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CORMIX2: Multiport Discharges

A multiport diffuser is a linear structure consisting of many more or less closely spaced ports or nozzles which inject a series of turbulent jets at high velocity into the ambient receiving water body. These ports or nozzles may be connected to vertical risers attached to an underground pipe or tunnel or they may simply be openings in a pipe lying on the bottom.

An alternating multiport diffuser for municipal wastewater discharge into a lake under construction (Photo: G. Jirka).
For complex hydrodynamic cases (e.g. alternating diffusers or an unstable near-field), CORMIX2 uses the "equivalent slot diffuser" concept and thus neglects the details of the individual jets issuing from each diffuser port and their merging process, but rather assumes that the flow arises from a long slot discharge with equivalent dynamic characteristics. Hence, if details of the effluent flow behavior in the immediate diffuser vicinity are needed, an additional CORMIX1 simulation for an equivalent partial effluent flow may be recommended.
Individual plumes merge in this unidirectional multiport diffuser discharge experiment (Photo: G. Jirka).

Additional Source Characterization Assumptions:

  • All subsystems require that the actual cross-section of the water body be described or schematized as a rectangular straight uniform channel that may be bounded laterally or unbounded. The ambient velocity is assumed to be uniform within that cross-section.
  • In addition to a uniform ambient density possibility, CORMIX2 allows for three generic types of ambient stratification profiles to be used for the approximation of the actual vertical density distribution.
  • All CORMIX subsystems are in principle steady-state models, however new developments allow the analysis of unsteady mixing in tidal environments.
  • All CORMIX systems can predict mixing for both conservative and non-conservative first-order decay processes, and can simulate heat transfer from thermal plumes.
Definition diagram and limits of applicability for CORMIX2 multiport diffuser discharges (larger image).

Diffusers Types Modeled By CORMIX2 & Visualized with CorSpy

CORMIX2 applies to three commonly used types of multiport diffuser discharges under the same general effluent and ambient conditions as CORMIX1. It analyzes unidirectional, staged, and alternating designs of multiport diffusers and allows for arbitrary alignment of the diffuser structure within the ambient water body, and for arbitrary arrangement and orientation of the individual ports.

Unidirectional Diffuser Types

In the unidirectional diffuser, all ports (or nozzles) point to one side of the diffuser line and are oriented more or less normally to the diffuser line and more or less horizontally. Definition sketches and CorSpy visualizations show these types with fanning and without fanning. The special case where all ports point directly to the water surface should be modeled within CORMIX2 as an alternating diffuser design as it imparts no net horizontal momentum flux to the flow.

Definition diagram for unidirectional diffuser specification within CORMIX2 (larger image).
CorSpy 3-D view of a unidirectional diffuser without fanning (larger image).
CorSpy side view of a unidirectional diffuser without fanning (larger image).
CorSpy plan view of a unidirectional diffuser without fanning (larger image).
CorSpy 3-D view of a unidirectional diffuser with fanning (larger image).
CorSpy side view of a unidirectional diffuser with fanning (larger image).
CorSpy plan view of a unidirectional diffuser with fanning (larger image).

Alternating Diffuser Types

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. Definition sketches and CorSpy visualizations show these types with fanning and without fanning.

Definition diagram for alternating diffuser specification within CORMIX2 (larger image).
CorSpy 3-D view of an alternating diffuser without fanning (larger image).
CorSpy side view of an alternating diffuser without fanning (larger image).
CorSpy plan view of an alternating diffuser without fanning (larger image).
CorSpy 3-D view of an alternating diffuser with fanning (larger image).
CorSpy side view of an alternating diffuser with fanning (larger image).
CorSpy plan view of an alternating diffuser with fanning (larger image).

Staged Diffuser Types

A staged diffuser is a design where all ports point in one direction generally following the diffuser line with small deviations to either side of the diffuser line and are oriented more or less horizontally. Definition sketches and CorSpy visualizations show these types with an internal angle BETA = 30 degrees.

Definition diagram for staged diffuser specification within CORMIX2 (larger image).
CorSpy 3-D view of a staged diffuser with GAMMA= 90, THETA = 0, SIGMA = 90, and BETA= 30 degrees (larger image).
CorSpy side view of a staged diffuser with GAMMA= 90, THETA = 0, SIGMA = 90, and BETA= 30 degrees (larger image).
CorSpy plan view of a staged diffuser with GAMMA= 90, THETA = 0, SIGMA = 90, and BETA= 30 degrees (larger image).