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Title:Study of flow past elliptic and circular cylinders using direct numerical simulation
Author(s):Mittal, Rajat
Doctoral Committee Chair(s):Balachandar, S.
Department / Program:Applied Mechanics
Engineering, Mechanical
Physics, Fluid and Plasma
Discipline:Applied Mechanics
Engineering, Mechanical
Physics, Fluid and Plasma
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Applied Mechanics
Engineering, Mechanical
Physics, Fluid and Plasma
Abstract:Flow over elliptic cylinders can be considered prototypical of flow over a range of bluff bodies since the geometry allows one to study the effect of both thickness and angle-of-attack on the flow field. Therefore a careful study of this flow should provide valuable insight into the phenomenon of unsteady separation and the structure of bluff body wakes. With this in mind, a single-domain, spectral collocation technique has been developed to simulate the full three-dimensional incompressible flow over elliptic cylinders. Results of two- and three-dimensional simulations for a range of flow and geometric parameters are presented. The results are compared with available experimental and numerical data and it is found that important quantities like the Strouhal number and lift and drag coefficients match well with established values.
It has been known for some time that two-dimensional numerical simulations of flow over nominally two-dimensional bluff bodies at Reynolds numbers for which the flow is intrinsically three-dimensional, lead to inaccurate prediction of the lift and drag forces. The details of the physical mechanisms that ultimately lead to the inaccurate prediction of surface pressure and consequently the lift and drag are still not clear. A detailed investigation has been performed and it is found that the over-prediction of mean drag force in two-dimensional simulations is directly related to higher Reynolds stresses in the wake.
The mechanism by which streamwise vortical structures are generated in free-shear flows is not completely understood. Some studies attribute the generation to a core-instability mechanism whereas others attribute it to a braid-instability. The present simulation afford us an opportunity to investigate this issue in detail. For the wake of a circular cylinder, it is observed that streamwise structures are formed in the near wake both due to stretching of core vorticity which escapes out of the core and due to stretching of small scale streamwise vorticity already present outside the core.
Issue Date:1995
Rights Information:Copyright 1995 Mittal, Rajat
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9624440
OCLC Identifier:(UMI)AAI9624440

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