Numerical Study of Flow Stabilization Mechanism of Stepped-Nosed Obstacle

Year 2010, Volume: 2 Issue: 4, 83 - 92, 01.12.2010

K. M. Rahman M. Mashud

Abstract

A rectangular obstacle the front corners of which are deformed in step form (called “stepped nosed obstacle”) may experience a much smaller drag force and lift force fluctuation. The underlying physics of this drag reduction and flow stabilization mechanism are explored in numerical and theoretical approaches. In the optimal step configuration that the flow separating from the front surface edges reattaches smoothly at the leading edge of the main body’s side surface. (1) The pressure drag force acting on the forebody almost vanishes because the strong vortices trapped in the stepped corners produce the thrust force which cancel the drag force acting on the front surface, and (2) The oscillation of lift force acting on the obstacle is largely suppressed and the scale of the Karman vortices is reduced because the large scale of the separated flow over the side surface is suppressed. The step size which brings about such optimal step flow condition is identified and the dependences of various flow characteristics on the step size are discussed in detail, which will be useful to consider another drag reduction treatment than streamlining the profile of obstacle in engineering application

Keywords

Drag Reduction, Numerical Simulation, Rectangular body, and Stepped nosed

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