Noise generation mechanisms in short ducted rotors

Open Access
Author:
Padala, V Santhosh
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 19, 2010
Committee Members:
  • Kenneth Steven Brentner, Thesis Advisor
Keywords:
  • aerodynamic noise
  • ducted rotors
  • unsteady loading response
  • strut wake
  • CFD
Abstract:
Ducted rotors are commonly used in helicopters as a tail rotor and in unmanned air vehicles for improved performance and safety. Proposed fan-craft vehicle designs also have ducted rotors as the primary lifting device. In addition to the conventional fan blades, ducted rotors have additional structural components such as struts and vanes to support the duct. As compared to the open rotor, these structures cause obstructions in the ow eld and hence generate additional noise. Due to the current aircraft noise regulations, it becomes necessary to study the e ects of the additional structural components on the noise generated by the rotor blades. This information will also assist in an optimum design for a quieter ducted rotor. To calculate noise from these additional sources, an unsteady blade loading model is used as input for noise calculations. This model is computationally inexpensive as compared to the full unsteady Navier-Stokes calculations and captures the physics as obtained in the present work. The sources from unsteady loading have been superimposed with the thickness and loading noise sources, in PSU-WOPWOP to obtain the total noise. The current study shows that the noise generation due to the struts and vanes is very important at low Mach numbers and contributes signi cantly to the total rotor noise. Parametric studies that highlight the e ect of the unsteady loading parameters on the noise levels are examined in this thesis