InVIGO’s big data analysis characterises air vortices
As successive generations of fuel-efficient bypass engines are becoming increasingly wider in diameter, a new concern for designers is the decreased distance between the (underwing mounted) engine and runway. Reduced ground clearance can accentuate ground interactions during taxi and take-off phases, and as a result of being so close to the ground, vortices have the potential to form, especially when there are crosswinds.
‘When an aircraft is taxiing or during take-off, if you have a crosswind, a vortex could be generated between the runway's surface and the leading edge of the nacelle, and this vortex could significantly affect the quantity of air sucked into the engine. This is exactly what's being investigated by the InVIGO project,’ says Andrzej Podsadowski, Clean Sky Engines ITD Project Officer.
Because these swirling vortices can potentially be ingested by the engine intake and cause damage to the fan blades – due to foreign object ingestion, dynamic loading and structural vibration – it is important to be able to predict and characterise these ground vortices at an early design phase, thereby providing valuable insights when designing the engine's fan blades. Numerical methods, typically using computational flow dynamics (CFD), can simulate the vortices, but validating the results is challenging.
Cue Clean Sky's InVIGO (INtake Vortex Ingestion on Ground Operations) project, which is on track with the development of a methodology to characterise ground vortices during an engine test survey, with tools compatible with the test constraints.
‘We lack data from vortex aerodynamic characteristics – this is hard and costly to measure during tests, because it requires very specific instrumentation,’ explains Safran Engines's William Roussel, InVIGO's initial topic manager.
‘If we put such instrumentation inside an engine, it needs to be very robust, because there are so many aerodynamic interactions between the measurement instrumentation and the fan.’
Because installation of instrumentation on a test rig using a real engine is just too complicated, the strategy is to get really detailed experimental data, correlate them with the CFD results at the mockup scale, do some CFD at engine scale, and carry out some more low-instrumented engine testing.
‘All of these input data would be fed into a model, like a big data analysis, and then we'll be able to infer some information for our design later on, without having to put all that instrumentation into a real engine test, which would be very tricky, and too costly in terms of risk, time and money,’ says Mathieu Gruber, who is the current topic manager for InVIGO at Safran.
All of these input data would be fed into a model, and we'll be able to infer some information for our design without having to put all that instrumentation into a real engine test
‘We're working with great partners – the CSTB scientific centre in France, and ALTRAN for the numerical methodologies and simulations which have real expertise in this first kind of testing and numerical analysis, and they're doing a really good job with this,’ adds Gruber.
‘The technology centre has a wind tunnel and it is using its knowledge in the InVIGO project to investigate different configurations of engine inlets relative to external parameters like speed and angle of the wind in order to have a numerical model of potential vortices and how they could affect engines.’
‘It's a perfect example of how, in Clean Sky, knowledge and expertise from other fields can be exploited in European aviation,’ says Podsadowski.
So far, InVIGO has carried out the first test campaign to establish that it would be possible to recreate the presence of the ground vortex using wind-tunnel tests with classic instrumentation or low flow instrumented tests. CFD runs have been performed to define a methodology to reproduce the expected phenomena, and CFD post-processing means have been set to capture the vortex characteristics.
Additionally, possible hi-fi instrumentation means have been studied, of which Stereo-PIV and particle tracking are top candidates for the two InVIGO test campaigns. A second test campaign in 2021 will focus on characterising in detail the aerodynamic behaviour of the vortex, and towards that objective the CSTB wind-tunnel facility is undergoing an upgrade to allow for InVIGO targeted mass flows.
The InVIGO project feeds into the UHPE engine.