| 1. |
- Malla, Bhupatindra, et al.
(författare)
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Proper Orthogonal Decomposition on LES and PIV Data Sets from a Mach 0.9 Jet.
- 2012
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Ingår i: 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition. - : AIAA. ; , s. 12-
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Konferensbidrag (refereegranskat)abstract
- This paper contains the complementary analysis of the results obtained through computational and experimental methods using the technique of Proper Orthogonal Decomposition (POD). A detailed study of the experimentally obtained flow field data using the method of POD has already been accomplished. The experimental data consists of the 2D visualization of the velocity field obtained using Particle Image Velocimetry (PIV). The computational process is initialized with the simulation of the 3D flow field using a steady state RANS flow solver. RANS is used as a platform to proceed towards capturing the unsteadiness of the flow field which is accomplished using the Large Eddy Simulation (LES). A significant match in the characteristics of the mode shapes has been observed, in both the axial and radial components of the velocity field, however, there is difference in the distribution of the energies over the modes. The LES predicts the energies to be higher at the lowest modes and the energy drop off rate is higher. On the contrary, PIV predicts lower energies at the first few modes, in comparison to the LES results, however the energy drop off rate is smaller.
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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. |
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| 5. |
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| 6. |
- Nilsson, Johan, et al.
(författare)
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Passive load control in backward-facing step flow by using chevrons
- 2016
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Ingår i: Proceedings of the 5th International Conference on Jets, Wakes and Separated Flows, ICJWSF 2015. - Cham : Springer International Publishing. - 9783319306001 ; 185, s. 223-239
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Konferensbidrag (refereegranskat)abstract
- The ability of chevrons at the top edge of a backward-facing step to reduce downstream surface pressure fluctuations is investigated numerically. Three different chevron configurations are compared against a baseline case without chevrons. Low frequency reduction in the surface pressure fluctuations is observed for two of the configurations. The chevrons do not appear to have a significant effect on the flow as the mean reattachment length for all configurations is nearly constant and there is only a small increase in streamwise turbulence for one configuration with the other configurations unchanged.
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| 7. |
- Stoddard, William, et al.
(författare)
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Simulations of Detonations Based Cycles in Tubes with Multiple Openings
- 2010
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Ingår i: 46<sup>th</sup> AIAA / ASME / SAE / ASEE Joint Propulsion Conference and Exhibit. - 9781600867477
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Konferensbidrag (refereegranskat)abstract
- Computational fluid dynamics (CFD) analysis on detonations, and the resulting exhaust dynamics are studied. Specifically the analysis seeks to quantify the relative ability of the cycles to refill with unburned air that can be mixed with fuel for pulsed detonation. The relative magnitude of the effects of ignition location, fuel location, and basic tube geometry on this self-aspiration are first investigated in smaller, more time-efficient simulations. From these, additional variables, such as ejectors, and different inlet shapes are tested with the most promising configuration of fuel ignition and overall pipe geometry. These further tests are carried out at scales more comparable to the experimental setups. The results obtained are compared with the previous pulse-jet configurations and known pulse detonation data. Steps are taken toward optimizing a static thrust self-aspirating valveless pulse detonation engine (PDE).
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| 8. |
- Semlitsch, Bernhard, et al.
(författare)
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The generation mechanism of higher screech tone harmonics in supersonic jets
- 2020
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 893:A9
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Tidskriftsartikel (refereegranskat)abstract
- The generation mechanism of screech harmonics in supersonic exhausts is revealed using shadowgraph imaging and acoustic far-field measurements for a rectangular, high aspect-ratio nozzle. The coherent information associated with screech and its harmonics, i.e. flow structures and acoustic radiation pattern, is extracted from the time-resolved shadowgraph images. We show that, for large lateral distortions of the jet plume, the passage of screech associated flow structures triggers the screech-cyclic formation of shocks, which travel downstream and merge with the original shocks. The interaction of the shock waves with the flow structures associated with screech alters the appearance of the perturbations in the mixing layer, which constitute the higher harmonics of screech. Visualisations of the acoustic radiation pattern expose that the third and higher screech tone harmonics originate from these interaction locations. Further, the occurrence of mode resonance between the screech and its harmonics is demonstrated, where the mode resonance location coincides with the screech tone origin
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| 9. |
- Ahn, MyeongHwan, et al.
(författare)
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Large-eddy simulations of flow and aeroacoustics of twin square jets including turbulence tripping
- 2023
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Ingår i: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 35:6
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the flow and aeroacoustics of twin square (i.e., aspect ratio of 1.0) jets by implicit large-eddy simulations (LESs) under a nozzle pressure ratio of 3.0 and a temperature ratio of 1.0 conditions. A second-order central scheme coupled with a modified Jameson's artificial dissipation is used to resolve acoustics as well as to capture discontinuous solutions, e.g., shock waves. The flow boundary layer inside of the nozzle is tripped, using a small step in the convergent section of the nozzle. The time-averaged axial velocity and turbulent kinetic energy of LES with boundary layer tripping approaches better to particle image velocimetry experimental data than the LES without turbulence tripping case. A two-point space–time cross-correlation analysis suggests that the twin jets are screeching and are coupled to each other in a symmetrical flapping mode. Intense pressure fluctuations and standing waves are observed between the jets. Spectral proper orthogonal decomposition (SPOD) confirms the determined mode and the relevant wave propagation. The upstream propagating mode associated with the shock-cell structures is confined inside jets. Far-field noise obtained by solving Ffowcs Williams and Hawkings equation is in good agreement with the measured acoustic data. The symmetrical flapping mode of twin jets yields different levels of the screech tone depending on observation planes. The tonalities—the fundamental tone, second and third harmonics—appear clearly in the far-field, showing different contributions at angles corresponding to the directivities revealed by SPOD.
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| 10. |
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Flow, Turbulence and Combustion : Special Issue: Jets, Wakes, and Separated Flows
- 2019
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Ingår i: Flow, Turbulence and Combustion. - : Springer Netherlands. - 1386-6184 .- 1573-1987.
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Samlingsverk (redaktörskap) (refereegranskat)abstract
- The Sixth International Conference on Jets, Wakes, and Separated Flows (ICJWSF17), was held at the University of Cincinnati, Ohio, USA in October 9–12, 2017. This special issue contains 14 papers selected from a total of 80 papers presented during the ICJWSF17 Conference. The conference goal was to give scientists, engineers and students from the US and other countries an opportunity to discuss research on jets, wakes, and separated flows, topics that are of significant importance and interest in the field of fluid mechanics, with impact on diverse fields of engineering such as aeroacoustics, combustion, heat transfer, multi-phase flows, and turbomachinery. The conference aims to promote exchange of information on advances in the field, and to spawn collaborative research between the participants. This special issue of Flow Turbulence and Combustion is the first to include selected papers from this conference. The papers were selected and reviewed on the basis of their quality as judged by the reviewers in relation to the aims and scope of the Journal.All papers published in this Special Issue were subjected to the same rigorous peer- review process as normal submissions to the Journal. It was therefore independent from the review of the conference submissions, which was used only in order to select the authors that were invited to submit a paper for this volume. The Guest Editors are grateful for the opportunity to publish this volume, which makes a substantial contribution to advancing the field of fluid mechanics.
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