On Unsteady Flow Analysis of a Round Spike Blunt Nose Afterbody in Mach 6 Flow

Abstract

An aerospike, in front of a blunt body, has largely been deemed as a key passive control device for effectively reducing the wave drag and aerodynamic heating associated with high-speed flows. In addition, it has been reported that the presence of a spike brings in unsteadiness in the form of oscillation and pulsation to the flow characteristics. Past researchers, having investigated mainly the aerothermodynamic coefficients, have hinted towards the suppressing of such oscillations with the use of a round nose spike over a sharp spike, though a thorough and a concrete result is yet to be established together with offering a detailed explanation of the flow physics and its dependence on the spike’s geometric characteristics (spike-length to afterbody-diameter ratio, L/D). Numerical investigation has been carried out using axisymmetric Navier-Stokes laminar flow solver at hypersonic Mach number of 6.0. A round-tip spike with a flat face cylindrical afterbody have been simulated for spike length ratios of L/D = 0.5 – 2.0, with spike diameter to-afterbody diameter (d/D) of 0.1. The behavior and subsequent control of flow pulsation for a round (hemispherical) spike with varying L/D-ratio has been established.

Mach Number Dependence of Flow Instability around a Spiked Body

“…Further, the Strouhal number remain almost constant and below 0.2 through out the Mach number change from 4 to 10, while the bow-shock oscillation frequency and amplitude increases. The Strouhal number computed by Vashishtha et al [12] was found to be at 0.25 in free-stream pressure and temperature conditions 253 Pa and 60 K, respectively at Mach 6 flow and spike length of L/D = 2. The bow shock in previous study fluctuates in pulsation mode with frequency of 2.93 kHz.…”

“…1b. The grid size is adopted based on the previous grid independence studies [12,13] performed. The minimum non-dimensional grid spacing near the wall is used here as 1 × 10 −4 .…”

“…Festzy et al [9,10,11] have studied the unsteadiness related to mechanical spike and provided explanation of the same at supersonic and hypersonic regimes. Recently, Vashishtha and Khurana [12,13] assessed the unsteady flow characteristics associated with a spiked body, and their dependence on geometric parameters of spike (including spike length and spike nose tip), and the attached afterbody of different shapes. In addition to the geometric parameters, it is believed that from the perspective of practical applications, the flow speeds (corresponding to the local atmospheric conditions in flight for a aerospike vehicle) could play an important role in the frequency and amplitude of pulsations generated.…”