Research on Aeroacoustic Control using Direct Numerical Simulation.

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To establish a technique for the reduction of aerodynamic noise, we investigated a cooperative analysis of flow and sound fields to predict the effect of flow control on the acoustic field. The difficulty is caused by the facts that these two fields have significantly different scales and that the acoustic pressure is some order of magnitude less than that of flow field. In this project, the following approach has been developed. First, the unsteady incompressible Navier-Stokes equations are solved by the Direct Numerical Simulation (DNS) or Large-eddy Simulation (LES) technique to obtain the sound source. Next, the acoustic component is separated from the flow field using the method of Hardin and Pope in the interfacial field. The far-filed sound-pressure is then calculated based on the acoustically approximated equation. The flow fields considered are turbulent round jet and the unsteady flow around a blade. The accuracy for reproducing the sound source by DNS and LES has been improved by introducing the higher-order and consistent finite-difference method. For the acoustic field, the application of the Hardin-Pose's method on the curvilinear coordinate system with higher-order accuracy has been developed. In addition, the mechanism of quasi-streamwise vortices near a flat plate and a numerical experiment of their control were carried out by the DNS.