Effect of the Lorentz force on cylinder drag reduction and its optimal location

Abstract

In this paper, the effects of the Lorentz force on drag reduction in a circular cylinder and its optimal location on the surface have been studied. The Lorentz force influence is found to be composed of two opposite parts: one acts directly on the cylinder and is named as the wall Lorentz force and the other operates on the fluid near the cylinder surface and is called the field Lorentz force. The wall Lorentz force leads to the generation of thrust, while the field Lorentz force results in a pressure drag increase. The former dominates the drag variation. Therefore, the drag may become negative (thrust) with large enough Lorentz forces. Moreover, the maximum thrust and the pressure drag location under the effects of wall and field Lorentz forces are found to be the same, θ = ± 90°. However, the optimal location of drag reduction under the total effects of wall and field Lorentz forces is found to be in the central area of the flow separation coverage on the cylinder surface for Re = 100–200.