Evaluation of Preliminary Buffet Forcing Function Development based on Wind-Tunnel Tests of Geometrically-similar Models

摘要

The current state-of-the-art for launch vehicle buffet environment estimation involves wind-tunnel testing of highly-instrumented rigid models followed by data processing of unsteady pressure measurements to estimate the fluctuating aerodynamic loads. The model and instrumentation requirements to accomplish this type of testing are significant. The rigid model, in particular, must be built with relatively high geometric fidelity to approximate the unsteady aerodynamic environments that occur during the flight of the full-scale vehicle. Due to this requirement, several iterative wind-tunnel tests are often required during maturation of the vehicle design. For preliminary buffet load estimation, however, data from previous launch vehicle wind-tunnel tests of geometrically-similar models may be used to provide initial buffet environment estimates before a wind-tunnel test of an appropriate geometric-fidelity model has been conducted. In this paper, two processes in this preliminary buffet estimation method are described: (1) assembly of buffet forcing functions from multiple data sources and (2) scaling of these buffet forcing functions to geometrically-similar components of a target vehicle configuration. The impacts of these development processes on the full-vehicle buffet forcing functions, including their longitudinal distribution along the vehicle, frequency-content at individual stations, and station-to-station coherence, are investigated. Considerations for using these methods to extrapolate wind-tunnel data to geometrically-similar models are discussed.