16.5.2 Defining the Flamelet Controls

When the steady laminar flamelet model is selected, and you have created or imported a flamelet, you can adjust the controls for the flamelet solution in the Control tab of the Species Model dialog box (Figure  16.5.2).

Figure 16.5.2: The Species Model Dialog Box ( Control Tab) for the Steady Laminar Flamelet Model

The Initial Fourier Number sets the first time step for the solution of the flamelet equations ( this equation and this equation in the separate Theory Guide). This first time step is calculated as the explicit stability-limited diffusion time step multiplied by this value. If the solution diverges before the first time step is complete, the value should be lowered.

The Fourier Number Multiplier increases the time step at subsequent times. Every time step after the first is multiplied by this value. If the solution diverges after the first time step, this value should be reduced.

During the numerical integration of the flamelet equations, the local error is controlled to be less than

where $\phi_i$ represents the species mass fractions and temperature at point $i$ in the 1D flamelet. $\epsilon_{\rm rel}$ is the value of the Relative Error Tolerance and $\epsilon_{\rm abs}$ is the value of the Absolute Error Tolerance, both of which you can specify.

Because steady laminar flamelets are obtained by time-stepping, they are considered converged only when the maximum absolute change in species fraction or temperature at any discrete mixture-fraction point is less than the specified Flamelet Convergence Tolerance. Between time steps, the flamelet species fractions and temperature will sometimes oscillate, which causes absolute changes that are always greater than the flamelet convergence tolerance. In such cases, ANSYS FLUENT will stop the flamelet calculation after the total elapsed time has exceeded the Maximum Integration Time.