Within the porous sheath, Darcy–Brinkman formulation is used:
| Parameter | Range | Increment | |-----------|-------|-----------| | Helical amplitude α | 0.05 – 0.15 | 0.025 | | Number of turns N | 2 – 8 | 2 | | Outer sheath thickness t_o | 0.5 mm – 2 mm | 0.5 mm | | Porosity gradient (φ_out – φ_in) | 0.10 – 0.25 | 0.05 | ladtboy tube
Table 1. Representative studies on passive drag‑reduction strategies. Data extracted from peer‑reviewed journals; drag‑reduction percentages refer to friction factor decrease at comparable Reynolds numbers. [ \beginaligned \nabla \cdot \mathbfu &= 0,\ \rho
[ \beginaligned \nabla \cdot \mathbfu &= 0,\ \rho \left( \frac\partial \mathbfu\partial t + \mathbfu\cdot\nabla\mathbfu \right) &= -\nabla p + \mu \nabla^2\mathbfu. \endaligned ] Within the porous sheath
¹Department of Mechanical Engineering, University of X ²Institute for Microfluidic Technologies, Y Research Center ³Department of Applied Physics, Z University