Effect on the drag coefficient of various spiked cylinders during buzz phenomenon subjected to hypersonic flows
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(2020) 42:288
TECHNICAL PAPER
Effect on the drag coefficient of various spiked cylinders during buzz phenomenon subjected to hypersonic flows R. Rajesh1 · S. G. Rakesh1 Received: 20 May 2019 / Accepted: 3 May 2020 © The Brazilian Society of Mechanical Sciences and Engineering 2020
Abstract Pulsation mode of transient flow behavior may occur in a violent manner in case of spiked cylinders depending on the geometry, type of spikes, and free stream conditions. Drastic pressure fluctuations near the face of the afterbody have been observed in most cases of pulsating flow mode and thus resulting in drastic variations in the coefficient of drag of the spiked body. The transient analysis of variations in Cd with spike length for various spiked cylinders have been carried out in the current work. The variations in Cd during one complete cycle as well as variations in time-averaged value of Cd with increase in L/D ratios have been analyzed. These variations have been explained with respect to the localized pressure fluctuations, shift in foreshock–aftershock interaction region, effect of effective shielding, and increasing spike lengths. It was found that aerodisk spiked cylinder had the least time-averaged Cd. The Cd for various other spiked bodies has also been summarized over a range of feasible spike lengths and an optimum design of the spiked body in terms of the spike shape and L/D has also been suggested. Keywords Buzz · Pulsation · Transient · Unsteady · Spike · Drag · Conical · Hemispherical · Blunt · Aerodisk
1 Introduction A reduction in aerodynamic drag and surface heat transfer rate was observed when spikes were used upstream of the main body, as reported by Anderson [1]. Either steady or unsteady flow behavior was observed depending on the spiked body geometry and the free stream conditions of the medium in which the body is in relative motion. In case of spiked bodies, the transient phenomenon (unsteady flow phenomenon) called ‘buzz’ occurs in two modes, namely: pulsation and oscillation. Periodical inflation and collapsing of the outer shock envelope have been observed in case of pulsations in the study conducted by Feszty et al. [2]. A fluctuation between convex and concave shape of the outer Technical Editor: Daniel Onofre de Almeida Cruz, D.Sc. * R. Rajesh [email protected] S. G. Rakesh [email protected] 1
Department of Mechanical Engineering, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Bengaluru, India
shock envelope is the main characteristic of the oscillation flow mode which appears in a comparatively less violent manner when compared to the pulsation flow mode which was reported by Feszty et al. [3]. The structural stability of the spiked body may be compromised, when they experience these high frequency Buzz phenomena [2]. A reduction in drag and maximum heat flux has been reported by Crawford [4] when a sharp spiked body was subjected to hypersonic flow of Mach 6.8. Few initial observations regarding unsteady flow phenomena have been discussed by Mair [5], wh
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