Bibin John

Performance comparison of flux schemes for numerical simulation of high-speed inviscid flows

Numerical investigations to assess the performance of different flux schemes for the spatial discretisation of the Euler equations have been performed. The schemes employed in the study include flux vector and flux difference splitting schemes as well as hybrid schemes. The schemes are cast in an unstructured high-order finite volume framework and are studied on typical engineering problems in the supersonic and hypersonic regimes. While all the flux schemes perform well in the supersonic and low hypersonic range, their performance show a marked change in the high Mach number regimes. Numerical experiments suggest that the AUSM family of schemes is the most accurate while the Rusanov scheme is the most robust for the range of Mach numbers considered in the study. These studies indicate that a robust and accurate numerical solver for high-speed compressible flows necessitate the use of blended schemes that provide a right balance between accuracy and numerical dissipation.

Effect of Fineness Ratio on Minimum-Drag Shapes in Hypersonic Flows

The importance of fineness ratio in determining the aerodynamic shapes of minimum-drag, zero-lift axisymmetric bodies in inviscid hypersonic flows is investigated using a shape optimization framework. The framework employs modified Newtonian theory for surface pressure computation, Bezier curves for geometric parameterization and a steepest-descent approach for minimization of the wave-drag coefficient. Studies are performed on axisymmetric bodies of a given length for fineness ratios varying from 1 to 6 and Mach numbers ranging from 6 to 12. It is shown that the optimal axisymmetric body for a given freestream Mach number is blunt-nosed for smaller fineness ratios but becomes sharp-nosed at larger fineness ratios. The fineness ratio at which the optimal body of revolution transitions from blunt-nosed to sharp-nosed is found to be nearly constant at hypersonic speeds and is around 3. Results indicate that the optimal bodies derived from the framework are superior in terms of wave drag to the von Karman og...

A reduced MIMO (R-MIMO) system using norm based approach (NBA) for transmit antenna selection (TAS)

For Multiple Input Multiple Output (MIMO) systems, antenna selection is a must since the Radio Frequency (RF) chains connected with antennas consumes a lot of power. This paper studies the effect of antenna selection at transmitter side since the base station power consumption is around 60-80% of the entire wireless system. The TAS is performed by a simple and computationally efficient NBA scheme. The NBA is employed at the receiver side, where channel estimation is performed, and the antenna indices corresponding to the selected transmit antennas are fed back to the transmitting side which in turn result in a considerable decrease in feedback data. It is seen that the reduced MIMO system provide with the same performance as the conventional full MIMO that uses all the antennas.

Hybrid antenna selection at transmitter (HAST) scheme for future broadband wireless system

In this paper, a new adaptive HAST scheme is proposed for Space Frequency Block Coded (SFBC)-Orthogonal Frequency Division Multiplexing (OFDM) system. This HAST scheme uses subcarrier by subcarrier antenna selection. The performance of the proposed scheme is analyzed for different antenna configurations with average Signal to Noise Ratio (SNR) gain and Bit Error Rate (BER) parameters. The simulation results prove that the performance of conventional SFBC-OFDM system is greatly improved with the proposed scheme.

Alterations in Critical Radii of Bluntness of Shock Wave Boundary Layer Interaction

AbstractAny configuration consisting of flat plate attached to a ramp experiences shock wave boundary layer interaction (SWBLI) at supersonic or hypersonic Mach numbers. This interaction can lead t...