Dipanjan MajumdarImperial College London | Imperial · Department of Civil and Environmental Engineering
Dipanjan Majumdar
Doctor of Philosophy
About
45
Publications
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Introduction
My keen research interest is to explore the exciting fluid dynamic phenomena associated with moving bodies immersed in a fluid. I have developed an in-house Navier-Stokes solver using the Immersed Boundary Method, and reported a chaotic transition in the flow-field of a flapping foil. Presently, I am studying the role of passive pitch on altering the dynamical behavior of the flow-field past an actively heaving foil, and also inspecting the gust mitigating capabilities of flapping foils.
Education
July 2015 - November 2022
August 2011 - June 2015
Publications
Publications (45)
The effect of stochastic inflow fluctuations on the jet-switching characteristics of a harmonically plunging elliptic foil at a low Reynolds number regime has been analysed in the present study. The inflow fluctuations are generated by simulating an Ornstein-Uhlenbeck process - a stationary Gauss-Markov process - with a chosen correlation function....
The present study focuses on identifying dynamical transition boundaries and presents an order-to-chaos map for the unsteady flow field of a flapping foil in the low Reynolds number regime. The effect of an extensive parametric space, covering a large number of kinematic conditions, has been investigated. It is shown that the conventional non-dimen...
Natural and artificial flapping-wing flyers generally do not exhibit chaos or aperiodic dynamic modes, though several experimental and numerical studies with canonical models of flapping foils have reported inevitable chaotic transition at high ranges of dynamic plunge velocity (κh). Here we considered the idealized case of a pitching-plunging flap...
Physics informed neural networks (PINNs) have been explored extensively in the recent past for solving various forward and inverse problems for facilitating querying applications in fluid mechanics. However, investigations on PINNs for unsteady flows past moving bodies, such as flapping wings are scarce. Earlier studies mostly relied on transferrin...
Effects of chord-wise flexibility as an instrument to control chaotic transitions in the wake of a flexible flapping foil have been studied here using an immersed boundary method-based in-house fluid-structure-interaction solver. The ability of the flapping foil at an optimum level of flexibility to inhibit chaotic transition, otherwise encountered...
uDALES is an open-source multi-physics microscale urban modelling framework, capable of performing large-eddy simulation (LES) of urban airflow, heat transfer, and pollutant dispersion. We present uDALES v2.0, which has two main new features: 1) an improved parallelisation that prepares the codebase for conducting exascale simulations; and 2) a con...
Dynamical route to chaos and the corresponding transitional onset is very crucial for the efficient design of flapping-based aerial and underwater vehicles. Different size, shape, and flight speed of the wide range of natural flyers/swimmers manifest different Reynolds numbers (Re). The present study investigates the effect of Re on the dynamical b...
The vortex-induced vibrations of an elastically mounted circular cylinder (with mass ratio 2) in stochastically fluctuating inflow are numerically studied at a Reynolds number of 150. Numerical simulations are carried out on a discrete forcing immersed boundary method (IBM) based in-house fluid–structure interactions (FSI) solver. The existence of...
The dissertation examined the details of unsteady flow past a flapping foil, under different kinematic situations. Nonlinear dynamical behaviour and dynamical transitions of the unsteady wake were in main focus. The initial part of the thesis explored the efficacy of a discrete forcing immersed boundary method (IBM) in capturing the transitional dy...
The present study focuses on identifying the dynamical transition boundaries and presents an order-to-chaos map for the unsteady flow-field past a flapping wing in the low Reynolds number regime. Such transitions are primarily dictated by the leading-edge vortex (LEV) growth and its transportation. Several kinematic and flow parameters can directly...
uDALES is an open-source large-eddy simulation framework designed for outdoor flows in the built environment. It is capable of simulating airflow, sensible and latent heat transfer, and pollutant dispersion within the urban atmospheric boundary layer at microscale resolution. Buildings are resolved using the immersed boundary method (IBM), with wal...
Recently, physics informed neural networks (PINNs) have been explored extensively for solving various forward and inverse problems and facilitating querying applications in fluid mechanics applications. However, work on PINNs for unsteady flows past moving bodies, such as flapping wings is scarce. Earlier studies mostly relied on transferring to a...
Unsteady flows past rigid or flexible moving bodies such as flapping wings are characterised by complex non-linear interactions across spatial and temporal scales. These flow field characteristics can be resolved using high-fidelity computational fluid dynamics approaches such as immersed boundary methods (IBM), simulating such unsteady flows on a...
Dynamical route to chaos and the corresponding transitional onset are very crucial for the efficient design of flapping-based aerial and underwater vehicles. Different size, shape and flight speed of the wide range of natural flyers/swimmers manifest different Reynolds numbers (Re). The present study investigates the effect of Re on the dynamical b...
High fidelity simulations of unsteady fluid flow are now possible with advancements in high performance computing hardware and software frameworks. Since computational fluid dynamics (CFD) computations are dominated by linear algebraic routines, they can be significantly accelerated through massive parallelisation on graphics processing units (GPUs...
Appropriate selection of the chord-wise flexibility can directly benefit the efficient design of flapping-type micro aerial vehicles and automated underwater vehicles. To that end, this work investigates the effect of chord-wise flexibility on the wake dynamics of a flexible flapping foil in comparison to a rigid foil having the same chord length a...
The effect of a chordwise flexible aft-tail of a rigid heaving aerofoil on the dynamical transitions of the trailing-wake is studied here. The two-way coupled fluid-solid dynamics is simulated using an in-house fluid-structure interaction (FSI) platform, comprising a discrete forcing immersed boundary method based incompressible Navier–Stokes solve...
Cost effective parametric surrogate models of unsteady aerodynamic loads acting on a
flapping wing are highly desirable. They would enable real time aerodynamic load prediction and optimal control of intelligent flapping wing flight devices. Given load time
histories obtained for a sample of input parameters, parametric surrogate modeling
involve t...
This study investigates the dynamical behaviour of the flapping filament subjected to a uniform inlet velocity at a low Reynolds number, considering the heaving amplitude as a bifurcation parameter. A discrete forcing immersed boundary method (IBM)-based in-house fluid-structure interaction (FSI) solver is used for the present simulations. The flap...
Flapping wings with suitable wing kinematics, wing shapes, and flexible structures can enhance lift as well as thrust by exploiting large-scale vortical flow structures under various conditions. However, it is also necessary to understand the dynamics of the
flow field, which may influence the flying performance. In the present study, an elliptic f...
Unsteady aerodynamics of moving/flapping wings or rotors commonly involve complex vortex interactions that need to be analysed for optimal design of engineering systems such as
bio-mimetic UAVs, wind turbines, etc. The need for problem specific numerical solvers with
higher customizability and parallisability warranted the development of an in-hous...
The present work explores the role of phase-difference on the transitional flow dynamics of a pitching-plunging foil. An extensive parameter space of plunge amplitude (h) and phase offset (ϕ) between pitch-plunge motions is considered keeping the pitch amplitude and non-dimensional flapping frequency constant (α=15o & k=4). Numerical simulations ar...
The flapping dynamics of a Dipteran flight motor have been studied numerically by using a discrete forcing type Immersed Boundary Method (IBM) based in-house fluid-structure interaction (FSI) solver at a Reynolds number of 100. A bifurcation study has been performed considering the amplitude of the wing actuation force as the control parameter. At...
The present study attempts to capture the fluid-structure interaction dynamics of a chord-wise flexible flapping wing system using a limited mode structural model coupled with a high-fidelity Navier-Stokes solver. The wing is modeled as two elliptic rigid foils connected by a non-linear torsional spring that incorporates the chord-wise bending stif...
The present study is focused on examining the flow-field dynamics of a flapping foil with a flexible aft tail as compared to a rigid configuration where tail flexibility is infinite. The flow around the oscillating body is governed by the incompressible Navier-Stokes equations. An in-house Fluid-Structure Interaction solver has been developed follo...
The present work focuses on investigating the underlying flow physics behind the transition from periodicity to aperiodicity in the flow past a harmonically plunging elliptic foil as the plunge amplitude is increased to a high value. Two-dimensional (2D) numerical simulations have been performed in the low Reynolds number regime using an in-house f...
![Fig. 1 Schematic of Dipteran flight motor model: a Click mechanism [9],...](profile/Chhote-Shah/publication/346392700/figure/fig1/AS:1014738108551171@1618943826357/Schematic-of-Dipteran-flight-motor-model-a-Click-mechanism-9-and-b-Duffing-oscillator_Q320.jpg)
A significant amount of research interest is focused on the development of nature-inspired Micro Areal Vehicle (MAV) due to their multifold potential in the futuristic civil and military applications over the years. Natural flyers (bird/insect) employ several flapping mechanisms to undergo complicated aerial manoeuver efficiently. The bistable “cli...
The present study focuses on formulating a fluid–structure interaction (FSI) framework by coupling a finite element analysis (FEA) based structural solver and a lumped vortex method (LVM) based potential flow solver to study the coupled dynamics involved in the undulatory and oscillatory swimming of fishes. The caudal fin of a carangiform fish is m...
Avians and insects have always intrigued human kind for they enjoy the boon of flight. Their flight typically has multiple stages and transitions of different time scales within those stage. The transitions in flight stages manifest through transient change in the kinematics of body and/or wing. Significant work has been done to numerically study t...
Natural flyers such as birds, insects and bats fly by exploiting the unsteady flows around their flapping-wings and this has been an inspiration in the development of flapping-wing Micro Air Vehicles (FMAVs) [1]. The secret to their flight has been attributed to different wing kinematics and the associated wake patterns. Usually in flapping wing st...
The present work focuses on investigating the underlying flow physics behind the transition from periodicity to aperiodicity in the flow past a harmonically plunging elliptic foil as the plunge amplitude is increased to a high value. Two-dimensional (2D) numerical simulations have been performed in the low Reynolds number regime using an in-house f...
![Fig. 1 Schematic of Dipteran flight motor model: a Click mechanism [9],...](profile/Chhote-Shah/publication/336512815/figure/fig1/AS:1014738431537152@1618943903312/Schematic-of-Dipteran-flight-motor-model-a-Click-mechanism-9-and-b-Duffing-oscillator_Q320.jpg)
A significant amount of research interest is focused on the development of nature-inspired Micro Areal Vehicle (MAV) due to their multi-fold potential in the futuristic civil and military applications over the years. Natural flyers (bird/insect) employ several flapping mechanisms to undergo complicated aerial maneuver efficiently. The bistable "cli...
The present work is focused on investigating the effect of noisy input fluctuations on a harmonically plunging elliptic foil in the low Reynolds number regime (Re=300). Simulations are carried out using a discrete forcing Immersed Boundary Method (IBM) based in-house Navier-Stokes solver. The stochastic noisy inlet velocity is modeled as the Ornste...
This work presents a high-fidelity in-house Fluid-Structure Interaction (FSI) solver developed by combining discrete forcing Immersed Boundary Method (IBM) with an RK-4 based structural solver. Classification of the grid points as fluid, solid and IB points in the IBM framework and the solution of the pressure correction equations are the two most...
This paper focuses on investigating the aerodynamic load generation of rigid and flexible wings undergoing asymmetric flapping motion through wind tunnel experiments in uniform inflow condition. The aerodynamic forces of the designed flapping wing setup are measured through a 6-dof force/torque sensor. A rigid wing and two different flexible membra...
The present study focuses on formulating an FSI framework by coupling a Finite Element Analysis
(FEA) based structural solver and a Lumped Vortex Method (LVM) based potential flow solver, to study the
coupled dynamics involved in the undulatory and oscillatory swimming of fishes. The caudal fin of a
carangiform fish is modelled as a continuous cant...
This paper investigates the role of chord-wise flexibility in the propulsive performance and the fluid structure interaction (FSI) dynamics of a flapping fin modelled as a chord-wise flexible cantilever beam with a sinusoidal support motion in an inviscid fluid. Finite element analyses and lumped vortex method have been employed to build the presen...
One of the viable technologies to actuate robotic systems such as quadruped or biped is the use of hydraulic energy through centralized electro-hydraulic systems. The use of huge motor-pump assembly resulting increase in the whole system dimension along with the piping arrangements to connect the different components limits its use for autonomous r...
Questions
Question (1)
I have written a code based on the direct forcing Immersed Boundary method proposed by Kim et al. (J. Kim, D. Kim, H. Choi, An immersed-boundary finite volume method for simulations of flow in complex geometries, Journal of Computational Physics 171 (2001) 132–150.) Also for the force calculation I have followed them (J. Lee, J. Kim, H. Choi, K.-S. Yang, Sources of spurious force oscillations from an immersed boundary method for moving-body problems, J. Comput. Phys. 230 (2011) 2677–2695) and (I. Lee, H. Choi, A discrete-forcing immersed boundary method for the fluid–structure interaction of an elastic slender body, J. Comput. Phys. 280 (2015) 529–546) where the fluid forces acting on the body are calculated by taking the sum of the Immersed Boundary forces.
First I tried the flow past a oscillating circular cylinder problem for which I got correct C_l time history and flow field but for the C_d I got values (mean C_d=1.75, Re=185) which is higher than that are available in literature (mean C_d=1.55, Re=185).
Also I tried to simulate the flow past a plunging elliptic foil. For this problem also I got correct time history for C_l but for kh=1 though the flow field is showing thrust producing reverse karman wake my C_d plot showing only drag.
Can anyone please tell my why the lift time histories are correct but the drags are wrong? Am I missing some thing? Is there any other method to calculate the forces with in IBM framework?
