Noise produced by aerodynamic interaction between a circular cylinder (rod) and an airfoil in a tandem arrangement is investigated numerically using incompressible large eddy simulations. Quasi-periodic shedding from the rod and the resulting wake impinges on the airfoil to produce unsteady loads on the two geometries. These unsteady loads act as sources of aerodynamic sound and the sound radiates to the far-field with a dipole directivity. The airfoil is set at zero angle of attack for the simulations and the Reynolds number based on the rod diameter is Red = 48 K. Comparisons with experimental measurements are made for (a) mean and root mean square surface pressure on the rod, (b) profiles of mean and root mean square streamwise velocity in the rod wake, (c) velocity spectra in the near field, and (d) far-field pressure spectra. Curle’s acoustic analogy is used with the airfoil surface pressure data from the simulations to predict the far-field sound. An improved correction based on observed spanwise coherence is used to account for the difference in span lengths between the experiments and the simulations. Good agreement with data is observed for the near-field aerodynamics and the far-field sound predictions. The straight leading edge airfoil is then replaced with a test airfoil with a serrated leading edge geometry while maintaining the mean chord. This new configuration is also analyzed numerically and found to give a substantial reduction in the far-field noise spectra in the mid- to high-frequency range. Source diagnostics show that the serrations reduce unsteady loading on the airfoil, reduce coherence along the span, and increase spanwise phase variation, all of which contribute to noise reduction.
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This content will become publicly available on November 1, 2024
Effects of Spanwise Spacing on the Interaction of Tandem Pitching Hydrofoils
The interaction between a pair of tandem in-line oscillating hydrofoils is presented. The hydrofoils undergo sinusoidal pitching about their leading edges with a fixed Strouhal number of [Formula: see text] and a Reynolds number of 10,000. The streamwise spacing, spanwise spacing, and phase offset between the hydrofoils are varied. Force measurements are employed to investigate changes in thrust, lift, spanwise force, power consumption, and propulsive efficiency. A method to mitigate confounding factors from connecting rod drag is employed using streamlined fairings. Near and far streamwise spacing regions are identified with a transition occurring near 0.875 chord lengths downstream. Decreasing streamwise spacing in the far region causes a rise in the maximum power consumption of the follower hydrofoil. Decreasing streamwise spacing in the near region results in an opposite trend, with a sharp drop in maximum average power consumption by the follower. An empirical model for power consumption of the follower is developed. Increased spanwise spacing is found to weaken the interaction between the hydrofoils, driving them toward their isolated performance. This phenomenon is related to the spanwise contraction of the wake shed by the leader and is a function of the overlap of the wake region impacting the follower.
more » « less- Award ID(s):
- 1653181
- NSF-PAR ID:
- 10481579
- Publisher / Repository:
- AIAA
- Date Published:
- Journal Name:
- AIAA Journal
- Volume:
- 61
- Issue:
- 11
- ISSN:
- 0001-1452
- Page Range / eLocation ID:
- 5121 to 5131
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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