Spanwise Variation in the Unsteady Stalling Flowfields of Two-Dimensional Airfoil Models

Recent investigations of two-dimensional airfoil stalling characteristics have revealed low-frequency and highly unsteady flow in some cases and large-scale three-dimensional structures in other cases. The latter were referred to as stall cells and can form on two-dimensional configurations where the ends of the airfoil model are flush with tunnel side walls or end plates. We present results of detailed investigations of the stalling characteristics of several airfoils that exhibited both low-frequency unsteadiness and large-scale three-dimensional structures. The airfoils were wind-tunnel tested in a two-dimensional configuration. The primary measurements were spanwise wake velocity and mini-tuft flow visualization. The results showed that airfoils with trailing-edge separations at and above maximum lift (static stall) exhibited stall-cell patterns. Conversely, airfoils that had leading-edge separation bubbles that grew in size as the angle of attack was increased into stall developed the low-frequency, highly unsteady flow

[1]  S. J. Kline,et al.  Describing Uncertainties in Single-Sample Experiments , 1953 .

[2]  Andy P. Broeren,et al.  Flowfield Measurements over an Airfoil During Natural Low-Frequency Oscillations near Stall , 1999 .

[3]  Donald E. Gault,et al.  Examples of three representative types of airfoil-section stall at low speed , 1951 .

[4]  Allen Winkelmann Flow field studies behind a wing at low Reynolds numbers , 1990 .

[5]  Andy P. Broeren,et al.  Experiments on airfoils at low reynolds numbers , 1996 .

[6]  J. Barlow,et al.  Flowfield Model for a Rectangular Planform Wing beyond Stall , 1980 .

[7]  Joseph Katz,et al.  Study of the Unsteady Flow Features on a Stalled Wing , 1998 .

[8]  Andy P. Broeren,et al.  An Experimental Study of Unsteady Flow Over Airfoils Near Stall , 2000 .

[9]  Andy P. Broeren,et al.  LOW-FREQUENCY FLOWFIELD UNSTEADINESS DURING AIRFOIL STALL AND THE INFLUENCE OF STALL TYPE , 1998 .

[10]  Andy P. Broeren,et al.  Phase-averaged LDV flowfield measurements about an airfoil in unsteady stall , 1996 .

[11]  Michael B. Bragg,et al.  Low-Frequency Flow Oscillation over Airfoils near Stall , 1993 .

[12]  Hugh W. Coleman,et al.  Experimentation and Uncertainty Analysis for Engineers , 1989 .

[13]  H. L. Seegmiller,et al.  Time-dependent behavior of a reattaching shear layer , 1987 .

[14]  Michael B. Bragg,et al.  Flow oscillation over an airfoil near stall , 1996 .

[15]  Thomas J. Mueller,et al.  Unsteady Stalling Characteristics of Thin Airfoils at Low Reynolds Number , 2001 .

[16]  Christopher L. Rumsey,et al.  A natural low-frequency oscillation of the flow over an airfoil near stalling conditions , 1989, Journal of Fluid Mechanics.