Ground Effects and Stability Analysis of Airfoil Accelerated by Electromagnetic Propulsion

Abstract

Aerospace vehicle launched by electromagnetic propulsion is a potential option for future reusable space transportation systems. Complex ground effects and stability issues are induced generally due to the introduction of electromagnetic levitation force. A dynamic model coupled with electromagnetic force and aerodynamic force was established for the two-dimensional wing (NACA0012). Numerical simulations were conducted on the flow characteristics, operational attitude, and aerodynamic characteristics of the wing during the Ma＝0~1.5 acceleration process. It indicates that ground effects can be divided into four stages. In the first stage, subsonic flows are presented on both the upper and lower wing surfaces, and there is basically no oscillation for the attitude and aerodynamic loads of the wing. In the second stage, transonic flow emerges on the upper wing surface, while the flow on the lower wing surface is dominated by a typical variable cross-section transonic flow accompanied by the transition from the choked flow mode to the unchoked one. In the third stage, the upper wing surface maintains transonic flows, while the lower wing surface undergoes choked flows which are fully expanded. In both the second and third stages, the wing attitude and aerodynamic loads oscillate significantly at low frequencies. In the fourth stage, the upper wing surface undergoes supersonic flows, while the lower wing surface maintains choked flows. The wing attitude and aerodynamic loads oscillate slightly at high frequencies. On this basis, the effects of suspension height, suspension stiffness and spacing between suspension magnets on the system stability were explored. It is found that increa-sing the suspension height is beneficial for improving system stability. Increasing the suspension stiffness or spacing between suspension magnets appropriately, while limiting the target speed of electromagnetic propulsion to be less than the critical Mach number of system oscillation divergence, is beneficial for significantly improving system stability.

Keywords

• electromagnetic launch
• ground effect
• elastic system
• choked flow
• stability