I. A modified k - epsilon turbulence model for high speed jets at elevated temperatures. II. Modeling and a computational study of spliced acoustic liners

A modification to the k - epsilon model aimed to extend its applicability to the computation of the mean flow and noise of high-speed hot jets is proposed. The motivation of the proposal arises from the observation that there is a large density induced increase in the growth rate of spatial instabilities of a mixing layer if the lighter fluid moves faster. This consideration leads to the incorporation of a density gradient related contribution to the turbulent eddy viscosity of the k - epsilon model. Computed jet mean flow profiles and centerline velocity distributions at elevated temperatures of high-speed jets are found to be in better agreement with experimental measurements if density modification is included. Noise predictions including density effect are also found to be in better agreement with microphone measurements. The good agreements offer strong support to the validity and usefulness of the proposed density correction formula.; A time-domain computational methodology has been developed to study the propagation and acoustic scattering of the fan tones by the spliced liners. The front portion of the engine is modelled as a duct. Significant acoustic scattering is observed for a frequency pretty close to cut-off. In this case, total scattered energy was found to be more than the energy in the incident mode. The spliced liners, in such conditions, are found to be less effective than the uniform liners. The performance of the liner was found to be dependent on the frequency. The results of the simulations agree qualitiatively well with the available experimental and theoretical work.