### 15.5.3. Specified Blend Factor

This selection enables you to set a blend factor between 0.0 and 1.0 for the advection scheme. A value of 0.0 is equivalent to using the first order advection scheme and is the most robust option. A value of 1.0 uses second order differencing for the advection terms; this is not the same as the high resolution advection scheme. This setting is more accurate but less robust. Values between 0.0 and 1.0 blend first and second order differencing, with increased accuracy and reduced robustness as you approach 1.0. At the higher values, overshoots and undershoots can appear. At lower values, excessive diffusivity can occur.

Important: If you are using `High Resolution` or a high blend factor value, it will be necessary to use a smaller timestep. It is recommended that you use a timestep of approximately 1/4 to 1/3 the physical timestep. For details, see Time Scale Control.

You cannot use this advection scheme for the volume fraction equation in a multiphase simulation.

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