Unsteady Pylon Loading Caused by Propeller-Slipstream Impingement for Tip-Mounted Propellers

Abstract

An experimental analysis was performed of the unsteady aerodynamic loading caused by the impingement of a propeller slipstream on a downstream lifting surface. When installed on an aircraft, this unsteady loading results in vibrations that are transmitted to the fuselage and are perceived inside the cabin as structure-borne noise. A pylonmounted tractor-propeller configuration was installed in a low-speed wind tunnel at Delft University of Technology. Surface-microphone and particle-image-velocimetry measurements were taken to quantify the pressure fluctuations on the pylon and visualize the impingement phenomena. It was confirmed that the propeller tip vortex is the dominant source of pressure fluctuations on the pylon. Along the path of the tip vortex on the pylon, a periodic pressure response occurs with strong harmonics. The amplitude of the pressure fluctuations increases with increasing thrust setting, whereas the unsteady lift coefficient displays a nonmonotonic dependency on the propeller thrust. The lowest integral unsteady loads were obtained for cases with approximately integer ratios between the pylon chord and the wavelength of the perturbation associated with the propeller tip vortices. This implies that structure-borne-noise reductions might be obtained by matching the pylon chord with an integer multiple of the axial separation between the propeller tip vortices.

Wingtip-Mounted Propellers: Aerodynamic Analysis of Interaction Effects and Comparison with Conventional Layout

“…The radial distributions of the blade chord and twist angle are provided in Ref. [13]. Compared to modern designs, the propeller had a low blade count, a low solidity, and no sweep.…”

“…The shedding of vorticity associated with the spanwise lift gradient also introduces velocities in the spanwise direction ( Figs. 15b and c), which distort the propeller slipstream during and after its interaction with the wing [8,13,21]. The resulting spanwise shearing of the slipstream is visualized in Fig.…”

“…The spanwise shearing of the slipstream modifies the local wing performance near the slipstream edge. Although this especially affects the unsteady lift and drag response [13,21], also the time-averaged wing loading is altered. This can be seen in Fig.…”

Validation and Comparison of RANS Propeller Modeling Methods for Tip-Mounted Applications

“…The propeller featured four straight blades and a diameter of 0.237 m, while the blade pitch angle was set to 23.9 • at 75 % of the radius. The radial distributions of the blade chord and twist angle are provided in Sinnige et al [16] Velocity and total-pressure data measured with the same propeller and nacelle in a sting-mounted configuration were taken from the same reference and used in the current paper to validate the simulations for the isolated propeller configuration. The nacelle was connected to a straight, symmetrical wing model with a chord length of 0.240 m, a semi-span of s w = 0.327 m, and a NACA 64 2 A015 profile with a round trailing edge of 0.0025t w radius.…”

Aerodynamic and Aeroacoustic Effects of Swirl Recovery Vanes Length

“…For this reason, the impingement, deformation and convection of the propeller wake and tip vortex helix on the SRVs [9] shall be considered. Once the tip vortex helix impinges on the vane, it splits over the two sides of the vane; the splitted vortices convect downstream following different trajectories to finally merge at the trailing edge [10] where an additional interaction with the SRVs' tip vortex might happen depending on the length of the SRVs [5]. The variation of the flow field due to the deformation of the wake can have an additional upstream effect on the propeller inflow, showing unsteady pressure fluctuations with frequencies that depend on the number of SRVs [1].…”