Fluid velocity profiles in the bifurcation interray zone (BI) and the primary interray zone (PI) highlight particular fluid motion at the interray bifurcation site. (A,B) Models of a fin consisting of a rigid plate supporting half-cylindrical rods used for the hydrodynamic profiles study in a version with three parallel rods (A), and a bifurcation in the central ray (B). The indicated primary interray areas (PI) and bifurcation interray area (BI) are used for the velocity components averages presented below. (C–F) Flow profiles (all color scales in meters per second) at two key positions during the plate’s oscillation period. The corresponding average measurements are shown in Figures 11B,C. (C,E) A lower fluid velocity parallel to the surface (V//) is typically associated with a thicker boundary layer, and hence a potentially better detection of chemical signal in the bifurcation region, owing to longer time reaction for the cellular receptors and better averaging of the signal. (D) Larger absolute values of the perpendicular velocity (V⊥ < 0) indicate a higher rate of fluid motion directly toward the bifurcation region and imply a better access to molecules advected by the fluid from outside the boundary layer. (F) The vertical velocity component (Vy) also reveals a global fluid motion toward the inter-bifurcation region (illustrated by the white arrows), naturally correlated with a movement perpendicularly away from the fin as indicated by the positive value of V⊥ in Figure 11C. The velocity fields correspond to averages over three (0° angle) to five timeframes (max. angle).
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