Novel mechanism of instability control using tapered spike in hypersonic flow
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A forward facing spiked blunt nose in high-speed flows is associated with pulsating flow behavior of varying amplitudes depending on spike-nose and length, the forebody geometry and flow conditions. A tapered spike has been proposed as a passive device for reducing these instabilities, which are induced in the flow in place by the straight spikes. Numerical investigation has been carried out using unsteady axisymmetric Navier-Stokes laminar flow solver at hypersonic Mach number 6.0. A flat-tip spike in front of a flat-faced cylindrical forebody, have been simulated for spike length to base diameter ratio, L/D of 0.5, 1.0, 1.5 and 2.0. It has been observed that introduction of taper leads to manipulate the root vortices by elongating it along taper length and reducing the size in transverse direction, which can introduce the stability in the flow field. Additionally, increase in taper angle will lead to reduction in the time-averaged drag coefficient in comparison to the straight spike for all the lengths. The pulsations fluctuations abruptly transition to steady flow with increase in taper (half-cone angle) for all the spike lengths except L/D = 0.5. The required half-cone angle to achieve non-pulsating and stationary flow around spike body reduces with increase in spike length. The corresponding Strouhal number for the flow exhibiting pulsating behaviour was observed higher than 0.1 for the current Mach number and operating conditions.
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