The effect of trip wire on transition of boundary layer on a cylinder
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AbstractThe 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 2×103≤𝑅𝑒≤5×105. 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 𝑑𝑇/𝐷=0.25%, via formation of a laminar separation bubble (LSB) and (b) direct, for a large trip of height 𝑑𝑇/𝐷=1.0%, 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 78° leads to a more delayed flow separation than one at 55° 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.
CitationChopra, G., & Mittal, S. (2022). The effect of trip wire on transition of boundary layer on a cylinder. Physics of Fluids, 34(5), 054103. https://doi.org/10.1063/5.0089512
SponsorsThe authors acknowledge the use of High-Performance Computational (HPC) and PARAllel Machine (PARAM) Sanganak facilities at the Indian Institute of Technology Kanpur (IITK), Cray XC-40, Shaheen, at King Abdullah University of Science and Technology (KAUST), Saudi Arabia. The HPC facility at IITK was established with the assistance of Department of Science and Technology (DST), Government of India. The PARAM Sanganak was implemented by Center for Development of Advanced Computing (C-DAC) and supported by the Ministry of Electronics and Information Technology and DST, Government of India, under the National Supercomputing Mission. The authors would like to thank Professor R. Samtaney of KAUST for his help in access to the Shaheen computational facility at KAUST. Authors would also like to thank Mr. Nitish Kovalam and Ms. Mahima Bhavsar for their help in carrying out some of the simulations and analysis.
JournalPhysics of Fluids