What is it about?

Train pantographs, aircraft landing gears, car axles and many engineering applications involve turbulent flow around a circular cylinder and the complex fluid dynamics is not yet fully known. The shear-layer instability near the cylinder causes the transition from laminar to turbulent flow and observed the weak flow reattachment after separation. Near wake, transition region and far wake are three distinct regions where predominance of blade shedding; decay of blade vortices and instability hike of shear; and predominance of oscillations of wake regions appear in the vertical axis among the bluff bodies, similar to that of wind/water turbine wake structures. This configuration has several uses in magnetic, solar and nuclear engineering. Turbulent effects on the flow like induced turbulence generation and higher viscous dissipation are difficult to be taken into account. In this study, ANSYS Fluent software MHD module is used to simulate MHD forced convection heat transfer in a rectangular duct filled with nanofluid, with a circular cylinder placed with constant heat flux. Nu enhancement is noticed in this study upon nanoparticle addition, increase in Re and bluff body diameter, whereas a reduction is seen with the augmentation of Hartmann number after a critical value.

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Why is it important?

Thermal and magnetohydrodynamic effects of turbulent nanofluid flows due to Brownian motion and thermophoresis employing Navier's slip condition are not yet reported. Multi-phase modelling considering the nanofluid heterogeneity and slip velocity is not explored in simulating nanofluid flow and heat transfer at higher Reynolds numbers. The flow patterns are not tackled and the relationship between flow behaviours and force variations due to the influencing parameters is not established. Current investigation focus to demonstrate the correlation between high Reynolds number values, size of bluff body in relation to duct height, nanoparticle volume fraction, magnetic field strength and heat transfer for magnetohydrodynamic flow. The best heat transfer enhancement case is reported with the identification of ideal influencing parameters. The significant finding is that the control of flow over a circular cylinder for heat transfer enhancement using different parameters significantly changes vortical structures in the wake and reduces mean drag and lift fluctuations, destabilize the shear layer and reattach the flow on the surface before main separation, which delays main separation and decreases drag and finally, reduce the lift fluctuations.


Instantaneous asymmetry consequent to periodicity in time repeat cyclically in turbulent flow and temperature profiles due to vortices. For peak efficiency case in this study, advection of the vortex pair to lower hot wall and maximum angular momentum makes higher speed to hot fluid transport.

Assistant Professor ARJUN K S
NSS College of Engineering, Dr. APJ Abdul Kalam Technological University, Kerala

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This page is a summary of: Heat transfer in magnetohydrodynamic nanofluid flow past a circular cylinder, Physics of Fluids, April 2020, American Institute of Physics, DOI: 10.1063/5.0005095.
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