The aerodynamics of a chined forebody

Abstract

A low-speed experimental study of the effects of angle of attack on the flowfield of a chined forebody has been performed. These tests were conducted in the University of Illinois low speed wind tunnel, and in the Boeing Shear Flow Facility. The high fidelity, NC machined aluminum model was sting mounted and positioned in pitch from 0° to 52° angle of attack (a) without sideslip. The effects of Reynolds number (Rj) were also investigated by running a range of tunnel velocities. Reynolds number, based on the 3-inch base width of the forebody, was varied from 1.4xl0 to 2.8xl0. Surface pressures were measured at all conditions using an array of 91 static pressure taps. Normal force and pitching moment were measured by an internal strain gauge balance. Laser Doppler velocimetry (LDV) data and smoke flow visualization were utilized to determine the vortex system. Surface oil flow visualization was utilized to define the surface flowfield and help interpret the surface pressure data. Steady flow visualization revealed the importance of boundary-layer separation on the leeward surface of the chined forebody. Primary separation was caused by the sharp chine edge, and resulted in the formation of large primary vortices. Secondary separation was caused by a steep spanwise surface pressure gradient between the chine edge and the suction peak associated with the primary vortex. This secondary separation resulted in the formation of small secondary vortices. This separation and vortex formation drove the aerodynamics of the chined forebody.