Developing flow of Newtonian fluids over superhydrophobic transverse grooves in circular tube

In this paper, the effects of dimensionless gas area fraction (delta) and normalized groove-rib periodic spacing (Lambda) on developing flow for Newtonian fluid past circular tube having alternating superhydrophobic transverse grooves were numerically investigated. Fluid flow at Re ranging from 0.001 to 10 over various superhydrophobic microstructures scales (0.05 < Lambda < 1, 0 <delta < 1) were studied. Numerical results show that the presence of superhydrophobic transverse grooves would consistently yield a longer hydrodynamic entrance length (L-h) as compared to that of smooth surface. This is principally owing to the flow redistribution with higher flow rate that is permitted in the vicinity of the superhydrophobic wall. However, the scale of the superhydrophobic transverse grooves yield non-monotonic trend on hydrodynamic entrance length, with reduced delaying effect at higher Lambda. Despite the L-h alteration, L-h arising from the presence of superhydrophobic transverse grooves in tube of diameter D, at low Re (i.e., Re < 1), is still bounded within tube length of D.