Aerodynamic Characteristics of Truncated Airfoils at High Angle of Attack

Thick airfoils are commonly used for wind turbine and propeller blade inboard sections, and for struts on aircraft. These airfoils are sometimes truncated for manufacturing convenience, or to save weight. The purpose of this investigation was to study the effects of systematic truncation on airfoil performance. In order to investigate these effects two basic airfoil shapes representative of wind turbine designs were tested: the NACA 23024 and the NACA 64₃-621. The trailing edges of the models were truncated in steps up to the maximum thickness point. Aerodynamic forces and pitching moments were measured for angles of attack from -10° to 90° for each truncated model. Wind tunnel tests were conducted in the Wichita State University 2.13m × 3.05m (7′ × 10′) Walter Beech Memorial Wind Tunnel, using constant chord reflection plane models. Tests were conducted at a nominal dynamic pressure of 718 Pa (15 psf), which corresponds to a Mach number of 0.10 and a Reynolds number of 0.65 × 10⁶ based on the full airfoil chord.

Test results show relatively small changes in the aerodynamic force and moment coefficients for chord reductions up to 10%. For larger chord reductions, stalling angle and C_LMAX values increase dramatically. C_D shows large increases, as expected. C_M changes are related to changes in camber associated with trailing edge truncation. For high angles of attack, the aerodynamic center moves aft for all configurations, an expected consequence of separation. Changes in C_N, normal force coefficient, are similar to changes in lift. C_S, leading-edge suction force coefficient shows surprisingly small change for moderate truncation. These results have important implications for rotor and strut design.