Date of Award

8-2017

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Graduate Studies

Committee Chair

Dr. Reda Mankbadi

First Committee Member

Dr. Vladimir Golubev

Second Committee Member

Dr. Anastasios Lyrintzis

Abstract

The need arises for developing quiet aircraft and silent Unmanned Aerial Vehicles (UAVs) to minimize the environmental effects as well as for stealth missions. We focus here on attempting to directly predict the noise associated with airframe by considering a single isolated airfoil. Developing an ability to directly predict the radiated noise and how it is generated is a first step for passive or active control of the generated noise. We choose herein a NACA0012 airfoil and specific flow condition to test whether we can directly predict the sound in accordance with the corresponding experimental data identified in the Benchmark Problems for Airframe Noise Computations (BANC, 2016). We implement a high-fidelity large-eddy simulation code initially developed by the U.S. Air Force Research Laboratory. To understand the mechanisms involved and possibly control it, we considered both the case of clean (untripped) airfoil as well as a tripped one.

Our results for flow near the airfoil surface show that our prediction of the boundary layer and turbulence intensities are consistent with that of experimental results. Tripping, while it does modify the initial transition process, has little effect on the flow fluctuations near the trailing edge.

The calculated spectra of the acoustic field as well as its directivity were found to be in close agreement with the experimental data. Tripping had little effect, if any, on the radiated sound. This indicates that, for this case, the dominant noise source is the scattering of the boundary layer fluctuations at the trailing edge. The calculated spectra of the acoustic field as well as its directivity were found to be in close agreement with the experimental data. Tripping had little effect, if any, on the radiated sound. This indicates that, for this case, the dominant noise source is the scattering of the boundary layer fluctuations at the trailing edge.

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