On the signal degradation induced by the interpolation and the sampling rate reduction in aeroacoustics hybrid methods

Abstract

SUMMARY Taking place within more extensive work that focuses on hybrid methods in aeroacoustics, the present study is devoted to the data transfer operations that are to be performed between two stages of a hybrid calculation. More precisely, the article focuses on two typical operations that usually accompany such data transfer, which are (i) the sampling rate reduction and (ii) the interpolation of the unsteady perturbations to be transmitted from one stage to the other. First part of the paper analyzes the two main issues of such operations, which are the spuriousing and the aliasing phenomena. For doing so, the usual notions of the interpolation theory are revisited before they are synthesized within an original approach. The here proposed formalism allows to understand better both the spuriousing and the aliasing phenomena, as well as to accurately predict the impact of the latter on the data to be transmitted in terms of signal degradation. Second part of the paper provides an illustration and a validation of these theoretical developments via a direct application to a typical aerodynamic noise problem (aeroacoustic emission by a 2D cylinder cross flow). There, it is further shown how the here proposed formalism can help in improving aeroacoustics hybrid calculations by predicting (and thus possibly minimizing) the bias to be induced on the acoustic extrapolation stage because of the aliasing and/or spuriousing effects inherited from the sampling rate reduction and/or interpolation of CFD data—which is likely to occur in any hybrid scenario. Copyright © 2012 John Wiley & Sons, Ltd.

An advanced hybrid method for the acoustic prediction

“…aerodynamic noise). On the same way, all the related outcomes were extensively documented through previous publications, either as journal articles or proceedings of international conferences [22][23][24][25][26][27][28][29][30][31]. The reason for summarizing these various works and associated outcomes here was that, although focusing each on a particular aspect (and deserving each an entire publication in itself), they all targeted the same common objective, which is the development of the advanced CAA-based hybrid approach that the present article is about.…”

“…non linear formulation [17,18], LOC Non Reflecting Boundary Condition [17,18,21]), several research actions were conducted [25][26][27][28][29][30], being primarily achieved by the present second author in the framework of his PhD thesis [30]. These works consisted in (i) characterizing [25,27,28] and (ii) possibly minimizing [26,29] the various impacts that its data manipulation may have onto a given acoustic signal, when the latter is to be transferred from one to another stage of an acoustic hybrid method. In addition to deliver fundamental insights that may help optimizing any kind of acoustic hybrid method (e.g.…”

“…the anechoicity requirement evocated above). Then, follow-on research actions [25][26][27][28][29][30] consisted in optimizing such overall hybrid method, for it can cope with all stringent constraints that are dictated by real-life applications without being jeopardized by some of their unavoidable side effects (e.g. signal degradation -see detail below).…”

“…those involving complex acoustic signal and/or requiring heavy computations). More precisely, works consisted in optimizing the overall hybrid procedure [25][26][27][28][29][30], for the latter can (i) cope with all stringent constraints that are dictated by real-life applications (ii) without being jeopardized by some of their unavoidable side effects (such as the signal degradation to which unsteady CFD data are subjected, when manipulated for being acoustically exploited [25]). To this end, and besides specific optimizations of the underlying CAA approach by the present first author (e.g.…”

Concurrent finite element simulation of quadrupolar and dipolar flow noise in low Mach number aeroacoustics

“…At each time step of the simulation, after solving (25) the domain Ω b has to be switched on and included for the computation of the incident acoustic pressure in (26), and then switched off to compute the diffracted sound field in (27). Besides, it should be noted that special care should be taken when interpolating the results from the CFD domain to the acoustic one to avoid spurious errors [43,44,45].…”