A new model of Crossflow fluid-structure instabilities for helicopter blades

Crossflows that induce fluid-structure instabilities arise in many engineering applications, such as flow over a road bridge or an aircraft wing. At a certain flow speed, an aeroelastic flutter instability is induced arising from the coupled translational and rotational movement of the structure. This instability is modified in a subgroup of these applications that include the additional effect of rotation, e.g., propellers. The structure now experiences a linearly varying effective mean flow (faster near the tip than at the root) and an induced stiffness (via tension) due to the centrifugal force that is also spatially varying. The flutter instability can create vibration fatigue issues and can also create a significant acoustic signature. This paper reports a newlinearised numerical model of the problem that fully couples a finite-difference Euler–Bernoulli beam model to a Theodorsen unsteady lift model that includes these effects of rotation. Comparisons with theoretical predictions in non-rotating flow demonstrate the effect on the trends for the onset of linear instability. The model is then applied to the problem of helicopter blade flutter, and the effects of various strategies for delaying the onset of linear instability are modelled.