An alternating multiport diffuser is a design where the ports do not point in
a nearly single horizontal direction.
In the latter case, the ports may point more or less horizontally in an alternating fashion to both sides of the diffuser line or they may point upward, more or less vertically.
An alternating multiport diffuser hence imparts NO net horizontal momemtum flux to the effluent discharge.
Definition sketches and CorSpy visualizations show these types with fanning and without fanning.
Please click on the slide images below to view CorSpy visualizations of various unidirectional multiport diffuser configrations.