B1.3 - Fast non-empiric prediction of propulsion installation related noise

With an ever more increasing integration of propulsor and airframe at modern and future aircraft, new sources of sound occur, which can neither be classically categorized into engine noise nor airframe noise. Instead, a new category of sound source occurs, which is due to the fact, that two or more aircraft components are in mutual aerodynamics interaction.

These sources are named “installation sources”, which occur only as a result of installing components at an aircraft and which would not be present, when considering these components in isolation. For instance, if a propeller is installed as a pusher configuration downstream of a wing, the wake of the wing produces unsteadiness on the propeller blade loading and thus additional excess noise with quite different characteristics as propeller-alone sound. This type of sound source is characteristic for all aircraft configurations considered in SE2A.

In view EU’s “Flightpath 2050” goal for an environmentally more friendly future aviation it is mandatory to assess the noise impact of any future technology and aircraft concepts proposed to reach the aggressive objectives of the EU. Such aircraft configurations are characterized by an unconventional propulsion integration, no matter if for a short, medium, or long range mission.

A new, necessarily non-empiric prediction approach is proposed for the quantification of sound generated as a result of the integration of propulsors (propeller, fan) at the aircraft. Since –by nature- empirical noise models do not exist for new engine integrations, the challenge to overcome is to enable predictions for largely arbitrary (tight) arrangements of propulsor and airframe, while being fast enough to cover a respective design space.

The proposed prediction concept therefore rests upon a non-empiric approach in the sense that modelling is restricted to mostly universal features of fluid mechanics and acoustics. This means turbulence modelling in the sense of a RANS approach to aerodynamics, as well as actuator disk approaches to model the effect of a propulsor aerodynamically. Moreover, by representing aerodynamic sound sources at rotor blades by respective (unsteady) forces the source wise installation as well as radiation wise installation may be described appropriately. In that way the modelling is configuration independent and the working hypothesis of the proposal is that with this aeroacoustic prediction approach the excess noise of arbitrary propulsor integration may be quantified.

Objectives

• quantify integration related excess noise generated at the propulsor (propeller or fan)
• determine the relation of noise reduction by shielding/reflection at the airframe vs. the above mentioned excess noise