PROPTER: tackling the complex aerodynamics of tomorrow’s rotorcraft

It’s hardly surprising that to create a new type of aircraft that flies as fast as an aeroplane but can also hover like a helicopter (and is in fact a blend of both types of vehicle) – presents a set of unique aerodynamic challenges. Clean Sky’s PROPTER project addresses the complex aerodynamic interactions presented by Airbus Helicopter’s RACER compound helicopter, which is equipped with an overhead rotor (like that of conventional helicopter) but also has a wing and two propellers installed on the wingtips.

The RACER (Rapid And Cost-Effective Rotorcraft) demonstrator – one of two demonstrators in development for Clean Sky’s ”Fast Rotorcraft” Innovative Aircraft Demonstrator Platform (IADP) – will fly faster than a regular helicopter (with a high cruise speed of 220 knots), yet will retain the agility and hover capability of a conventional helicopter. This elicits uncommon aeronautical challenges for its designers, and these are being addressed by Clean Sky’s PROPTER consortium – comprised of Netherlands Aerospace Centre NLR and Delft University of Technology – which is focused on the performance analysis and design of the propellers under the influence of the wing, overhead rotor and fuselage of the rotorcraft. The topic leader is Airbus Helicopters.

For European aviation such a rotorcraft makes intercity flights such as Paris-London or Paris- Brussels possible in less than an hour, with the added advantage of vertical take-off and landing for urban accessibility. And for medical emergency and evacuation flights it means getting further and faster to those in need, enlarging the mission footprint of that ever-critical ’Golden Hour’. But to deliver this versatile capability, a well-founded knowledge of the complex aerodynamics around the compound helicopter is a prerequisite.

”PROPTER generates such knowledge by means of large-scale high-fidelity computer simulations, the so-called Computational Fluid Dynamics (CFD), revealing the involved physics of the flow and produces high-confidence numerical figures” says Bambang Soemarwoto, Senior Scientist at NLR – Netherlands Aerospace Centre. ”Additionally, the project addresses the design of the propellers to minimize power required, and therefore minimises fuel consumption, eventually contributing to reduction of CO2 and NOx emissions”. PROPTER encompasses an analysis and design process with a wide range of physical complexity and method fidelity, from a rather simple configuration (an isolated propeller) – but with a challenging set of tasks: the propeller design has to cope with multiple flight cases. This means that there’s a complex interactional flow between the propellers mounted on the wings, the main overhead rotor, and the airframe. And to scrutinise the aerodynamics of this complex set-up, PROPTER deploys the best of two worlds of CFD software: ENFLOW, a research code developed at NLR in various European and national research programmes, and ANSYSFLUENT, a commercial code used at Airbus Helicopters. To cross-check these two sets of analyses, a code-to-code comparison, both for analysis results and design results, will give a sound understanding of the modelling and best practices applied, providing assurance of the fidelity of the numerical results and their integration in the industrial environment.

"PROPTER generates such knowledge by means of large-scale high-fidelity computer simulations, the so-called Computational Fluid Dynamics (CFD), revealing the involved physics of the flow and produces high-confidence numerical figures"
says Bambang Soemarwoto, Senior Scientist at NLR – Netherlands Aerospace Centre.

"The kind of computer simulations conducted during the course of the project is unique"

 

”The kind of computer simulations conducted during the course of the project is unique” adds Soemarwoto. ”Important knowledge on the interactional aerodynamics has been generated for the three most important flight modes: cruise, hover and autorotation. Aerodynamic sensitivities due to variations within these flight modes have also been assessed, contributing to the design of the control law. And thanks to the highfidelity computer simulations, an in-depth understanding of the interactional flow field around the compound helicopter configuration and its impacts to propeller aerodynamic characteristics will be obtained by the end of the project. In the design aspects of the propeller, the project results will show that, through an advanced aerodynamic design optimisation methodology, a significant power reduction is possible”.

Airbus Helicopters has scheduled the first flight of the RACER demonstrator for the end of 2020, and in terms of dissemination and exploitation of the project, a webinar will be organised. Unique innovations have been generated during the course of the project, and in the context of aerodynamic analysis and design of propellers, some of the innovations are considered to have significant potential to deliver benefits to propeller manufacturers, and these will be shown in the webinar.

”We think that some of the results of our activities will be useful to European propeller manufacturers. I’ve identified that there are 25 propeller manufacturers in the EU and most of them are SMEs, so we’re now in the process of inviting them to this webinar where we can show the things that we have used in the project and share what we have experienced” says Soemarwoto.

"We think that some of the results of our activities will be useful to European propeller manufacturers. I’ve identified that there are 25 propeller manufacturers in the EU and most of them are SMEs, so we’re now in the process of inviting them to this webinar where we can show the things that we have used in the project and share what we have experienced"

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