quartz discs are attached to the same mounting frame. The specific configuration of this mounting frame, covered by the patent, makes it possible to obtain near total independence of the vibrations of the two resonators, despite the fixed configuration of the sensor. The result is a more compact instrument with fewer assembly operations and thus a simpler manufacture that performs at least as well as the VIA. " It's actually a true MEMS (Micro-Electro-Mechanical System) " states an enthusiastic Le Traon, adding that in the area of vibrating accelerometers, "ONERA is a major player." The next stage is the negotiation of licensing agreements to start an industrial transfer process by the end of this year.

360° PSP used successfully on a Falcon 7X model

In April, at the Modane centre, a ONERA team carried out a "first" by measuring the pressure field on the whole surface of a Falcon 7X with a technique they called "360° PSP". " In industrial wind tunnels, we generally use these pressure-sensitive paints (PSP) to study a particular area of the model, for instance the upper wing surface. In this case the measurement device has a single camera. The technique is also used to examine local stress on a rudder, and here two cameras are used" explains Clodoald Robert, a test engineer. For this test, where the entire model had been coated with PSP, the measurement device was equipped with four computer-operated cameras assisted by a four UV-lamp lighting system each of which fed two small illuminators.

The test campaign was conducted as part of technical development funded by ONERA equity. It produced results whose quality was noted by Dassault Aviation, the company that had agreed to lend its model of the Falcon 7X. The process is now in an optimisation phase before moving to an industrial phase. " We must achieve uniform lighting over the surface of the model. Overall setting up 360° PSP in the wind tunnel still takes too long, with the result that the cost is too high for an industrial test. It's mainly in this area that we need to make progress " opined the engineer. An additional test should suffice to optimise this technique which it seems is already used by the US Air Force and made available by the DLR.

Operational fielding of the NEC SX8

A powerful tool for vector calculus, the NEC SX8, equipped with the currently fastest processor in the world, has been operational since April 7th at ONERA, which thus benefits from a vector calculation speed of 493 Gflops as opposed to 192 Gflops previously. However this operation is only a first step. " Additional installation options are planned for late 2006 and late 2007, which should allow ONERA to again position itself at an international level in this area. The peak power of this machine would then reach 1.4 Tflops in late 2006 and nearly 2 Tflops in late 2007 " explains Paul Levart, a manager at the department of Scientific Networks and Computing. In the meantime ONERA will be equipped with a parallel and scalar machine whose computing power, along with that of the NEC SX8, will allow it to hold an enviable position in an international community where the teraflops now represents the obligatory "entry ticket".

" The NEC SX8 is both very familiar in certain ways and very different from the machines that preceded it. Its mastery has required significant efforts, but users have suffered little from these changes " notes Paul Levart who points out that the NEC SX8 should reach its best efficiency level this September. Indeed the delivery of such a machine implies the development of specific tools, most often from existing products. Note that over 80% of the calculations carried out on this new machine will be at the request of departments involved in fluid mechanics.

Filing of a patent with very promising applications

The Optical Instrument Design unit (CIO) managed by Jérôme Primot within the Department of Theoretical and Applied Optics (DOTA) applied for a new patent in February entitled: "Wave front analysis using differential multilateral interferometry." " Analysing a wave front presupposes that one is truly measuring what one calls a surface " notes the unit manager. " A PhD candidate discovered that the interferometry technique developed in our unit could be applied not only to surfaces but also to quasi-surfaces, which contain breaks and jumps. " There is nonetheless a limitation. For instance, a defect corresponding to n times the wavelength cannot be distinguished from one that measures once the wavelength. Thus the idea of the researchers in the Palaiseau team was to make use of a relatively common solution in optics, that of working with two wavelengths that differ slightly.

A PhD candidate will focus on this starting in September. In March of this year, ONERA obtained the authorisation to make public this patent whose applications are very promising, to start with in the area of astronomy, with the development of segmented mirrors during the next few years. " The method we are developing could also be of use in the area of lasers. One idea currently mooted to design powerful lasers at reasonable cost is to focus several medium-power lasers set up in parallel. This implies the ability to measure the jumps between the various beams so as to correct them before they are used. Our method should, in theory, make it possible to correct defects of significant magnitude, with great accuracy " adds Jérôme Primot. Another area that may prove to be of interest is that of industrial control, where applications seem considerable, from Fresnel optics to circuit boards to retinal flatness, to mention but a few examples.

 
Measurement of a chequered optical part made up of two levels whose difference in height is greater than the wavelength.
Left: one of the interferograms obtained for a wavelength. Right: the reconstruction.

A "first" on the MICAEDI bench to increase the performances of aircraft motors and reduce polluting emissions

The first test campaign, funded by ONERA equity as part of a research programme on combustion instabilities, was launched in the autumn of 2005 on the MICAEDI bench and lasted until the end of March. MICAEDI is notable in that its flow has a high Reynolds number, contrary to the smaller test benches used in most university laboratories. " The advantage of this bench is its mirroring of reality. Its combustion behaviour is close to that of real systems " asserts Vladimir Sabelnikov, a research director and specialist in turbulence.

Having relied solely on Particle Image Velocimetry (PIV) at the start of the campaign, the engineers then produced a first by associating a PIV measurement with a high-frequency visualisation of the OH radical in UV light by intensified high-speed camera. " It is of course important to know how the flow velocity field varies within the chamber . However this type of information is only of interest if it is associated with the unsteady pressure signal. The data is of even greater interest if it can be linked to the way in which the flame structure changes. What is most important is to gather all this data simultaneously " says research engineer Christophe Brossard.

What remains is to process the data obtained before it is analysed and interpreted. " We were notably able to observe a low frequency (roughly 1 Hz) phenomenon during which the flame disappeared. It's by attempting to understand this kind of phenomenon that manufacturers will be able to increase aircraft motor performance and reduce polluting emissions. Currently, all calculations are based on modelling that the lack of experimental data prevents us from improving " notes Vladimir Sabelnikov. Hence the importance of this work which once again could not be carried out without MICAEDI, a test bench that is unique in France .

MICAEDI combustor
In blue: connected flame behind the backward-facing step
In green: laser sheet used for PIV speed measurements

Last Update: 1 August 2006- © ONERA 2009 - Terms of use