A Solution Strategy to Include the Opening of the Opercular Slits in Moving-Mesh CFD Models of Suction Feeding

Abstract

The gill cover of fish and pre-metamorphic salamanders has a key role in suction feeding by acting as a one-way valve. It initially closes and avoids an inflow of water through the gill slits, after which it opens to allow outflow of the water that was sucked through the mouth into the expanded buccopharyngeal cavity. However, due to the inability of analytical models (relying on the continuity principle) to calculate the flow of fluid through a cavity with two openings and that was changing in shape and size, stringent boundary conditions had to be used in previously developed mathematical models after the moment of the valve's opening. By solving additionally for the conservation of momentum, computational fluid dynamics (CFD) has the capacity to dynamically simulate these flows, but this technique also faces complications in modeling a transition from closed to open valves. Here, I present a relatively simple solution strategy to incorporate the opening of the valves, exemplified in an axisymmetrical model of a suction-feeding sunfish in ANSYS Fluent software. By controlling viscosity of a separately defined fluid entity in the region of the opercular cavity, early inflow can be blocked (high viscosity assigned) and later outflow can be allowed (changing viscosity to that of water). Finally, by analyzing the CFD solution obtained for the sunfish model, a few new insights into the biomechanics of suction feeding are gained.

Function of the hypobranchial muscles and hyoidiomandibular ligament during suction capture and bite processing in white-spotted bamboo sharks, Chiloscyllium plagiosum

“…3). The preactivation period of the CA is similar to that observed in feeding muscles of vertebrates that use power-amplified feeding mechanisms such as pipefish (de Lussanet and Muller, 2007;Van Wassenbergh et al, 2008), seahorse (Roos et al, 2009;Van Wassenbergh et al, 2014), toads (Lappin et al, 2006) and chameleons (Herrel et al, 2000;de Groot and van Leeuwen, 2004;Anderson and Deban, 2012). The interaction of the CH and CA results in a total mean shortening velocity of −22.58± 0.94 FL s −1 for the CH (Table 2).…”

“…Many suction feeding teleosts compensate for the trade-off by using combinations of orobranchial depressors (hypobranchials) and the much larger trunk muscles (epaxials and hypaxials) to aid in expansion of the orobranchial cavity (Tchernavin, 1953;Lauder, 1982;Carroll, 2004;Carroll and Wainwright, 2006;Coughlin and Carroll, 2006;Van Wassenbergh, 2007;Camp and Brainerd, 2014). Other species also use catch mechanisms that allow for storage and release elastic strain energy in elastic elements, such as tendons, to amplify power production during suction feeding (de Lussanet and Muller, 2007;Van Wassenbergh et al, 2008;Roos et al, 2009;Van Wassenbergh et al, 2014).…”

Hydrodynamic regime drives flow reversals in suction feeding larval fishes during early ontogeny

“…We build on a previous model of mouth cavity expansion suggested by (Bishop et al, 2008; Yaniv et al, 2014), but added the opening of the opercular slits, a hallmark of suction feeding across fishes (Van Wassenbergh, 2015). In brief, the model was composed of three compartments of constant axial lengths, L 1 , L 2 and L 3 (Fig.…”

“…The dynamic meshing corresponds to changing of the mesh geometry over time and space based on the prescribed kinematics of the cavity. The kinematic motion of the mouth cavity was prescribed within the fluent solver using the user defined function ‘DEFINE_GRID_MOTION’ (Ansys, 2009; Van Wassenbergh, 2015). This procedure was performed using a user defined function that was compiled and assigned to each length sections of the mouth cavity.…”

“…Following Yaniv et al (Yaniv et al, 2014), we constructed a model of an expanding buccal cavity, which incorporates an anterior-to-posterior wave of buccal expansion (Bishop et al, 2008) over time. Our modeling included the opening of the opercula covers at the posterior end of the mouth, a hallmark feature of suction feeding in fishes, which generate unidirectional flows into the mouth while it is closing (Van Wassenbergh, 2015). The model was parametrized based on observed strike kinematics of Sparus aurata larvae ranging from first feeding to metamorphosis.…”