Verification of Calculation Procedure for Unsteady Aerodynamic Forces on a Launch Vehicle

Abstract

Unsteady aerodynamic forces on large, slender aerospace structures are established in wind-tunnel tests that employ a limited number of dynamic pressure sensors and use a correlation-based approach that, so far, cannot be directly verified. This paper describes a robust procedure based on frequency-specific correlation lengths, and it provides validation from an experiment on a generic, space vehicle model. The model was coated with unsteady pressure sensitive paint, which provided time histories of pressure fluctuations on a large number of points. At first, the entire dataset was integrated to determine the “true” unsteady forces. In the next step, progressively fewer points were used as “virtual sensors,” and the correlation-based procedure was applied to determine the “modeled” forces. By comparing the time histories and power spectra, it was observed that as few as 16 virtual sensors (four rings, with each containing four sensors and separated by half a diameter) were able to replicate the true fluctuations on a model segment with a reasonable accuracy. The modeled levels were typically higher, and they approached the true levels with an increase in the number of the virtual sensors. The procedure showed better agreement when pressure fluctuations were more coherent over a buffet zone.