Singularity Methods for Modeling Dynamic Stall of Lifting Surfaces

Airfoil flow separation impacts a number of applications including wind and hydrokinetic turbines, gas turbine generators, and bio-inspired micro-aerial vehicles. In order to achieve maximum performance, some devices operate near the edge of flow separation, and others use dynamic flow separation advantageously. Engineers must take in to account the extreme and unsteady loads that result from flow separation. Currently, evaluating these forces requires full Navier-Stokes simulations, with run-times on the order of days. Therefore, there is a need for fast simulation methods to evaluate the forces on lifting surfaces in separated flows and facilitate engineering design.;This work presents a novel unsteady vortex lattice method that takes into account the effects of leading-edge flow separation, with run-times on the order of seconds to minutes. The ability of the method to capture dynamic stall is evaluated for a number of airfoil geometries and kinematics, with comparisons to Navier-Stokes solutions and experimental data. Specifically, we consider two classes of airfoil kinematics: rigid body motions (pitch-up-and-hold, pitch-up-hold-pitch-down); and dynamic trailing edge flap deflections. Results show that our method is accurate for rigid-body motions resulting in single dynamic stall events that exhibit formation and shedding of a large leading-edge vortex. Our model is also able to qualitatively capture trailing edge flap events. Surprisingly, although the model is able to capture these dynamic events, the model performs poorly in steady fully-separated flow scenarios, typically over predicting the lift force.;This work provides a fast engineering design tool for evaluating the forces on airfoils in separated flow. The model is available open-source to the academic and engineering community. It is easily adaptable to different airfoil geometries and kinematics, which makes it broadly useful for a number of applications.