Simultaneous Control of Vortex-Sizes Around Spike Root and Body Base for a Blunt-Nosed Cylindrical Body

Abstract

Forward-facing spike has been identified as a passive flow control technique to render the strong pressure envelope at the nose to become weaker, thereby resulting in reduced pressure over the nose, as a consequence of vortices positioned at the root end, leading to drag reduction. Attention is focused on understanding this aspect of the flow process at low Reynolds number (incompressible flow). It is known that the vortices at the attached end of the spike are responsible for reducing the high-pressure over the nose, leading to drag reduction. In this research, it has been observed that these vortices at the root of the spike would also influence the vortices (wake-expanse) at the base. It would be of great significance for drag reduction if the functional dependence of the size of these vortices (spike-root as well as wake) on spike characteristics can be established. Therefore, in this study, emphasis is focused on ascertaining the simultaneous dependence of the size of the vortices, at the root end of the spike and at the base of the body, on the flow Reynolds number and spike-nose geometry. This had been achieved by visualizing the flow past a blunt-nose body with and without spike at Reynolds number 3170. It is found that there exists a specific length-to-diameter ratio for every spike nose-configuration, resulting in the largest vortex both at the spike base and at body base, leading to significant reduction of drag.