Domestic lawn mower blade noise and influence of machine geometry

Martin, Nathanael John (2013) Domestic lawn mower blade noise and influence of machine geometry. [USQ Project]

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Abstract

It is commonly held in domestic lawn mower noise control literature that under-deck noise sources are a major contributor to the total machine noise. Although disparity exists among authors a resounding theme is that these noise sources are due solely to blade motion. In this thesis I develop a concise argument for the importance of reducing this source, investigate previous efforts for redressing the problem, and develop quantitative experimental procedures and numerical investigations. These analyses identify the influence blade and machine geometries play in noise control for a particular machine and somewhat isolate noise sources and their relative dominant frequencies. The results show structural vibration is a dominant source at low frequencies and possess resonance at 50 Hz intervals through to 500 Hz. Higher frequencies (>500 Hz) are attributable to the aerodynamic noise of the blades and do not possess any dominant frequencies to be redressed. Raised blade wings are monotonically noisier with increasing wing angle. Modification to the blade tip and trailing edge produce a 2.6 dB(A) reduction in noise from the standard blade by reducing tip vortices, validated by CFX analyses, with little reduction to the machines catching function. While this reduction is encouraging the benefits are lost when the machine is used for cutting. To cut grass produces a sound pressure level at least 8 dB(A) higher than the machine noise at idle. The key implication being the strongest noise level produced arises from cutting, eroding the value of mitigating blade induced noise. Moreover, being an electric machine to reduce noise at idle it can be turned off.


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Item Type: USQ Project
Item Status: Live Archive
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering
Supervisors: Snook, Chris
Date Deposited: 04 Apr 2014 12:10
Last Modified: 09 Apr 2014 04:45
Uncontrolled Keywords: lawn mower; blade noise; influence; machine geometry
Fields of Research : 09 Engineering > 0913 Mechanical Engineering > 091301 Acoustics and Noise Control (excl. Architectural Acoustics)
URI: http://eprints.usq.edu.au/id/eprint/24685

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