Affiliation:
1. Department of Aerospace Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
Abstract
The effect of height of a trip and its location on the transition of boundary layer on a cylinder is studied using large eddy simulations for [Formula: see text]. The Reynolds number, Re, is based on the free stream speed and diameter of the cylinder ( D). Two modes of transition are observed: (a) natural, for a relatively small trip of height [Formula: see text], via formation of a laminar separation bubble (LSB) and (b) direct, for a large trip of height [Formula: see text], wherein the formation of LSB is bypassed and the trip disturbs the flow enough to cause separation of the boundary layer and its subsequent turbulent reattachment. Transition delays the final separation leading to a very significant reduction in drag, often referred to as drag crisis. The delay is more for natural as compared to direct transition. Consequently, the drag at the end of crisis is lower for natural transition. The 1.0% trip at [Formula: see text] leads to a more delayed flow separation than one at [Formula: see text] from the front stagnation point. The drag crisis takes place in two stages for a cylinder with trip. During each of the two stages, asymmetric transition on the two sides results in generation of circulation and lift force. The effect of trip is felt even by the non-trip side. The cylinder experiences a relatively large “reverse lift” during the second stage of drag crisis. While natural transition is accompanied by intermittency of LSB, direct transition is associated with intermittency in laminar vs turbulent attachment of the flow following its separation at the trip.
Subject
Condensed Matter Physics,Fluid Flow and Transfer Processes,Mechanics of Materials,Computational Mechanics,Mechanical Engineering
Cited by
7 articles.
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