Research on the suspension-feeding apparatus of fishes has led recently to the identification of novel filtration mechanisms involving vortices. Structures inside fish mouths form a series of ‘backward-facing steps’ by protruding medially into the mouth cavity. In paddlefish and basking shark mouths, porous gill rakers lie inside ‘slots’ between the protruding branchial arches. Vortical flows inside the slots of physical models have been shown to be important for the filtration process, but the complex flow patterns have not been visualized fully. Here we resolve the three-dimensional hydrodynamics by computational fluid dynamics simulation of a simplified mouth cavity including realistic flow dynamics at the porous layer. We developed and validated a modelling protocol in ANSYS Fluent software that combines a porous media model and permeability direction vector mapping. We found that vortex shape and confinement to the medial side of the gill rakers result from flow resistance by the porous gill raker surfaces. Anteriorly directed vortical flow shears the porous layer in the centre of slots. Flow patterns also indicate that slot entrances should remain unblocked, except for the posterior-most slot. This new modelling approach will enable future design exploration of fish-inspired filters.

This folder contains:

The CAD geometry input files in IGES format (size units in mm)
Full CFD domain: Geom_full_domain.igs
Only the cross-step filter: Geom_filter.igs

Fluent version 2019 R1 case and data files for the three cross-step models used in the publication:

(1) the original model: Fluent_2019R1_cross_step_01.cas/dat files
(2) the model with half the porous resistance: Fluent_2019R1_cross_step_02.cas/dat files
(3) the model without porous resistance: Fluent_2019R1_cross_step_03.cas/dat files

The user-defined function used to convert scalar gradients into direction vectors is given (C language; to be compiled in Ansys Fluent):
2046962_UDF_ID11.c

Fluent version 2019 R1 case and data files for the porous media model verification - 36 pore fragment versus porous media model under angle of attack of 30 degrees

(1) model with physically modelled pores: Fluent_2019R1_filter_fragment_30degrees_physical_pores.cas/dat
(2) model using the porous media model: Fluent_2019R1_filter_fragment_30degrees_porous_media_model.cas/dat

This information is also given as an 'README.txt' file.

Ansys Fluent 2019 R1 .cas and .dat files can be opened with Ansys Fluent 2019 R1 or later versions, or the results included in these files can be viewed with CFD-post 2019 R1 (Ansys) or later versions. CFD-post software included in 'Ansys Student' software can be used for this. This software is currently provided for free to run on Windows, and can be downloaded from https://www.ansys.com/academic/students/ansys-student