How-to-cite FELiCS
If you use FELiCS we kindly ask you to cite the following publication:
Kaiser, Thomas Ludwig; Demange, Simon; Müller, Jens S; Knechtel, Sophie; Oberleithner, Kilian FELiCS: A Versatile Linearized Solver Addressing Dynamics in Multi-Physics Flows Book Chapter In: American Institute of Aeronautics and Astronautics, 2023. @inbook{Kaiser2023b,View Video Presentation: https://doi.org/10.2514/6.2023-3434.vidThis manuscript provides a brief description of the linearized flow solver FELiCS and reviews six applications of the software to flow configurations that exhibit different multiphysics problems. Linearization of the governing equations of a flow around its base state is a method that has been used in science for more than a century to improve the understanding of flow dynamics in generic configurations. However, in recent years, more complicated flow problems involving multiphysics phenomena such as turbulent mixing, heat conduction, plasmas, and reacting flows have been studied using linearized mean flow analysis. As a result, the theoretical basis of the respective flow problems is becoming more complicated. This increases the demand for a reliable and well validated, but versatile framework in which new models can be implemented. At the same time, the ability to address multiphysics problems makes the approach more interesting for industrial applications, such as gas turbine combustors, noise generation in airfoils, flow instabilities in water turbines, aeronautical applications and more, which raises demand for application in complicated geometries as well as a smooth workflow. The linearized flow solver FELiCS, presented in this manuscript, attempts to address these challenges. The object-oriented Python programming environment combined with PETSc and SLEPc enables the combination of flexibility and fast implementation of new models with efficient numerical treatment of the linear algebra arising in the linearized framework. The code takes advantage of the Fenics software package, which uses FE method on unstructured grids in two and three dimensions. This allows FELiCS to be applied to academic problems with simple geometries as well as to engineering configurations with high geometric complexity. The numerous implemented linearized equations can be selected by the user depending on the flow problem. A graphical interface facilitates the adjustment of a new user to the code considerably. In addition to that, an operator-based notation of the linearized transport equations, in combination with the operators being defined for both cylindrical as well as Cartesian coordinates, makes an adjustment of the implemented equations to the needs of the user particularly easy. |
Most recent publications
Complete publication list
2025 |
Villié, Alexandre; Schmitter, Sebastian; Saldern, Jakob G R; Demange, Simon; Oberleithner, Kilian In: Physics of Fluids, vol. 37, no. 2, pp. 025194, 2025, ISSN: 1070-6631. @article{10.1063/5.0252852,In this study, we use physics-informed neural networks (PINNs) to assimilate the turbulent mean flow fields from Cartesian time-resolved three-dimensional phase-contrast magnetic resonance imaging [known as four-dimensional (4D) flow MRI] measurements in an in vitro axis-symmetric stenosis. 4D flow has emerged as a prominent tool for the hemodynamic assessment of cardiovascular pathologies such as aortic stenosis. However, the standard, Cartesian-based 4D flow acquisitions suffer from displacement artifacts and limited spatiotemporal resolution, which bias the quantification of the velocity field. The goal of this study is to enhance noisy 4D flow measurements by correcting the displacement artifact and assimilating the mean pressure and Reynolds stresses. We consider a transitional stenotic flow that exhibits flow separation. In the first step, a PINN is trained on noisy phase-contrast MRI time-averaged velocity data and informed by the continuity equation. The validation against synchronized single-point imaging (Sync SPI) MRI experimental data reveals a substantial reduction of the displacement artifact and effective denoising. This PINN-corrected mean velocity field is used to assimilate the mean pressure and Reynolds stresses by training a PINN based on the Reynolds-averaged Navier–Stokes (RANS) equations closed with the Spalart–Allmaras turbulence model. The mean pressure and Reynolds stress assimilations are validated using a numerical RANS dataset and then applied to experimental 4D flow data. Our results demonstrate that PINNs are effective for post-processing 4D flow measurements. They enable displacement error correction, data denoising, and identifying unknown quantities. Such post-processing can bridge the quality gap between short acquisition-time standard 4D flow and Sync SPI measurements. |
2024 |
Knechtel, S. J.; Kaiser, T. L.; Orchini, A.; Oberleithner, K. Arbitrary-order sensitivities of the incompressible base flow and its eigenproblem Journal Article In: Journal of Fluid Mechanics, vol. 985, pp. A32, 2024, ISSN: 0022-1120. @article{Knechtel2024,<p>First-order sensitivities and adjoint analysis are used widely to control the linear stability of unstable flows. Second-order sensitivities have recently helped to increase accuracy. In this paper, a method is presented to calculate arbitrary high-order sensitivities based on Taylor expansions of the incompressible base flow and its eigenproblem around a scalar parameter. For the incompressible Navier–Stokes equations, general expressions for the sensitivities are derived, into which parameter-specific information can be inserted. The computational costs are low since, for all orders, a linear equation system has to be solved, of which the left-hand-side matrix stays constant and thus its preconditioning can be exploited. Two flow scenarios are examined. First, the cylinder flow equations are expanded around the inverse of the Reynolds number, enabling the prediction of the two-dimensional cylinder base flow and its leading eigenvalue as a function of the Reynolds number. This approach computes accurately the base flow and eigenvalue even in the unstable regime, providing, when executed subsequently, a mean to calculate unstable base flows. This case gives a clear introduction into the method and allows us to discuss its constraints regarding convergence behaviour. Second, a small control cylinder is introduced into the domain of the cylinder flow for stabilization. Higher-order sensitivity maps are calculated by modelling the small cylinder with a steady forcing. These maps help to identify stabilizing areas of the flow field for Reynolds numbers within the laminar vortex shedding regime, with the required number of orders increasing as the Reynolds number rises. The results obtained through the proposed method align well with numerically calculated eigenvalues that incorporate the cylinder directly into the grid.</p> |
Moczarski, Lukas; Treleaven, Nicholas C. W.; Oberleithner, Kilian; Schmidt, Simon; Fischer, André; Kaiser, Thomas Ludwig Interacting Linear Modes in the Turbulent Flow of an Industrial Swirled Combustor Journal Article In: AIAA Journal, vol. 62, iss. 3, pp. 979-988, 2024, ISSN: 0001-1452. @article{Moczarski2024,<p>Swirled flows often feature global modes that become manifest as skew-symmetric helical vortices, also known as precessing vortex cores, which dominate the flow dynamics. This study uses linear stability analysis (LSA) and bispectral mode decomposition (BMD) to elucidate the interactions of such modes in the turbulent, nonreacting, swirled flow of an industrial, three-passage, aeroengine fuel injector obtained via large-eddy simulation. A discrete Fourier transform in time retrieves the modes as narrow-banded, evenly spaced peaks in the spectral amplitude of the turbulent signal, where the second mode is dominant. Similar arrangements are known to appear as a consequence of a saturated global mode, which amplifies its higher harmonic frequencies due to nonlinear effects. We show that each mode appears in the spectrum of LSA eigenvalues, indicating that the subdominant peaks are caused not only due to nonlinear interactions but that they have an underlying linear mechanism. A structural sensitivity analysis based on the adjoint LSA shows that the observed helical modes originate close to the exit plane of the fuel injector. Finally, the BMD reveals significant nonlinear interaction between the individual modes. It is hypothesized that this interaction amplifies the modes, which are linearly stable, leading to the strong dynamics in the flow.</p> |
Demange, S.; Yuan, Z.; Jekosch, S.; Hanifi, A.; Cavalieri, A. V. G.; Sarradj, E.; Kaiser, Thomas Ludwig; Oberleithner, K. Resolvent model for aeroacoustics of trailing edge noise Journal Article In: Theoretical and Computational Fluid Dynamics, 2024, ISSN: 0935-4964. @article{Demange2024,This study presents a physics-based, low-order model for the trailing edge (TE) noise generated by an airfoil at low angle of attack. The approach employs incompressible resolvent analysis of the mean flow to extract relevant spanwise-coherent structures in the transitional boundary layer and near wake. These structures are integrated into Curle’s solution to Lighthill’s acoustic analogy to obtain the scattered acoustic field. The model has the advantage of predicting surface pressure fluctuations from first principles, avoiding reliance on empirical models, but with a free amplitude set by simulation data. The model is evaluated for the transitional flow ($$textbackslashtext Re = 5e4$$) around a NACA0012 airfoil at 3 deg angle of attack, which features TE noise with multiple tones. The mean flow is obtained from a compressible large eddy simulation, and spectral proper orthogonal decomposition (SPOD) is employed to extract the main hydrodynamic and acoustic features of the flow. Comparisons between resolvent and SPOD demonstrate that the physics-based model accurately captures the leading coherent structures at the main tones’ frequencies, resulting in a good agreement of the reconstructed acoustic power with that of the SPOD (within 4 dB). Discrepancies are observed at high frequencies, likely linked to nonlinearities that are not considered in the resolvent analysis. The model’s directivity aligns well with the data at low Helmholtz numbers, but it fails at high frequencies where the back-scattered pressure plays a significant role in directivity. This modeling approach opens the way for efficient optimization of airfoil shapes in combination with low-fidelity mean flow solvers to reduce TE noise. |
Müller, Jens S; Saldern, Jakob G R; Kaiser, T. L.; Oberleithner, Kilian Linear amplification of inertial-wave-driven swirl fluctuations in turbulent swirling pipe flows: a resolvent analysis approach Journal Article In: Journal of Fluid Mechanics, vol. 1000, pp. A91, 2024. @article{Müller_2024,Linear amplification of inertial-wave-driven swirl fluctuations in turbulent swirling pipe flows: a resolvent analysis approach |
Müller, Jens Satria; Reumschüssel, Johann Moritz; Kaiser, Thomas Ludwig; Knechtel, Sophie Johanna; Oberleithner, Kilian Combining Bayesian optimization with adjoint-based gradients for efficient control of flow instabilities Proceedings Article In: 2024. @inproceedings{nokey,This work presents an efficient framework for shape optimization to control flow insta- bilities and coherent structures in laminar and turbulent flows by combining a Bayesian optimization approach with adjoint-based gradient information (BOA). Linear stability and resolvent analyses are used to yield physically meaningful cost functions. In addition, adjoint methods are employed to compute the sensitivity of the cost functions to shape parameter changes. These physics-based function and gradient information are embed- ded into a global Bayesian optimization framework, which also handles uncertainties that may arise from the provided data or linear model. The BOA framework is tested on the task of designing a hydrofoil to control the wake instability and it is compared against a gradient-free Bayesian optimizer and a purely gradient-based method. |
2023 |
Kaiser, Thomas Ludwig; Demange, Simon; Müller, Jens S; Knechtel, Sophie; Oberleithner, Kilian FELiCS: A Versatile Linearized Solver Addressing Dynamics in Multi-Physics Flows Book Chapter In: American Institute of Aeronautics and Astronautics, 2023. @inbook{Kaiser2023b,View Video Presentation: https://doi.org/10.2514/6.2023-3434.vidThis manuscript provides a brief description of the linearized flow solver FELiCS and reviews six applications of the software to flow configurations that exhibit different multiphysics problems. Linearization of the governing equations of a flow around its base state is a method that has been used in science for more than a century to improve the understanding of flow dynamics in generic configurations. However, in recent years, more complicated flow problems involving multiphysics phenomena such as turbulent mixing, heat conduction, plasmas, and reacting flows have been studied using linearized mean flow analysis. As a result, the theoretical basis of the respective flow problems is becoming more complicated. This increases the demand for a reliable and well validated, but versatile framework in which new models can be implemented. At the same time, the ability to address multiphysics problems makes the approach more interesting for industrial applications, such as gas turbine combustors, noise generation in airfoils, flow instabilities in water turbines, aeronautical applications and more, which raises demand for application in complicated geometries as well as a smooth workflow. The linearized flow solver FELiCS, presented in this manuscript, attempts to address these challenges. The object-oriented Python programming environment combined with PETSc and SLEPc enables the combination of flexibility and fast implementation of new models with efficient numerical treatment of the linear algebra arising in the linearized framework. The code takes advantage of the Fenics software package, which uses FE method on unstructured grids in two and three dimensions. This allows FELiCS to be applied to academic problems with simple geometries as well as to engineering configurations with high geometric complexity. The numerous implemented linearized equations can be selected by the user depending on the flow problem. A graphical interface facilitates the adjustment of a new user to the code considerably. In addition to that, an operator-based notation of the linearized transport equations, in combination with the operators being defined for both cylindrical as well as Cartesian coordinates, makes an adjustment of the implemented equations to the needs of the user particularly easy. |
Kaiser, Thomas Ludwig; Varillon, Gregoire; Polifke, Wolfgang; Zhang, Feichi; Zirwes, Thorsten; Bockhorn, Henning; Oberleithner, Kilian Modelling the response of a turbulent jet flame to acoustic forcing in a linearized framework using an active flame approach Journal Article In: Combustion and Flame, vol. 253, pp. 112778, 2023, ISSN: 0010-2180. @article{Kaiser2023,This study performs a linear mean field analysis of a turbulent reacting methane-air jet flame, with the goal of predicting the response of the reacting flow to upstream acoustic actuation. Unlike previous studies, this work develops and applies an active flame approach by taking the heat release oscillations of the flame resulting from the acoustic fluctuations into account. For an active flame approach in the linear mean field analysis, a linearized combustion model is necessary. Linearizing Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) combustion models leads to closure problems, making their application in this context troublesome, whereas Reynolds-averaged Navier Stokes (RANS) combustion models prove to circumvent this problem making them suitable candidates for this purpose. The RANS combustion models are linearized around the temporal mean state variables of the turbulent jet flame, which is obtained by LES. An a priori analysis shows that a linearized RANS–Eddy Break Up (EBU) model is the best suited among all investigated combustion models for the investigated set-up and reproduces with high accuracy the fluctuations in reaction rate obtained in the LES. Furthermore, the linearized governing equations of the flow including the linearized EBU model for the reaction rate are solved for incoming acoustic perturbations. The response modes show that the reaction rate oscillations are caused by Kelvin–Helmholtz vortex rings, which perturb the jet flame. The results are in good agreement with the LES simulations in terms of the mode shapes of both reaction rate and velocity fluctuations. This study represents a basis for linear mean field analysis of turbulent flames and monolithic modelling approaches for thermoacoustic instabilities in gas turbine combustors. |
Saldern, Jakob G; Reumschüssel, Johann M; Kaiser, Thomas Ludwig; Schmidt, Oliver T; Jordan, Peter; Oberleithner, Kilian Self-consistent closure modeling for linearized mean field methods Proceedings Article In: American Institute of Aeronautics and Astronautics, 2023. @inproceedings{Saldern_23b,View Video Presentation: https://doi.org/10.2514/6.2023-4351.vidModeling the coherent component of the Reynolds stresses to close the linearized mean field equations has received little attention in recent years, despite the great surge of linearized mean field methods. In this study, we present a modeling approach to account for the coherent component of the Reynolds stresses that is based on a Boussinesq-like model known from steady and unsteady Reynolds-averaged Navier Stokes (RANS) equations. The presented approach is based on two features. Unlike many previous studies, we consider not only a mean eddy viscosity field, but also a fluctuating field derived from linearized algebraic models. Moreover, we introduce the concept of mean field consistency; the mean eddy viscosity field is determined to satisfy the RANS equations along with the other mean field quantities. Practically, this is implemented by assimilating the model constants of the eddy viscosity model from the mean fields, taking into account the RANS equations, which is achieved with a physics-informed neural network. To evaluate the models thus assembled, we propose to perform an a priori analysis. A concept in which the modeled Reynolds stress fluctuations are directly compared to the respective measured quantities. The proposed methods are demonstrated and evaluated on a jet flow at Reynolds number of 50000 and Mach number 0.4. |
2022 |
Wang, Chuhan; Kaiser, Thomas Ludwig; Meindl, Max; Oberleithner, Kilian; Polifke, Wolfgang; Lesshafft, Lutz Linear instability of a premixed slot flame: flame transfer function and resolvent analysis Journal Article In: Combustion and Flame, vol. 240, pp. 112016, 2022. @article{Wang2022,The response to forcing of a 2D laminar premixed slot flame is investigated by means of linear analysis, based on the compressible flow equations with a two-step reaction scheme for methane combustion. The flame transfer function (FTF) is computed from this linear model, in excellent agreement with reference nonlinear calculations. The input-output gain between externally applied forcing and the global heat release rate response is computed, and peaks in the gain are related to intrinsic thermoacoustic (ITA) modes. The receptivity of the flame to arbitrary flow forcing is characterised by the resulting amplitude of global heat release rate fluctuations. Linear resolvent analysis is used to identify optimal forcing structures and their associated flame response, leading to a discussion of the dominant mechanisms for the amplification of flow perturbations, which trigger flame oscillations. These seem to involve a resonance with ITA instability modes. |
Müller, Jens S; Lückoff, Finn; Kaiser, Thomas Ludwig; Oberleithner, Kilian On the relevance of the runner crown for flow instabilities in a Francis turbine Proceedings Article In: pp. 12053, 2022. @inproceedings{Müller22,The precessing vortex core (PVC), also known as vortex rope, in a draft tube of a Francis-99 hydro turbine is investigated. The goal is to increase our comprehension of the root of the PVC in order to attenuate or suppress the PVC, thus extending the stable operational range below the best efficiency point at part load conditions. Unsteady Reynolds-averaged Navier– Stokes simulations are conducted and used as a basis for all the analyses performed in this work. The discrete Fourier transform (DFT) and the spectral proper orthogonal decomposition (SPOD) as data-driven methods and the linear stability analysis (LSA) as a physics-based, operator-driven method are used to examine the PVC in detail. With the DFT and SPOD, two dominant modes are found inside the draft tube. Likewise, the LSA reveals two distinct linear instabilities of single-helical and double-helical shape, which agree with the findings of the SPOD in terms of spatial shape and temporal frequency. A particular focus is laid upon the region upstream of the draft tube. An adjoint-based sensitivity analysis reveals that both instability modes are highly sensitive to mean flow modifications inside the transitional segment between runner and draft tube, such as induced by passive control devices. The knowledge of these sensitivities will guide to an optimized runner and draft tube design for controlling the PVC and the double-helical mode. |
Müller, Jens S; Lückoff, Finn; Kaiser, Thomas Ludwig; Paschereit, C Oliver; Oberleithner, Kilian In: Journal of Engineering for Gas Turbines and Power, vol. 144, iss. 1, 2022, ISSN: 0742-4795. @article{Mueller2022modal,In order to determine the flame transfer function of a combustion system, different mechanisms have been identified that need to be modeled. This study focuses on the generation and propagation of one of these mechanisms, namely, the swirl fluctuations downstream of a radial swirl combustor under isothermal conditions. Swirl fluctuations are generated experimentally by imposing acoustic perturbations. Time-resolved longitudinal and crosswise particle image velocimetry (PIV) measurements are conducted inside the mixing tube and combustion chamber to quantify the evolution of the swirl fluctuations. The measured flow response is decomposed using spectral proper orthogonal decomposition to unravel the contributions of different dynamical modes. In addition a resolvent analysis is conducted based on the linearized Navier–Stokes equations to reveal the intrinsically most amplified flow structures. Both, the data-driven and analytic approach, show that inertial waves are indeed present in the flow response and an inherent flow instability downstream of the swirler, which confirms recent theoretical works on inertial waves. However, the contribution of the identified inertial waves to the total swirl fluctuations turns out to be very small. This is suggested to be due to the very structured forcing at the swirler and the additional amplification of shear-driven modes. Overall, this work confirms the presence of inertial waves in highly turbulent swirl combustors and evaluates its relevance for industry-related configurations. It further outlines a methodology to analyze and predict their characteristics based on mean fields only, which is applicable for complex geometries of industrial relevance. |
Casel, Mario; Oberleithner, Kilian; Zhang, Feichi; Zirwes, Thorsten; Bockhorn, Henning; Trimis, Dimosthenis; Kaiser, Thomas Ludwig Resolvent-based modelling of coherent structures in a turbulent jet flame using a passive flame approach Journal Article In: Combustion and Flame, vol. 236, pp. 111695, 2022, ISSN: 00102180. @article{Casel2022,Motivated by the recent success in finding coherent structures in turbulent flows and describing their noise emission using the Resolvent Analysis (RA), the method is applied to a turbulent jet flame at and a corresponding non-reacting flow to investigate their axisymmetric dynamics. The RA, which in this study assumes a passive flame and neglects compressibility effects, is based on the governing equations linearized around the temporal mean state. It is validated against Spectral Proper Orthogonal Decomposition (SPOD) obtained from time-resolved snapshots. Both the temporal mean state and the snapshots are obtained by Large Eddy Simulation (LES). The SPOD reveals that an axisymmetric, convective Kelvin–Helmholtz (KH) instability is the dominant hydrodynamic mechanism in the jet flame within a narrow frequency band and incorporates up to of the turbulent kinetic energy. Results show that the RA is capable of reproducing the mode shapes seen in the SPOD. The RA furthermore allows to address the origin of these hydrodynamic structures: While the corresponding KH mode in a non-reacting turbulent jet flow is most sensitive to perturbations in the nozzle boundary layer, the same dominant mode in the turbulent Bunsen flame is most receptive to perturbations in the region between the nozzle edge and the annular pilot burner. The results suggest that the strong density gradients in this region initiate perturbations in the baroclinic torque, which are feeding the KH mode. Finally, a linear stability analysis proves that the high sensitivity of the KH structure is due to resonance with stable linear eigenmodes, which explains its high energy content. By applying the RA to a turbulent reacting flow, this study opens up a new pathway in analyzing the role of hydrodynamic structures in reacting flows. |
2021 |
Kaiser, Thomas Ludwig; Oberleithner, Kilian A global linearized framework for modelling shear dispersion and turbulent diffusion of passive scalar fluctuations Journal Article In: Journal of Fluid Mechanics, vol. 915, pp. A111, 2021, ISSN: 0022-1120. @article{Kaiser2021,In the field of gas-turbine engineering, entropy waves and fluctuations in fuel–air mixing are of significant importance. The impact of either mechanism on thermoacoustic stability of the engine and combustion noise considerably depends on how they are convected in the combustion chamber. In this work, a novel method is employed to analyse their convection. Both effects are modelled using a transport equation of a passive scalar linearized around the mean field. The linearized transport equation is discretized using finite elements. It is shown that turbulent passive scalar transport can be described by an eddy diffusivity in the linear framework. The method is furthermore validated against direct numerical simulation (DNS) of passive scalar transport in a turbulent channel flow. Taking the mean flow from the DNS as input, the method reproduces transport of periodic passive scalar fluctuations with high accuracy at negligible numerical expense. Previous studies investigated destructive interference of the passive scalar due to a non-uniform mean flow profile, a process termed mean flow shear dispersion. The method introduced in this study, however, allows us to additionally quantify the impact of molecular and turbulent diffusion. For the channel flow under investigation, mean flow shear dispersion is the dominant mechanism at low frequencies while, at higher frequencies, turbulent diffusion needs to be accounted for to reproduce the DNS results. Molecular diffusion, however, only has a minor effect on the overall convection in the turbulent channel flow. |
Lückoff, Finn; Kaiser, Thomas Ludwig; Paschereit, Christian Oliver; Oberleithner, Kilian Mean field coupling mechanisms explaining the impact of the precessing vortex core on the flame transfer function Journal Article In: Combustion and Flame, vol. 223, pp. 254-266, 2021, ISSN: 00102180. @article{Lueckoff2020a,The flame transfer functions (FTF) is a key quantity to assess the thermoacoustic properties of combustion systems. It is known to depend on the hydrodynamic instabilities of the combustor flow. This work investigates how the FTF is affected by a global flow instability known as the precessing vortex core (PVC) which is often observed in swirl flames. To study the exclusive effect of the PVC on the FTF, a perfectly premixed swirl flame is considered where the PVC mode is damped with a close to zero growth rate. An active flow control system is applied in the region of high receptivity to excite the PVC at precisely controlled amplitudes. The conducted experiments show that the excited mode corresponds to the least stable global mode predicted from mean field stability analysis and that the most responsive frequency is equal to the predicted global mode frequency, which brings credibility to the control approach. FTF measurements conducted at different PVC actuation amplitudes show that the FTF gain decreases significantly with increasing PVC amplitude while the FTF phase remains unchanged. The FTF gain reduction is explained by two mechanisms: the reduction in gain of the Kelvin–Helmholtz instability through mean field modifications and the upstream movement of the flames center of mass due to enhanced coherent fluctuations at the flame root. The unchanged FTF phase is traced back to an unchanged location of the most influential heat release rate fluctuations at the flame tip. This study suggests that the control of the PVC is an effective way to avoid or mitigate thermoacoustic instabilities. The control is thereby very efficient as it exploits the natural global hydrodynamic instability of the flow. |
2019 |
Kaiser, Thomas Ludwig; Lesshafft, Lutz; Oberleithner, Kilian Prediction of the Flow Response of a Turbulent Flame to Acoustic Pertubations Based on Mean Flow Resolvent Analysis Journal Article In: Journal of Engineering for Gas Turbines and Power, vol. 141, iss. 11, pp. 111021, 2019, ISSN: 0742-4795. @article{Kaiser2019f,Resolvent analysis is applied to a nonreacting and a reacting swirled jet flow. Time-averaged flows as input for the resolvent analysis and validation for the results of the resolvent analysis are obtained by experiments. We show that in the nonreacting (cold) flow case, the resolvent analysis is capable of predicting the hydrodynamic response to upstream harmonic acoustic forcing if the flow shows low-rank behavior. This is the case for low and moderate acoustic forcing amplitudes. Even for very strong acoustic velocity amplitudes that are of the same order of magnitude as the flow velocity, the resolvent analysis still provides reasonable results. The method also yields very good results for the reacting flow in terms of velocity fluctuation and heat release response to the acoustic forcing. This confirms the idea that the resolvent method could be applied to estimate the flame transfer function (FTF) based on the mean flow and flame. |
Kaiser, Thomas Ludwig; Oberleithner, Kilian; Selle, Laurent; Poinsot, Thierry Examining the Effect of Geometry Changes in Industrial Fuel Injection Systems On Hydrodynamic Structures with Biglobal Linear Stability Analysis Journal Article In: Journal of Engineering for Gas Turbines and Power, 2019, ISSN: 0742-4795. @article{Kaiser2019e,Shape optimization with respect to the suppression or enhancement of dynamical flow structures is an important topic in combustion research and beyond. In this paper, we investigate the flow in an industrial fuel injection system by experimental means, as well as large eddy simulation (LES) and linear stability analysis (LSA) for two configurations of the swirler. In the first configuration, the reference geometry, a precessing vortex core (PVC) occurs. In the second configuration, a center body is mounted in the interior of the injector. It is shown by both experiments and LES that the PVC is suppressed by the presence of the center body, while the mean flow remains nearly unaffected. The method of LSA is applied in order to explain the effect of the geometry change. The work shows that LSA is capable of explaining the occurrence or disappearance of coherent structures evolving on the turbulent flows if the geometry is changed. This is an important step in using LSA in the context of shape optimization of industrial fuel injectors. |
Kuhn, Phoebe; Kaiser, Thomas Ludwig; Soria, Julio; Oberleithner, Kilian Spectral decomposition of the turbulent self-similar jet and recomposition using linear dynamics Proceedings Article In: 2019, ISSN: 2642-0554. @inproceedings{Kuhn2019, |
2018 |
Kaiser, Thomas Ludwig; Poinsot, Thierry; Oberleithner, Kilian Stability and Sensitivity Analysis of Hydrodynamic Instabilities in Industrial Swirled Injection Systems Journal Article In: Journal of Engineering for Gas Turbines and Power, vol. 140, iss. 5, pp. 051506, 2018, ISSN: 0742-4795. @article{Kaiser2018,The hydrodynamic instability in an industrial, two-staged, counter-rotative, swirled injector of highly complex geometry is under investigation. Large eddy simulations (LES) show that the complicated and strongly nonparallel flow field in the injector is superimposed by a strong precessing vortex core (PVC). Mean flow fields of LES, validated by experimental particle image velocimetry (PIV) measurements, are used as input for both local and global linear stability analysis (LSA). It is shown that the origin of the instability is located at the exit plane of the primary injector. Mode shapes of both global and local LSA are compared to dynamic mode decomposition (DMD) based on LES snapshots, showing good agreement. The estimated frequencies for the instability are in good agreement with both the experiment and the simulation. Furthermore, the adjoint mode shapes retrieved by the global approach are used to find the best location for periodic forcing in order to control the PVC. |