Direct simulation of duct aeroacoustics using CE/SE method

Subsonic How through duct has been a topic of interest among aeroacoustics researchers. Seldom can the fluid inside the ductworks flow through without encountering any obstructions or restrictions. In reality because of design requirements and space limitations, the flow needs to change direction, thus leading to branching and the necessity to introduce internal guide vanes to smooth transition, bends, and different types of junctions. As a result, devices/elements are introduced into the flow and they will invariably affect the flow structure and behavior inside the air-conditioning and ventilation ductworks. Turbulence is also generated at these duct devices. It is a common goal of the engineering designers that the occurrence of high-pressure amplitude oscillations should be minimized since they are the major sourcc of destructive unsteady loads and noise. Because of high complexity of the sound-flow interaction at duct devices/elements, a direct solution of the duct aero-acoustics is desired for understanding of the relevant flow physics. Owing to the scale disparity between acoustic and unsteady flow disturbances, high-order Pade scheme is needed for duct aero-acoustics simulation using DNS. In addition non-reflecting inlet/outlet buffer regions are required to suppress spurious numerical waves. The buffer region size is usually comparable to the computational domain to ensure satisfactory performance and the computational resources incurred are significant. In the present paper direct numerical simulation scheme for subsonic duct aeroacoustics based on conservation-element/ solution-element (CE/SE) method is developed. The CE/SE method is built with strict conservation within a 'conservation element' spanning in spatial and time dimensions; therefore, the scheme can ensure local and global flux conservation for both in time and space. The generation of the numerical error waves is expected to be less severe and inlet/outlet buffer regions are not required for an accurate solution. Benchmark comparison with DNS solutions will be reported in the present paper to reveal the effectiveness and efficiency of the CE/SE based simulation.