On Some Flux-Type Advection Schemes for Dispersion Modelling Application

The advection scheme TRAP (from TRAPezium) was elaborated for the Bulgarian dispersion model EMAP, a PC-oriented Eulerian multi-layer model. The TRAP scheme is explicit, positively definite and conservative with limited numerical dispersion and good transportivity. Displaying the same properties as Bott’s scheme [1], the TRAP scheme turns out to be faster. In the Bott scheme the flux area is calculated by integrating the polynomial fit over the neighbouring grid values. In the TRAP scheme, the flux area is supposed trapezoidal. It is determined as a product of the Courant number and a single value of the approximating polynomial referring the middle of the passed distance. In the TRAP scheme, the same 4th order polynomial is used and Bott’s normalisation is also applied.