Date of Award

Summer 8-2021

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Committee Chair

Dr. Reda Mankbadi

First Committee Member

Dr. William MacKunis

Second Committee Member

Dr. Vladimir Golubev

Third Committee Member

Dr. Tasos Lyrintzis

Abstract

This work analytically and numerically examines the effects of bi-modal excitation on a Mach 1.5 heated planar jet. Starting with the Navier-Stokes equations, triple decomposition is applied to the flow components. A reduced order model is derived, turning the Navier-Stokes partial differential equations into a set of coupled ordinary differential equations, relating the momentum thickness and amplitudes of a fundamental and subharmonic mode to the streamwise location along the jet. Computational fluid dynamics data from the minor plane of a Mach 1.5 heated rectangular jet is used to verify a hyperbolic tangent profile for the mean flow at various streamwise locations. Locallyparallel linear stability theory is used to compute the shape assumptions for the coherent structure components involved in the set of ordinary differential equations. The set of ordinary differential equations is first solved for a single mode. The trends for the single mode excitation qualitatively compared well with previous work. In the initial region, the nonlinear amplitude generally agreed well with the linear solution. Bi-modal excitation is then examined for the fundamental Strouhal number 0.10, which has been identified as a dominant noise source. Cases were considered separately with adding the subharmonic and the harmonic as a means of reducing the amplitude of the fundamental. Adding the subharmonic had minimal effects on reducing the fundamental unless both initial amplitudes are large. However, adding the harmonic could be very effective at reducing the fundamental even at low initial amplitudes. It is ultimately determined that adding the subharmonic may or may not be effective as a noise-reducing mechanism but adding the harmonic can be effective depending on the initial phase difference between the two excitations.

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