Vortex-induced vibration of a heavy-lift launch vehicle during transonic flight

摘要

The Titan IV, like many other heavy-lift launch vehicles, is composed of three bodies. At Mach 1.1, 17-Hz pressure oscillations have been observed on the Titan IV center body. The associated lateral structural responses often exceed in amplitude those for all other flight events. Computational fluid dynamic (CFD) simulations conducted for the Titan IV show that pairs of vortices are shed due to strong crossflow acceleration towards the center body, and that these vortex pairs form periodically on alternate sides of the launch vehicle. The phenomenon is analogous to von Karman vortex shedding over a cylinder, with Strouhal number 0.14-0.17. The CFD simulations were used to generate forcing functions for structural dynamic analyses. The resulting structural responses are in good agreement with transonic flight measurements. The structural dynamic analyses also show that the degree of alignment of the aerodynamic force amplitudes with the mission-specific structural mode shapes has a strong effect on the flight responses.