Special techniques have been developed to carry out aerodynamic testing to investigate phenomena such as flutter and divergence in 1.2m tunnel. Flutter refers to dynamic aeroelastic instability involving interaction between aerodynamic, elastic and inertia forces. Onset of flutter is determined by testing an aeroelastically scaled and instrumented model under increasing dynamic pressure levels and observing the diverging trend in the fluctuation levels of strain-gauge output signals. Retractable shrouds are used for protecting the model from high transient loads that occur during start and termination of blowdown. In contrast to models used for conventional measurements, wind tunnel models used for aeroelastic testing are fragile. To conduct tests on such fragile models in the 1.2m tunnel special model protection devices were designed and built to enable tests on such models at supersonic speeds. The model protection device is deployed during starting and stopping of the tunnel and it remains in retracted position during steady flow in the tunnels. Figure shows an example of the model protection device used for testing a wall-mounted flutter model at Mach number of 3.3 in the 1.2m tunnel.
Special model protection device deployed for fin flutter testing (a). shows the protection device shielding the model during tunnel starting /stopping, and (b) shows the protection device in related position and the model exposed to free stream.