Testing Propeller Tip Modifications to Reduce Acoustic Noise Generation on a Quadcopter Propeller

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Kenneth W. Van Treuren ◽  
Charles F. Wisniewski

Abstract If vertical lift vehicles are to operate near population centers, they must be both quiet and efficient. The goal of this research is to develop a propeller that is more efficient and generates less noise than a stock DJI Phantom 2 quadcopter propeller. Reducing the generated tip vortex was the main objective. After studying the literature, seven promising tip treatments were selected and applied to a stock DJI Phantom 2 propeller to reduce the tip vortex. Several different configurations were tested for each tip treatment to determine the rpm and required power to hold 0.7 lbf thrust, the static hover condition. For each test, operating at the hover condition, a radial traverse 1 in. behind the propeller permitted the measurement of the near field sound pressure level (SPL) to find the maximum SPL and its radial location. Several configurations tested resulted in 8–10 dBA reductions in SPL when compared to the stock propeller; however, these configurations also resulted in an unacceptable increase in the power required to achieve the desired thrust. The most promising tip treatment tested was the trailing edge (TE) notch at a radial location of 0.95 r/R with a double slot width and a double depth (DSDD). The DSDD configuration as tested reduced the SPL 7.2 dBA with an increase in power required of only 3.96% over the stock propeller. This tradeoff, while not the largest reduction in noise generation measured, had an acceptable power increase for the decrease in SPL achieved.

2012 ◽  
Vol 217-219 ◽  
pp. 2590-2593 ◽  
Author(s):  
Yu Wang ◽  
Bai Zhou Li

The flow past 3D rigid cavity is a common structure on the surface of the underwater vehicle. The hydrodynamic noise generated by the structure has attracted considerable attention in recent years. Based on LES-Lighthill equivalent sources method, a 3D cavity is analyzed in this paper, when the Mach number is 0.0048. The hydrodynamic noise and the radiated mechanism of 3D cavity are investigated from the correlation between fluctuating pressure and frequency, the near-field sound pressure intensity, and the propagation directivity. It is found that the hydrodynamic noise is supported by the low frequency range, and fluctuating pressure of the trailing-edge is the largest, which is the main dipole source.


Author(s):  
M Reeves ◽  
N Taylor ◽  
C Edwards ◽  
D Williams ◽  
C. H. Buckberry

The out-of-plane surface vibration of a brake disc during naturally excited squeal has been investigated using a combination of high-speed electronic speckle pattern interferometry (ESPI) and near-field sound pressure measurements. Both techniques provide visualization and quantification of the time-resolved surface velocity. A mathematical description of disc brake squeal modal behaviour is proposed that predicts accurately all of the experimentally observed interferometry and sound field measurements. The complex mode description proposed here is in agreement with that proposed by others for drum brake squeal. This assumes that two identical diametral modes are excited simultaneously, identical except for a spatial and temporal phase shift. The use of a near-field microphone array provided a convenient multipoint, non-contacting vibration probe which may find use in the study of other vibrations characterized by high surface amplitudes and efficient sound radiation. The high-speed ESPI provided a real-time visualization of surface deformation analogous to double- pulsed holographic interferometry, with the benefit of giving a true time series of the surface deformation during a single vibration cycle.


2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Derek Kuo ◽  
Y. C. Shiah ◽  
Jin H. Huang

This paper presents a modal analysis and the sound pressure field for the vibrator membrane of an actual portable loudspeaker. Unlike the conventional way to model the membrane’s edge under a simply supported condition, the present approach takes the glued edge to be elastically supported. With theoretical derivations for such treatment, this paper also presents the associated near-field and far-field sound pressures that have not been reported in the open literature. Fundamentally, calculation of the near-field sound pressure solution for the elastically supported membrane has difficulty with numerical convergence. In this paper, integral regularization is employed to enforce the convergence. From the viewpoint of acoustic engineers, the analysis may effectively help to tailor the design of a loudspeaker that caters to consumers’ preference.


Author(s):  
Kenneth Van Treuren ◽  
Charles Wisniewski

Abstract Electric propulsion is gaining popularity with over 100 electrically propelled aircraft in development worldwide. There is a growing interest in vertical lift vehicles either for package delivery or for urban air taxis. If these vehicles are to operate near population centers, they must be both quiet and efficient. The goal of this research is to develop a propeller that is more efficient and generates less noise than a stock DJI Phantom 2 quadcopter propeller. Since a large contribution of near field noise generation for a propeller comes from the tip vortex, reducing or minimizing this generated tip vortex was the main objective. After studying the literature on aircraft wing tip vortices and techniques proposed to minimize the wing tip vortex, seven promising tip treatments were selected and applied to a stock DJI Phantom 2 propeller in an attempt to reduce the tip vortex, and, thus, the generated noise. These tip treatments were: 1. Leading Edge Notch, 2. Trailing Edge Notch, 3. Hole, 4. Vortex Generators, 5. Tip Thread, 6. Trailing Edge Sawtooth, and 7. Reverse Half-Delta. An optimum design would be one that reduces near field noise while at the same time minimizes any additional required power. Several different configurations were tested for each tip treatment to determine the RPM and required power to hold 0.7 lbf thrust, which simulated a static hover condition. For each test, a radial traverse one inch behind the propeller permitted the measurement of the Sound Pressure Level (SPL) to find the maximum SPL and its radial location. Several configurations tested resulted in 8–10 dBA reductions in SPL when compared to the stock propeller, however, these configurations also resulted in an unacceptable increase in the power required to achieve the desired thrust. Thus, in these cases a decrease in SPL comes at the expense of power, a tradeoff that must be considered for any propeller modification. The most promising tip treatment tested was the Trailing Edge Notch at a radial location of 0.95 r/R with a Double Slot width and a Double Depth (DSDD). The DSDD configuration as tested reduced the SPL 7.2 dBA with an increase in power required of only 3.96% over the stock propeller. This tradeoff, while not the largest reduction in noise generation measured, seems to be an acceptable power increase for the decrease in SPL achieved. Smoke visualization confirms that the tip vortex is minimized for this configuration.


Author(s):  
Dragos¸ Moroianu ◽  
Arne Karlsson ◽  
Laszlo Fuchs

An important component of the aircraft generated noise, especially ahead of it, is the fan noise created by the high velocity variation near the blades and the interaction of the rotating fan with the fluid. In order to predict the sound, the method used involves the acoustical analogy developed by Ffowcs Williams and Hawkings. Computation of the flow field is performed in the incompressible LES framework, while the noise is evaluated using a non-homogeneous wave equation. In this work the influence of the angle between the fan and ground, on the total sound spectrum, the noise generation and the noise propagation is investigated. It is found that the near field is dominated by the blade passage frequency and an upward inclination of the fan will produce a slightly different sound pressure level than a horizontal or downward inclination.


Author(s):  
Hossein Mansour ◽  
Siamak Arzanpour ◽  
Hedayat Alghassi ◽  
Mehdi Behzad

This study aims to evaluate the amount of energy transfers through the bridge in Setar, a Persian long-necked lute. Stringed musical instruments are among the most complicated acoustical systems. When the string is plucked, its vibration distributes into the entire vibrating system (i.e. body, string, air enclosure) and produces sound. The resultant sound consists of three parts: the first is the string’s direct sound; the second is that part of sound-box vibration being excited by string’s direct sound, and the third is the part of sound-box vibration being excited by string force passing through bridge. The last part believed to have the major share and the others have minor effect. For this research, a specific fixture has been made and a precise plucking machine is installed to hold and pluck the instrument uniformly. Also, a novel approach is utilized to evaluate the share of each abovementioned part in the output near-field sound produced by Setar.


2015 ◽  
Vol 138 (3) ◽  
pp. 1313-1324 ◽  
Author(s):  
Alan McAlpine ◽  
James Gaffney ◽  
Michael J. Kingan

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