National Transonic Facility Model and Tunnel Vibrations

Since coming online in 1984, the National Transonic Facility cryogenic wind tunnel at the NASA Langley Research Center has provided unique high Reynolds number testing capability. Although turbulence levels in the tunnel, expressed in terms of percent of dynamic pressure, are typical of other transonic wind tunnels, the significantly increased load levels used to achieve flight Reynolds numbers, in conjunction with the unique structural design requirements for cryogenic operation, have brought forward the issue of model and model support-structure vibrations. This paper reports computational results and experimental measurements documenting aerodynamic and structural dynamics processes involved in such vibrations experienced in the National Transonic Facility. In particular, evidence of local unsteady airloads developed about the model support strut is shown and related to well-documented acoustic features known as Parker modes. Two-dimensional unsteady viscous computations illustrate this model support-structure loading mechanism.

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