| 1. |
- Lindblad, Daniel, 1989, et al.
(författare)
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A Nonreflecting Formulation for Turbomachinery Boundaries and Blade Row Interfaces
- 2019
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Ingår i: AIAA Scitech 2019 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624105784
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Konferensbidrag (refereegranskat)abstract
- Applying a nonreflecting formulation of a boundary condition or blade row interface is sometimes of paramount importance for obtaining an accurate prediction of turbomachinery blade flutter or tonal noise, just to name a few examples. Although the theoretical foundations for these type of boundary conditions have existed for several decades, nonreflecting boundary conditions still remain an area of active research. Today, much focus appears to be put towards obtaining more generic, higher-order and numerically stable formulations. In this work, a quasi-three-dimensional nonreflecting formulation based on the exact, nonreflecting boundary condition for a single frequency and azimuthal wave number developed by Giles is presented. The proposed formulation is applicable without modifications to both steady and unsteady simulations. An implementation strategy which is consistent for both a boundary condition and blade row interface is also presented. This implementation strategy does also partly address the stability problems often encountered when the type of formulation considered in the presented work is used together with a pseudo-time integration approach for converging the flow residual. Results from a set of two-dimensional validation cases are also presented to verify the formulation.
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| 2. |
- Lindblad, Daniel, 1989, et al.
(författare)
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Implementation of a Quasi-Three-Dimensional Nonreflecting Blade Row Interface for Steady and Unsteady Analysis of Axial Turbomachines
- 2018
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Ingår i: Turbomachinery and Core Noise. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624105609 ; 5
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Konferensbidrag (refereegranskat)abstract
- Higher order nonreflecting blade row interfaces are today widely used for performing both steady and unsteady simulations of the flow within axial turbomachines. In this paper, a quasi-three-dimensional nonreflecting interface based on the exact, two-dimensional nonreflecting boundary condition for a single frequency and azimuthal wave number developed by Giles is presented. The formulation has been implemented to work for both steady simulations as well as unsteady simulations employing the nonlinear Harmonic Balance method. The theory behind the construction of the nonreflecting interface is presented and details on the numerical implementation is also provided. The implementation is verified for two dimensional wave propagation along a straight cascade. It is shown that the interface correctly absorbs incoming waves, but also found that the chosen implementation strategy may be ill-posed. A simple solution to stabilize the implementation is therefore implemented, but future work should seek a more generic solution to this problem.
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| 3. |
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| 4. |
- Capitao Patrao, Alexandre, 1988, et al.
(författare)
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Aerodynamic and aeroacoustic comparison of optimized high-speed propeller blades
- 2018
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Ingår i: 2018 Joint Propulsion Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- The Boxprop is a high-speed propeller concept intended for aircraft engines, which features blade pairs connected at the tip in order to decrease tip vortex strength, possibly reducing noise and improving aerodynamic performance relative to conventional high-speed propellers. This paper investigates the aerodynamic and aeroacoustic performance of three aerodynamically optimized high speed propellers; a 6-bladed conventional propeller, a 12-bladed conventional propeller, and a 6-bladed Boxprop. Performance results will be be compared for the three designs, with a focus on sectional performance and wake flow characteristics, and will show that the 6-bladed Boxprop performance lies somewhat in-between its 6 and 12-bladed conventional counterparts. The noise level at various observer positions is presented, and shows that the noise roughly follows the values of efficiency for the three propellers, with the Boxprop noise level being higher than the 12-bladed conventional propeller, but lower than the 6-bladed one. The lower blade loading and higher efficiency of the Boxprop relative to the 6-bladed conventional propeller results in slightly lower levels of noise at cruise.
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| 5. |
- Lindblad, Daniel, 1989, et al.
(författare)
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Aeroacoustic Analysis of a Counter Rotating Open Rotor based on the Harmonic Balance Method
- 2018
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Ingår i: AIAA Aerospace Sciences Meeting, 2018. - Reston, Virginia : American Institute of Aeronautics and Astronautics. ; 2018:210059
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Konferensbidrag (refereegranskat)abstract
- The Counter Rotating Open Rotor (CROR) powerplant is an interesting architecture for future regional aircraft propulsion since it offers higher propulsive efficiency and thereby lower fuel consumption than the conventional Turbofan engine. The noise levels generated are however potentially larger compared to a Turbofan due in part to the absence of a ducting nacelle. This raises the need for efficient, high fidelity tools that can be used for the design and evaluation of new blade concepts capable of meeting strict noise regulations. In this paper, a Computational Aeroacoustics (CAA) platform for CRORs based on the Harmonic Balance method is presented. The method is formulated in the time domain and solves for the dominant frequencies of the flow by expressing the solution as a truncated Fourier series in time. Coupling between the resolved frequencies is furthermore possible since the nonlinear URANS equations are solved for. The far field acoustic signature is obtained by solving a convective form of the Ffowcs Williams-Hawkings equations for permeable surfaces. The CAA platform is applied to a generic, full scale, pusher type CROR operating at cruise conditions.
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| 6. |
- Lindblad, Daniel, 1989, et al.
(författare)
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Convergence Acceleration of the Harmonic Balance Method using a Time-Level Preconditioner
- 2020
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Ingår i: AIAA Scitech 2020 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624105951 ; 3
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Konferensbidrag (refereegranskat)abstract
- The Harmonic Balance method is nowadays widely applied for numerically solving problems that are known to possess time-periodic solutions. Key reasons for its success are its wide range of applicability, relative ease of implementation, and computational efficiency compared to time-accurate approaches. The computational efficiency of the Harmonic Balance method is partly derived from the fact that it searches directly for a periodic solution, instead of integrating the governing equations in time until a periodic solution is reached. Convergence acceleration techniques such as multigrid, implicit residual smoothing and local time stepping may also be used to improve the efficiency of the Harmonic Balance method. This paper considers another option for accelerating convergence, namely a novel time-level preconditioner that can be applied to the Harmonic Balance residual locally in each computational cell. This preconditioner is derived from a rigorous stability analysis of the Harmonic Balance equations and is shown to give a speed-up factor of 2 when applied to simulations of laminar vortex shedding behind a circular cylinder.
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| 7. |
- Lindblad, Daniel, 1989, et al.
(författare)
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Convergence Acceleration of the Harmonic Balance Method using a Time-Level Preconditioner
- 2020
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Ingår i: AIAA Journal. - 1533-385X .- 0001-1452. ; 58:11, s. 4908-4922
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Tidskriftsartikel (refereegranskat)abstract
- The harmonic balance method is nowadays widely applied for numerically solving problems that are known to possess time-periodic solutions. Key reasons for its success are its wide range of applicability, relative ease of implementation, and computational efficiency compared to time-accurate approaches. The computational efficiency of the harmonic balance method is partly derived from the fact that it searches directly for a periodic solution instead of integrating the governing equations in time until a periodic solution is reached. Convergence acceleration techniques such as multigrid, implicit residual smoothing, and local time stepping may also be used to improve the efficiency of the harmonic balance method. This paper considers another option for accelerating convergence, namely, a novel time-level preconditioner that can be applied to the harmonic balance residual locally in each computational cell. The benefit of employing this preconditioner is analyzed both from a theoretical perspective, by performing a rigorous stability analysis based on the linearized Euler equations, and from a numerical perspective, by applying it to two test cases.
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| 8. |
- Lindblad, Daniel, 1989
(författare)
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Implementation of a Harmonic Balance Solver into a Compressible CFD Code
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this project the Harmonic Balance technique for solving time periodic problems in fluid dynamics has been implemented into the parallel Navier-Stokes solver G3D::Flow. Performanceissues with regards to the original implementation are identified using two profilingtools, Cachegrind and Allinea-Map 6.11. These findings are used to derive a numericalalgorithm that benefits from both improved cache locality and loop performanceby utlizing blocked matrix multiplication and vectorization. The scaling properties of theHarmonic Balance technique are also demonstrated by deriving an approximate performancemodel and comparing it to numerical results obtained at the Triolith and Hebbe computerclusters at Linköping and Chalmers Univeristy.
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| 9. |
- Lindblad, Daniel, 1989, et al.
(författare)
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Minimizing Aliasing in Multiple Frequency Harmonic Balance Computations
- 2022
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Ingår i: Journal of Scientific Computing. - : Springer Science and Business Media LLC. - 0885-7474 .- 1573-7691. ; 91:2
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Tidskriftsartikel (refereegranskat)abstract
- The harmonic balance method has emerged as an efficient and accurate approach for computing periodic, as well as almost periodic, solutions to nonlinear ordinary differential equations. The accuracy of the harmonic balance method can however be negatively impacted by aliasing. Aliasing occurs because Fourier coefficients of nonlinear terms in the governing equations are approximated by a discrete Fourier transform (DFT). Understanding how aliasing occurs when the DFT is applied is therefore essential in improving the accuracy of the harmonic balance method. In this work, a new operator that describe the fold-back, i.e. aliasing, of unresolved frequencies onto the resolved ones is developed. The norm of this operator is then used as a metric for investigating how the time sampling should be performed to minimize aliasing. It is found that a time sampling which minimizes the condition number of the DFT matrix is the best choice in this regard, both for single and multiple frequency problems. These findings are also verified for the Duffing oscillator. Finally, a strategy for oversampling multiple frequency harmonic balance computations is developed and tested.
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| 10. |
- Lindblad, Daniel, 1989
(författare)
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Numerical Methods for Aeroacoustic Analysis of Turbomachinery
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Air transportation is today an integral part of many peoples life and it continuously grow to serve more of us in new and ingenious ways. There are however negative sides to this growth as well, such as increased noise around airports and more CO2 emissions, which must be addressed if aviation is to be part of a sustainable future. A key ingredient to successfully addressing these issues is accurate and reliable numerical tools that can be used to investigate and/or optimize new and existing technologies. This thesis presents a computational framework for predicting the noise generated by a fuel efficient aircraft engine propulsor known as the Counter Rotating Open Rotor (CROR). The framework solves the Favre-Averaged Navier Stokes equations using the Finite Volume method for spatial discretization and the Harmonic Balance method for temporal discretization in order to obtain a numerical solution of the transient flow field around the CROR blades. This solution is further coupled with an acoustic analogy in which a convective form of the Ffowcs Williams-Hawkings equation for permeable integration surfaces is used to determine the far field noise signature of the CROR at any arbitrary observer location. The underlying theory of both the temporal discretization scheme (Harmonic Balance method) and the acoustic analogy (Ffowcs Williams-Hawkings equation) are presented in detail in order to investigate the applicability of these methods for predicting CROR noise. It is found that the Harmonic Balance method performs well for predicting turbomachinery noise in general, but also that issues with aliasing might impair the accuracy of the results when the flow-field becomes strongly nonlinear. The acoustic analogy is found to perform well for propagating the types of noise generated by a CROR. Issues may however occur when wakes and shock waves cross the integration surface. This makes the placement of the integration surface a complicated task for the particular formulation of the Ffowcs Williams - Hawkings equation used in this work
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| 11. |
- Lindblad, Daniel, 1989
(författare)
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Numerical Methods for Aeroacoustic Analysis of Turbomachines
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Numerical simulations are important tools for developing new aircraft that can meet future needs. When numerical simulations are used to compute aircraft noise, a two-step procedure is often employed. In the first step, the noise sources are determined using, e.g., computational fluid dynamics. In the second step, noise propagation between the sources and the observers is then computed, often by solving an acoustic analogy. In this thesis, a range of numerical methods that are useful when turbomachinery tonal noise is computed based on such a two-step procedure are considered. For the first step, the time-domain Harmonic Balance method proposed by Hall et al. is used. To improve the accuracy of this method, the impact of time sampling on aliasing is investigated for both the single frequency and the multiple frequency problem. A new oversampling strategy for the multiple frequency problem is also developed for this purpose. Another challenge associated with the Harmonic Balance method is numerical instabilities. This problem is investigated using a von Neumann stability analysis. Based on knowledge gained from this analysis, a novel preconditioner that stabilizes an explicit Harmonic Balance solver is then developed. To minimize reflections of waves against boundaries of the computational domain, a generic formulation of the exact, nonlocal, nonreflecting boundary condition introduced by Giles is also derived and implemented to work with the Harmonic Balance method. For the second step, the convective Ffowcs Williams - Hawkings equation for permeable surfaces proposed by Najafi-Yazidi et al. is used. A detailed derivation of this equation is first presented. The solution to this equation for the case when the surface is stationary relative to the observer is then derived. Finally, a tool for computing duct modes based on a normal mode analysis of the linearized Euler equations is presented. In summary, the work reported in this thesis provides a detailed analysis of the aforementioned methods, that should be valuable for people who are interested in adopting them. It also provides some improvements, which can help to further improve the results obtained with these methods.
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| 12. |
- Lindblad, Daniel, 1989, et al.
(författare)
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Validating the Harmonic Balance Method for Turbomachinery Tonal Noise Predictions
- 2017
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Ingår i: AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- A computational method for predicting turbomachinery tonal noise is presented. It is based on the Harmonic Balance method, which solves for the dominant frequencies of the flow generated by bladerow interaction. Coupling between the resolved frequencies is furthermore enabled since the Harmonic Balance method is applicable to the nonlinear Euler or Navier-Stokes equations. The implementation is also validated against two cases from the Fourth Computational Aeroacoustics Workshop on Benchmark Problems hosted by NASA. The computational setup is explained in detail and specific challenges encountered in both benchmark problems are discussed. Results generally show very good agreement with data published by several other authors, giving confidence in the capability of the method. Some remaining challenges for the implemented method necessary to compute full scale turbomachinery noise are also identified and discussed.
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| 13. |
- Minelli, Guglielmo, 1988, et al.
(författare)
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Using horizontal sonic crystals to reduce the aeroacosutic signature of a simplified ICE3 train model
- 2021
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Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 172
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Tidskriftsartikel (refereegranskat)abstract
- The design of noise barriers for high-speed trains is challenging due to the flow interaction between the train body and barriers. A failed design could affect the flow that in turn introduces additional aerodynamic loads to the train and generates extra noise. This study is the first investigation to numerically explore the detailed effects of noise barriers on high-speed trains. In particular, horizontal sonic crystals are compared to vertical, closed at the ground barriers in order to investigate the detailed effects of different noise screens on high-speed trains. The compressible IDDES is used to simulate the flow. The focus of this study is twofold. The first is to test if an alternative barrier typology can effectively reduce the noise signature, without having an impact on the train’s aerodynamic performance. The second is to explore the connection between the near-field velocity fluctuations and the far-field noise. A few specific tonal frequency components have been commonly reported but not clearly explained in the literature. It is unclear if the specific tonal components are less dependent on the Reynolds numbers, although, in general, energetic flow structures are dependent on inflow speeds. Concerning the noise reduction, the results show that the sonic crystal barrier case has a significantly better performance. A modal analysis is used to explore the causes of the tonal peaks and the association of the underbody swirling vortices to the far-field noise is described.
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| 14. |
- Montero Villar, Gonzalo, 1992, et al.
(författare)
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Effect of Airfoil Parametrization on the Optimization of Counter Rotating Open Rotors
- 2019
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Ingår i: AIAA Scitech 2019 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- The present study compares two optimizations performed on Counter Rotating Open Rotors (CRORs) running at the same operating condition. The main difference between the two optimizations is the airfoil profile used to construct the blades. The first, uses the NACA 16 family of airfoils, whereas the second one, uses a parametrized airfoil type, CST. Two independent multi-objective optimizations are carried out using approximately the same computational resources. All the design variables except those concerning the airfoil profile, are kept with the same design freedom so that a fair comparison can be made. Both sets of configurations are aerodynamically optimized for maximum thrust coefficient and efficiency at top of climb conditions. The optimization is performed using multi-objective Differential Evolution (DE) coupled with 3D RANS simulations and Radial Basis Function (RBF) meta-modeling.
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| 15. |
- Montero Villar, Gonzalo, 1992, et al.
(författare)
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Investigation of Phase-Lagged Boundary Conditions for Turbulence Resolving Turbomachinery Simulations
- 2020
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Ingår i: AIAA AVIATION 2020 FORUM. - Reston, Virginia : American Institute of Aeronautics and Astronautics. ; 1
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Konferensbidrag (refereegranskat)abstract
- The present work explores whether phase-lagged boundary conditions can be used to perform scale resolving simulations of turbomachines. The phase-lagged approach considered is based on storing the flow signal, both at the pitch-wise boundaries and the rotor-stator interface, as its temporal Fourier coefficients for a finite number of harmonics. The method is implemented in an in-house CFD solver, G3D::Flow, which can perform both URANS and hybrid RANS/LES simulations. In order to evaluate the performance of the phase-lagged boundary condition, a comparison is made with a sliding mesh simulation on a compressor cascade. Furthermore, the possibility of breaking an error feedback loop generated in the sampling process by including multiple blade passages is also investigated. It is found that this approach greatly improves convergence and accuracy of the sampling.
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| 16. |
- Montero Villar, Gonzalo, 1992, et al.
(författare)
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Multi-Objective Optimization of a Counter Rotating Open Rotor using Evolutionary Algorithms
- 2018
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Ingår i: 2018 Multidisciplinary Analysis and Optimization Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624105500
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Konferensbidrag (refereegranskat)abstract
- In the present work, a recently developed platform for turbomachinery design and optimization based on Evolutionary Algorithms (EAs) is presented. Two types of evolutionary algorithms are implemented. The first one based on Genetic Algorithms (GAs) and the second one on Differential Evolution (DE), both able to handle single- and multi-objective as well as constrained and unconstrained optimization problems. Meta-modeling based on Radial Basis Functions (RBFs) is used in order to help accelerate the optimization when the objective function is too expensive to be evaluated inside the EA. Details on the implementation as well as validation results for a set of well-known benchmark cases are presented. The platform is also combined with 3D CFD simulations to optimize the aerodynamic performance of a Counter Rotating Open Rotor (CROR). Results from the CROR optimization are discussed and analyzed.
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| 17. |
- Wukie, Nathan A., et al.
(författare)
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Noisyduck: An open-source python tool for computing eigenmode decompositions of duct flows
- 2019
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Ingår i: 25th AIAA/CEAS Aeroacoustics Conference, 2019. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- Wave propagation in ducts is a rich topic that is important to consider in the design of turbomachinery components for aero-engine applications. In order to describe how the waves propagate inside a duct, an eigenmode decomposition of the equations modeling the fluid problem can be performed. The resulting eigenmodes may be used to construct nonreflecting boundary conditions, to investigate flow physics, or for post-processing numerical simulations to track the evolution of modal content through a computational domain. In the present work, an open-source Python tool, called noisyduck, was developed to compute eigenmode decompositions of the linearized Euler equations that model linear wave propagation in a duct with constant cross-section. The numerical method is verified against analytical solutions and reported results from the literature for uniform axial flow and swirling flow in an annulus. The noisyduck tool is made available as a public resource with the intent of reducing duplicated research efforts, and clarifying equation sets and formulations with respect to the literature in the area of eigenmode decompositions for problems in duct acoustics.
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