Measurement of noise and its correlation to performance and geometry of small aircraft propellers

Abstract

Abstract.A set of small model and UAV propellers is measured both in terms of aerodynamic performance and acoustic noise under static conditions. Apart from obvious correlation of noise to tip speed and propeller diameter the influence of blade pitch, blade pitch distribution, efficiency and shape of the blade is sought. Using the measured performance data a computational model for calculation of aerodynamic noise of propellers will be validated. The range of selected propellers include both propellers designed for nearly static conditions and propellers that are running at highly offdesign conditions, which allows to investigate i.e. the effect of blade stall on both noise level and performance results.

Integration of acoustic compliance and noise mitigation in path planning for drones in human–robot collaborative environments

“…Instead, a combination of active and passive mitigation strategies and hearing protection gear (e.g., ear muffs/plugs) have been found to be most feasible. Among these are attempts to tweak propeller dimensions (Molland et al, 2014; Tinney and Sirohi, 2018), propeller geometry (Štorch et al, 2016; Demoret and Wisniewski, 2019), number of propeller blades (Metzger, 1995), or the use of additional propeller ducts (Oleson and Patrick, 1988) and Helmholtz-resonator-based metasurfaces (Zhao et al, 2017) to reduce the generated noise. In the active domain, active noise cancellation (ANC) techniques (Miljković, 2018; Leventhall and Wong, 1988) have been adopted using complex electronic hardware to counter the UAV’s propeller noise output.…”

Experimental assessment of aerodynamic and aeroacoustic interaction effects of wingtip-mounted propellers

“…On the other hand, the broadband noise (Figure 10), more challenging to model and control than the BPF tonal noise, has a component that behaves as an acoustic dipole that is related to the vortex shedding at different periodicities on the trailing edge of the blades according to the speed and thickness in each radial position. Another component of the propeller's broadband noise behaves like an acoustic quadrupole and is related to the turbulence produced in the shear layer between the propeller stream tube and the surrounding air (KURTZ; MARTE, 1970;SMITH, 1989;ŠTORCH et al, Figure 9 -Sources of propeller and rotor aerodynamic noise. Source: Adapted from Kurtz and Marte (1970).…”

“…2016). Furthermore, conditions such as non-uniformity or inclination of the inflow about the propeller disk are also significant sources of noise (KURTZ; MARTE, 1970;SMITH, 1989;ŠTORCH et al, 2016). The theoretical patterns of directivity (polar distribution of acoustic energy) for each of these noise sources are shown in Figure 11.…”

“…Propeller noise results from a complex combination of different aeroacoustic mechanisms (Figure 9), each with specific sound characteristics regarding spectral content and directivity pattern (KURTZ; MARTE, 1970;ZORUMSKI;WEIR, 1986). The periodic displacement of air caused by the rotation of the blades gives rise to the tonal peaks at the blade passing frequency (BPF) and its harmonics observed in the propellers sound spectra (Figure 10) (SMITH, 1989;ŠTORCH et al, 2016). The intensity of these tonal peaks, which have acoustic monopole (thickness noise) and dipole (loading noise) characteristics, is directly related to the blade loading condition and grows with the propeller rotational speed, with the tip speed (related to the diameter and rotational speed), with the pitch angle and with blade thickness (KURTZ; MARTE, 1970;SMITH, 1989;ŠTORCH et al, 2016).…”

“…Thus, understanding the relationship between traditional performance metrics (such as thrust and torque coefficients and efficiency) and noise generation metrics is paramount to making UAM aircraft viable. Ingraham, Gray and Lopes (2019) emphasize that the availability of design tools that allow engineers to evaluate this trade-off between aeropropulsive performance and reduced noise emission is a current need since more efficient propellers from a propulsive point of view tend to produce more noise (ŠTORCH et al, 2016). These tools, however, need experimental validation for their outputs to be of practical use.…”