Knowledge Bank

Rectangular twin jet engines used on tactical aircraft have several advantages compared to circular twin jet engines, namely, reducing an aircraft's weight and drag, improving its maneuverability, and integration of propulsion and aerodynamics. However, relatively little research has been done on the flow and acoustic characteristics of rectangular twin jet engines. Coupling between the two jets due to their close proximity introduces unsteady pressure fluctuations in the near field and noise in the far field which, if not controlled, can cause high levels of sonic fatigue as well as intense radiated noise. This can damage critical components close to the nozzles and is a health concern for those nearby. This project will investigate the use of Localized Arc Filament Plasma Actuators (LAFPAs). LAFPAs, controlled electronically, create plasma arcs at the nozzle lip, producing thermal perturbations with desired frequencies in the flow which interrupt the predominant mechanism of jet noise, screech. Additionally, LAFPAs can alter the coupling behavior of the jets. However, due to the complex nature of the flow, it is difficult to predict the behavior of the jets to excitation by LAFPAs. As such, a physics-based empirical model has been developed to predict the response of the flow to certain actuation parameters. To accurately model this response, two important parameters must be determined: the locations of shock cells within the flow and the velocity of the large-scale flow structures convecting downstream within the jet, interacting with the shock waves, and generating screech tones. In this research, a method for empirically predicting streamwise shock locations based solely on flow Mach number is developed. Additionally, a novel method of estimating convective velocity is presented using Empirical Mode Decomposition (EMD) to isolate the hydrodynamic pressure from the measured overall (acoustic and hydrodynamic) pressure just outside the jets.