Abstract

Finite-state models are useful tools in modeling the aerodynamics of rotorcraft in flight simulators. 2-D and 3-D finite-state models have been developed and compared to closed form solutions, however these models are currently unable to handle situations where the freestream changes directions and the rotor re-enters its own wake. A 2-D finite state model was previously developed that includes a parameter that accounts for the change in free stream. This model, however, contains an inherent stability issue at the instant that the velocity changes direction.

The effects of this instability can be mitigated in certain flow conditions. A purely oscillatory free-stream will go unstable upon wake reentry, as predicted by Robert Loewy. Other free-stream conditions which include periods of constant flow direction are able to stabilize and model the effects of repeated wake re-entries. There are other parameters of the flow that also have an impact on the stability such as the angle of attack and the reduced frequency. The angle of attack is responsible for generating the initial segment of vorticity as well as any other vorticity segments while the reduced frequency affects how long or short actions develop.

The 2-D finite state model presented in this thesis is shown to remain stable for “likely” flow conditions where the model craft oscillates its flow direction for single to few oscillations. This behavior is more likely to represent flight conditions where a rotorcraft makes a transient maneuver to avoid a single to few obstacles.

Committee Chair

David Peters

Committee Members

Philip Bayly, Swami Karunamoorthy

Degree

Master of Science (MS)

Author's Department

Mechanical Engineering & Materials Science

Author's School

McKelvey School of Engineering

Document Type

Thesis

Date of Award

5-2026

Language

English (en)

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