R&D case: Optimising disruptive airframe-propulsion integration concepts

Project: ENODISE (Enabling Optimised Disruptive Airframe-Propulsion Integration Concepts)

To reduce the energy consumption and emissions of future aircraft, tighter integration between the propulsion system and airframe can be advantageous. However, integrating the propulsion system leads to significant complexity in the aerodynamic and acoustic interactions between propellers, the airframe, and lifting surfaces. These effects were addressed in the ENODISE project through experimentation, modelling, and simulation of a series of simplified yet representative integrated propulsion system configurations.

The challenge

The aim of this project was to provide the required knowledge and methods to enable the development of next-generation aircraft concepts by:

understanding the beneficial and detrimental aerodynamic and aeroacoustic airframe-propulsion interactions
assessing current numerical capabilities for simulating and optimising these interactions
evaluating the potential of flow and noise control strategies to enhance the aeropropulsive benefits while mitigating adverse noise effects.

The solution

Six different integrated propulsion system configurations have been studied through experiments and high-fidelity simulations. The resulting data have been used to develop and validate computationally efficient low-fidelity tools, which enable rapid parameter variation and are therefore particularly useful in the early design phase. Subsequently, optimisation is carried out by varying the propeller position relative to the airframe and by applying noise mitigation strategies, such as liners and porous materials.

All generated data are shared publicly in the Zenodo repository and can be used for benchmarking purposes.

What did we do?

NLR contributed by investigating over-the-wing propulsion, which promises favourable aeropropulsive effects due to the propeller-induced flow and a reduced noise signature as a result of shielding. As a proof-of-concept study, a mock-up featuring five spanwise-distributed propellers was investigated using aerodynamic and aeroacoustic measurements in NLR’s aeroacoustic wind tunnel and unsteady-RANS simulations (Reynolds-Averaged Navier-Stokes).

Additionally, two new low-fidelity prediction tools were designed:

a semi-analytical aeropropulsive and aeroacoustic performance model for over-the-wing propulsion (developed in collaboration with TU Delft)
an iterative toolchain for integrated propulsion systems, combining steady-RANS simulations with a lifting-line formulation.

The results show beneficial aeropropulsive and aeroacoustic installation effects during cruise, but complex aerodynamic interactions lead to a substantial increase in noise when operating at high-thrust and under a large angle-of-attack.

Project partners:

Von Karman Institute, TU Delft, University of Twente, Roma Tre University, University of Bristol, Ecole Centrale de Lyon, RWTH Aachen, NLR, DLR, ONERA, GPU-Prime, Pipistrel Vertical Solutions, Siemen