Ph.D Thesis

Ph.D StudentWilson Erich Andrew
SubjectCompressible Flow and Thrust-Vectoring Nozzle Performance
DepartmentDepartment of Mechanical Engineering
Supervisors PROFESSOR EMERITUS Dan Adler


Thrust-vectoring flight control is a leading-edge technology now being implemented in production aircraft such as the F-22 and Su-37. It significantly increases aircraft maneuverability and capability through enabling the use of jet-deflection as an alternative to conventional aircraft flight control. Analytical modeling of thrust-vectoring nozzles is at best fragmentary in the open literature. For robust nozzle modeling not only the internal fluid mechanics need to be considered, but the dynamic geometry of the nozzle as well as the influence on the forces obtained from the jet by the flight velocity and angle of attack of the aircraft. With the fervent research into vertical flight capabilities as in the Joint Strike Fighter program, among other aircraft, the influence of the ground effect on the jet and hence on nozzle performances must also be considered.

The dynamic geometry of thrust-vectoring nozzles requires the envelope of modern compressible fluid dynamics to be expanded to not only include axisymmetric geometrical variations, but non-axisymmetric geometrical variations in time. Further, there is a real need to analytically model the real flow characteristics in order to explicitly predict the nozzle performances through an analytical model. This work clarifies and outlines the analytical foundation of thrust-vectoring nozzle performances. Here, a dynamic analytical compressible flow model has been developed. The model implements an explicit solution to the combined nonsimple flow of area-change and friction flow. This analytical solution allows the prediction of real losses in compressible flow and the elimination of empirical efficiency constants. This bridges the gap between empirical data and the modeling of the same systems.

Advantages and drawbacks of the developed analytical model are presented and discussed. Further application of the analytical model is possible in thermodynamic jet engine simulations. Here also, performance coefficients can now be explicitly calculated rather than given empirically and improve the robustness of engine performance simulations. This work is relevant to the civil and military fields of aircraft for all types and sizes to improve flight control, safety and maneuverability. Applications vary from near-term fighter aircraft emulating vertical or short takeoff and landing capabilities to future civilian transport jets for enhancing flight safety and aircraft performance. Thrust vectoring can also help to reduce, or to eliminate, the vertical tail and thus decrease signatures, fuel consumption and/or fleet operating costs.