On Boundary Conditions for Acoustic Computations in Non-Uniform Mean Flows

Abstract

Many acoustic problems involve acoustic wave radiation to the exterior field. A common approach in numerical simulations is to restrict the computational domain to a finite region with artificial boundaries. The so-called radiation or non-reflecting boundary conditions must be imposed at those artificial boundaries. Most existing non-reflecting boundary conditions are derived for computing disturbances propagating in a known uniform mean flow near the boundaries. In many applications such as the computation of jet noise or turbofan noise, the mean flow at an artificial boundary is non-uniform and unknown. The mean flow also needs to be computed in these cases. Incorrect computation of this mean flow at the boundary could directly affect the near field physics as well as the far field acoustics. In the present paper, a set of boundary conditions is proposed which focuses on computing the correct mean solution at an artificial boundary, while still maintaining the non-reflecting feature for the outgoing transient and acoustic waves.

The separation of radiating and non-radiating near-field pressure fluctuations in supersonic jets

“…In the current numerical studies, Dong's modified radiation boundary condition [23] is imposed at the radial and downstream boundaries. Total pressures and total temperatures are specified at the fan and core stream inlets.…”

Improved Block Interface Conditions for Aeroacoustic Problems with Grid Discontinuities

“…(24) and Ei+l j in Eq. (26), and more generally, an analogy between FV discretized equation (21) and FD discretized equation (25). It is noted that, when the grids are not uniform, extra terms associated with (dF/dx)(dS/dx)JS±x2 will remain on the right side of Eq.…”

Piezoelectric Pulsed Microjets

“…Optimized prefactored fourth-order accurate compact finite difference schemes [26] and sixth-order accurate compact filters [27] ensure a high-quality numerical solution for multiscale, multi-physics problems while temporally second-order accurate implicit time stepping [28] brings great savings in computing cost for wall-bounded problems in particular. State-of-the-art nonreflecting boundary conditions are used for far-field and inflow/outflow boundaries [29,30], while characteristic-type boundary conditions are applied on solid walls [31]. Sixth-order accurate explicit Lagrangian interpolation is employed for data exchange between overset grids [32].…”