Two-dimensional flow over a circular cylinder placed in-line behind a control rod of the same diameter is studied with and without the influence of a plane wall. Thermal patterns observed during various vortex shedding modes are discussed in detail. POD analysis of temperature data reveals that, with the decrease in wall height, modal structures are moved closer to the cylinder surface, which increases the heat transfer fluctuation. The plane wall increases the heat transfer from the bottom surface of the cylinder and decreases the heat transfer from the top surface, while the rotation of control rod contributes in an opposite manner. As the cylinder is moved closer to the wall, the time-averaged Nusselt number increases for a stationary control rod. In the case of a rotating control rod, the rotation of the control rod acts in the opposite sense to nullify this wall effect. © 2014 Taylor & Francis Group, LLC.

S. Vengadesan

Department of Applied Mechanics

Circular cylinders

Heat transfer

CYLINDER SURFACE

Heat transfer characteristics

MODAL STRUCTURES

STATIONARY CONTROLS

Temperature data

Two-dimensional flow

UPSTREAM CONTROL RODS

Vortex-shedding modes

CONTROL RODS

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IIT Madras

Heat Transfer Characteristics of Flow over a Circular Cylinder with an Upstream Control Rod in Wall Vicinity

Numerical Heat Transfer; Part A: Applications

Efficient visualization techniques are required to understand the flow physics for any numerical simulation. For convective heat transfer problems, most widely used techniques to visualize the fluid flow and heat transfer are streamlines and isotherms respectively. These methods are not sufficient to address the degrees of complexity associated with the complicated convective problems. Thus, different visualization techniques have been developed to represent the results depending on the problem. In this article, an effort has been made to collate visualization techniques in literature for convective heat transfer system like, heatlines, energy streamlines, energy flux vectors, proper orthogonal decomposition (POD), Poincare map etc. The fundamentals of different techniques are briefly discussed, applications of these techniques are shown with proper examples. The usefulness and limitations of these techniques are also discussed. Heatline is found to be the best visualization tool for two dimensional steady situations. However, in 3D and transient scenario Lagrangian approach or POD can be used. © 2017 Elsevier Ltd

International Journal of Heat and Mass Transfer

Heatlines and other visualization techniques for confined heat transfer systems

Laminar flow past a rotating cylinder near a plane wall is studied numerically using a second-order accurate immersed boundary method. The wake-wall interactions are investigated in detail, for different wall heights and varying rotational rates. Flow patterns are classified based on the wake structure and the effect of rotation on critical wall heights is discussed for both clockwise and counterclockwise rotation. For the configuration studied i.e. rotating cylinder above a bottom plane wall, counterclockwise rotation of cylinder favors the wake-wall interactions, while clockwise rotation influences in an adverse manner. In addition to conventional analysis, the evolution of the vortical structures in the wake region are examined using Lagrangian analysis of individual vortical structures. The diffusion of the positive vortex shed from the wall facing side of the cylinder is accelerated due to the influence of boundary layer with net negative vorticity. The wall augmented diffusion of positive cylinder vortices is compensated by the creation of secondary wall vortices from the bottom wall boundary layer. Counterclockwise rotation of cylinder increases the shear inside boundary layer resulting in more pronounced diffusion. © 2017 Elsevier Ltd

Ocean Engineering

Effect of rotating cylinder on the wake-wall interactions

Navier-Stokes simulations over an idealized flapping insect wing reveal a new strategy for vertical force generation in inclined stroke plane hovering: insects use their wing as bluff and streamlined bodies during downstroke and upstroke, respectively. This strategy helps insects to stay aloft. Furthermore, qualitative and quantitative results from our 2-D simulations determine to what extent the delayed stall mechanism is significant for enhanced flight performance in inclined plane hovering. Copyright © Taylor & Francis Group, LLC.

The functional significance of delayed stall in insect flight

The influence of the staggering position of a rotating rod on flow past a main circular cylinder is investigated numerically. The rod is rotated at a constant speed ratio of 3. The effect of the diameter ratio of the rotating rod is studied by considering two different diameter ratios. The investigation is carried out at a fixed pitch length of 1. The study is carried out for two Reynolds number, viz., 100 and 500. The momentum injection from the rod is found to alter the flow characteristics behind the main cylinder. For a certain arrangement of stagger angle and diameter ratio, the vortex shedding behind the main cylinder gets suppressed. The corresponding configuration for which minimum drag coefficient is achieved is suggested from this study. Copyright © 2008 by ASME.

Journal of Fluids Engineering, Transactions of the ASME

Influence of staggering angle of a rotating rod on flow past a circular cylinder

Three-dimensional unsteady flow over a bluff body located parallel to a wall, kept at different gap height from the wall, has been studied numerically. The bluff body considered is a rectangular cylinder with two different aspect ratios, B/D=1 and B/D=2, where B and D are the width and height of the cylinder, respectively. The flow is considered as a laminar flow, and the Reynolds number based on the height of the cylinder cross section and oncoming reference velocity is 450. Numerical study is carried out by varying the distance of the cylinder from the wall, and the development of the vortex shedding phenomenon under the influence of the wall is investigated. From previous experiments, it is observed that as the distance between the wall and the cylinder decreases, the wake behind the cylinder becomes stationary and the vortex shedding is suppressed. The present numerical study confirms a similar trend. Periodic activity in the downstream of the flow is disturbed completely with decreasing gap between the wall and the cylinder.

Flow characteristics behind rectangular cylinder placed near a wall

Journal of Fluid Mechanics

Dynamics and stability of the wake behind tandem cylinders sliding along a wall

Three-dimensional flow around a square cylinder near a wall

Heat transfer characteristics of flow over a circular cylinder with an upstream control rod in wall vicinity

Journal	Data powered by TypesetNumerical Heat Transfer; Part A: Applications
Publisher	Data powered by TypesetTaylor and Francis Ltd.
ISSN	10407782
Open Access	No