The dynamics and timescales of static stall

Airfoil stall plays a central role in the design of safe and efficient lifting surfaces. We typically distinguish between static dynamic based on unsteady rate change an airfoil’s angle attack. Despite somewhat misleading denotation, force flow development airfoil undergoing are highly boundary with is not clearly defined. experimentally investigate forces acting two-dimensional that subjected to two manoeuvres leading stall: slow continuous increase attack reduced pitch 1.3 × 10?4 step-wise from 14.2°to 14.8°within 0.04 convective times. systematically quantify reaction delay, or timespan moment blade exceeds its critical onset stall, for many repetitions these manoeuvres. The marked by distinct drop lift coefficient. delay ramp-up manoeuvre influenced kinematics occurrence histogram normally distributed around 32 compared delays motions rates ranging 9 0.14 sinusoidal pitching different airfoils at higher Reynolds numbers up 1 106. all conditions follow same power law decrease times most steady case down asymptotic value 3 above 0.04. Static phenomenologically than merely typical low where separation promoted kinematics. Based our results, we suggest conventional measurements load curves should be conducted using uniform motion frequency 10?4.