Numerical Comparison of Dynamic Stall for Two-Dimensional Airfoils and an Airfoil Model in the DNW-TWG

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 two-dimensional (2D) dynamic stall computations, suitable for airfoil design studies considering unsteady characteristics, with computational fluid dynamics simulations of the wind tunnel environment taking into account three dimensionality and wall effects. Differences between experiment and 2D computations can be partly attributed to sidewall effects, which alter the effective angle of attack at the midsection pressure measurement plane. 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.