Date of Award

5-2017

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Graduate Studies

Committee Chair

Dr. J. Gordon Leishman

First Committee Member

Dr. William Engblom

Second Committee Member

Dr. Tasos Lyrintzis

Abstract

The performance of a coaxial rotor system has been analyzed by establishing a proper basis of comparison between a conventional single rotor and coaxial rotor. An attempt has also been made to better understand the complicated aerodynamic interactions associated with coaxial rotor wakes by using a free-vortex methodology (FVM). The FVM is a Lagrangian-based wake convection methodology, which solves for the evolution of the vortical wake produced by the rotor blades under the influence of an external flow. The extent to which the two rotors interact with each other was found to be highly dependent on the inter-rotor spacing. To this end, parametric variations of inter-rotor spacing were performed to show the effect on performance on each rotor and also as a system. An attempt was made to quantify the effect of aerodynamic interference on the performance of the upper and lower rotor by comparing them to an isolated rotor. It was shown that the equivalent single rotor performs better than the coaxial rotor at moderately high advance ratios, while the coaxial rotor performs better in hover. The inter-rotor spacing profoundly affected the performance of the coaxial rotor system, giving higher power requirements at lower inter-rotor spacing. Finally, it was shown that the upper rotor becomes affected by the lower rotor in hover, and while this was an expected result in hover and low advance ratios, the performance of the upper rotor was also affected at higher advance ratios.

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