# how to use finite-rate/eddy-dissipation?

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 September 28, 2007, 00:41 how to use finite-rate/eddy-dissipation? #1 muro Guest   Posts: n/a Dear friends, I've got problem on using finite-rate/eddy-dissipation in the non-premixed combustion simulation. By patching some zones to the high temperature value, I also found that the combustion is not occurred in the chamber. So, please help me to fix this problem. Thank you very much. Muhad

 July 26, 2012, 07:11 #2 New Member   Prakash Ghose Join Date: Dec 2011 Posts: 29 Rep Power: 6 The Pressure-Based coupled algorithm which is a good alternative to density-based solvers of ANSYS Fluent when dealing with applications involving high shear flow was employed. The following spatial discretization schemes were used:  For gradient – the least square cell based method was employed; and  The second – order upwind scheme was employed for density, momentum, modified turbulent viscosity and the energy equations. Under relaxation factor of 0.8 was used for the species, energy and density while a value of 0.6 was applied for the momentum, turbulent kinetic energy, turbulent kinetic dissipation rate and turbulent viscosity. In order to monitor convergence as the calculations (iterations) progressed, the following residual quantities: continuity, x-velocity, y-velocity, energy, turbulent kinetic energy, k, turbulent dissipation rate, , and all the species were monitored. The absolute convergence criteria which were set for these quantities are: continuity 10−3, x-velocity 10−3, y-velocity 10−3 and energy 10−4 for cold flow calculations. For the reacting flow computations, the initial temperature field was patched to initiate the combustion process. The absolute convergence criteria for the species were then lowered to 10−6. The initial calculations were performed assuming that all properties except density were constant. Using constant transport properties (viscosity, thermal conductivity, and mass diffusion coefficients) is acceptable here because the flow is fully turbulent. The molecular transport properties will play a minor role compared to turbulent transport. The assumption of constant specific heat, in contrast, has a strong effect on the combustion solution, and this property was represented with a polynomial function during the reacting flow computation. The solution was then initialized. Thereafter, the Full Multigrid (FMG) feature was run. Full Multigrid initialization often facilitates an easier start-up, thereby, obviating the need for Courant- Friedrichs-Lewy (CFL) condition ramping, consequently reducing the number of iterations required for convergence.

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