Development and Validation of an Aeroelastic Ground Wind Loads Analysis Tool for Launch Vehicles

Abstract

An analytical modal response tool was developed to investigate the characteristics of and to estimate static and dynamic launch vehicle responses to ground wind loads (GWL). The motivation of this study was to estimate the magnitude of response of the Ares I-X launch vehicle to ground winds and wind-induced oscillation (WIO) during roll-out and on the pad. This method can be extended to other launch vehicle designs or structures that possess a nearly cylindrical cross-section. Presented in this thesis is an overview of the theory used, a comparison of the theory with wind tunnel data, further investigation of the data to support the assumptions used within the analysis, and a prediction of the full-scale Ares I-X response. Additionally, an analytical investigation is presented that estimates the effect of atmospheric turbulence on WIO response.

Most of the wind tunnel data presented in this report is taken from the GWL Checkout Model tested in the NASA Langley Transonic Dynamics Tunnel (TDT) in April 2007. The objective of the GWL Checkout Model was to reestablish and evaluate the capability of the facility to conduct GWL testing and to operate the associated equipment. This wind tunnel test was not necessarily intended to predict the full scale Ares vehicle response to GWL; however, it can be used to help validate the newly developed analytical method described in this thesis.

A detailed GWL test incorporating updated vehicle designs and launch pad configurations of the Ares I-X flight test vehicle was also conducted in the TDT during the fall of 2008. This test provides more accurate predictions of the second bending mode response of the Ares I-X, and it models effects of the nearby tower and support structures. The proposed analytical method is also compared to select data from the Ares I-X GWL test; however, it is presented as normalized values to protect the sensitivity of the data.

Results of the proposed analytical method show reasonable correlation to wind tunnel data. Also, this method was the first to determine that second bending mode WIO response was not only possible for the Ares I-X, but will also produce the most critical loads. Finally, an explanation is offered in this thesis regarding discrepancies between wind tunnel and full-scale WIO response data.

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Keywords
Ground Wind Loads, Aeroelasticity, Launch Vehicle, Vortex Shedding
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