Date of Award

Fall 2022

Access Type

Thesis - Open Access

Degree Name

Master of Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Ebenezer Gnanamanickam

First Committee Member

J. Gordon Leishman

Second Committee Member

Anastasios Lyrintzis

College Dean

James W. Gregory

Abstract

The airwake of a model Simple Frigate Shape 2 (SFS2) was studied in a low-speed wind tunnel. This airwake was measured using a novel time-dependent, dual plane, stereoscopic particle image velocimetry approach. Two flow planes over the flight deck, one parallel and one perpendicular to the free-stream were simultaneously measured. Measurements were carried out over four such pairs of streamwise-spanwise plane combinations. Additionally, the airwake with and without a simulated atmospheric boundary layer (sABL) was studied. The synchronicity of the measurements were taken advantage of to carry out conditional averages of the flow field to isolate and study certain flow events (and its footprint) within the airwake. Those flow events that are likely relevant to rotorcraft operations in the vicinity of ships were chosen to carry out this conditional analysis.

Conditionally averaged statistics of the large vertical fluctuations in the shear layer over the flight deck revealed sharp velocity gradients as well as large-scale flow features above and over large portions of the deck. The fields conditioned on large positive vertical fluctuations were opposite in sign (or the mirror) of those with large negative vertical fluctuations, pointing to a temporal symmetry associated with the oscillation of the shear layer. The flow scenario with the sABL showed similar turbulence levels with almost identical flow structures. An examination of the two stable flow states of the hangar door wake, based on conditional statistics, revealed that each state influenced nearly the entire flow field. Additionally, the mean temporal and spatial evolution of the airwake as the flow transitions between these two states was established. In the case of the flow with the sABL, both flow states persisted for shorter time periods. Overall this study strengthened the growing body of evidence that points to the airwake being a flow field that is a coupled or encapsulating flow structures that are interacting.

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