| Autor(en) | Akkermans, Rinie | Bernicke, Paul | Ewert, Roland |
|---|---|
| Titel | Zonal Overset-LES with Stochastic Volume Forcing |
| Herausgeber | International Journal of Heat and Fluid Flow, Vol. 70, pp. 336–347, 2018 |
| Erscheinungsjahr | 2018 |
| Abstract | In this contribution, a hybrid Zonal LES tool is presented that uses a stochastic volume forcing for “inflow” turbulence generation. The here used hybrid approach is based on an implementation of the Non-Linear Perturbation Equations extended with fluctuating viscous terms, denoted as “Overset” since a perturbation analysis is performed on top of a background flow. A turbulent flat plate is considered to investigate the generation of inflow turbulence and how this artificial turbulence is seeded into the computational domain. At the inflow region, turbulence is stochastically generated (in three-dimensional space and time) with the Fast Random Particle-Mesh method and subsequently injected in the Overset-LES domain with the eddy-relaxation source term. This eddy-relaxation source term is shown to pilot the hydrodynamics while leaving the acoustics untouched (i.e., transparent for acoustic). The application of the Overset-LES method to a NACA0012 trailing edge at zero angle-of-attack is furthermore presented. Mean flow and turbulence characteristics in the wake show a good agreement with experimental data. Finally, a possible way to couple the turbulent sound sources into a CAA simulation is described. Comparison between directivities obtained with this method and reference data revealed good agreement. |
| Autor(en) | Ananthan, V.B. | Akkermans, R.A.D. | Bernicke, P. | Ewert, R. | Dierke, J. | Rossian, L. |
|---|---|
| Titel | Investigation of effect of Porous Material on Trailing Edge Noise by Overset-LES |
| Herausgeber | ETMM12, Montpellier, France, 2018 |
| Erscheinungsjahr | 2018 |
| Abstract | In the framework of the project Collaborative Research Centre 880 - The fundamentals of High lift for future commercial aircrafts, the current paper presents the efforts at scale resolving simulation by means of Overset-LES (OLES) of an asymmetrical, loaded DLR-F16 trailing edge to identify the noise mechanisms and subsequent application of a porous media to reduce this noise. The Overset-LES is a novel hybrid zonal RANS-LES approach where the Navier-Stokes equations are solved in the perturbation form with a RANS base flow. A set of Volume Averaged Navier- Stokes (VANS) equations are solved in the porous region. The inflow turbulence for such an approach is realized through an acoustically transparent stochastic turbulence generator called fast Random Particle Mesh (fRPM). Finally, the application of Overset-LES to solid and porous trailing edge is presented. The resulting differences in the turbulent boundary layer (TBL) are discussed along with its effects on the farfield acoustics with the help of two-point spatial correlation. |
| Autor(en) | Bernicke, Paul | Akkermans, Rinie | Bharadwaj Ananthan, Varun | Ewert, Roland | Rossian, Lennart | Dierke, Jürgen |
|---|---|
| Titel | Overset LES of a Solid and Porous NACA0012 Trailing Edge |
| Herausgeber | 24rd AIAA/CEAS Aeroacoustics Conference, AIAA 2018–3454, pp. 1-11, Atlanta, 2018 |
| Erscheinungsjahr | 2018 |
| Abstract | In this contribution, a hybrid zonal simulation tool with stochastic volume forcing for inflow turbulence generation is applied to trailing-edge noise computations of a NACA0012 airfoil. The governing equations constitute the non-linear perturbation Equations with viscous terms, i.e., the full Navier-Stokes equations which allows a perturbation analysis. Together with a suitable forcing of inflow turbulence, a hybrid RANS/LES method is established which leads to a significant reduction of the computational domain size to the region containing the sound sources itself. In case of trailing-edge noise this encloses the trailing-edge region. The seeding of inflow turbulence takes place where the upstream domain intersects with the airfoils boundary layer. Here, turbulence is generated with the aid of the Fast Random Particle-Mesh method and subsequently injected in the Overset-LES domain with the eddy-relaxation source term. Once the sound sources are captured, i.e., here in the form of the perturbed Lamb vector, it can be propagated into the far-field with a subsequent CAA-computation. In the present proceeding, simulations of a solid and porous NACA0012 trailing edge are presented. The numerical treatment of porous media by a volume-averaging approach is concisely described. A possible sound reduction by the application of porous materials compared to the solid NACA0012 is described by means of a single vortex convecting over the trailing edge. |
| Autor(en) | Bernicke, Paul | Akkermans, Rinie | Ewert, Roland | Dierke, Jürgen |
|---|---|
| Titel | Overset-LES with Stochastic Forcing for Sound Source Simulation |
| Herausgeber | Notes on Numerical Fluid Mechanics and Multidisciplinary Design, New Results in Numerical and Experimental Fluid Mechanics XI, Vol. 136, pp. 601–610, 2018 |
| Erscheinungsjahr | 2018 |
| Abstract | An application of a hybrid RANS/LES method to trailing-edge noise, is presented in this contribution. The numerical framework of the CAA-code PIANO offers a basis for extending the Non-Linear Perturbation equations with viscous terms. As a result, a full Navier-Stokes equations perturbation analysis, denoted with “Overset”, can be performed on top of a steady background flow. With such a scale-resolving simulation tool, consisting of optimized higher-order numerical schemes for aeroacoustics, the investigation of sound source mechanism on first principals become feasible. An issue of such hybrid zonal approaches, namely the seeding of proper inflow turbulence, is solved with the Fast Random Particle-Mesh method in combination with the Eddy-Relaxation source term. The overall process chain of the intended Overset-LES usage is illustrated by means of NACA0012 trailing-edge noise computations at moderate Reynolds number and zero angle-of-attack. |
| Autor(en) | Ewert, Roland | Ewert, Roland |
|---|---|
| Titel | Linear and Non-Linear Perturbation Equations with Relaxation Source Terms for Forced Eddy Simulation of Aeroacoustic Sound Generation |
| Herausgeber | 20th AIAA/CEAS Aeroacoustics Conference, Atlanta, USA, AIAA Paper 2016-3053 |
| Erscheinungsjahr | 2018 |
| Abstract | Turbulence related sound is generated by the dynamics of fluctuating vorticity. For example, trailing edge noise is caused by vorticity traveling past the trailing edge. To excite fluctuating vorticity by forcing the linearized Euler equations (LEE) with right-hand side source terms, one peculiar problem is observable: while the rise of vorticity levels by external sources poses no problem, to properly lower them, the right-hand side terms must act as a sink, being exactly in anti-phase to the vorticity levels as present in the LEE solution. However, the accurate prediction of vorticity in terms of phase cannot be guaranteed, especially for approximately modeled sources e.g. using stochastic methods. Thus in general there will be a mismatch between actual induced and intended levels of vorticity. In this paper a new class of relaxation source terms is introduced that enables the proper excitation of vorticity levels in linear and non-linear perturbation equations and as such enables an accurate control over the vorticity magnitudes. The source can be formulated to act selectively in wave-number space, i.e. without directly affecting the dynamics of resolved low wave-number vorticity components whereas the resolved high wave-number part is piloted by the fluctuating vorticity imposed as a reference solution. The reformulation of the Navier-Stokes equations in primitive variables and non-linear perturbation form is presented. Direct noise computation of sound radiated from a vortex shedding cylinder in laminar cross flow verify their implementation. The relaxation source term without forcing is applied to the unstable jet problem of the 4th CAA Workshop on Benchmark Problems. The forcing of frozen and decaying stochastic turbulence in conjunction with the relaxation source term is studied. First results for high-lift noise prediction with forced eddy simulation are presented. |
| Autor(en) | Bernicke, Paul | Akkermans, Rinie | Ewert, Roland | Dierke, Jürgen |
|---|---|
| Titel | Overset LES for Trailing-Edge Noise Computations |
| Herausgeber | 23rd AIAA/CEAS Aeroacoustics Conference, AIAA 2017–3170, pp. 1-13, Denver, 2017 |
| Erscheinungsjahr | 2017 |
| Abstract | In this paper a hybrid Zonal LES tool is applied to trailing-edge noise. The so-called "Overset" analysis represents a non-linear perturbation analysis on top of a steady background flow (the latter typically obtained from a steady RANS solution). The non-linear Euler equations are extended with viscous terms and therefore represent full Navier-Stokes equations in disturbance form. The important aspect of inflow turbulence, common to all hybrid RANS/LES methods, is tackled with the aid of the Fast Random Particle-Mesh method (FRPM). FRPM generates artificial turbulence whose statistics match that of the underlying RANS. The stochastic turbulence is subsequently injected into the Overset LES simulation via the eddy-relaxation source term. A 3D NACA0012 Overset LES covering a restricted regime around the trailing edge itself acts as a prove of concept for the desired trailing-edge noise study. The given results are supplemented by a 2D aeroacoustic trailing-edge noise analysis that yield promising results and furthermore, illustrates that the eddy-relaxation term is acoustically transparent. |
| Autor(en) | Akkermans, R.A.D. | Buchmann, N. | Dierke, J. | Ewert, R. |
|---|---|
| Titel | Overset DNS with Application to Homogeneous Decaying Turbulence |
| Herausgeber | In: Notes on Numerical Fluid Mechanics and Multidisciplinary Design, New Results in Numerical and Experimental Fluid Mechanics X, Vol. 132, pp. 699–707 |
| Erscheinungsjahr | 2016 |
| Abstract | In this contribution an application of a computational aeroacoustics code as a hybrid Zonal DNS tool is presented. The derivation of the Non-Linear Perturbation Equations (NLPE) extended with viscous terms is shown as well as information related to the numerical method is given. The application of the simulation tool to a generic three-dimensional test case, i.e., the Taylor-Green Vortex (TGV), is presented. This TGV, initially consists of only one length scale, develops into homogeneous decaying turbulence. Results of energy spectrum and grid convergence study are given. It is shown that the observed accuracy of the numerical code matches well with the expected theoretical order of four. |
| Autor(en) | Bernicke, Paul | Akkermans, Rinie | Ewert, Roland | Dierke, Jürgen |
|---|---|
| Titel | Overset LES with an Acoustic Relaxation Term for Sound Source Simulations |
| Herausgeber | 22th AIAA/CEAS Aeroacoustics Conference, AIAA 2016–3031, pp. 1-14, Lyon, 2016 |
| Erscheinungsjahr | 2016 |
| Abstract | A novel Overset LES approach in perturbation form is presented to provide adequate turbulent information for the description of aerodynamically induced noise, but at the same time keep the computational effort within reasonable limits as compared to DNS. Solving the perturbation equations on top of a steady base flow leads to a hybrid approach, where scale-resolving simulation is only performed in necessary regions. The procedure is carried out in two steps. After capturing sound sources via the aforementioned methodology, the sound propagation is predicted by employing the Acoustic Perturbation equations. An Acoustic Relaxation Term is introduced to suppress pressure based grid-to-grid oscillations leaving other modes untouched. Its damping characteristics has been shown to be favourably frequency selective. The Acoustic Relaxation Term is able to damp or excite acoustic waves and in that way it potentially enables the excitement of prescribed acoustics in the Acoustic Perturbation equations for future applications. The governing equations are presented as well as the subgrid scale model. This subgrid scale model is calibrated with decaying isotropic turbulence. |
| Autor(en) | Akkermans, R.A.D. | Ewert, R. | Moghadam, S.M.A. | Dierke, J. | Buchmann, N. |
|---|---|
| Titel | Overset DNS with Application to Sound Source Prediction |
| Herausgeber | In: Progress in Hybrid RANS-LES Modelling, Papers contributed to the 5th Symposium on Hybrid RANS-LES Methods, 19-21 March 2014, College Station, Texas, USA. In: Notes on Numerical Fluid Dynamics and Multidisciplinary Design, Vol. 130, Springer Verlag, pp. 59–68, 2015 |
| Erscheinungsjahr | 2015 |
| Abstract | In this contribution, we present an application of a computational aeroacoustics code as a hybrid Zonal DNS tool. The extension of the Non-Linear Perturbation Equations (NLPE) with viscous terms is presented as well as information related to the numerical method. The applicability of the simulation tool is illustrated with two testcases, i.e., a 2D circular cylinder in a uniform flow at moderate Reynolds numbers and a 3D decaying flow initialised with Taylor-Green vortices. Both testcases provide results which match well with data reported in literature. The cylinder testcase verifies that the viscous terms are indeed correctly implemented (at least in 2D) and the Taylor-Green vortex case illustrates that the numerical scheme introduced minimal numerical dissipation. |