Predictive Modelling of Particle-laden, Turbulent Flows. Quarterly Progress Report No. 2, January 1, 1993--March 31, 1993 PDF Download
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Author: Publisher: ISBN: Category : Languages : en Pages : 22
Book Description
The excellent comparison between the data of Bader et al (1988) and the predictions using the fully-developed flow model of Sinclair and Jackson (1989) have not yet been repeated with any other experimental data set for riser flow. This may be due to the fact that the data sets investigated thus far have reflected gas-solid flow in a developing state (low L/D ratios). In addition, the model of Sinclair and Jackson (1989) neglected gas phase turbulence which should have an effect on the solid concentration distribution. Hence, a dilute, particle-laden, turbulent flow model is developed here. Model predictions highlight the importance of an independent measurement of the specularity factor, an appropriate representation of the kinetic contribution to the total particle phase stress for very low solid loadings in confined flows, and a correct representation of the interaction between the fluctuating velocity components for the two phases.
Author: Publisher: ISBN: Category : Languages : en Pages : 22
Book Description
The excellent comparison between the data of Bader et al (1988) and the predictions using the fully-developed flow model of Sinclair and Jackson (1989) have not yet been repeated with any other experimental data set for riser flow. This may be due to the fact that the data sets investigated thus far have reflected gas-solid flow in a developing state (low L/D ratios). In addition, the model of Sinclair and Jackson (1989) neglected gas phase turbulence which should have an effect on the solid concentration distribution. Hence, a dilute, particle-laden, turbulent flow model is developed here. Model predictions highlight the importance of an independent measurement of the specularity factor, an appropriate representation of the kinetic contribution to the total particle phase stress for very low solid loadings in confined flows, and a correct representation of the interaction between the fluctuating velocity components for the two phases.
Author: Publisher: ISBN: Category : Languages : en Pages : 29
Book Description
An Eulerian two-fluid mathematical model is considered for the flow prediction of gas-particle systems. The model expands on the Sinclair and Jackson model by recognizing a turbulent continuous phase. Both the gas- and the particle-phase velocity fields are composed of by a mean and a fluctuating component, and the important physical phenomena arising from the interaction of these components are included in the model. The gas turbulence is modeled by a single-phase closure, namely the k-{var_epsilon} low Reynolds model by Myong and Kasagi, modified to account for the presence of a dilute particle phase. The solid phase is considered as a rapid granular flow; hence, a closure based on the kinetic-theory analogy is used for the description of the stresses associated with this phase. Along with the relation between the fluxes of both phases and the pressure drop, the model is capable of predicting features related to the local flow structure, such as the mean and fluctuating velocity components and the concentration of both phases. In this report, the model is applied to the case of steady, fully developed flow in a vertical cylindrical pipe. An extensive comparison of the model predictions with experimental data is included. The sensitivity of the model predictions to the properties describing the particle collisions is also explored.
Author: Publisher: ISBN: Category : Languages : en Pages : 18
Book Description
The successful prediction of particle-laden, turbulent flows relies heavily on the representation of turbulence in the gas phase. Several types of turbulence models for single-phase gas flow have been developed which compare reasonably well with experimental data. In the present work, a l̀̀ow-Reynolds̀̀ k-?, closure model is chosen to describe the Reynolds stresses associated with gas-phase turbulence. This closure scheme, which involves transport equations for the turbulent kinetic energy and its dissipation rate, is valid in the turbulent core as well as the viscous sublayer. Several versions of the low-Reynolds k-? closure are documented in the literature. However, even those models which are similar in theory often differ considerably in their quantitative and qualitative predictions, making the selection of such a model a difficult task. The purpose of this progress report is to document our findings on the performance of ten different versions of the low-Reynolds k-? model on predicting fully developed pipe flow. The predictions are compared with the experimental data of Schildknecht, et al. (1979). With the exception of the model put forth by Hoffman (1975), the predictions of all the closures show reasonable agreement for the mean velocity profile. However, important quantitative differences exist for the turbulent kinetic energy profile. In addition, the predicted eddy viscosity profile and the wall-region profile of the turbulent kinetic energy dissipation rate exhibit both quantitative and qualitative differences. An effort to extend the present comparisons to include experimental measurements of other researchers is recommended in order to further evaluate the performance of the models.
Author: Publisher: ISBN: Category : Languages : en Pages : 18
Book Description
The successful prediction of particle-laden, turbulent flows relies heavily on the representation of turbulence in the gas phase. Several types of turbulence models for single-phase gas flow have been developed which compare reasonably well with experimental data. In the present work, a low-Reynolds'' k-[epsilon], closure model is chosen to describe the Reynolds stresses associated with gas-phase turbulence. This closure scheme, which involves transport equations for the turbulent kinetic energy and its dissipation rate, is valid in the turbulent core as well as the viscous sublayer. Several versions of the low-Reynolds k-[epsilon] closure are documented in the literature. However, even those models which are similar in theory often differ considerably in their quantitative and qualitative predictions, making the selection of such a model a difficult task. The purpose of this progress report is to document our findings on the performance of ten different versions of the low-Reynolds k-[epsilon] model on predicting fully developed pipe flow. The predictions are compared with the experimental data of Schildknecht, et al. (1979). With the exception of the model put forth by Hoffman (1975), the predictions of all the closures show reasonable agreement for the mean velocity profile. However, important quantitative differences exist for the turbulent kinetic energy profile. In addition, the predicted eddy viscosity profile and the wall-region profile of the turbulent kinetic energy dissipation rate exhibit both quantitative and qualitative differences. An effort to extend the present comparisons to include experimental measurements of other researchers is recommended in order to further evaluate the performance of the models.
Author: Publisher: ISBN: Category : Languages : en Pages : 44
Book Description
Earlier work of Sinclair and Jackson which treats the laminar flow of gas-solid suspensions is extended to model dilute turbulent flow. The random particle motion, often exceeding the turbulent fluctuations in the gas, is obtained using a model based on kinetic theory of granular materials. A two-equation low Reynolds number turbulence model is, modified to account for the presence of the dilute particle phase. Comparisons of the model predictions with available experimental data for the mean and fluctuating velocity profiles for both phases indicate that the resulting theory captures many of the flow features observed in the pneumatic transport of large particles. The model predictions did not manifest an extreme sensitivity to the degree of inelasticity in the particle-particle collisions for the range of solid loading ratios investigated.
Author: Publisher: ISBN: Category : Languages : en Pages : 34
Book Description
The lack of a mathematical description of the interactions of fluid turbulence with other physics-chemical processes is a major obstacle in modeling many industrial program. Turbulent two-phase flow is a phenomenon that is of significant practical importance to coal combustion as well as other disciplines. The interactions of fluid turbulence with the particulate phase has yet to be accurately and efficiently modeled for these industrial applications. On 15 May 1991 work was initiated to cover four major tasks toward the development of a computational submodel for turbulent particle dispersion that would be applicable to coal combustion simulations. Those four tasks are: 1. A critical evaluation of the 2-D Lagrangian particle dispersion submodel, 2. Development of a 3-D submodel for turbulent particle dispersion, 3. Evaluation of the 3-D submodel for turbulent particle dispersion, 4. Exploration of extensions of the Lagrangian dispersion theory to other applications including chemistry-turbulence interactions.
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