Noise Reduction Using a Direct-Hybrid CFD/CAA Method

A direct-hybrid CFD/CAA method based on lattice Boltzmann and acoustic perturbation equations

“…The noise generating source terms, i.e., the fluctuating Lamb vector for the spinning vortex case and the subsonic cylinder flow, are obtained from the instantaneous flow field and are communicated to the CAA solver. All methods are formulated on hierarchical Cartesian grids, where the coupled solvers share a joint mesh with an independent grid refinement level for each solver as described in [2]. Here, the grid spacing D n for the grid refinement level n is given by D n = D 0 /2 n , where D 0 is a predefined length of the level n = 0.…”

“…This allows for the concurrent execution of both solvers with an in-memory data exchange of the acoustic source terms thus fully avoiding disk I/O. Furthermore, by employing a joint hierarchical Cartesian grid, which is partitioned on a coarse level via a space-filling curve, both solvers are efficiently coupled and parallelized, whereas the use of solution adaptive meshes with dynamic load balancing is possible [2]. Thus, the direct-hybrid method combines the advantages of the direct and hybrid solution strategies, i.e., minimizes I/O and exploits the different length scales in the acoustic and flow fields, such that it is a good candidate to perform large-scale simulations of three-dimensional turbulent aeroacoustic problems.…”

Jet noise analysis using an efficient LES/high-Order acoustic coupling method

“…Nonetheless, the use of this method will be indicative of the acoustic energy contain in the FWH surface. The experimental data of Bogey et al [7] and the LES/APE results of Niemöller et al [68] and Koh et al [31] are also shown for comparison. All these studies are for a round isothermal jet at a similar condition (Re ≈ 500, 000, M a = 0.9 and laminar inlet flow) to the one used in the present work.…”

“…[7] and the two APE sets of data of Refs. [31,68]. On the contrary, due to the higher numerical dissipation of the second-order LES method, the S LES6 case starts to have a lower sound level from x/D j ≈ 8, with a difference of 3dB in the OASPL for the furthest location.…”

Synergy between Noise Reduction Techniques Applied in Different Industries: A Review

“…While hybrid methods use computational fluid dynamics (CFD) techniques and acoustic solver methods separately, In other words hybrid methods use CFD to solve flow field and numerical acoustic methods to find sound sources [13,14]. One of the best hybrid CFD-CAA approaches consists of a large-eddy simulation (LES) to compute the unsteady turbulent flow field and a consequent CAA step, in which, e.g., the acoustic perturbation equations (APE) are solved [15] It always has been difficult to calculate the noise generated by fluid flow due to the nonlinear governing equations. In addition to conducting experimental tests, there are many problems in calculating wind noise, such as separating background noise, as well as the model scale problem according to the Strouhal and Reynolds numbers.…”