Development of Non-Reflecting Boundary Condition for Application in 3D Computational Fluid Dynamics Codes

Abstract

Numerical computations are commonly used for better understanding the unsteady processes in internal combustion engine components and their acoustic behavior. The acoustic characterization of a system requires that reflections from duct terminations are avoided, which is achieved either by using highly dissipative terminations or, when an impulsive excitation is used, by placing long ducts between the system under study and the duct ends. In the latter case, the simulation of such a procedure would require a large computational domain with the associated high computational cost, unless non-reflecting boundary conditions are used. In this paper, first the different non-reflecting boundary conditions available in ANSYS-FLUENT are evaluated. Then, the development and implementation of an anechoic termination in a 3D-CFD code is presented. The performance of the new implementation is first validated in the classic Sod's shock tube problem, and then checked against numerical and experimental results of the flow and acoustic fields in automotive exhaust mufflers. The results obtained compare favorably with those from the conventional CFD approach and experiments, while the computational cost is significantly reduced.

Numerical and experimental analysis of automotive turbocharger compressor aeroacoustics at different operating conditions

“…which are inspired by the Method of Characteristics (MoC), as described by Torregrosa et al [29]. Averaging of flow field variables at inlet and outlet cross-sections (see Fig.…”

Simulations and measurements of automotive turbocharger compressor whoosh noise

“…which are derived in the spirit of the Method of Characteristics, following the same notation as Torregrosa, Fajardo, Gil, and Navarro (2012), i.e., u is the axial velocity, γ is the ratio of specific heats and p and p 0 are the pressure and reference pressure, respectively. The methodology developed by Broatch et al (2014) is used as follows: temporal traces of pressure, axial velocity and speed of sound cross-section average are extracted from the simulations, calculating then the pressure components by means of Equation 2.…”

Acoustic and pressure characteristics of a ported shroud turbocompressor operating at near surge conditions

“…The recoded pressure traces are then treated to obtain the spectral characteristics. Inlet and outlet duct spectra are computed from the decomposed pressure waves obtained using the Linearly-Constrained Minimum Variance (LCMV) beamforming [14] and Method of Characteristics (MoC) [23]. The spectra of the diffuser and near impeller locations are directly calculated from the pressure fluctuations recorded by the probes.…”

“…Experimentally measured pressure fluctuations are decomposed using LCMV beamforming based method to compute the duct spectra. Numerical results are computed from the pressure wave decomposed using beamforming as well as from the pressure wave reconstructed from the flow-field information using MoC) [23].…”