Experimental Study of the Flow Around an Axisymmetric Body at High Angles of Attack

摘要

The investigation of the flow field around an axisymmetric body inclined at an angle with respect to the oncoming free stream constitutes a challenging task due to the complex nature of the flow. However, understanding the as yet unanswered question as to what causes flow asymmetries over a symmetric body at high angles of attack would improve the maneuverability of such bodies. In the present work, the flow field about a blunted nose cylinder was studied at various pitch and yaw angles by carrying out pressure measurements, employing oil film and smoke flow visualization techniques. The study was conducted in the subsonic wind tunnel of the Aerodynamics Laboratory of the National Technical University of Athens, Greece. Based on pressure measurements and flow visualization the flow field around a blunted nose cylinder at angles of attack up to 40 degrees and Re=1.85x10(exp 5) had the following characteristics: (a) Flow asymmetries were not systematic, a fact that agrees with the general experience that cylinders with pointed noses are most susceptible to flow asymmetries. (b) Along the circumferential direction there are two pressure plateau, one close to 90 degrees far from the stagnation point generator and the other one at the lee symmetry plane, suggesting the existence of two separation regions. The separation lines do not follow a generator, being closer to the leeside symmetry plane in the nose area and moving far from it in the afterbody. (c) In the longitudinal direction along the leeside symmetry plane, starting from the nose, the pressure is favorable (in the spherical nose surface), then there is a small plateau and next it becomes positive until eventually in the afterbody it becomes level. (d) Keeping the pitch angle constant and increasing the yaw angle, the flow remains symmetric with the only difference being that the axis of symmetry is tilted a certain angle, since it is a function of the yaw and pitch angles. (13 figures, 11 refs.).