LAUNCH VEHICLE BUFFETING WITH AEROELASTIC COUPLING EFFECTS

Launch vehicle structural responses can couple with transonic flow state transitions at the nose of payload fairings. This self-sustained coupling yields a nonlinear equation of motion that can be analyzed using the force–response relationship and the periodicity condition. The traditional analysis approach for this phenomenon, however, linearizes the equation of motion by converting the alternating flow forces into an aerodynamic damping term and defines a stability criterion as the response amplitude that yields zero net system damping. This work clarifies the relationship between the present and traditional methods, and compares results and conclusions. The feasibility of modifying a launch vehicle response analysis of buffeting (random pressure fluctuations caused by turbulent flow) to include aeroelastic coupling effects is also explored. The aerodynamic stiffness and damping terms formulated herein are consistent with trends observed in wind-tunnel test data. It is shown, however, that the modified buffet analysis can be inaccurate, particularly when the aeroelastic coupling contribution does not dominate the system response.