Prediction of turbulent combustion flowfields behind a backward-facing step

Abstract

Turbulent combustion flowfields behind a backward-facing step are examined by using different boundary conditions and various computational assumptions. The effect of combustion on the flow is also studied. Hydrogen and methane are the two gaseous fuels chosen for this investigation. Both a conventional law of the wall method and a recently developed low Reynolds number model are tested. Two types of statistical models are employed in the combustion simulations to take into account species fluctuations. The results are primarily fourfold: 1) The fluctuation of the fuel mass fraction is insignificant for the Reynolds number examined in this paper; 2) different statistical models produce almost identical results; 3) the law of the wall model predicts a shorter reattachment length than the low Reynolds number model does; and 4) the effect of combustion is to shorten the reattachment length of the flow field, and the reattachment length is more a function of the amount of heat input to the system than a function of the type of fuel or a function of the injection rate in a reactive flow system.Xj x y e 17 ri " K //, v p a r Nomenclature statistical mean Favre covariance of the mixture fraction specific turbulence kinetic energy, m 2 /s 2 probability density function pressure, N/m 2 residual source term in an equation temperature, K streamwise velocity, m/s Cartesian velocity component, m/s Favre fluctuation of velocity component I//, m/s transverse velocity, m/s Cartesian coordinate, m streamwise coordinate, m transverse coordinate, m turbulence dissipation rate, m 2 /s 3 mixture fraction Favre fluctuation of mixture fraction von Karman constant laminar viscosity, kg/m • s eddy viscosity, kg/m • s M + A*r kinematic viscosity, m 2 /s density, kg/m 3 statistical variance stress, kg/m • s 2 any dependent variable Subscripts I = quantities inside the viscous sublayer v = quantities at the edge of the viscous sublayer 0 = wall values 1 = first grid point outside the viscous sublayer or off the wall Received