Term of Award

Summer 2023

Degree Name

Master of Science, Mechanical Engineering

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Mechanical Engineering

Committee Chair

Marcel Ilie

Committee Member 1

Valentin Soloiu

Committee Member 2

Mosfequr Rahman

Abstract

As the world becomes more environmentally conscious, noise pollution is of increasing concern. In this study, shallow dimples are applied to a NACA 0012 airfoil at multiple angles of attack (AoA) with the intent of reducing aeroacoustic noise emissions. Both Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) models are used for aerodynamic and aeroacoustic investigations, respectively, at a fixed Reynolds number of 4.8 x 105. Altering the dimple depth to diameter ratio (d/D) from 2.5% to 15% is first investigated, with a d/D of 5% or lower resulting in the least aerodynamic impact. The transition from shallow dimples to dimpled vortex generators is also found to occur at a 7.5% d/D, as defined by differing flow structures. An aeroacoustic analysis shows a 3.3% d/D ratio is optimal for a 5.71 dB Overall Averaged Sound Pressure Level (OASPL) reduction with a 2.66% average drag increase. A staggered array of dimples with this depth covering the latter 20%, 33% and 50% X/c is then investigated. Far-field noise characteristics are reduced up to 7 dB, with broadband noises below 3000 Hz showing the most improvement. The shallow dimpled array application is found to break up the spanwise coherence, shifting the generated noise towards higher frequencies where it can be more easily dissipated. As such, the application of shallow dimples on the latter portion of an airfoil can be considered a potential candidate for passive noise reduction.

Research Data and Supplementary Material

No

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