The Kato-Launder modification is an ad-hoc modification of the turbulent production term in the k equation. The main purpose of the modification is to reduce the tendency that two-equation models have to over-predict the turbulent production in regions with large normal strain, i.e. regions with strong acceleration or decelleration.
The transport equation for the turbulent energy, , used in most two-equation models can be written as:
Where is the turbulent production normally given by:
is the turbulent shear stress tensor given by the Boussinesq assumption:
Where is the eddy-viscosity given by the turbluence model and is the trace-less viscous strain-rate defined by:
In incompressible flows, where , the production term can be rewritten as:
Production term modification
The proposal by Kato and Launder is to replace one of the strain-rates, , in the turbulent production term with the vorticity, . The Kato-Launder modified production then becomes:
In pure shear-flows like boundary-layers and wakes the Kato-Launder modified production term will give exactly the same result as the unmodified production term. However, outside of boundary-layers and wakes the Kato-Launder modified production term will give very different results. Essentially what it does is to turn off the turbulent production outside of the boundary-layers and wakes. This has the good effect that
Kato, M. and Launder, B. E. (1993), "The Modeling of Turbulent Flow Around Stationary and Vibrating Square Cylinders", Proc. 9th Symposium on Turbulent Shear Flows, Kyoto, August 1993, pp. 10.4.1-10.4.6.