Kjell Rian - Academia.edu (original) (raw)

Papers by Kjell Rian

Large Eddy Simulations (LES) of the Sandia Flame D methane diffusion flame are carried out. An ex... more Large Eddy Simulations (LES) of the Sandia Flame D methane diffusion flame are carried out. An extended LES version of the Eddy Dissipation Concept (EDC) model is used as a turbulence combustion closure model. In LES the computational cost is high due to the fine grid resolution and unsteady nature of the governing equations. Using a detailed chemical mechanism in LES with EDC is too expensive, and hence, to reduce computational cost reduced mechanisms are preferred. In this study a number of PSR calculations for methane-air combustion using two reduced methane mechanisms and one detailed methane mechanism are carried out. The reduced mechanisms tend to strongly overpredict the temperature and major species mass fraction in either the lean or the rich mixture zone. Both mechanisms overpredict temperature for lean mixtures. The two reduced methane mechanisms are also studied with LES for the Sandia Flame D. The results of the two reduced mechanisms are compared with the fast chemistry approach and it is observed that in the lean mixture zone of the jet the reduced mechanisms overpredict the temperature and H2O mass fraction. Prediction with fast chemistry approach compared well with the experimental data. The present study emphasize the need of using fast chemistry approach instead of reduced mechanism when using the EDC combustion model.

Flow Turbulence and Combustion, Jul 7, 2014

ABSTRACT

Int J Hydrogen Energ, 2007

The aim of this work is to improve the knowledge of modeling NOxNOx formation in hydrogen flames.... more The aim of this work is to improve the knowledge of modeling NOxNOx formation in hydrogen flames. Four different detailed reaction mechanisms have been tested for eight laminar flames, and two of these mechanisms have been tested for a turbulent jet flame. The numerical results have been compared with experimental data from the literature. Sensitivity and integral reaction flow analyses are applied to identify important reaction steps. Formation of NO through NNH radicals was found to be important in the hydrogen-air flames investigated. This work suggests that the H2/O2 mechanism of Li et al. for pure hydrogen combustion may be combined with the N/H/O subset from Glarborg et al. for prediction of NOxNOx in hydrogen-air flames. However, the pressure-dependency of the reaction N2O+M⇌N2+O+MN2O+M⇌N2+O+M should be further investigated and accounted for. For the turbulent hydrogen jet flame, the agreement between the predicted and measured NO levels was better with the mechanism of Glarborg et al.

In this work the reaction-rate response of different species to inlet flow variations have been s... more In this work the reaction-rate response of different species to inlet flow variations have been studied using an unsteady perfectly stirred reactor model. Transient simulations of variations in mass flow rate, temperature and mixture equivalence ratio at the reactor inlet have been conducted. Combustion of methane and propane, with both global single-step and detailed chemical kinetic mechanisms, has been simulated. The detailed mechanisms predict similar general trends. The global and detailed mechanism for methane predict almost the same reaction rates, whereas the predicted reaction rates from the global and detailed mechanism for propane are very different at high equivalence ratios, near stoichiometry. The reaction-rate oscillations were not very sensitive to imposed small oscillations on the inlet temperature. An imposed small oscillation on the inlet mass flow rate gave reaction-rate oscillations that were almost constant at both rich and lean mixtures. The largest variations in reaction rate oscillations between rich and lean mixtures were found when imposing a small oscillation on the equivalence ratio of the mixture at the inlet. The present study indicates that variations in the inlet mixture equivalence ratio may lead to combustion instabilities in lean premixed combustion.

Plane turbulent bluff-body flows were numerically analysed using compressible formulation of the ... more Plane turbulent bluff-body flows were numerically analysed using compressible formulation of the conventional URANS approach. The low-Reynolds-number k−ǫ turbulence model of Launder and Sharma was applied for the closure problem. Numerical simulation was carried out using the state-of-the-art OpenFOAM technology for the three popular test problems in fluid dynamics : 1) plane laminar compressible flow (Re=140, M=0.2) over a circular cylinder; 2) turbulent bluff-body flow in the channel (Re = 17500, M = 0.03) replicating the Fujii lab-test conditions; 3) turbulent bluff-body flow in the channel (Re = 45000, M = 0.05) replicating the Volvo test rig. Satisfactory agreement between numerical and measured data for the main integral and local flow characteristics was achieved which indicates on the adequacy and accuracy of the established numerical method, implemented in the OpenFOAM library, for prediction plane fully-developed turbulent bluff-body flows.

Chemical Engineering Transactions

ABSTRACT

Journal of Wind Engineering and Industrial Aerodynamics, 2015

Flow, Turbulence and Combustion, 2014

ABSTRACT

Flow, Turbulence and Combustion, 2014

ABSTRACT

Advances in Fluid Mechanics VIII, 2010

ABSTRACT Modeling of turbulence-chemistry interaction is still a challenge. Turbulence modeling w... more ABSTRACT Modeling of turbulence-chemistry interaction is still a challenge. Turbulence modeling with Large Eddy Simulation (LES) has been matured enough for industrial problems. In LES eddies up to the filter width are resolved on the grid scales, but the fine structures where combustion takes place are still not resolved, which calls for combustion modeling in LES. Combustion closure in LES is achieved through a Turbulence Chemistry Interaction Model (TCIM). Most of the developed TCIM are based on the already existing RANS model. In the present study, a TCIM based on the Eddy Dissipation Concept (EDC) is proposed for large eddy simulation. The model is formulated from subgrid viscosity and filtered strain rate tensor. EDC model constants are modified to account for the partial energy cascading in LES. The other model used in this study is the steady state Flamelet model. Another issue with reacting flows is the solution of the pressure correction Poisson’s equation with density time derivative term, which causes severe time constraint per iteration. Density time derivative is the most destabilizing part of the calculation when the density from equation of state is used. In the present study density is formulated from species mass fraction, which is numerically stable and computationally less expensive. LES of the H2/N2 “FlameH3” non-premixed unconfined turbulent jet flame is performed using LES-EDC and Flamelet model. The Reynolds number based on nozzle diameter and jet bulk velocity is 10,000. The chemistry used for LES-EDC model is a fast-chemistry. Results of the simulations in the form of means and variances of velocity and scalars are compared to experimental data. All these quantities are in satisfactory agreement with experiments.

Communications in Applied Numerical Methods, 1992

The paper describes the implementation and applicability of the Large eddy simulation (LES) techn... more The paper describes the implementation and applicability of the Large eddy simulation (LES) technique for simulating turbulent flows. The LES approach is implemented in the in-house RANS research code Spider-3D. The Spider-LES code is validated by studying the unsteady flow over a backward-facing step (BFS). The LES simulation over the BFS is carried out at a Reynolds number of 5100 based on the inlet free-stream velocity. Finite-volume discretization schemes for the non-linear convective terms and sub-grid stress (SGS) models used for LES approach are discussed in the present study. To investigate mesh dependency, two types of grid resolution are studied. The results computed from Spider-LES are validated against DNS reference data by Le et al. The mean longitudinal, vertical velocity profile and the turbulence intensities compare satisfactory with the DNS data at the normalized coordinates X * = (x − X r ) /X r . The reattachment length X r in the longitudinal direction, varies from 7.2h to 7.4h with different SGS models used as compared to the DNS value of 6.28h.

Energy Procedia, 2014

ABSTRACT

Inter J Fluid Mech Res, 2011

International Journal of Aeroacoustics, 2014

ABSTRACT

International Journal of Hydrogen Energy, 2007

ABSTRACT

Flow, Turbulence and Combustion, 2012

ABSTRACT

Flow, Turbulence and Combustion, 2013

ABSTRACT

Computers & Fluids, 2013

ABSTRACT

Large Eddy Simulations (LES) of the Sandia Flame D methane diffusion flame are carried out. An ex... more Large Eddy Simulations (LES) of the Sandia Flame D methane diffusion flame are carried out. An extended LES version of the Eddy Dissipation Concept (EDC) model is used as a turbulence combustion closure model. In LES the computational cost is high due to the fine grid resolution and unsteady nature of the governing equations. Using a detailed chemical mechanism in LES with EDC is too expensive, and hence, to reduce computational cost reduced mechanisms are preferred. In this study a number of PSR calculations for methane-air combustion using two reduced methane mechanisms and one detailed methane mechanism are carried out. The reduced mechanisms tend to strongly overpredict the temperature and major species mass fraction in either the lean or the rich mixture zone. Both mechanisms overpredict temperature for lean mixtures. The two reduced methane mechanisms are also studied with LES for the Sandia Flame D. The results of the two reduced mechanisms are compared with the fast chemistry approach and it is observed that in the lean mixture zone of the jet the reduced mechanisms overpredict the temperature and H2O mass fraction. Prediction with fast chemistry approach compared well with the experimental data. The present study emphasize the need of using fast chemistry approach instead of reduced mechanism when using the EDC combustion model.

Flow Turbulence and Combustion, Jul 7, 2014

ABSTRACT

Int J Hydrogen Energ, 2007

The aim of this work is to improve the knowledge of modeling NOxNOx formation in hydrogen flames.... more The aim of this work is to improve the knowledge of modeling NOxNOx formation in hydrogen flames. Four different detailed reaction mechanisms have been tested for eight laminar flames, and two of these mechanisms have been tested for a turbulent jet flame. The numerical results have been compared with experimental data from the literature. Sensitivity and integral reaction flow analyses are applied to identify important reaction steps. Formation of NO through NNH radicals was found to be important in the hydrogen-air flames investigated. This work suggests that the H2/O2 mechanism of Li et al. for pure hydrogen combustion may be combined with the N/H/O subset from Glarborg et al. for prediction of NOxNOx in hydrogen-air flames. However, the pressure-dependency of the reaction N2O+M⇌N2+O+MN2O+M⇌N2+O+M should be further investigated and accounted for. For the turbulent hydrogen jet flame, the agreement between the predicted and measured NO levels was better with the mechanism of Glarborg et al.

In this work the reaction-rate response of different species to inlet flow variations have been s... more In this work the reaction-rate response of different species to inlet flow variations have been studied using an unsteady perfectly stirred reactor model. Transient simulations of variations in mass flow rate, temperature and mixture equivalence ratio at the reactor inlet have been conducted. Combustion of methane and propane, with both global single-step and detailed chemical kinetic mechanisms, has been simulated. The detailed mechanisms predict similar general trends. The global and detailed mechanism for methane predict almost the same reaction rates, whereas the predicted reaction rates from the global and detailed mechanism for propane are very different at high equivalence ratios, near stoichiometry. The reaction-rate oscillations were not very sensitive to imposed small oscillations on the inlet temperature. An imposed small oscillation on the inlet mass flow rate gave reaction-rate oscillations that were almost constant at both rich and lean mixtures. The largest variations in reaction rate oscillations between rich and lean mixtures were found when imposing a small oscillation on the equivalence ratio of the mixture at the inlet. The present study indicates that variations in the inlet mixture equivalence ratio may lead to combustion instabilities in lean premixed combustion.

Plane turbulent bluff-body flows were numerically analysed using compressible formulation of the ... more Plane turbulent bluff-body flows were numerically analysed using compressible formulation of the conventional URANS approach. The low-Reynolds-number k−ǫ turbulence model of Launder and Sharma was applied for the closure problem. Numerical simulation was carried out using the state-of-the-art OpenFOAM technology for the three popular test problems in fluid dynamics : 1) plane laminar compressible flow (Re=140, M=0.2) over a circular cylinder; 2) turbulent bluff-body flow in the channel (Re = 17500, M = 0.03) replicating the Fujii lab-test conditions; 3) turbulent bluff-body flow in the channel (Re = 45000, M = 0.05) replicating the Volvo test rig. Satisfactory agreement between numerical and measured data for the main integral and local flow characteristics was achieved which indicates on the adequacy and accuracy of the established numerical method, implemented in the OpenFOAM library, for prediction plane fully-developed turbulent bluff-body flows.

Chemical Engineering Transactions

ABSTRACT

Journal of Wind Engineering and Industrial Aerodynamics, 2015

Flow, Turbulence and Combustion, 2014

ABSTRACT

Flow, Turbulence and Combustion, 2014

ABSTRACT

Advances in Fluid Mechanics VIII, 2010

ABSTRACT Modeling of turbulence-chemistry interaction is still a challenge. Turbulence modeling w... more ABSTRACT Modeling of turbulence-chemistry interaction is still a challenge. Turbulence modeling with Large Eddy Simulation (LES) has been matured enough for industrial problems. In LES eddies up to the filter width are resolved on the grid scales, but the fine structures where combustion takes place are still not resolved, which calls for combustion modeling in LES. Combustion closure in LES is achieved through a Turbulence Chemistry Interaction Model (TCIM). Most of the developed TCIM are based on the already existing RANS model. In the present study, a TCIM based on the Eddy Dissipation Concept (EDC) is proposed for large eddy simulation. The model is formulated from subgrid viscosity and filtered strain rate tensor. EDC model constants are modified to account for the partial energy cascading in LES. The other model used in this study is the steady state Flamelet model. Another issue with reacting flows is the solution of the pressure correction Poisson’s equation with density time derivative term, which causes severe time constraint per iteration. Density time derivative is the most destabilizing part of the calculation when the density from equation of state is used. In the present study density is formulated from species mass fraction, which is numerically stable and computationally less expensive. LES of the H2/N2 “FlameH3” non-premixed unconfined turbulent jet flame is performed using LES-EDC and Flamelet model. The Reynolds number based on nozzle diameter and jet bulk velocity is 10,000. The chemistry used for LES-EDC model is a fast-chemistry. Results of the simulations in the form of means and variances of velocity and scalars are compared to experimental data. All these quantities are in satisfactory agreement with experiments.

Communications in Applied Numerical Methods, 1992

The paper describes the implementation and applicability of the Large eddy simulation (LES) techn... more The paper describes the implementation and applicability of the Large eddy simulation (LES) technique for simulating turbulent flows. The LES approach is implemented in the in-house RANS research code Spider-3D. The Spider-LES code is validated by studying the unsteady flow over a backward-facing step (BFS). The LES simulation over the BFS is carried out at a Reynolds number of 5100 based on the inlet free-stream velocity. Finite-volume discretization schemes for the non-linear convective terms and sub-grid stress (SGS) models used for LES approach are discussed in the present study. To investigate mesh dependency, two types of grid resolution are studied. The results computed from Spider-LES are validated against DNS reference data by Le et al. The mean longitudinal, vertical velocity profile and the turbulence intensities compare satisfactory with the DNS data at the normalized coordinates X * = (x − X r ) /X r . The reattachment length X r in the longitudinal direction, varies from 7.2h to 7.4h with different SGS models used as compared to the DNS value of 6.28h.

Energy Procedia, 2014

ABSTRACT

Inter J Fluid Mech Res, 2011

International Journal of Aeroacoustics, 2014

ABSTRACT

International Journal of Hydrogen Energy, 2007

ABSTRACT

Flow, Turbulence and Combustion, 2012

ABSTRACT

Flow, Turbulence and Combustion, 2013

ABSTRACT

Computers & Fluids, 2013

ABSTRACT