About PhD Research at IIT Kharagpur

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Subhrangshu joined the PhD program at IIT Kharagpur on 9th July 2019 as a full time scholar in the Department of Civil Engineering under Prof. Mohammad Saud Afzal. Due to his excellent performance in the coursework, his name was recommended for PMRF in May 2020 cycle via Lateral Entry Scheme. His current focus is to decipher the complex flow characteristics associated with the incompressible flow past bluff bodies of elliptical cross-section under different boundary conditions.

Further, he is actively associated with the other members of the group working on the analytical determination of the equilibrium scour depth under the combined action of the waves and the current in marine environments. He has co-authored a paper on the same theme.

Details of PhD Coursework

List of Subjects Taken

Viscous Fluid Flow
Free Surface Flows
Statistical Methods
English for Technical Writing

CGPA Acquired = 9.47/ 10

Seminars Delivered

Registration Seminar - Delivered on 1st October 2021
PMRF Half Yearly Review - Delivered on 1st November 2021
PMRF National Review - December 2021

Present Research Focus

The hydrodynamics around bluff bodies is a classical problem of fluid mechanics and is widely studied by researchers for academic as well as industrial applications. Roshko (1993) asserted that a bluff body is characterized by a separated flow over a significant portion of the body. The flow detaches from the surface of the body in the regions where the pressure gradient is adverse (positive along the stream-wise direction). The study of the bluff-body hydrodynamics involves investigating the behavior of this separated flow in conjunction with the hydrodynamic forces (drag and lift) and vortex shedding phenomena. Tritton (1977) explained the physics of flow separation around circular bluff bodies and elucidated on the pattern of vortex shedding at different flow Reynolds number.

The topic of flow past cylinders having different cross-sections has been explored vastly due to many significant engineering applications. Few of the application areas, but not limited to, are listed below:

Cylindrical structures like skyscrapers, towering structures, long-spanned bridges and wires exhibit vortex-shedding when immersed in cross freestream wind. Periodic shedding of vortices is responsible for vibrations in the structure (vortex induced vibrations). Structural engineer's main focus is to control this vortex shedding.
The hydrodynamic considerations related to the movement of underwater vehicles near an erodible sea or river bed can be explored by simulating the flow past a cylinder of desired cross-section in the presence of a bottom moving wall.
The hydrodynamic considerations relevant to the laying of underwater pipelines for oil transport can be achieved from the study of flow past cylinders.
For deducing the hydrodynamic forces acting on hydraulic and marine structures it is essential to explore the flow past bluff bodies.

It is noteworthy that a circular cylinder is an elliptical cylinder with aspect ratio (AR) equal to 1. Further, an elliptical bluff body with very large or very small aspect ratio closely resembles a flat plate. Hence, investigations pertaining to hydrodynamics around elliptical cylinders are generalized cases.

The present research is focused on the numerical modelling of the flow past elliptical cylinders under different boundary conditions at low Reynolds number. After a detailed literature survey, it has been noticed that there are many gaps in our understanding of the flow behavior around an elliptical cylinder, in both two- and three-dimensions. In the present research, an effort shall be made to improve our understanding of the flow past elliptic bluff bodies in the presence of different bottom boundary conditions.