Experimental Study of Controlled Surface Imperfection Effects on Vortex Asymmetry of Conical Bodies at High Angles of Incidence

• Other Authors: Rodriguez, Joseph (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Mechanical engineering
• Online Access: http://purl.flvc.org/fsu/fd/FSU_SUMMER2017_Rodriguez_fsu_0071N_14107

At high angles of attack, asymmetric vortices are formed on the leeward side of flight vehicles with pointed forebodies due to the random surface imperfections near the forebody apex. These vortices induce adverse side forces and yaw moments. The forces generated are too large to be controlled using conventional control surfaces and can result in flight instability and loss of control. Although many studies have reported that random surface imperfections trigger vortex asymmetry, there is a lack of understanding of how these imperfections directly correlate to the varying side force with roll orientation. The present study is aimed at gaining a better insight into the underlying flow physics of vortex asymmetry. This is accomplished by performing flow field measurements using Particle Image Velocimetry and force measurements using a six-component strain gage balance on an unpolished and a highly-polished 12° semi-apex angle cone at subsonic speeds. Measurements were carried out with and without the implementation of controlled surface imperfections. All experiments were performed at a fixed Reynolds number of 0.3 × 10^6 based on the base diameter of the cone model. The force measurements indicate that the vortices caused by the random surface imperfections are highly dependent on the magnitude of surface roughness. The results show that the side force was significantly reduced and was relatively less dependent on roll orientation for the polished cone. Flow field results show that the ratio of imperfection height to the local cross-flow boundary layer thickness was observed to be critical in influencing the vortex location and growth. Furthermore, the region of incipient boundary layer separation was highly sensitive to the controlled imperfections. === A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. === Summer Semester 2017. === July 14, 2017. === Thermal Fluids === Includes bibliographical references. === Rajan Kumar, Professor Directing Dissertation; William S. Oates, Committee Member; Kourosh Shoele, Committee Member.