Nonlinear dynamic characteristics of rotating ramjet rotor supported by hybrid gas bearing

Abstract

The nonlinear dynamic characteristics of rotating ramjet rotor supported by hybrid gas bearing are studied. The compression inlet flow field at different back pressure levels is analyzed and the normal working back pressure level is determined. The periodic movement phenomenon of normal shock wave in compression inlet is presented. The influence on the compression inlet flow field with the variation of structure dimension is introduced. Then, the nonlinear compression inlet flow force generated from the whirling of the rotor is obtained. The model for the rotating ramjet rotor supported by the hybrid gas bearing is established by the finite element method. The equation of motion for the rotating ramjet rotor is numerically solved and coupled with the gas lubricated Reynolds equation considering the time terms. The vibration characteristics of the rotating ramjet with different supply pressure and unbalanced mass eccentricities are solved by the Newmark method. The orbit trajectory diagram, frequency spectrum diagram, and time response diagram are obtained. Then, the stability of the rotating ramjet rotor system is discussed. The results indicate that the compression inlet is under the condition of high adverse pressure gradient, the shock wave, expansion wave, reflections and crossings of the shock waves, boundary layer–shock wave interference, and separation of the flow, which lead to the unstable flow of the compression inlet. The nonlinear compression inlet flow force can cause sub-synchronous vibration. If the supply pressure and eccentricities are properly designed, the vibration amplitudes can be decreased and the stability will be improved, which will make the foundation for the vibration control of the rotating ramjet system.