| 1. |
- Fistler, Marco, 1989, et al.
(författare)
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A new LES subgrid-scale approach for turbulence modulation by droplets
- 2020
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Ingår i: ICLASS 2018 - 14th International Conference on Liquid Atomization and Spray Systems. ; 14
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Konferensbidrag (refereegranskat)abstract
- We present a new modelling approach for turbulence modulation by droplets on the subgrid-scale (SGS) level of Large-Eddy-Simulations (LES). Many SGS models exist for the effect of gas phase SGS on the droplet phase, but very few for the mechanisms vice versa on the turbulent intensity of the gas phase. The reasons are a lack of physical understanding and limited computational resources for extensive DNS studies. To address both problems a dimension-reduced and consequently less costly model, namely One-Dimensional- Turbulence (ODT), is used to gather information about this specific flow phenomena. ODT is a stochastic tool simulating turbulent flows along a notional 1D line of sights. For modeling the turbulent advection instantaneous maps are applied to the line which represent the effect of individual eddies on property fields and the dispersed phase. After validating the general test case of a droplet-laden shear flow against DNS data, a concept is presented on how to gather turbulence modulation for several parameter ranges in a data base and how to make them accessible on the flight for LES. The three most significant parameters, the unladen flow Reynolds number, the droplet loading and the particle momentum number, are chosen to construct an efficient data base.
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| 2. |
- Fistler, Marco, 1989, et al.
(författare)
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Numerical studies of turbulent particle-laden jets using spatial approach of one-dimensional turbulence
- 2017
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Ingår i: 28TH CONFERENCE ON LIQUID ATOMIZATION AND SPRAY SYSTEMS, ILASS-EUROPE 2017. - 9788490485804 ; , s. 83-89
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Konferensbidrag (refereegranskat)abstract
- To challenge one of the major problems for multiphase flow simulations, namely computational costs, a dimension reduced model is used with the goal to predict these types of flow more efficiently. One-dimensional turbulence (ODT) is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps that represent the effect of individual turbulent eddies on property fields. As the particle volume fraction is in an intermediate range above 10(-5) for dilute flows and under 10(-2) for dense ones, turbulence modulation is important and can be sufficiently resolved with a two-way coupling approach, which means the particle phase influences the fluid phase and vice versa. For the coupling mechanism the ODT multiphase model is extended to consider momentum transfer and energy in the deterministic evolution and momentum transfer during the particle-eddy interaction. The changes of the streamwise velocity profiles caused by different solid particle loadings are compared with experimental data as a function of radial position. Additionally, streamwise developments of axial RMS and mean gas velocities along the centerline are evaluated as functions of axial position. To achieve comparable results, the spatial approach of ODT in cylindrical coordinates is used here. The investigated jet configuration features a nozzle diameter of 14.22 cm and a Reynolds number of 8400, which leads to a centerline inlet velocity of 11.7 m/s. The particles used are glass beads with a density of 2500 kg/m(3). Two different particle diameters (25 and 70 mu m) were tested for an evaluation of the models capability to capture the impact of a varying Stokes number and also two different particle solid loadings (0.5 and 1.0) were evaluated. It is shown that the model is capable of capturing turbulence modulation of particles in a round jet.
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| 3. |
- Fistler, Marco, 1989, et al.
(författare)
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Numerical study of stochastic particle dispersion using One-Dimensional-Turbulence
- 2017
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Ingår i: ILASS-Americas 29th Annual Conference on Liquid Atomization and Spray Systems.
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Konferensbidrag (refereegranskat)abstract
- A stochastic model to study particle dispersion in a round jet configuration using the one-dimensional-turbulence model (ODT) is evaluated. To address one of the major problems for multiphase flow simulations, namely computational costs, the dimension-reduced model is used with the goal of predicting these flows more efficiently. ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps which represent the effect of individual turbulent eddies on property fields. As the impact of the particles on the carrier fluid phase is negligible for cases considered, a one-way coupling approach is used, which means that the carrier-phase is affecting the particle dynamics but not vice versa. The radial dispersion and axial velocity are compared with jet experimental data as a function of axial position. For consistent representation of the spatially developing round jet, the spatial formulation of ODT in cylindrical coordinates is used. The investigated jet configuration has a nozzle diameter of 7 mm and Reynolds numbers ranging from 10000 to 30000. The flow statistics of the ODT particle model are compared with experimental measurements for two different particle diameters (60 and 90 μm), thereby testing the Stokes number dependence predicted by ODT.
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| 4. |
- Fistler, Marco, 1989
(författare)
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Turbulence-droplet interaction modelled by One-Dimensional-Turbulence
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A stochastic model to study droplet/particle influence on the gas phase using the One-Dimensional-Turbulence model (ODT) is evaluated. To address one of the major problems for multiphase flow simulations, namely computational costs, the dimension-reduced model is used with the goal of predicting certain classes of these flows more efficiently. ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps which represent the effect of individual turbulent eddies on property fields. A Lagrangian particle tracking method developed by Schmidt et al. was modified and extended. For validation purposes flow configurations of turbulent particle-laden round jet were simulated with the developed model. It could be shown that the model has the capability to capture the impact of varying Stokes numbers and also different particle loadings. This shows that turbulence modulation is possible to capture with the model and it can be used for investigations of turbulent-droplet interaction at parameter ranges which are not accesible by DNS or LES simulations.
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| 5. |
- Fistler, Marco, 1989
(författare)
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Turbulence modulation effects caused by small droplets using one-dimensional-turbulence
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a stochastic model to study turbulence modulation effects on gas phases caused by small droplets or more generally speaking particles to achieve a better understanding about the physics and with the aim to provide data for a subgrid-scale (SGS) model for Large-eddy-simulations. The one-dimensional-turbulence (ODT) model addresses one of the major issues for multiphase flow simulations, namely computational costs. It is a dimension-reduced model resolving all turbulent time and length scales and reaching parameter ranges, which are inaccessible for Direct-Numerical-Simulations (DNS). ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps which represent the effect of individual turbulent eddies on property fields. For an efficient investigation of turbulence modulation effects, ODT has been extended in this thesis in many ways. First, the Lagrangian particle tracking method developed by Schmidt et al. was modified for spatial, cylindrical flow simulations. Therefore, the two-way coupling mechanism was extended as well. This case serves to study the overall influence of particles on a jet configuration, which conforms with the droplet-laden flow in the dilute region of a spray. Here, the most significant effects are expected. Secondly, a concept for developing a SGS model is presented. Based on this concept, ODT was modified to capture two canonical test cases of stationary, forced isotropic turbulence (HIT) and homogeneous shear turbulence (HST). For this purpose, a forcing scheme that maintains statistical stationarity and a new energy redistribution mechanism during the eddy events are introduced. The latter enables ODT to predict anisotropic turbulent structures. ODT is validated against several data sets of DNS studies and showed its capability to access parameter ranges beyond previous limits. It turned out to have a lot of potential to contribute to a SGS closure of LES for turbulence modulation caused by small droplets.
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| 6. |
- Fistler, Marco, 1989, et al.
(författare)
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Turbulence modulation in particle-laden stationary homogeneous isotropic turbulence using one-dimensional turbulence
- 2020
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Ingår i: Physical Review Fluids. - 2469-990X. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- Turbulence modulation in particle-laden stationary homogeneous isotropic turbulence is investigated using one-dimensional turbulence (ODT), a low-dimensional stochastic flow simulation model. For this purpose, ODT is extended in two ways. First, a forcing scheme that maintains statistical stationarity is introduced. Unlike direct numerical simulation (DNS) of forced turbulence, the ODT framework accommodates forcing that is not directly coupled to the momentum equation. For given forcing the ODT energy dissipation rate is therefore the same in particle-laden cases as in the corresponding single-phase reference case. Second, previously implemented one-way-coupled particle phenomenology is extended to two-way coupling using the general ODT methodology for flow modulation through interaction with any specified energy and momentum sources and sinks. As in a DNS comparison case for Re-lambda = 70, turbulence modulation is diagnosed primarily on the basis of the fluid-phase kinetic-energy spectrum. Because ODT involves subprocesses with straightforward physical interpretations, the ODT mechanisms of particle-induced turbulence modulation are clearly identified and they are plausibly relevant to particleladen Navier-Stokes turbulence. ODT results for the ratio of particle-phase and fluid-phase kinetic energies as a function of particle Stokes number and mass loading are reported for the purpose of testing these predictions in the future when these quantities are evaluated experimentally or using DNS.
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| 7. |
- Fistler, Marco, 1989, et al.
(författare)
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Turbulence modulation in particle-laden stationary homogeneous shear turbulence using one-dimensional turbulence
- 2020
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Ingår i: Physical Review Fluids. - 2469-990X. ; 5:12
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Tidskriftsartikel (refereegranskat)abstract
- Turbulence modulation in particle-laden stationary homogeneous shear turbulence (HST) is investigated using one-dimensional turbulence (ODT), a low-dimensional stochastic flow simulation model. For this purpose, an ODT formulation previously used to study turbulence modulation in forced homogeneous isotropic turbulence (HIT) is extended, so that the model emulates the anisotropic character of HST and, potentially, anisotropic turbulence in general. This is done by limiting the kinetic-energy redistribution during an eddy event to an exchange involving two velocity components, where the three possible choices of the omitted component define three eddy types whose relative likelihoods control the anisotropy. Comparisons of ODT and direct-numerical-simulation results with reference to signatures of turbulence modulation are the basis of a broader ODT parameter study that is reported. Owing to the reduced dimensionality of ODT, it is found that the fidelity of the model for single-phase HST does not extend to particle effects on flow anisotropy, but for quantities averaged over components, parametric trends are captured. The consistent approach to case comparisons that was introduced in the HIT study to evaluate sensitivities to particle-phase parameters in a given flow configuration is extended here to a cross-comparison of HST and HIT model results, and its efficacy is again confirmed. The results provide an overall characterization of the potential for ODT to support the incorporation of particle-induced turbulence modulation into subgrid-scale closures of large-eddy simulations.
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| 8. |
- Lignell, David, et al.
(författare)
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One-dimensional turbulence modeling for cylindrical and spherical flows: model formulation and application
- 2018
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Ingår i: Theoretical and Computational Fluid Dynamics. - : Springer Science and Business Media LLC. - 1432-2250 .- 0935-4964. ; 32:4, s. 495-520
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Tidskriftsartikel (refereegranskat)abstract
- The one-dimensional turbulence (ODT) model resolves a full range of time and length scales and is computationally efficient. ODT has been applied to a wide range of complex multi-scale flows, such as turbulent combustion. Previous ODT comparisons to experimental data have focused mainly on planar flows. Applications to cylindrical flows, such as round jets, have been based on rough analogies, e.g., by exploiting the fortuitous consistency of the similarity scalings of temporally developing planar jets and spatially developing round jets. To obtain a more systematic treatment, a new formulation of the ODT model in cylindrical and spherical coordinates is presented here. The model is written in terms of a geometric factor so that planar, cylindrical, and spherical configurations are represented in the same way. Temporal and spatial versions of the model are presented. A Lagrangian finite-volume implementation is used with a dynamically adaptive mesh. The adaptive mesh facilitates the implementation of cylindrical and spherical versions of the triplet map, which is used to model turbulent advection (eddy events) in the one-dimensional flow coordinate. In cylindrical and spherical coordinates, geometric stretching of the three triplet map images occurs due to the radial dependence of volume, with the stretching being strongest near the centerline. Two triplet map variants, TMA and TMB, are presented. In TMA, the three map images have the same volume, but different radial segment lengths. In TMB, the three map images have the same radial segment lengths, but different segment volumes. Cylindrical results are presented for temporal pipe flow, a spatial nonreacting jet, and a spatial nonreacting jet flame. These results compare very well to direct numerical simulation for the pipe flow, and to experimental data for the jets. The nonreacting jet treatment overpredicts velocity fluctuations near the centerline, due to the geometric stretching of the triplet maps and its effect on the eddy event rate distribution. TMB performs better than TMA. A hybrid planar-TMB (PTMB) approach is also presented, which further improves the results. TMA, TMB, and PTMB are nearly identical in the pipe flow where the key dynamics occur near the wall away from the centerline. The jet flame illustrates effects of variable density and viscosity, including dilatational effects.
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