Progress in aerodynamic and aeroacoustic integration of CROR propulsion systems

Abstract

Contra-Rotating Open Rotor (CROR) propulsion systems have seen renewed interest as an economic and environmentally friendly powerplant for future transport aircraft. Installation effects, i.e. the mutual interactions between airframe components and the rotors, have a pronounced impact on the aerodynamic and aeroacoustic performance for this type of engine. In the past five years, DLR's Institute of Aerodynamics and Flow Technology has performed a number of numerical studies investigating important aspects relating to engine-airframe integration of CROR engines. In this article an overview of coupled aerodynamic and aeroacoustic simulations investigating representative pusher-configuration CROR engines will be given, focusing on the impact on aerodynamic performance and aeroacoustics caused by the presence of a pylon, the potential for noise reduction by employing trailing-edge blowing at the pylon trailing edge as well as the performance and noise variations caused by different senses of rotation of the rotors. It is shown that the interaction with the pylon strongly impacts blade performance and front rotor noise emissions but that the use of active flow control in the form of pylon trailing-edge blowing can alleviate these adverse installation effects to a notable extent.

Numerical Analysis of Pylon-Blowing Systems for Pusher-Propeller Applications

“…As a result, the blades periodically experience a reduction in inflow velocity, causing an unsteady angle-ofattack perturbation. This leads to unsteady blade loads and an associated noise penalty, as confirmed in the literature for both single-rotating 2,3 and contra-rotating [4][5][6][7] propeller configurations.…”

“…Therefore, pylon-wake control can be applied to mitigate the pylon-installation effects. Among the possible flow-control strategies, the active technique of pylon blowing has shown to successfully eliminate the noise penalty due to the wake-impingement effects in various experimental 4-6, 8, 9 and numerical 7,10 studies. The work by Sinnige et al 9 confirmed that the achieved noise reductions are due to the abatement of the unsteady blade-load fluctuations, which is a direct result of the improved uniformity of the propeller inflow with blowing enabled.…”

Mitigation of Pusher-Propeller Installation Effects by Pylon Trailing-Edge Blowing

“…This causes periodic unsteady blade loading, as confirmed by flight tests [2,3] and numerical simulations [4]. The associated increase in tonal noise emissions has been substantiated both experimentally and numerically for single-rotating [5] and contra-rotating [4,6,7] propellers. It was found that the noise penalty due to the installation of the pylon is especially pronounced in the directions away from the propeller plane.…”

Characteristics of helicopter engine exhaust through scaled experiments using stereoscopic particle image velocimetry

“…17 Some benefits of a coaxial rotor over an equivalent single rotor system include its efficiency and the elimination of the need of a tail rotor due to the cancellation of the torque from the rotors; some disadvantages include the increased mechanical complexity and audio signal. 18 Interested readers are directed to the following studies [19][20][21][22] on the historical development and aeroacoustic research on coaxial rotors.…”