Blunt nose shapes such as flat-face, hemisphere and ellipse are of supreme interest among the bodies moving at supersonic speeds due to the need for housing payloads, radar or infrared seekers. This bluntness in the nose shape leads to high drag. One common solution for drag reduction is the use of a spike, a slender rod mounted at the stagnation point. Unfortunately, past studies have reported various types of unsteadiness associated with mounted spikes. These oscillations could be detrimental to the purpose of the spike, flow stability and the vehicle structure itself. The main motivation for the present study is to gain a better understanding of the mechanism involved behind this flow unsteadiness in order to control and alleviate it.
In the present research, three different forebody shapes (flat-face, hemispherical and elliptical) mounted with a sharp tip spike are considered. First, parametric studies have been carried out to investigate the sensitiveness of the spike and forebody geometry on the drag reduction as well as flow unsteadiness. Then, the flow unsteadiness arising over these configurations are captured and differentiated. The mechanism behind the shock related unsteadiness has been proposed qualitatively using time-resolved high-speed shadowgraphs and explained quantitatively using unsteady pressure measurements along with the data based modal decomposition methods and numerical simulations. Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) methods have been used to extract and study the dominant spatio-temporal modes. Finally, one example of unsteadiness alleviation has been demonstrated.
