Study of Dynamic Stall Vortex Development Using Two-Dimensional Data from the AFDD Oscillating Wing Experiment

摘要

The purpose of this study is to examine the previously unpublished instantaneous pressure data of the Aeroflightdynamics Directorate Two- Dimensional (2D) and Three-Dimensional (3D) Oscillating Wing Experiment to better understand the process of dynamic stall vortex development on the NACA 0015 airfoil. This report presents representative 2D instantaneous pressure data for the upper and lower surfaces of the airfoil at various chordwise locations obtained at specific angles of attack during upstroke and downstroke cycles. Furthermore, the report contains a complete set of plots of instantaneous pressure distributions for the upper surface for all the 2D data sets obtained in the experiment. First, the lift, drag and pitching moment data of various testing conditions are reviewed and analyzed to classify the data both with and without a boundary layer trip into 'no stall,' 'moderate stall,' and 'deep stall' data. Next, instantaneous pressure distributions on the upper surface of the airfoil are examined for the study of vortex development. The lift and pitching moment data are analyzed to document the dynamic overshoot which delays the development of the stall on the airfoil. Next, the range of angles of attack are selected where the lift and pitching moment data shows significant changes from unsteady flow behavior daring oscillation cycles. Furthermore, based on the unsteady flow characteristics found in each classification of dynamic stall, analysis is continued to identify the conditions where the reduced frequency clearly affects the unsteady flow behavior of the airfoil during the oscillation. This can result in a change of the dynamic stall classification of the airfoil response under various unsteady flow conditions. These conditions are discussed in detail in the comparative studies.