Numerical Comparison of Dynamic Stall for 2D-Airfoils and an Airfoil Model in the DNW-TWG
A. Klein, K. Richter, A.D. Gardner, A.R.M. Altmikus, Th. Lutz, E. Krämer, 37th European Rotorcraft Forum, September 13-15, Gallarate, Varese - Italy, 2011
The airfoil sections of helicopter rotors experience a wide range of flow conditions in forward flight from transonic flow on the advancing blade to subsonic flow and high angles of attack on the retreating blade. Most notably, the dynamic stall phenomenon has been a research topic for decades and various models have been introduced to predict the unsteady characteristics of the rotor blade undergoing unsteady separation. The objective of the present paper is to compare 2D dynamic stall computations, suitable for airfoil design studies considering unsteady characteristics, with wind tunnel environment CFD simulations taking into account three-dimensionality and wall effects. Differences between experiment and 2D computations can be partly attributed to side wall effects which alter the effective angle of attack at the mid-section pressure measurement plane. In order to gain more insight into these effects, investigations are presented which show the wind tunnel wall boundary layers and separation effects at the sidewall-airfoil junction.