To support the proposition that the new noise component is the result of indirect combustion noise,we would first like
to demonstrate by numerical simulation that the passage of hot and cold spots through a military-style nozzle(see Fig. 35)
would lead to the generation and radiation of indirect combustion noise. This is the best we can do for now as no
experimentally measured flow and temperature data of the F-22A jets have been published. Since the geometry and
operating conditions of military engines are classified information, we will use a model configuration, a static temperature,
and a static pressure inside the afterburner, based on the best information available. To simplify the problem, we will
assume that the nozzle flow is quasi-one-dimensional. The size and spectrum of hot spots/entropy waves coming out of the afterburner of an F-22 aircraft are unknown and might not have even been measured. For this reason, we will consider two simulations. The first simulation has a single hot spot or an entropy wave pulse entering the upstream end of the computational domain as input.This simulation allows us to demonstrate that the indirect combustion noise generated
consists both fast and slow acoustic waves. The second simulation uses a temperature wave train at a specified frequency as input.These simulations explore the effects of unsteady entropy wave input on indirect combustion noise generation.