Pylon Trailing Edge Blowing for the Control of CROR Unsteady Blade Loads

22nd AIAA/CEAS Aeroacoustics Conference

Eitelberg

et al. 2016

Pylon-mounted pusher propellers suffer from installation effects due to the interaction between the pylon and the propeller. The impact of angular inflow on these installation effects was quantified at the Large Low-Speed Facility of the German-Dutch wind tunnels (DNW-LLF). Particle-image-velocimetry measurements showed that the pylon wake's width and velocity deficit were hardly affected by the introduction of a six-degree sideslip angle. Application of pylon trailing-edge blowing reduced the integral velocity deficit in the wake by up to 65%. Evaluations of the surface pressures on the blades confirmed the sinusoidal loading behavior in angular inflow and the impulsive loading peak due to the pylon-wake encounter. The circumferential velocity components induced by the pylon tip vortex strongly affected the steady-state propeller performance by modifying the effective advance ratio sensed by the blades. Increased performance was measured when the rotation direction of the pylon tip vortex was opposite to that of the propeller. Angular inflow affected the propeller noise emissions due to the resulting unsteady blade loads and the circumferential variation of the effective Mach number of the blade sections. The installation of the pylon added a noise source due to the unsteady blade loads caused by the pylon-wake encounter. Depending on the sideslip angle, application of blowing eliminated a large part of the installation noise penalty, despite remaining non-uniformities in the blown wake profiles.

Section: -9supporting

confidence: 71%

Pusher-Propeller Installation Effects in Angular Inflow

22nd AIAA/CEAS Aeroacoustics Conference

Eitelberg

et al. 2016

“…4 The adverse pylon-installation effects can be mitigated by eliminating the momentum deficit in the pylon wake. This can be achieved using pylon blowing, as confirmed previously by experimental research with single-rotating [5][6][7] and contra-rotating [8][9][10][11] propellers, as well as numerical investigations 12 . The experimental studies published so far focused on the beneficial effects of pylon blowing on the far-field noise levels.…”

Section: Introductionsupporting

confidence: 70%

Pusher-Propeller Blade Loading With and Without Pylon Trailing-Edge Blowing

34th AIAA Applied Aerodynamics Conference

Eitelberg

et al. 2016

The aerodynamic interaction effects characteristic of pusher propellers were studied at the Large Low-Speed Facility of the German-Dutch wind tunnels (DNW-LLF). A propeller model was positioned downstream of a pylon equipped with a trailing-edge blowing system. Surface-pressure transducers integrated into the propeller blades confirmed the local impact of the pylon wake on the blade loads. At an intermediate thrust setting, the sectional lift impulsively increased by 30% during the wake passage. The application of pylon blowing decreased the integral velocity deficit in the pylon wake by up to 77% compared to the unblown case. As a result, the load fluctuations during the wake encounter were practically eliminated, thereby mitigating the adverse installation effects.

“…This has been shown previously by experimental research with single-rotating 1, 2 and contra-rotating propellers, [3][4][5][6] as well as numerical investigations. 7 Although these studies all confirmed the potential of blowing as a means to reduce the pylon installation effects, no thorough quantitative data of the aerodynamic and aeroacoustic effects are yet available.…”

Section: Introductionmentioning

confidence: 99%

Aerodynamic and Aeroacoustic Effects of Pylon Trailing Edge Blowing on Pusher Propeller Installation

Lynch

21st AIAA/CEAS Aeroacoustics Conference

et al. 2015

The aerodynamic and aeroacoustic effects of pylon trailing edge blowing on the propulsive performance and noise emissions of a propeller installed in a pusher configuration were studied in a wind tunnel. A propeller model and a pylon equipped with a trailing edge blowing system were installed in the large low-speed facility of the German-Dutch wind-tunnels (DNW-LLF). Particle image velocimetry measurements of the flow field downstream of the pylon confirmed a wake re-energization obtained through blowing, with a momentum deficit recovery of 80% compared to the unblown case. For the symmetric inflow conditions considered, the effect of pylon installation on the propulsive performance was found small. Increases in thrust and torque of 1% up to 6% were measured at high and low thrust settings, which was comparable to the measurement variability. Acoustic data obtained using out-of-flow microphones confirmed the strong interaction effects resulting from the installation of the upstream pylon, with an increase in noise levels due to the presence of the pylon of up to 12 dB at a medium propeller thrust setting. The application of pylon trailing edge blowing successfully eliminated the installation effects, resulting in noise levels equal to those of the isolated propeller over the entire axial directivity range. At higher thrust settings the change in blade angle of attack due to the pylon wake impingement is smaller, and the steady blade loads are larger compared to the unsteady loads experienced during the wake passage. Consequently, in this operating regime the propeller noise emissions were dominated by steady sources for all but the most upstream observer positions.