CaltechAUTHORS
  A Caltech Library Service

Stochastic and nonlinear forcing of wavepackets in a Mach 0.9 jet

Towne, Aaron and Colonius, Tim and Jordan, Peter and Cavalieri, André and Brès, Guillaume A. (2015) Stochastic and nonlinear forcing of wavepackets in a Mach 0.9 jet. In: 21st AIAA/CEAS Aeroacoustics Conference, 22-26 June 2015, Dallas, TX. https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322227

[img] PDF - Submitted Version
See Usage Policy.

14Mb
[img] PDF (Correction to Equation 16) - Erratum
See Usage Policy.

59Kb

Use this Persistent URL to link to this item: https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322227

Abstract

Recent studies have shown that while linear wavepacket models accurately reproduce experimentally observed, low azimuthal-wavenumber pressure fluctuations in the near field of turbulent jets, they significantly under-predict the intensity of the acoustic radiation produced in the subsonic case. In a linear context, "jittering" of the wavepackets, which can arise due to both stochastic and nonlinear interactions that force the wavepackets, has been hypothesized as a mechanism by which the radiation efficiency of wavepackets is greatly increased. We use data from a carefully validated large-eddy-simulation of a Mach 0.9 turbulent jet to explore this hypothesis. We analyze the LES data in frequency space using windowed segments of a set of snapshots spanning two thousand acoustic time units. We apply the linearized Navier-Stokes operator to this data in order to compute the non-linear forcing field that occurred in the LES simulations, and propose several techniques for educing the relation between the forcing and the observed flow fields. In particular, we employ empirical techniques to identify high energy modes (via proper orthogonal decomposition) in both the flow and acoustic fields, as well as a set of empirical resolvent modes that maximize either the gain between the forcing and flow fields, or the gain between the forcing and acoustic fields. The high gain modes are similar to the high energy modes in both cases, suggesting that the forcing fields are nearly uncorrelated in each realization. Both flow and acoustic fields appear to be driven by largely incoherent forcing corresponding to turbulence in the region of strong shear and, in particular, close to the critical layer. With the caveat that we have thus far only analyzed the axisymmetric mode of the disturbance fields, the results suggest that accurate linear wavepacket models that capture both the coherent flow and acoustic fields can be constructed if appropriate parameterizations of the stochastic forcing can be found, i.e. such forcings will excite the high gain modes to produce the observed coherent structures in both the near and far field.


Item Type:Conference or Workshop Item (Paper)
Related URLs:
URLURL TypeDescription
https://doi.org/10.2514/6.2015-2217DOIConference Paper
https://arc.aiaa.org/doi/pdf/10.2514/6.2015-2217PublisherConference Paper
ORCID:
AuthorORCID
Towne, Aaron0000-0002-7315-5375
Colonius, Tim0000-0003-0326-3909
Jordan, Peter0000-0001-8576-5587
Cavalieri, André0000-0003-4283-0232
Brès, Guillaume A.0000-0003-2507-8659
Additional Information:© 2015 American Institute of Aeronautics and Astronautics. Published Online: 18 Jun 2015. We are grateful for support from the Center for Turbulence Research at Stanford University where a preliminary version of this analysis was performed during the 2014 Summer Program. TC and AT acknowledge earlier support of our jet noise work by the Office of Naval Research under contract N0014-11-1-0753. We would also like to thank Profs. Sanjiva Lele and Joseph Nichols for helpful discussions on this research.
Funders:
Funding AgencyGrant Number
Office of Naval Research (ONR)N0014-11-1-0753
Subject Keywords:Aeroacoustics
Other Numbering System:
Other Numbering System NameOther Numbering System ID
AIAA Paper2015-2217
Record Number:CaltechAUTHORS:20190712-112322227
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322227
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97113
Collection:CaltechAUTHORS
Deposited By: Melissa Ray
Deposited On:15 Jul 2019 20:52
Last Modified:09 Mar 2020 13:18

Repository Staff Only: item control page