Local Mean Age

Local mean age (LMA) is the average time τ for fluid to travel from the selected inlet opening to the point with taking both the velocity and the diffusion into account.

It is determined by solving the following equation:

	(1)

where xi is the i-th coordinate, ρ is the density, ui is the i-th velocity component, μ is the dynamic viscosity coefficient, μt is the turbulent eddy viscosity coefficient, σ and σt are the laminar and turbulent Schmidt numbers. The equation is solved under the τ = 0 boundary condition on the inlet opening.

Dimensionless LMA (τ*) is the LMA divided by the V/Q ratio, where V is the computational domain fluid volume, Q is the volume flow rate of the air entering this fluid volume.

LACI (Local Air Change Index) is equal to 1/(τ*), i.e. reciprocal to the Dimensionless LMA.

By default, the calculation of these parameters is disabled. You can enable the calculation of LMA, Dimensionless LMA and LACI in the Calculation Control Options.