Linear- and Non-Linear Perturbation Equations with Relaxation Source Terms for Forced Eddy Simulation of Aeroacoustic Sound Generation

Ewert, Roland; Dierke, Jürgen; Neifeld, Andrej; Moghadam, Mohsen Alavi

doi:10.2514/6.2014-3053

Cited by 32 publications

(24 citation statements)

References 21 publications

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“…Fluctuating vorticity as generated by the fRPM method over a given background flow is coupled with the CAA solver PIANO by applying the LEE-relaxation formulation [31]. This method adds a relaxation term to the impulse equations,…”

Section: Coupling Of Frpm and Caa Methodsmentioning

confidence: 99%

“…The well-known dispersion-relationpreserving finite difference scheme by Tam and Webb [29] was utilized for the spatial discretization and the low-dispersion low-dissipation Runge-Kutta method [30], for time-integration. The LEE for time-varying Navier-Stokes background flow can be derived by neglecting the turbulent stresses, viscous effects, heat fluxes and non-linear terms in the non-linear Navier-Stokes equations in perturbation form [31] without limitations to slow changes of u 0 . Using the tensor notation u 0 = u 0 i e i , it reads:…”

Section: Computational Aeroacoustics (Caa)mentioning

confidence: 99%

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Impact of cyclostationarity on fan broadband noise prediction

Wohlbrandt

Kissner

Guérin

2018

Journal of Sound and Vibration

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One of the dominant noise sources of modern Ultra High Bypass Ratio (UHBR) engines is the interaction of the rotor wakes with the leading edges of the stator vanes in the fan stage. While the tonal components of this noise generation mechanism are fairly well understood by now, the broadband components are not. This calls to further the understanding of the broadband noise generation in the fan stage. This article introduces the cyclostationary stochastic hybrid (CSH) method, which accommodates in-depth studies of the impact of cyclostationary wake characteristics on the broadband noise in the fan stage. The Random Particle Mesh (RPM) method is used to synthesize a turbulence field in the stator domain using a URANS simulation characterized by time-periodic turbulence and mean flow. The rotor-stator interaction noise is predicted by a two-dimensional CAA computation of the stator cascade. The impact of cyclostationarity is decomposed into various effects investigated separately. This leads to the finding that the periodic turbulent kinetic energy (TKE) and periodic flow have only a negligible effect on the radiated sound power. The impact of the periodic integral length scale (TLS) is, however, substantial. The limits of a stationary representation of the TLS are demonstrated making the CSH method indispensable when background and wake TKE are of comparable level. Good agreement of the CSH method with measurements obtained from the 2015 AIAA Fan Broadband Noise Prediction Workshop are also shown.

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Section: Coupling Of Frpm and Caa Methodsmentioning

confidence: 99%

Section: Computational Aeroacoustics (Caa)mentioning

confidence: 99%

Impact of cyclostationarity on fan broadband noise prediction

Wohlbrandt

Kissner

Guérin

2018

Journal of Sound and Vibration

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“…In further works, the proposed relaxation source term by Ewert et al 11 is planned to be applied to the computational cases, which have been used here with the T&A source model. The triggering of the vortical fluctuations is believed to solve the problem with the underrepresented trailing edge noise generation.…”

Section: Discussionmentioning

confidence: 99%

“…In this case a generalized form of governing system is needed. As proposed by Ewert et al, 11 it is possible to trigger and damp out the vorticity fluctuations with the linear and non-linear Euler equations, if the term…”

Section: B Governing Equationsmentioning

confidence: 98%

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Towards Prediction of Jet Noise Installation Effect using Stochastic Source Modeling

Neifeld

Ewert

Keller

et al. 2014

20th AIAA/CEAS Aeroacoustics Conference

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Previously, the prediction of jet mixing noise from hot and cold isolated nozzle configurations has been studied with the means of RPM (Random Particle M esh) method using the Tam & Auriault or rather Tam, Pastouchenko and Viswanathan source model. The acoustical sources are generated as a reproduction of experimentally observed two-point cross-correlation functions using as input the turbulence statistics from RANS data. The sound propagation and extrapolation are performed with the linearized Euler equations in the near-field and with the Ffowcs-Williams & Hawkings method in the far-field. Efficient CAA computations are achieved exploiting the advantage of Fourier series decomposition for isolated axisymmetric and quasi-axisymmetric nozzle geometries. For investigation of installation effects the azimuthal-modal approach is however not applicable due to highly three-dimensional flow interactions, e.g. if a jet engine is mounted below an airfoil. Therefore, in contrast to the isolated nozzle configurations, in this case the resolution of computational domain in all three spatial dimensions is needed. Next to the RPM method, which is solely capable to generate two-dimensional acoustical sources, the FRPM method is available that is able to generate both, 2-D and 3-D sources. First test computations with FRPM method were conducted for a single stream jet, whereas the azimuthal-modal results of RPM were used as reference solution. The installed jet configurations are subsequently studied building on the FRPM computations of the single stream jet.

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