| 1. |
- Ahlman, Daniel, et al.
(författare)
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Direct numerical simulation of mixing in a plane compressible and turbulent wall jet
- 2005
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Ingår i: 4th International Symposium on Turbulence and Shear Flow Phenomena. ; , s. 1131-1136
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Konferensbidrag (refereegranskat)abstract
- Direct numerical simulation (DNS) is used to simulate the mixing of a passive scalar in a plane compressible and turbulent wall jet. The Mach number of the jet is M = 0.5 at the inlet. The downstream development of the jet is studied and compared to experimental data. Mixing in the inner and outer shear layers of the wall jet is investigated through scalar fluxes, the probability density function of the scalar concentration and the joint probability density function of the wall normal velocity fluctuation and the scalar concentration
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| 2. |
- Bai, X. S., et al.
(författare)
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Closing Remarks
- 2022
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Ingår i: Advanced Turbulent Combustion Physics and Applications. - : Cambridge University Press. ; , s. 460-463
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Brethouwer, Gert, et al.
(författare)
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A numerical study of homogeneous turbulence and passive scalar transport in rotating shear flow
- 2005
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Konferensbidrag (refereegranskat)abstract
- Direct numerical simulations of homogeneous turbulent shear flow subject to spanwise rotation have been carried out. A passive scalar field with an imposed mean gradient was also included in the simulations. The flow reached a state close to the equilibrium structure with a slowly varying turbulence anisotropy and nondimensional shear number SK/ε. Different rotation numbers have been used in the simulations and the rotation either accelerated the growth of kinetic energy or slowed it down. The growth was approximately exponential in a few cases at intermediate shear times. At longer shear times the kinetic energy was growing linearly in most of the cases. The rotation affected considerably the anisotropy of the flow and the velocity correlations. The scalar-velocity fluctuation correlations and the direction of the turbulent scalar flux vector were according to the simulations also strongly influenced by rotation, even as the mechanical to scalar time scale ratio.
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| 4. |
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| 5. |
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| 6. |
- Brethouwer, Gert
(författare)
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Heat transfer in rotating channel flow
- 2019
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Ingår i: 11th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2019. - : International Symposium on Turbulence and Shear Flow Phenomena, TSFP.
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Konferensbidrag (refereegranskat)abstract
- In the present study (Brethouwer, 2018, 2019) heat transfer in rotating turbulent channel flow is investigated through DNS at moderate Reynolds numbers. It is shown that rotation has a large influence on the mean temperature profiles and heat fluxes and also on the structure of the temperature field. The turbulent Prandtl number on the unstable side is strongly reduced by rotation, implying that the Reynolds analogy for momentum-heat transfer does not necessarily hold for rotating turbulent channel flow.
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| 7. |
- Brethouwer, Gert, et al.
(författare)
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Investigation of fluid particle dispersion in stably stratified turbulence
- 2009
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Ingår i: 6th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2009. - : International Symposium on Turbulence and Shear Flow Phenomena, TSFP. ; , s. 1160-1163
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Konferensbidrag (refereegranskat)abstract
- Numerical simulations are used to study vertical dispersion of fluid particles in homogeneous turbulent flows with a stable stratification (Brethouwer and Lindborg, 2009). The results of direct numerical simulations are in good agreement with the relation for the long time fluid particle dispersion, δz2 = 2εP t/N2, derived by Lindborg and Brethouwer (2008), though with a small dependence on the buoyancy Reynolds number. Here, δz2 is the mean square vertical particle displacement, εP is the dissipation of potential energy, t is time and N is the Brunt-Väisälä frequency. Simulations with hyperviscosicity are performed to verify the relation δz2 = (1 + πCP L)2εP t/N2 for N−1 t T, where N is the Brunt-Väisälä frequency and T is the turbulent eddy turnover time. The simulation results approach the relation for increasing stratification and we find that CP L is about 3 in strongly stratified fluids. The onset of a plateau in δz2 is observed in the simulations at t ∼ T .
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| 8. |
- Brethouwer, Gert
(författare)
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Much faster heat/mass than momentum transport in rotating Couette flows
- 2021
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 912
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Tidskriftsartikel (refereegranskat)abstract
- Heat and mass transport are generally closely correlated to momentum transport in shear flows. This so-called Reynolds analogy between advective heat or mass transport and momentum transport hinders efficiency improvements in engineering heat and mass transfer applications. I show through direct numerical simulations that in plane Couette and Taylor-Couette flow, rotation can strongly influence wall-to-wall passive tracer transport and make it much faster than momentum transport, clearly in violation of the Reynolds analogy. This difference between passive tracer transport, representative of heat/mass transport, and momentum transport is observed in steady flows with large counter-rotating vortices at low Reynolds numbers as well as in fully turbulent flows at higher Reynolds numbers. It is especially large near the neutral (Rayleigh's) stability limit. The rotation-induced Coriolis force strongly damps the streamwise/azimuthal velocity fluctuations when this limit is approached, while tracer fluctuations are much less affected. Accordingly, momentum transport is much more reduced than tracer transport, showing that the Coriolis force breaks the Reynolds analogy. At higher Reynolds numbers, this strong advective transport dissimilarity is accompanied by approximate limit cycle dynamics with intense low-frequency bursts of turbulence when approaching the neutral stability limit. The study demonstrates that simple body forces can cause clear dissimilarities between heat/mass and momentum transport in shear flows.
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| 9. |
- Brethouwer, Gert, et al.
(författare)
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Numerical simulations of particle dispersion in stratified flows
- 2009
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Ingår i: ADVANCES IN TURBULENCE XII. - Berlin, Heidelberg : Springer Berlin Heidelberg. ; , s. 51-55
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Konferensbidrag (refereegranskat)abstract
- Several researchers have examined the vertical dispersion of fluid particles in stratified flows to obtain a better understanding of mixing in geophysical flows. Pearson et al. [5] used a Langevin model to predict that the mean square of vertical fluid particle displacements reaches a plateau with in stationary stratified flows. Here, w is the vertical velocity fluctuation and N is the Brunt-Väisälä frequency. At long times, they predict that, when molecular diffusion alters the particle density. Venayagamoorthy and Stretch [6] examined the role of the changing particle density on vertical dispersion in DNS of decaying stratified turbulence and observed that after one eddy turnover time diabatic dispersion dominated. Van Aartrijk et al. [1] studied particle dispersion in DNS of stationary strat-ified turbulence and observed a plateau with. However, some of the DNS showed that at long times caused by density changes of fluid particles by molecular diffusion.
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| 10. |
- Brethouwer, Gert
(författare)
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Passive scalar transport in rotating turbulent channel flow
- 2018
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Ingår i: Journal of Fluid Mechanics. - : CAMBRIDGE UNIV PRESS. - 0022-1120 .- 1469-7645. ; 844, s. 297-322
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Tidskriftsartikel (refereegranskat)abstract
- Passive scalar transport in turbulent channel flow subject to spanwise system rotation is studied by direct numerical simulations. The Reynolds number R-e= U(b)h/nu is fixed at 20 000 and the rotation number R-o= 2 Omega h/U-b is varied from 0 to 1.2, where U-b is the bulk mean velocity, h the half channel gap width and Omega the rotation rate. The scalar is constant but different at the two walls, leading to steady scalar transport across the channel. The rotation causes an unstable channel side with relatively strong turbulence and turbulent scalar transport, and a stable channel side with relatively weak turbulence or laminar-like flow, weak turbulent scalar transport but large scalar fluctuations and steep mean scalar gradients. The distinct turbulent-laminar patterns observed at certain Ro on the stable channel side induce similar patterns in the scalar field. The main conclusions of the study are that rotation reduces the similarity between the scalar and velocity field and that the Reynolds analogy for scalar-momentum transport does not hold for rotating turbulent channel flow. This is shown by a reduced correlation between velocity and scalar fluctuations, and a strongly reduced turbulent Prandtl number of less than 0.2 on the unstable channel side away from the wall at higher Ro. On the unstable channel side, scalar scales become larger than turbulence scales according to spectra and the turbulent scalar flux vector becomes more aligned with the mean scalar gradient owing to rotation. Budgets in the governing equations of the scalar energy and scalar fluxes are presented and discussed as well as other statistics relevant for turbulence modelling.
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