In this paper, we present measurements of velocity, temperature, salinity, and turbulence collected in Prydz Bay, Antarctica, during February, 2005. The dissipation rates of turbulent kinetic energy （e） and diapycna...In this paper, we present measurements of velocity, temperature, salinity, and turbulence collected in Prydz Bay, Antarctica, during February, 2005. The dissipation rates of turbulent kinetic energy （e） and diapycnal diffusivities （Ks） were estimated along a section in front of the Amery Ice Shelf. The dissipation rates and diapycnal diffusivities were spatially non-uniform, with higher values found in the western half of the section where E reached 10.7 W/kg and Kz reached 10.2 mVs, about two and three orders of magnitude higher than those in the open ocean, respectively. In the western half of the section both the dissipation rates and diffusivities showed a high-low-high vertical structure. This vertical structure may have been determined by internal waves in the upper layer, where the ice shelf draft acts as a possible energy source, and by bottom-generated internal waves in the lower layer, where both tides and geostrophic currents are possible energy sources. The intense diapycnal mixing revealed in our observations could contribute to the production of Antarctic Bottom Water in Prydz Bay.展开更多
The multifractality of energy and thermal dissipation of fully developed intermittent turbulence is investigated in the urban canopy layer under unstable conditions by the singularity spectrum for the fractal dimensio...The multifractality of energy and thermal dissipation of fully developed intermittent turbulence is investigated in the urban canopy layer under unstable conditions by the singularity spectrum for the fractal dimensions of sets of singularities characterizing multifractals. In order to obtain high-order moment properties of smallscale turbulent dissipation in the inertial range, an ultrasonic anemometer with a high sampling frequency of 100 Hz was used. The authors found that the turbulent signal could be singular everywhere. Moreover, the singular exponents of energy and thermal dissipation rates are most frequently encountered at around 0.2, which is significantly smaller than the singular exponents for a wind tunnel at a moderate Reynolds number. The evidence indicates a higher intermittency of turbulence in the urban canopy layer at a high Reynolds number, which is demonstrated by the data with high temporal resolution. Furthermore, the temperature field is more intermittent than the velocity field. In addition, a large amount of samples could be used for verification of the results.展开更多
Presently developed two-phase turbulence models under-predict the gas turbulent fluctuation, because their turbulence modification models cannot fully reflect the effect of particles. In this paper, a two-time-scale d...Presently developed two-phase turbulence models under-predict the gas turbulent fluctuation, because their turbulence modification models cannot fully reflect the effect of particles. In this paper, a two-time-scale dissipation model of turbulence modification, developed for the two-phase velocity correlation and for the dissipation rate of gas turbulent kinetic energy, is proposed and used to simulate sudden-expansion and swirling gas-particle flows. The proposed two-time scale model gives better results than the single-time scale model. Besides, a gas turbulence augmentation model accounting for the f＇mite-size particle wake effect in the gas Reynolds stress equation is proposed. The proposed turbulence modification models are used to simulate two-phase pipe flows. It can properly predict both turbulence reduction and turbulence enhancement for a certain size of particles observed in experiments.展开更多
The modulation of turbulence by particles has been rigorously investigated in the literature yielding either a reduction or an enhancement of the turbulent kinetic energy at different spatial length scales.However,a g...The modulation of turbulence by particles has been rigorously investigated in the literature yielding either a reduction or an enhancement of the turbulent kinetic energy at different spatial length scales.However,a general description of the turbulence modulation in multiphase flows due to the presence of an interphase force has attracted less attention.In this paper,we investigate the turbulent modulation for interfacial and fluid-particle flows analytically and numerically,where surface tension and drag define the interphase coupling,respectively.It is shown that surface tension and drag appear as additional production/dissipation terms in the transport equations for the turbulent kinetic energies(TKE),which is of particular importance for the turbulence modelling of multiphase flows.Furthermore,we study the modulation of turbulence in decaying homogenous isotropic turbulence(HIT)for both types of multiphase flow.The results clearly unveil that in both cases the energy is reduced at large scales,while the small-scale energy is enhanced compared to single-phase flows.Particularly,at large scales surface tension works against the turbulent eddies and hinders the ejection of droplet from the corrugated interface.In contrast,at the small scales,the surface tension force and the velocity fluctuations are aligned leading to an enhancement of the energy.In the case of fluid-particle flows,particles retain their energy longer than the surrounding fluid increasing the energy at the small scales,while at the large scales the particles do not follow exactly the surrounding fluid reducing its energy.For the latter effect,a considerable dependence on the particle Stokes number is found.展开更多
基金Supported by the National Natural Science Foundation of China(Nos.40906004,40890153,41176008,and 91028008)the National High Technology Research and Development Program of China(863 Program)(No.2008AA09A402)+2 种基金the Polar Science Strategic Foundation of China(No.20080206)the Key Lab Open Research Foundation of China(No.KP201006)the National Key Technology Research and Development Program of China(No.2006BAB18B02)
文摘In this paper, we present measurements of velocity, temperature, salinity, and turbulence collected in Prydz Bay, Antarctica, during February, 2005. The dissipation rates of turbulent kinetic energy （e） and diapycnal diffusivities （Ks） were estimated along a section in front of the Amery Ice Shelf. The dissipation rates and diapycnal diffusivities were spatially non-uniform, with higher values found in the western half of the section where E reached 10.7 W/kg and Kz reached 10.2 mVs, about two and three orders of magnitude higher than those in the open ocean, respectively. In the western half of the section both the dissipation rates and diffusivities showed a high-low-high vertical structure. This vertical structure may have been determined by internal waves in the upper layer, where the ice shelf draft acts as a possible energy source, and by bottom-generated internal waves in the lower layer, where both tides and geostrophic currents are possible energy sources. The intense diapycnal mixing revealed in our observations could contribute to the production of Antarctic Bottom Water in Prydz Bay.
基金supported by the National Natural Science Foundation of China(Grant Nos.11472272 and 91215302)the Special Fund for Meteorological Research in the Public Interest(Grant No.GYHY201206041)
文摘The multifractality of energy and thermal dissipation of fully developed intermittent turbulence is investigated in the urban canopy layer under unstable conditions by the singularity spectrum for the fractal dimensions of sets of singularities characterizing multifractals. In order to obtain high-order moment properties of smallscale turbulent dissipation in the inertial range, an ultrasonic anemometer with a high sampling frequency of 100 Hz was used. The authors found that the turbulent signal could be singular everywhere. Moreover, the singular exponents of energy and thermal dissipation rates are most frequently encountered at around 0.2, which is significantly smaller than the singular exponents for a wind tunnel at a moderate Reynolds number. The evidence indicates a higher intermittency of turbulence in the urban canopy layer at a high Reynolds number, which is demonstrated by the data with high temporal resolution. Furthermore, the temperature field is more intermittent than the velocity field. In addition, a large amount of samples could be used for verification of the results.
基金Supported by the State Key Development Program for Basic Research of China （No.2006CB200305）, the National Natural Science Foundation of China （No.50376004）, and Ph.D. Program Foundation of Ministry of Education of China （No.20030007028）.
文摘Presently developed two-phase turbulence models under-predict the gas turbulent fluctuation, because their turbulence modification models cannot fully reflect the effect of particles. In this paper, a two-time-scale dissipation model of turbulence modification, developed for the two-phase velocity correlation and for the dissipation rate of gas turbulent kinetic energy, is proposed and used to simulate sudden-expansion and swirling gas-particle flows. The proposed two-time scale model gives better results than the single-time scale model. Besides, a gas turbulence augmentation model accounting for the f＇mite-size particle wake effect in the gas Reynolds stress equation is proposed. The proposed turbulence modification models are used to simulate two-phase pipe flows. It can properly predict both turbulence reduction and turbulence enhancement for a certain size of particles observed in experiments.
基金This work was supported by the Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development. The authors further want to acknowledge the funding support of K1-MET GmbH, metallurgical competence center. The research programme of the K1-MET competence center is supported by COMET (Competence Center for Excellent Technologies), the Austrian programme for competence centers. COMET is funded by the Federal Ministry for Transport, Innovation and Technology, the Federal Ministry for Digital and Economic Affairs and the provinces of Upper Austria, Tyrol and Styria. Beside the public funding from COMET, this research project is partially financed by the industrial partners Primetals Technologies Austria GmbH, voestalpine Stahl Donawitz GmbH, RHI Magnesita GmbH and voestalpine Stahl GmbH.
文摘The modulation of turbulence by particles has been rigorously investigated in the literature yielding either a reduction or an enhancement of the turbulent kinetic energy at different spatial length scales.However,a general description of the turbulence modulation in multiphase flows due to the presence of an interphase force has attracted less attention.In this paper,we investigate the turbulent modulation for interfacial and fluid-particle flows analytically and numerically,where surface tension and drag define the interphase coupling,respectively.It is shown that surface tension and drag appear as additional production/dissipation terms in the transport equations for the turbulent kinetic energies(TKE),which is of particular importance for the turbulence modelling of multiphase flows.Furthermore,we study the modulation of turbulence in decaying homogenous isotropic turbulence(HIT)for both types of multiphase flow.The results clearly unveil that in both cases the energy is reduced at large scales,while the small-scale energy is enhanced compared to single-phase flows.Particularly,at large scales surface tension works against the turbulent eddies and hinders the ejection of droplet from the corrugated interface.In contrast,at the small scales,the surface tension force and the velocity fluctuations are aligned leading to an enhancement of the energy.In the case of fluid-particle flows,particles retain their energy longer than the surrounding fluid increasing the energy at the small scales,while at the large scales the particles do not follow exactly the surrounding fluid reducing its energy.For the latter effect,a considerable dependence on the particle Stokes number is found.
