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Research Papers: Flows in Complex Systems

Numerical and Experimental Studies of Oscillatory Airflows Induced by Rotation of a Grass-Cutting Blade

[+] Author and Article Information
F. Abbasian

Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, ON, M5B 2K3, Canadafabbasia@ryerson.ca

J. Cao

Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, ON, M5B 2K3, Canadajcao@ryerson.ca

S. D. Yu

Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, ON, M5B 2K3, Canadasyu@ryerson.ca

J. Fluids Eng 130(3), 031104 (Mar 03, 2008) (8 pages) doi:10.1115/1.2842225 History: Received February 03, 2007; Revised July 04, 2007; Published March 03, 2008

Three-dimensional oscillatory airflows induced by a rotating grass-cutting blade in a cylindrical chamber are studied experimentally and numerically in this paper. Experimental pressure results are obtained using a sound pressure transducer and a data acquisition system. The measured pressure data contain background noise and high-frequency sound signals due to the blade vibrations. The background noise is separately measured; its effect on the signal is determined from a spectral subtraction algorithm. A time-accurate finite volume numerical solution to the three-dimensional incompressible unsteady Navier–Stokes equations is also sought using the sliding frame technique and the unstructured tetrahedral mesh. Convergence studies are conducted using various combinations of mesh sizes and time increments to ensure the stability of the numerical scheme. The experimental and numerical pressure results are in good agreement.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

The experimental setup for studying aerodynamics of a lawn care system

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Figure 2

Illustration of experimental setup and coordinate systems

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Figure 3

Measured and calculated pressures versus elapsed time and iterations

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Figure 4

Comparison between the background noise and the noisy signal

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Figure 5

Fast Fourier transform of the experimental data normalized to the blade passing frequency ω0

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Figure 6

Computational model (top right), front view of the model (top left), top view of the associated grid (bottom left), and grid of rotating part (bottom right)

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Figure 7

Illustration of sliding mesh scheme: (a) radial interface only, (b) both radial and axial interfaces, and (c) movement of the radial rotating interface relative to the stationary frame

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Figure 8

Pressures near the largest dip obtained using different meshes

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Figure 9

Pressure obtained using different time increments

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Figure 10

Velocity path lines (m/s) on the blade surface at different angular positions: (a) θ=0 and (b) θ=π∕2

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Figure 11

Velocity vectors (m/s) around the blade from the top view at different angular positions: (a) θ=0 and (b) θ=π∕2

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Figure 12

Calculated pressure with different vertical gaps between the blade tip and the observation spot

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Figure 13

Aerodynamic forces on the blade surface versus blade angular positions

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