| 1. |
- Abou-Taouk, Abdallah, 1982, et al.
(författare)
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CFD investigation of a Stirling engine f exi-fuel burner based on MILD combustion
- 2015
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Ingår i: Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer. - 2377-2816. ; 0, s. 855-858
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Konferensbidrag (refereegranskat)abstract
- This paper presents the comparison of results from tests and 3D CFD combustion simulations based on both RANS and hybrid URANS/LES (SAS-SST model) turbulence models applied to an industrial Stirling engine combustion chamber at atmospheric pressure. Both natural gas and landf ll gas mixture were simulated. The combustor is designed to operate in the MILD combustion mode which is characterized by low f ame temperatures and low NOX emissions. The kinetics for the landf ll gas was represented by a new optimized 4-step global mechanism, named AAT4NR, which was optimized for the present landf ll mixture. The new mechanism is developed using well-established optimization tools, where the coeff cients of the 4-step global chemistry are determined from a set of reference detailed chemistry solutions. A good agreement with measurements is found concerning major emissions, temperatures and NOX-levels.
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| 2. |
- Cuppoletti, Daniel, et al.
(författare)
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Elimination of shock associated noise in supersonic jets by destructive wave interference
- 2018
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Ingår i: AIAA Aerospace Sciences Meeting, 2018. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- A novel application of fluidic injection was developed to investigate and understand the effects of discrete fluidic injection internal to the jet nozzle. Various injection locations, angles, and conditions were studied resulting in unique acoustic behavior and flow field modifications. For most conditions the acoustics are relatively unaffected or increased, but for very specific conditions noise was drastically decreased. For optimized conditions the shock noise was completely eliminated and in other cases a jet instability was generated that significantly decreased high frequency noise. Measurements of the velocity field indicated that shock interaction due to shocks from the injection jet interact with the primary jet shocks, and significantly reduce the shock strength, attributing massive shock noise reduction. Validation of the experimental results was achieved with LES, which provided additional insight into the shock suppression due to resolution of the flowfield internal to the nozzle. Optimal injection parameters resulted in reduction of OASPL of -7 dB at the upstream and downstream angles simultaneously through a combination of shock disruption and streamwise vorticity introduction. A new mechanism of supersonic jet noise reduction, destructive interference of the shock structure in the jet is reported.
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| 3. |
- Cuppoletti, Daniel, et al.
(författare)
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Elimination of Shock-Associated Noise in Supersonic Jets by Destructive Wave Interference
- 2019
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Ingår i: AIAA Journal. - 1533-385X .- 0001-1452. ; 57:2, s. 720-734
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Tidskriftsartikel (refereegranskat)abstract
- A novel application of fluidic injection was developed to investigate and understand the effects of discrete fluidic injection internal to the jet nozzle. Various injection locations, angles, and conditions were studied, resulting in unique acoustic behavior and flowfield modifications. For most conditions, the acoustics are relatively unaffected or increased, but for very specific conditions, noise was drastically decreased. For optimized conditions, the shock noise was completely eliminated, and in other cases, a jet instability was generated that significantly decreased high-frequency noise. Measurements of the velocity field indicated that shock interaction, due to shocks from the injection jets, interacts with the primary jet shocks and significantly reduces the shock strength, attributing massive shock noise reduction. Validation of the experimental results was achieved with large-eddy simulation, which provided additional insight into the shock suppression due to resolution of the flowfield internal to the nozzle. Optimal injection parameters resulted in reduction of overall sound pressure level of -7 d B at the upstream and downstream angles simultaneously through a combination of shock disruption and streamwise vorticity introduction. A new mechanism of supersonic jet noise reduction and destructive interference of the shock structure in the jet is reported.
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| 4. |
- Larusson, Ragnar, 1986, et al.
(författare)
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Investigation of supersonic jet flow using modal decomposition
- 2014
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Ingår i: 20th AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102851
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Konferensbidrag (refereegranskat)abstract
- Supersonic jet noise has been an important research topic for decades, both for its relevance within the aeronautical industry and for its scientific value. In the present study, the jet flow field produced by a slightly over expanded conical convergent-divergent nozzle was studied using modal decomposition. The nozzle exit Mach number is 1.58 at a nozzle pressure ratio of 4.0. The nozzle has an engine like geometry with a relatively sharp throat, creating an internal shock wave. Two different methods for modal decomposition were applied to the supersonic jet flow, namely Dynamic Mode Decomposition (DMD) and a method based on the Arnoldi algorithm. The DMD algorithm returns the eigenmodes of an approximate linear flow operator, which is constructed from the data set used in the algorithm. In the present study, the DMD algorithm was applied to observational data from a Large Eddy Simulation (LES) and 2D axisymmetric URANS simulation, respectively. The Arnoldi algorithm uses a 2D linearized flow solver to project the linear flow dynamics onto a reduced order Krylov subspace and computes the eigenmodes of that projection. Here, A steady state RANS solution of the jet flow was used as a reference state in the linear solver. The Results of the Arnoldi analysis for a azimuthal wavenumber m = 0 were directly compered with the DMD modes of a URANS simulations. It was found that both methods produce nearly identical modes in this case. The DMD modes of the LES data are comparable with the Arnoldi and URANS DMD modes in terms of frequency, acoustic radiation, and shock-cell movement. They were however, found to be significantly more damped. An additional Arnoldi analysis was performed with azimuthal wavenumber m = 1 and the resulting least damped mode had a frequency close to the experimentally observed screech frequency for the same nozzle geometry and operating condition. An animation of the evolution of the eigenmode reveals a feedback loop mechanisms that might contribute to the formation of screech tones.
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| 5. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
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Noise Control of Supersonic Jet with Steady and Flapping Fluidic Injection
- 2015
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Ingår i: AIAA Journal. - 1533-385X .- 0001-1452. ; 53:11, s. 3251-3272
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Tidskriftsartikel (refereegranskat)abstract
- Large-eddy simulation is used to investigate steady-state mass flow injection into a supersonic jet stream with and without flapping motion of the microjets. The results are validated with particle image velocimetry and acoustic measurements. The effect of microjet penetration on the far-field acoustics is studied by altering the number of injectors, the cross-sectional area of each injector, and the injection mass flow. The injectors are evenly distributed around the nozzle exit. The injection angle is 90 deg relative to the main jet flow. This research is a continuation of a previous large-eddy simulation study of pulsed injection that showed that the unsteady injection-induced pressure pulses in the jet caused increased tonal noise for far-field observers at low angles. Flapping jet injection was shown to minimize the creation of the pressure pulses, except for high-amplitude flapping angles and high injection mass flows, where the injections divert out of the shear layer and introduce periodic superposition of the double shock-cell structure. Furthermore, the flapping injection did not show improved noise reduction compared with the steady injection, which is essentially promising because steady injection proves to be a more practical solution for implementation in real jet engine applications.
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| 6. |
- Larusson, Ragnar, 1986, et al.
(författare)
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Comparison of Eigenmode Extraction Techniques for Separated Nozzle Flows
- 2014
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Ingår i: 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and exhibit 2014; Cleveland; United States; 28 July 2014 through 30 July 2014. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624103032
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Konferensbidrag (refereegranskat)abstract
- Results of a previously published Arnoldi eigenmode analysis on a separated flow inside a convergent-divergent nozzle are compared with results obtained using a Dynamic Mode Decomposition (DMD) algorithm. The Arnoldi analysis employs a linearized flow solver and as a result, does not consider nonlinearity and turbulence. The DMD method is a snapshot- based approach, which approximates the Koopman modes of the nonlinear flow. In the present study the DMD algorithm has been applied to a data set from a two-dimensional URANS simulation of the separated nozzle flow. As such, it can take into account the full information of the nonlinear flow, including turbulence. The objective of this study is to investigate the effects of turbulence on the linear analysis. The results show that the Arnoldi and the DMD algorithms do in certain cases produce almost identical modes in terms of frequency, damping and structure. This indicates that even though the Arnoldi method needs an explicit linearization of the flow dynamics and excludes turbulence, it does reveal modes with discrete frequency that could be excited in the nonlinear flow with modeled turbulence.
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| 7. |
- Larusson, Ragnar, 1986, et al.
(författare)
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Investigation of Screech in Supersonic Jets Using Modal Decomposition
- 2014
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Ingår i: Proceedings of NSCM-27: the 27th Nordic Seminar on Computational Mechanics. - 0348-467X. ; , s. 25-28
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The present study attempts to identify the eigenmodes that are associated with the screech mechanism by means of Dynamic Mode Decomposition (DMD) and a method based on the Arnoldi eigenvalue algorithm, respectively.
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| 8. |
- Larusson, Ragnar, 1986, et al.
(författare)
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Linear Stability Analysis Using the Arnoldi Eigenmode Extraction Technique Applied to Separated Nozzle Flow
- 2013
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Ingår i: 49TH AIAA/ASME/SAE/ASEE JOINT PROPULSION CONFERENCE, July 14 - 17, 2013. San Jose, CA, USA. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102226 ; 1:Part F
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Konferensbidrag (refereegranskat)abstract
- A linear stability analysis method, employing a linearized flow solver combined with the Arnoldi algorithm for eigenmode approximation, was applied to a separated supersonic flow inside an axially symmetric convergent-divergent nozzle. The eigenmodes were analyzed in terms of frequency, structure and damping. For the case demonstrated, four different types of axial modes and four different types of tangential modes were identified. Results show that the least damped axial modes displayed a relatively low frequency range, 60 Hz to 300 Hz. These modes showed a movement of the shock pattern inside the nozzle. The other mode types exhibited higher frequencies, strong shear layer interactions and acoustic waves. Additionally, the method revealed the presence of a continuous spectrum in the nozzle flow field.
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