Riley, JJ
1992
A Study of Favre Averaging Turbulent Flows with Chemical Reaction
Chen, C; Riley, J.J. and McMurtry, P.A.
Combustion and Flame, 87:257-277, 1992. Funded by Office of Naval Research and ACERC.
This article presents an investigation of the Favre averaging method for turbulent flows with chemical reaction. A set of data from direct numerical simulations of a chemically reacting turbulent mixing layer is employed. Favre-averaged quantities are compared directly with their corresponding Reynolds-averaged values. The gradient transport assumptions in the kappa-epsilon model in Favre-averaged form are also tested. Finally the transport equations for the Reynolds stress and scalar flux of the chemical product are studied term by term. Some Favre-averaged quantities such as u, ˜c, and ˜k are very similar numerically to their Reynolds-averaged values. Other Favre-averaged quantities, however, like ˜e, ˜p, ˜u, and ˜v, are significantly different from their Reynolds-averaged values. The gradient transport models generally work rather well when the mixing layer is in a naturally developing turbulent state, although some important weaknesses are noted. Some significant effects of pressure on they Reynolds stress and scalar flux are exhibited.
1991
A Study of Favre Averaging Turbulent Flows with Chemical Reaction
Chen, C; Riley, J.J.; and McMurtry, P.A.
Combustion and Flame, 1991 (in press). Funded by ACERC.
This article presents an investigation of the Favre averaging method for turbulent flows with chemical reaction. A set of data from direct numerical simulations of a chemically reacting turbulent mixing layer is employed. Favre-averaged quantities are compared directly with their corresponding Reynolds-averaged values. The gradient transport assumptions in the k - model in Favre-averaged form are also tested. Finally the transport equations for the Reynolds stress and scalar flux of the chemical product are studied term by term. Some Favre-averaged quantities such as are very similar numerically to their Reynolds-averaged values. Other Favre-averaged quantities, however, like and , are significantly different from their Reynolds-averaged values. The gradient transport models generally work rather well when the mixing layer is in a naturally developing turbulent state, although some important weaknesses are noted. Some significant effects of pressure on they Reynolds stress and scalar flux are exhibited.
1988-1986
Effects of Heat Release on the Large-Scale Structure in Turbulent Mixing Layers
McMurtry, P.A.; Riley, J.J. and Metcalfe, R.W.
To appear in Journal of Fluid Mechanics, 1988. Funded by NASA Lewis Research Center and Office of Naval Research.
The effects of chemical heat release on the large-scale structure in a chemically reacting, turbulent mixing layer are investigated using direct numerical simulations. Three-dimensional, time-dependent simulations are performed for a binary, single-step chemical reaction occurring across a temporally developing turbulent mixing layer. It is found that moderate heat release slows the development of the large-scale structures and shifts their wavelengths to larger scales. The resulting entrainment of reactants is reduced, decreasing the overall chemical product formation rate. The simulation results are interpreted in terms of turbulence energetics, vorticity dynamics, and stability theory. The baroclinic torque and thermal expansion in the mixing layer produce changes in the flame vortex structure that result in more diffuse vortices than in the large-scale structures. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers are shown to result from vorticity generation by baroclinic torques.
The Use of Direct Numerical Simulation in the Study of Turbulent Chemically-Reacting Flows
Riley, J.J. and McMurtry, P.A.
To appear in Analysis of Reacting Flows, Springer-Verlag, 1988. Funded by NASA Lewis Research Center, Office of Naval Research, University of Washington, and US Office of Basic Energy Sciences.
At the present time the role of direct numerical simulation as applied to turbulent, chemically reacting flows is twofold; to understand the physical processes involved, and to develop and test theories. In this paper we present and example of the former. We employ full turbulence simulations to study the effects of chemical heat release on the large-scale structures in turbulent mixing layers. This work not only aids in understanding this phenomenon, but also gives insight into strengths and limitations of the methodology.
We find, in agreement with previous laboratory experiments, the heat release is observed to lower the rate at which the mixing layer grows and to reduce the rate at which chemical products are formed. The baroclinic torque and thermal expansion in the mixing layer are shown to produce changes in the flame vortex structure the act to produce more diffuse vortices than in the constant density case, resulting in lower rotation rates of the large scale structures. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers are shown to result from vorticity generation by baroclinic torques. The density reductions also lower the generation rates of turbulent kinetic energy and the turbulent shear stresses, resulting in less turbulent mixing of fluid elements.
Calculations of the energy in the various wave numbers shows that the heat release has a stabilizing effect on the growth rates of individual modes. A linear stability analysis of a simplified model problem confirms this, showing that low-density fluid in the mixing region will result in a shift in the frequency of the unstable modes to lower wave numbers (longer wavelengths). The growth rates of the unstable modes decrease, contributing to the slower growth of the mixing layer.
Finally, we find that this methodology can be confidently applied for Reynolds numbers less than several hundred and for Damkohler numbers less than about ten. With some modification it is possible to treat the infinite Damkohler number case using a conserved scalar.
Direct Numerical Simulations of a Reacting Mixing Layer with Chemical Heat Release
McMurtry, P.A.; Metcalfe, R.W.; Jou, W.H. and Riley, J.J.
AIAA Journal, 24, (6), 962, 1986. Funded by NASA Lewis Research Center.
To study the coupling between chemical heat release and fluid dynamics, we have performed direct numerical simulations of a two-dimensional mixing layer undergoing a simple single-step chemical reaction with heat release. The reaction is function only of the species concentrations and does not depend on temperature. We have treated the fully compressible equations, as well as an approximate set of equations that is asymptotically valid for low Mach number flows. These latter equations have the computational advantage that high-frequency acoustic waves have been filtered out, allowing much larger time steps to be taken in the numerical solution procedure. A derivation of these equations along with an outline of the numerical solution technique is given. Simulation results indicate that the rate of chemical product formed, the thickness of the mixing layer, and the dynamics are studied to analyze and interpret some effects of heat release on the fluid motion.
Riley, JJ
1992
A Study of Favre Averaging Turbulent Flows with Chemical Reaction
Chen, C; Riley, J.J. and McMurtry, P.A.
Combustion and Flame, 87:257-277, 1992. Funded by Office of Naval Research and ACERC.
This article presents an investigation of the Favre averaging method for turbulent flows with chemical reaction. A set of data from direct numerical simulations of a chemically reacting turbulent mixing layer is employed. Favre-averaged quantities are compared directly with their corresponding Reynolds-averaged values. The gradient transport assumptions in the kappa-epsilon model in Favre-averaged form are also tested. Finally the transport equations for the Reynolds stress and scalar flux of the chemical product are studied term by term. Some Favre-averaged quantities such as u, ˜c, and ˜k are very similar numerically to their Reynolds-averaged values. Other Favre-averaged quantities, however, like ˜e, ˜p, ˜u, and ˜v, are significantly different from their Reynolds-averaged values. The gradient transport models generally work rather well when the mixing layer is in a naturally developing turbulent state, although some important weaknesses are noted. Some significant effects of pressure on they Reynolds stress and scalar flux are exhibited.
1991
A Study of Favre Averaging Turbulent Flows with Chemical Reaction
Chen, C; Riley, J.J.; and McMurtry, P.A.
Combustion and Flame, 1991 (in press). Funded by ACERC.
This article presents an investigation of the Favre averaging method for turbulent flows with chemical reaction. A set of data from direct numerical simulations of a chemically reacting turbulent mixing layer is employed. Favre-averaged quantities are compared directly with their corresponding Reynolds-averaged values. The gradient transport assumptions in the k - model in Favre-averaged form are also tested. Finally the transport equations for the Reynolds stress and scalar flux of the chemical product are studied term by term. Some Favre-averaged quantities such as are very similar numerically to their Reynolds-averaged values. Other Favre-averaged quantities, however, like and , are significantly different from their Reynolds-averaged values. The gradient transport models generally work rather well when the mixing layer is in a naturally developing turbulent state, although some important weaknesses are noted. Some significant effects of pressure on they Reynolds stress and scalar flux are exhibited.
1988-1986
Effects of Heat Release on the Large-Scale Structure in Turbulent Mixing Layers
McMurtry, P.A.; Riley, J.J. and Metcalfe, R.W.
To appear in Journal of Fluid Mechanics, 1988. Funded by NASA Lewis Research Center and Office of Naval Research.
The effects of chemical heat release on the large-scale structure in a chemically reacting, turbulent mixing layer are investigated using direct numerical simulations. Three-dimensional, time-dependent simulations are performed for a binary, single-step chemical reaction occurring across a temporally developing turbulent mixing layer. It is found that moderate heat release slows the development of the large-scale structures and shifts their wavelengths to larger scales. The resulting entrainment of reactants is reduced, decreasing the overall chemical product formation rate. The simulation results are interpreted in terms of turbulence energetics, vorticity dynamics, and stability theory. The baroclinic torque and thermal expansion in the mixing layer produce changes in the flame vortex structure that result in more diffuse vortices than in the large-scale structures. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers are shown to result from vorticity generation by baroclinic torques.
The Use of Direct Numerical Simulation in the Study of Turbulent Chemically-Reacting Flows
Riley, J.J. and McMurtry, P.A.
To appear in Analysis of Reacting Flows, Springer-Verlag, 1988. Funded by NASA Lewis Research Center, Office of Naval Research, University of Washington, and US Office of Basic Energy Sciences.
At the present time the role of direct numerical simulation as applied to turbulent, chemically reacting flows is twofold; to understand the physical processes involved, and to develop and test theories. In this paper we present and example of the former. We employ full turbulence simulations to study the effects of chemical heat release on the large-scale structures in turbulent mixing layers. This work not only aids in understanding this phenomenon, but also gives insight into strengths and limitations of the methodology.
We find, in agreement with previous laboratory experiments, the heat release is observed to lower the rate at which the mixing layer grows and to reduce the rate at which chemical products are formed. The baroclinic torque and thermal expansion in the mixing layer are shown to produce changes in the flame vortex structure the act to produce more diffuse vortices than in the constant density case, resulting in lower rotation rates of the large scale structures. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers are shown to result from vorticity generation by baroclinic torques. The density reductions also lower the generation rates of turbulent kinetic energy and the turbulent shear stresses, resulting in less turbulent mixing of fluid elements.
Calculations of the energy in the various wave numbers shows that the heat release has a stabilizing effect on the growth rates of individual modes. A linear stability analysis of a simplified model problem confirms this, showing that low-density fluid in the mixing region will result in a shift in the frequency of the unstable modes to lower wave numbers (longer wavelengths). The growth rates of the unstable modes decrease, contributing to the slower growth of the mixing layer.
Finally, we find that this methodology can be confidently applied for Reynolds numbers less than several hundred and for Damkohler numbers less than about ten. With some modification it is possible to treat the infinite Damkohler number case using a conserved scalar.
Direct Numerical Simulations of a Reacting Mixing Layer with Chemical Heat Release
McMurtry, P.A.; Metcalfe, R.W.; Jou, W.H. and Riley, J.J.
AIAA Journal, 24, (6), 962, 1986. Funded by NASA Lewis Research Center.
To study the coupling between chemical heat release and fluid dynamics, we have performed direct numerical simulations of a two-dimensional mixing layer undergoing a simple single-step chemical reaction with heat release. The reaction is function only of the species concentrations and does not depend on temperature. We have treated the fully compressible equations, as well as an approximate set of equations that is asymptotically valid for low Mach number flows. These latter equations have the computational advantage that high-frequency acoustic waves have been filtered out, allowing much larger time steps to be taken in the numerical solution procedure. A derivation of these equations along with an outline of the numerical solution technique is given. Simulation results indicate that the rate of chemical product formed, the thickness of the mixing layer, and the dynamics are studied to analyze and interpret some effects of heat release on the fluid motion.