  A forward-facing aerospike have been identified as a passive flow control
device for enhancing the aerodynamic efficiency and reducing the heat transfer
in 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
structure. Previous researchers have investigated the aerothermodynamic
coefficients, together with offering a detailed explanation of the flow physics
and associated unsteadiness, and their dependence on the spike's geometric
characteristics (spike nose, and length-to-fore-body diameter ratio, L/D). This
work focuses on ascertaining the role of flow speeds (free-stream Mach number),
and their energy content, in governing the physics around a spiked body, which
is yet to be established. Numerical investigation has been carried out using
axisymmetric Navier-Stokes laminar flow solver for Mach number range of 2.0 to
7.0. A round-tip spike with flat-face cylindrical after-body have been
simulated for spike length ratio of L/D = 2.0, with spike diameter to fore-body
diameter of 0.1. The flow unsteadiness has been analyzed with drag and pressure
coefficients variation at different Mach numbers. It was found that the flow
field around the spiked blunt nose behaves in pulsation mode at lower Mach
numbers 2, 3 and transition to oscillatory mode at higher Mach numbers 5, 6 and
7, while remain almost stable at Mach 4. The limit of Strouhal Number for
characterizing the pulsation and oscillation modes at various Mach numbers for
spike length of L/D = 2 with flat after-body is observed as 0.2, however it may
very well depend on other geometric parameters of spike and after-body.
