Versione italianaStack tip downwash
The stack tip downwash can occur when the stack exit velocity is small compared to the wind speed at stack height. In this case, low pressure in the wake of the stack may cause the plume to be drawn downward behind the stack. Consequences of the stack tip downwash are decreased plume rise and increased downwind concentrations close to the stack.
The stack tip downwash is modelled by decreasing the stack height, so that the plume rise starts below the actual stack height, as shown in figure. This tool allows to estimate the reduced stack height due to stack tip downwash.
The stack tip downwash is one of the algorithms incorporated in the LAPMOD dispersion model.