Hiroshi Maekawa

Transition of supersonic plane jet due to symmetric/antisymmetric unstable modes

Results from viscous linear stability analysis are presented for plane jets with different convective Mach numbers (Mc). The convective Mach number characterizes the stability modes. It is found that the dominant mode is two-dimensional antisymmetric (A1) for Mc less than 0.8, three-dimensional antisymmetric (A1) for Mc larger than 0.8 and less than 1.5 and two-dimensional symmetric (S2) for Mc larger than 1.5. Two-dimensional spatially developing and three-dimensional temporally developing direct numerical simulations are performed using high-order compact schemes. The flow structures perturbed with various unstable modes and their sound fields are examined. Two-dimensional simulations for Mcu2009=u20091.55 and 1.17 indicate that two-dimensional A1 modes of supersonic phase velocity lead to noise radiation. The results of three-dimensional simulations, for Mcu2009=u20091.17, forced with the most unstable two-dimensional S2 mode, the supersonic two-dimensional A1 mode and a pair of oblique A1 modes show that the steep co...

Application of a High-Resolution Compact Finite Difference Method to Computational Aeroacoustics of Compressible Flows

WCNS is an efficient high-resolution nonlinear scheme for solving flow-fields including discontinuity. In the present paper, a two-dimensional, unsteady, compressible flow field produced by the interaction between a strong planar shock wave and a strong vortex are simulated numerically using WCNS. The simulation shows the effects of the vortex on a planar shock and the production of acoustic waves by the shock-vortex interaction. At the early times of interaction, the shock wave is perturbed by the vortex and a precursor is produced; with the shock wave emerges from the vortex flow field, a Mach structure was generated and the secondary acoustic wave was formed by the interaction of the reflected shock (MR2) with the precursor. Both components of acoustic wave (the precursor and the second sound wave) propagate radially and have a quadrupolar nature. By this simulation, the ability of WCNS for computational aeroacoustic problems is confirmed.Copyright

“Vortex Dynamics“ of a Vortex Ring Introduced into a Laminar Boundary Layer

In the present work, the motion of a single vortex ring introduced in a laminar boundary layer was observed by means of flow visualization. The turbulent flow evolves from the vortex ring depends on the initial configuration of the vortex ring in a laminar boundary layer. The initial evolution process is strongly dependent on the direction of circulation of the vortex ring in the layer. Furthermore, the turbulent region evolves from the primary vortex was investigated using pseudo-synchronized hot-wire measurements. Breakdown of the vortex ring in a laminar boundary layer leads to the high fluctuation velocity fields within the turbulent bloblike structure.

Visualization of the Structures in a Plane Mixing Layer

Direct numerical simulation of time-developing mixing layers has been performed. The structure of the mixing layer is visualized by means of the vorticity contour and passive scalar. Numerical results were compared with the smoke patterns. Mixing layer was generated behind a splitter plate towed in a straight long tunnel. Acoustic forcing was applied to excite the shear layer and also to induce wave resonance in the free shear layer. We found that scalar distributions is similar to smoke pattern in the vortical structure in prior to pairing. This paper describes the structure recognition by visualization technique.