טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSahoo Devabrata
SubjectUnsteady Supersonic Flow Over Spiked Blunt Body
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Jacob Cohen


Abstract

Blunt nose shapes such as flat-face, hemisphere and ellipse are of utmost 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 cause flow instabilities and be detrimental to 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 future.

In the present research, three different forebody shapes (flat-face, hemisphere and ellipse) 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 (Proper Orthogonal Decomposition, POD and Dynamic Mode Decomposition, DMD) and numerical simulations. Finally, following the gained knowledge of the present study, one example of unsteadiness alleviation has been demonstrated.

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