Flutter-a scary instability AAE 556 - Aeroelasticity Flutter-a scary instability small disturbances - big effects Purdue Aeroelasticity

Purdue Aeroelasticity Lockheed Electra - 1959 Purdue Aeroelasticity

Purdue Aeroelasticity Quasi-steady flutter Flutter is a self-excited, dynamic, oscillatory instability requiring the interaction between two different modes of motion and an external energy supply Quasi-steady aerodynamic loads ignore the unsteadiness of the flow created by lags between motion and developing forces and momemts Purdue Aeroelasticity

Purdue Aeroelasticity What we are looking for Purdue Aeroelasticity

Unsteady aerodynamics Purdue Aeroelasticity

Airfoil start-up with vortices Purdue Aeroelasticity

Wagner function - response to a sudden increase in angle of attack Purdue Aeroelasticity

We’ll start with simplified models of the airloads due to motion V lift Purdue Aeroelasticity

Free vibration with quasi-steady loads START divide by FINISH Purdue Aeroelasticity

Purdue Aeroelasticity Warning – algebra!!!! Purdue Aeroelasticity

Define new collections of terms Purdue Aeroelasticity

Aerodynamic loads in terms of displacements Purdue Aeroelasticity

Finally - free vibration with the wind blowing Purdue Aeroelasticity

Solve these equations by assuming a harmonic time solution results after division by eiwt Purdue Aeroelasticity

Combine terms and look for similarity parameters Purdue Aeroelasticity

Purdue Aeroelasticity Define new parameters bw=speed Reduced velocity Purdue Aeroelasticity

Purdue Aeroelasticity Nondimensional parameters called reduced velocity, frequency ratios... Characterize the models and phenomena causing flutter Purdue Aeroelasticity

Non-dimensionalization 1/b 1/b2 Purdue Aeroelasticity

Purdue Aeroelasticity The prize Purdue Aeroelasticity