| 1. |
- Guo, Chunyu, et al.
(författare)
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Influence of jet flow on hydrodynamic performance of a ducted propeller
- 2023
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Ingår i: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 35:12
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Tidskriftsartikel (refereegranskat)abstract
- This study introduces a concept that jet technology in the aeronautical field is used for active flow control to improve the hydrodynamic performance of a ducted propeller. Jet flow is added in front of the ducted propeller, and it produces a circumferential velocity that is opposite to the rotation direction of the rotor. An international standard ducted propeller was adopted to demonstrate this concept. The unsteady Reynolds-averaged Navier-Stokes method and the shear stress transport k − ω turbulence model were employed for the simulations. The open-source platform OpenFOAM was utilized. The overall efficiency η 0 of the ducted propeller first increases and then decreases with increasing the jet flow velocity R j f from 1 to 3 and the distance L to the rotation center from 0.2 D to 0.4 D . When the jet flow is at the optimal condition of R j f = 2 and L = 0.3 D , the maximum efficiency improvement of 3.1% is achieved for the ducted propeller. The reason is that the jet flow contributes to a pressure increase in the flow through the rotor. This effect is related to tip and hub vortices, which are disrupted by the jet flow and have relatively low vorticity magnitudes compared to the reference case without jet. The findings in this study have the potential to advance the development of active flow control technology for ships.
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| 2. |
- Guo, Chunyu, et al.
(författare)
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Numerical investigation of the scale effects of pump-jet propulsor with a pre-swirl stator
- 2023
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Ingår i: Physics of Fluids. - : AIP Publishing. - 1089-7666 .- 1070-6631. ; 35
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the performance of a pump-jet propulsor (PJP) with pre-swirl stator in open water is numerically investigated. Both full-scale and model-scale configurations are considered. The Reynolds-averaged Navier–Stokes equations and shear stress transport ?−? turbulence model are used in the numerical calculation. The computational domain is discretized using structured grids, and a rotating grid is affixed to the rotor to deal with the relative motion between the rotor and stationary components. The mesh quality is determined based on a grid uncertainty analysis. The numerical method is validated using model-scale experimental data. The simulation results reveal the influences of the scale size on the hydrodynamic performance and the distributions of the velocity, pressure and vorticity under three advance coefficients. With the increase in the advance coefficients, the scale influences on the efficiency become more obvious, and the efficiency of the full-scale PJP is always higher than that of the model-scale PJP. The full-scale configuration is found with a more significant instability in the gap vortex development, because it presents larger interaction between tip leakage vortex (TLV) and the inner wall of the duct. As the main velocity increases, the TLV shedding is delayed. Finally, the development process of gap vortices is analyzed for the difference operation conditions.
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| 3. |
- Lappalainen, Hanna K., et al.
(författare)
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Pan-Eurasian Experiment (PEEX) : towards a holistic understanding of the feedbacks and interactions in the land-atmosphere-ocean-society continuum in the northern Eurasian region
- 2016
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:22, s. 14421-14461
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Tidskriftsartikel (refereegranskat)abstract
- The northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes during the next decades. The Arctic-boreal natural environments play a crucial role in the global climate via albedo change, carbon sources and sinks as well as atmospheric aerosol production from biogenic volatile organic compounds. Furthermore, it is expected that global trade activities, demographic movement, and use of natural resources will be increasing in the Arctic regions. There is a need for a novel research approach, which not only identifies and tackles the relevant multi-disciplinary research questions, but also is able to make a holistic system analysis of the expected feedbacks. In this paper, we introduce the research agenda of the Pan-Eurasian Experiment (PEEX), a multi-scale, multi-disciplinary and international program started in 2012 (https://www.atm.helsinki.fi/peex/). PEEX sets a research approach by which large-scale research topics are investigated from a system perspective and which aims to fill the key gaps in our understanding of the feedbacks and interactions between the land-atmosphereaquatic-society continuum in the northern Eurasian region. We introduce here the state of the art for the key topics in the PEEX research agenda and present the future prospects of the research, which we see relevant in this context.
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| 4. |
- Yang, Chun, et al.
(författare)
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Serration of the duct trailing edge to affect the hydrodynamics and noise generation for a pump-jet propulsor
- 2024
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Ingår i: Physics of Fluids. - 1089-7666 .- 1070-6631. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- Inspired by the silent gliding feather of owl wings, the trailing edge of the duct of a pump-jet propulsor was designed with a similar serrated structure in order to reduce noise generation. Two distinct serrated structures were proposed and evaluated using the detached eddy simulation method with the shear stress transport k-omega turbulence model. The findings indicated that while the hydrodynamic efficiency changed within 1% upon the inclusion of the serrated trailing edge, a significant alteration existed in vortex structures of the wake. More horseshoe and secondary vortices were generated since large-scale vortices induced by the duct were disrupted circumferentially. This phenomenon expedited the distortion and mixing of trailing-edge vortices, causing flow instability. Furthermore, the serrated trailing-edge structure led to noise reduction. Particularly in the 0–1000 Hz range, the sound pressure level behind the duct showed a maximum reduction of 4.43 dB.
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| 5. |
- Yao, Huadong, 1982, et al.
(författare)
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A kinematic subgrid scale model for large eddy simulation of turbulence-generated sound
- 2009
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Ingår i: Journal of Turbulence. - 1468-5248. ; 10:19, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- In the hybrid approach of large-eddy simulation (LES) and Lighthill's acoustic analogy for turbulence-generated sound, the turbulence source fields are obtained using an LES and the turbulence-generated sound at far fields is calculated from Lighthill's acoustic analogy. As only the velocity fields at resolved scales are available from the LES, the Lighthill stress tensor, serving as a source term in Lighthill's acoustic equation, has to be evaluated from the resolved velocity fields. As a result, the contribution from the unresolved velocity fields is missing in the conventional LES. The sound of missing scales is shown to be important and hence needs to be modeled. The present study proposes a kinematic subgrid-scale (SGS) model which recasts the unresolved velocity fields into Lighthill's stress tensors. A kinematic simulation is used to construct the unresolved velocity fields with the imposed temporal statistics, which is consistent with the random sweeping hypothesis. The kinematic SGS model is used to calculate sound power spectra from isotropic turbulence and yields an improved result: the missing portion of the sound power spectra is approximately recovered in the LES
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| 6. |
- Yao, Huadong, 1982, et al.
(författare)
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Computation of Turbulence-Generated Noise by Large-Eddy Simulation
- 2009
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Ingår i: New Trends in Fluid Mechanics Research Proceedings of the Fifth International Conference on Fluid Mechanics. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783540759959 ; , s. 83-86
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Konferensbidrag (refereegranskat)abstract
- The hybrid method of large eddy simulation (LES) and the Lighthill analogy is being developed to compute the sound radiated from turbulent flows. The results obtained from the hybrid method are often contaminated by the absence of small scales in LES, since the energy level of sound is much smaller than that of turbulent flows. Previous researches investigate the effects of subgrid sacle (SGS) eddies on the frequency spectra of sound radiated by isotropic turbulence and suggest an SGS noise model to represent the SGS contributions to the frequency spectra. Their investigations are conducted in physical space and are unavoidably influenced by boundary conditions. In this paper, we propose to perform such calculations in Fourier space so that the effects of boundary conditions can be correctly treated. Posteriori tests are carried out to investigate the SGS contribution to the sound. The results obtained recover the -7/2 law within certain wave-number ranges, but under-estimate the amplitudes of the frequency spectra. The reason for the underestimation is also discussed.
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| 7. |
- Yao, Huadong, 1982, et al.
(författare)
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Time correlations of pressure in isotropic turbulence
- 2008
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Ingår i: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 20:025105
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Tidskriftsartikel (refereegranskat)abstract
- The time correlations of pressure modes in stationary isotropic turbulence are investigated under the Kraichnan and Tennekes “random sweeping” hypothesis. A simple model is obtained which predicts a universal form for the time correlations. It implies that the decorrelation process of pressure fluctuations in time is mainly dominated by the sweeping velocity, and the pressure correlations have the same decorrelation time scales as the velocity correlations. These results are verified usingdirect numerical simulations of isotropic turbulence at two moderate Reynolds numbers; the mode correlations collapse to the universal form when the time separations are scaled by wavenumber times the sweeping velocity, and the ratios of the correlation coefficients of pressure modes to those of velocity modes are approximately unity for the entire range of time separation.
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