Numerical study on the propulsive performance of a submerged wiggling micromachine in straight conduit

Abstract

The propulsive performance of a submerged micromachine wiggling in a straight conduit is numerically analysed. The micromachine, whose geometry is similar to a hydrofoil, is mounted in a straight conduit of width W, and the wiggling motion is expressed by a progressive wave. The flow around the micromachine is simulated by a two-dimensional finite element method. The Reynolds number Re, based on the flow velocity upstream of the micromachine and the micromachine length L, is varied from 1 to 100, while the blockage ratio L/W is independently changed in the range of 0.36 ≤ L/W ≤ 1.25. The flow around the micromachine varies according to the wiggling motion, and it presents complicated behaviour owing to the large-scale eddies. The increment of L/W reduces the minimum pressure on the micromachine surface, while it increases the velocity near the micromachine. The propulsive performance is more affected by L/W at Re = 10 than at Re = 100. When L/W is increased in the case of Re = 10, the thrust force decreases at 0.36 ≤ L/W ≤ 0.81 and increases at L/W ≥ 0.81. The decrement is due to the increase of the skin friction, and the increment is attributable to the change in the pressure distribution. The lift force and the power become larger with L/W. The efficiency takes its minimum value at L/W = 0.81.