Extension of a helicopter aerodynamics model by unsteady stall effects

Abstract

Presently a comprehensive simulation program for the aeromechanics of helicopters named VAST - Versatile Aeromechanics Simulation Tool - is being developed by the Institute of Flight Systems of DLR. This work aims to include the indicial response model to compute the 2D airfoil lift, pitching moment, and chord force for rotor air loads prediction in VAST. Leishman and Crouse developed the state-space formulation for Leishman and Beddoe's indicial response method. The state-space formulation accounts for the attached and separated flow and respective circulatory and non-circulatory loading effects. Non-linear effects produced due to the Trailing Edge Separation (TES) are accounted by modifying the Kirchhoff flow. The onset of the Leading Edge Separation (LES) or Shock-induced separation was denoted by a generalized criterion. However, the VAST model uses two extra states. One to track the non-dimensional vortex travel time and another for the track direction of airfoil pitching. To get the progressive transition from the vortex lift strength accumulation and exponential decay. The results are validated with experimental data and the Leishman-Crouse model data for stall onset, moderate and deep dynamic stall conditions from Leishman-Crouse, and a reasonable to a good agreement was found.