A new second-order moment two- phase turbulence model accounting for particle wake effect was established and used to simulate gas-particle flow in a horizontal channel for different values of wall roughness. The resu...A new second-order moment two- phase turbulence model accounting for particle wake effect was established and used to simulate gas-particle flow in a horizontal channel for different values of wall roughness. The results show that compared with the model without considering the particle wake effect, the present model gives simulation results agreeing much better with the experimental results for the gas turbulence modulation, but the predicted results for particle motion with the two kinds of models are quite close.展开更多
A semi-empirical turbulence enhancement model accounting for the particle-wake effect was incorporated into the second-order moment two-phase turbulence model and employed to simulate gas-particle flows in a swirling ...A semi-empirical turbulence enhancement model accounting for the particle-wake effect was incorporated into the second-order moment two-phase turbulence model and employed to simulate gas-particle flows in a swirling sudden-expansion chamber. The simulated results for two-phases mean velocities and fluctuation velocities coincide well with the experiment ones, which demonstrates that this model, in comparison with the turbulence model not accounting for the wake effect, leads to higher calculating accuracy.展开更多
A k - ε-PDF model based on statistical theory for turbulent gas-particle flows is proposed,and a numerical procedure combining the finite difference and finite fluctuating-velocity -group methods is used.The obtained...A k - ε-PDF model based on statistical theory for turbulent gas-particle flows is proposed,and a numerical procedure combining the finite difference and finite fluctuating-velocity -group methods is used.The obtained statistically averaged equations have the same form as those obtained by using the Reynolds averaging.Using the k -ε-PDF model (PDF particle turbulence model combined with the k - ε gas turbulence model),many terms,such as the diffusion term in particle Reynolds Stress equations,can be accurately calculated for verifying the second-moment-closure model.The k - ε- PDF model is used to simulate sudden-expansion particle-laded flow.comparison of the predictions using both k -ε-PDF and the k - ε- kp models with experimental results shows that the k - ε-PDF model give more reasonable non-isotropic features of particle turbulence.展开更多
The turbulence enhancement by particle wake effect is studied by large eddy simulation （LES） of turbulent gas flows passing a single particle. The predicted time-averaged and root-mean-square fluctuation velocities ...The turbulence enhancement by particle wake effect is studied by large eddy simulation （LES） of turbulent gas flows passing a single particle. The predicted time-averaged and root-mean-square fluctuation velocities behind the particle are in agreement with the Reynolds-averaged Navier-Stokes modeling results and experimental results. A semi-empirical turbulence enhancement model is proposed by the present-authors based on the LES resuits. This model is incorporated into the second-order moment two-phase turbulence model for simulating vertical gas-particle pipe flows and horizontal gas-particle channel flows. The simulation results show that compared with the model not accounting for the particle wake effect, the present model gives simulation results for the gas turbulence modulation in much better agreement with the experimental results.展开更多
he paper focuses on the turbulence modulation problem in gas–particle flow with the use of probability density function（PDF） approach. By means of the PDF method, a general statistical moment turbulence modulation ...he paper focuses on the turbulence modulation problem in gas–particle flow with the use of probability density function（PDF） approach. By means of the PDF method, a general statistical moment turbulence modulation model without considering the trajectory difference between two phases is derived from the Navier–Stokes equations. A new turbulence production term induced by the dispersed-phase is analyzed and considered. Furthermore, the trajectory difference between two media is taken into account. Subsequently, a new k–ε turbulence modulation model in dilute particle-laden flow is successfully set up. Then, the changes to several terms, including the turbulence production, dissipation, and diffusion terms, are well described consequently. The promoted model provides a more probable explanation for the modification of particles on the turbulence. Finally, we applied the model to simulate a gas–particle turbulence flow case in a wall jet, and found that the simulation results agree well with the experimental data.展开更多
Dense gas-particle flows are frequently encountered in fluidized beds,riser and downer reactors,pneumatic transport and the near-wall zone of dilute gas-particle flows.Particle-particle collision plays an important ro...Dense gas-particle flows are frequently encountered in fluidized beds,riser and downer reactors,pneumatic transport and the near-wall zone of dilute gas-particle flows.Particle-particle collision plays an important role in the behavior of two-phase flows.In this paper a USM-Q two-phase turbulence model for dense gas-particle flows is proposed to account for both two-phase turbulence and inter-particle collision.For two-fluid large-eddy simulation of gas-particle flows,the author proposed a unified second-order moment(USM) two-phase SGS stress model and a two-phase k-kp SGS energy-equation stress model.The proposed models can fully account for the interaction between the gas and particle SGS stresses.展开更多
Turbulence model of kg-εg-kp-εp-kpg-θ is proposed.In the model,the two-phase velocity correlation turbulent kinetic energy k pg is modeled by transport equation.To close this turbulence model,algebraic expressions ...Turbulence model of kg-εg-kp-εp-kpg-θ is proposed.In the model,the two-phase velocity correlation turbulent kinetic energy k pg is modeled by transport equation.To close this turbulence model,algebraic expressions of two-phase Reynolds stresses and two-phase velocity correlation variable are established by considering both gas-particle interaction and anisotropy.This turbulence model is used to simulate dense gas-particle flow in a riser and in a downer.The predicted results show the core-annulus flow structure observed in the riser and the skin effect of particle concentration in the downer.The present model gives simulation results in much better agreement with the experimental results than those obtained by kg-εg-kp-εp-θmodel which is simply closed using a semi-empirical dimensional analysis.展开更多
Turbulence enhancement by particle wake effect is studied by numerical simulation of gas turbulent flows passing over particle under various particle sizes, inlet gas velocities, gas viscosity, gas density and the dis...Turbulence enhancement by particle wake effect is studied by numerical simulation of gas turbulent flows passing over particle under various particle sizes, inlet gas velocities, gas viscosity, gas density and the distance of particles. By performing dimension analysis and using the form of gas-particle interaction source term for reference, a new semi-empirical turbulence enhancement model by the particle-wake effect is proposed. The turbulence model is then incorporated into second-order moment model for simulating gas-particle flows in a horizontal channel with different wall roughness and a sudden-expansion chamber. The results show that this model is with higher calculating accuracy than another two turbulence models in comparison with the experimental results.展开更多
The momentum and heat coupling between carrier fluid and particles are a complex and challenge topic in turbulent reactive gas-solid flow modeling.Most observations on this topic,either numerical or experimental,are b...The momentum and heat coupling between carrier fluid and particles are a complex and challenge topic in turbulent reactive gas-solid flow modeling.Most observations on this topic,either numerical or experimental,are based on Eulerian framework,which is not enough for developing the probability density function(PDF) model.In this paper,the instantous behavior and multi-particle statistics of passive scalar along inertial particle trajectory,in homogenous isotropic turbulence with a mean scalar gradient,are investigated by using the direct numerical simulation(DNS).The results show that St^1.0 particles are easy to aggregate in high strain and low vorticity regions in the fluid field,where the scalar dissipation is usually much higher than the mean value,and that every time they move across the cliff structures,the scalar change is much more intensive.Anyway,the self-correlation of scalar along particle trajectory is significantly different from the velocities observed by particle,for which the prefer-concentration effect is evident.The mechanical-to-thermal time scale ratio averaged along the particles,<r> p,is approximately two times smaller than that computed in the Eulerian frame r,and stays at nearly 1.77 with a weak dependence on particle inertia.展开更多
基金the China Postdoctoral Science Foundation (Grant No.2004036239)the Foundation of Jiangxi Educational Committee (Grant No.GJJ08230)
文摘A new second-order moment two- phase turbulence model accounting for particle wake effect was established and used to simulate gas-particle flow in a horizontal channel for different values of wall roughness. The results show that compared with the model without considering the particle wake effect, the present model gives simulation results agreeing much better with the experimental results for the gas turbulence modulation, but the predicted results for particle motion with the two kinds of models are quite close.
基金the China Postdoctoral Science Foundation (Grant No.2004036239).
文摘A semi-empirical turbulence enhancement model accounting for the particle-wake effect was incorporated into the second-order moment two-phase turbulence model and employed to simulate gas-particle flows in a swirling sudden-expansion chamber. The simulated results for two-phases mean velocities and fluctuation velocities coincide well with the experiment ones, which demonstrates that this model, in comparison with the turbulence model not accounting for the wake effect, leads to higher calculating accuracy.
文摘A k - ε-PDF model based on statistical theory for turbulent gas-particle flows is proposed,and a numerical procedure combining the finite difference and finite fluctuating-velocity -group methods is used.The obtained statistically averaged equations have the same form as those obtained by using the Reynolds averaging.Using the k -ε-PDF model (PDF particle turbulence model combined with the k - ε gas turbulence model),many terms,such as the diffusion term in particle Reynolds Stress equations,can be accurately calculated for verifying the second-moment-closure model.The k - ε- PDF model is used to simulate sudden-expansion particle-laded flow.comparison of the predictions using both k -ε-PDF and the k - ε- kp models with experimental results shows that the k - ε-PDF model give more reasonable non-isotropic features of particle turbulence.
基金Supported by the Major Project of National Natural Science Foundation of China (No.10632070) the Postdoctoral ScienceFoundation (No.2004036239).
文摘The turbulence enhancement by particle wake effect is studied by large eddy simulation （LES） of turbulent gas flows passing a single particle. The predicted time-averaged and root-mean-square fluctuation velocities behind the particle are in agreement with the Reynolds-averaged Navier-Stokes modeling results and experimental results. A semi-empirical turbulence enhancement model is proposed by the present-authors based on the LES resuits. This model is incorporated into the second-order moment two-phase turbulence model for simulating vertical gas-particle pipe flows and horizontal gas-particle channel flows. The simulation results show that compared with the model not accounting for the particle wake effect, the present model gives simulation results for the gas turbulence modulation in much better agreement with the experimental results.
基金Project supported by the National Natural Science Foundation of China(Grant No.51176044)
文摘he paper focuses on the turbulence modulation problem in gas–particle flow with the use of probability density function（PDF） approach. By means of the PDF method, a general statistical moment turbulence modulation model without considering the trajectory difference between two phases is derived from the Navier–Stokes equations. A new turbulence production term induced by the dispersed-phase is analyzed and considered. Furthermore, the trajectory difference between two media is taken into account. Subsequently, a new k–ε turbulence modulation model in dilute particle-laden flow is successfully set up. Then, the changes to several terms, including the turbulence production, dissipation, and diffusion terms, are well described consequently. The promoted model provides a more probable explanation for the modification of particles on the turbulence. Finally, we applied the model to simulate a gas–particle turbulence flow case in a wall jet, and found that the simulation results agree well with the experimental data.
基金supported by the National Key Project of Fundamental Research of China (Grant No. G1999-0222-07-08)the Projects of the National Natural Science Foundation of China (Grant Nos. 50736006 and 50606026)the Foundation of the State Key Laboratory of Engines, Tianjin University (Grant No. K-2010-07)
文摘Dense gas-particle flows are frequently encountered in fluidized beds,riser and downer reactors,pneumatic transport and the near-wall zone of dilute gas-particle flows.Particle-particle collision plays an important role in the behavior of two-phase flows.In this paper a USM-Q two-phase turbulence model for dense gas-particle flows is proposed to account for both two-phase turbulence and inter-particle collision.For two-fluid large-eddy simulation of gas-particle flows,the author proposed a unified second-order moment(USM) two-phase SGS stress model and a two-phase k-kp SGS energy-equation stress model.The proposed models can fully account for the interaction between the gas and particle SGS stresses.
基金the National Natural Science Foundation of China (No.51066006)the Aero-Science Fund(No.2009ZB56004)the Jiangxi Provincial Natural Science Foundation (No.2009GZC0100)
文摘Turbulence model of kg-εg-kp-εp-kpg-θ is proposed.In the model,the two-phase velocity correlation turbulent kinetic energy k pg is modeled by transport equation.To close this turbulence model,algebraic expressions of two-phase Reynolds stresses and two-phase velocity correlation variable are established by considering both gas-particle interaction and anisotropy.This turbulence model is used to simulate dense gas-particle flow in a riser and in a downer.The predicted results show the core-annulus flow structure observed in the riser and the skin effect of particle concentration in the downer.The present model gives simulation results in much better agreement with the experimental results than those obtained by kg-εg-kp-εp-θmodel which is simply closed using a semi-empirical dimensional analysis.
基金the National Natural Science Foundation of China(No.50736006)the Aero-Science Fund(No.2009ZB56004)the Jiangxi Provincial Natural Science Foundation(Nos.2009GZC0100 and 2008GZW0016)
文摘Turbulence enhancement by particle wake effect is studied by numerical simulation of gas turbulent flows passing over particle under various particle sizes, inlet gas velocities, gas viscosity, gas density and the distance of particles. By performing dimension analysis and using the form of gas-particle interaction source term for reference, a new semi-empirical turbulence enhancement model by the particle-wake effect is proposed. The turbulence model is then incorporated into second-order moment model for simulating gas-particle flows in a horizontal channel with different wall roughness and a sudden-expansion chamber. The results show that this model is with higher calculating accuracy than another two turbulence models in comparison with the experimental results.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50936001,51021065,50976042)the State Key Fundamental Research Program,Ministry of Science and Technology,China (Grant Nos. 2010CB227004,2011CB707301)
文摘The momentum and heat coupling between carrier fluid and particles are a complex and challenge topic in turbulent reactive gas-solid flow modeling.Most observations on this topic,either numerical or experimental,are based on Eulerian framework,which is not enough for developing the probability density function(PDF) model.In this paper,the instantous behavior and multi-particle statistics of passive scalar along inertial particle trajectory,in homogenous isotropic turbulence with a mean scalar gradient,are investigated by using the direct numerical simulation(DNS).The results show that St^1.0 particles are easy to aggregate in high strain and low vorticity regions in the fluid field,where the scalar dissipation is usually much higher than the mean value,and that every time they move across the cliff structures,the scalar change is much more intensive.Anyway,the self-correlation of scalar along particle trajectory is significantly different from the velocities observed by particle,for which the prefer-concentration effect is evident.The mechanical-to-thermal time scale ratio averaged along the particles,<r> p,is approximately two times smaller than that computed in the Eulerian frame r,and stays at nearly 1.77 with a weak dependence on particle inertia.
