Investigation of supersonic flow over an axisymmetric protuberance
The behavior of a supersonic fluid flow field over an axisymmetric cylindrical body has been simulated using ANSYS Fluent computational fluid dynamics software. The simulated body was altered for successive simulations to incorporate a protuberance interrupting the one dimensional flow along the surface. The effect of introducing this protuberance was investigated for Mach numbers ranging from 1.5 to 5.5 in increments of 0.5. To account for flow characteristics not associated with an infinite wall simulation, the body was modeled as a 2.5 caliber Tangent Ogive nose cone profile leading a cylindrical wall in free stream conditions. Once the initial shock is formed, the flow downstream is investigated for the behavior it exhibits in the presence of a surface protuberance. The surface protuberance will cause the flow to wrap around the curvature of the surface. This abrupt change in direction and redirection results in a separation in the flow structure from the wall, which creates a region known as a recirculation zone. Flow becomes discontinuous due to the turning angle of the surface and therefore detaches and must resume parallel flow farther past the protuberance. Flow reattachment downstream of such an obstacle is determined in this research in order to develop a relationship between flow speed, protuberance geometry and recirculation region length. Pressure distributions along the surface beyond the separation point caused by the protuberance angle were used to find the reattachment length. Each pressure distribution contained a point where the rate of change leveled off from the initial chaotic region following the protuberance apex. These points were considered the beginning of the reattachment region and thus the end of the separation region. Correlations for such behavior as a function of the protuberance length scale and Mach number are developed and discussed. The dominance of the Mach number influence in the reattachment length of the separation region is apparent in the final data analysis, as well as a negative correlation of increasing protuberance height. It is apparent that an increased Mach number results in a longer reattachment length. However, as the aspect ratio of the protuberance increases, the reattachment length decreases.