A study of the lift, drag, and pitching moment characteristics of wings of low aspect ratio operating at low Reynolds numbers is presented. Wind-tunnel tests of wings with aspect ratios between 0.5 and 2.0, four distinct planforms (rectangular, Zimmerman, inverse Zimmerman, and elliptical), thickness-to-chord ratios of 2%, and 5-to-1 elliptical leading edges have been conducted as part of this research. The Reynolds numbers considered were in the range of 7 x 104 to 2 x 105. The angle of attack was varied from alpha = -10 deg to either alpha = 40 deg (aspect ratio >= 1,50) or alpha =50 deg (aspect ratio <= 1,25). The comparison of lift-curve slope, nonlinear equation approximations, maximum lift coefficient, and center of lift shows: 1) Wings of aspect ratio below 1.25 have highly nonlinear lift curves that are characterized by high values of alpha (CL, max) (angle of attack at maximum lift) and non-constant lift-curve slopes. 2) Above an aspect ratio of 1.25, most of the planforms exhibit lift curves that are more linear. As predicted by theory, the higher the aspect ratio, the more linear the relationship between lift and angle of attack. 3) For aspect ratios below 1.00 a performance advantage is seen for the rectangular, inverse Zimmerman, and elliptical planforms over the Zimmerman planform at angles of attack greater than 15 deg. 4) Above an aspect ratio of 1.50, the difference between planforms becomes less clear. For the higher aspect ratios, the elliptical planform is seen to be more efficient (higher lift with lower drag) than the other planforms. This observation is an indication that as the aspect ratio increases, classical aerodynamic theories become effective, especially in terms of the higher efficiency of elliptical planforms. 5) Aspect ratio is by far the most important parameter affecting the aerodynamic characteristics of LAR wings at low Reynolds number. Wing planform is the next most important factor, followed by Reynolds number. 6) The low thickness-to-chord ratio is expected to be responsible for the observed absence of hysteresis. Additional analysis of the aerodynamic data revealed that analytical expressions for the lift-curve slope (Prandtl's lifting line theory and equations suggested by Lowry and Polhamus (NACA TN 3911, 1957) and Hoerner and Borst (Hoerner Fluid Dynamics, Brick Town, NJ, 1965, Chap. 7)) are not very accurate over the entire range of aspect ratios and planforms. Nonlinear equations for lift, drag and moment coefficient, proposed by Polhamus and Lamar, model the experimental data quite well if optimum parameter values are used.


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    Title :

    Low-aspect-ratio wing aerodynamics at low Reynolds numbers


    Additional title:

    Aerodynamik von Tragflächen mit kleinem Seitenverhältnis bei kleinen Reynoldszahlen


    Contributors:

    Published in:

    AIAA Journal ; 42 , 5 ; 865-873


    Publication date :

    2004


    Size :

    9 Seiten, 21 Bilder, 1 Tabelle, 30 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English