Ganesh Natarajan

Indian Institute of Technology Guwahati | IIT Guwahati · Department of Mechanical Engineering

The present study offers a novel strategy for the implementation of adiabatic boundary conditions over solidfluid interface using the partially-saturated-cells (PSC) approach, which hitherto has not been discussed in the open literature. We implement the adiabatic boundary condition within the framework of a conjugate heat transfer solver by choosi...

This paper proposes a novel evolution equation for simulating conjugate heat transfer (CHT) phenomena in an immersed boundary-lattice Boltzmann (IB-LB) framework. Unlike the existing LB methodologies that reconstruct the unknown energy distribution function or add an additional source term to satisfy the interfacial boundary conditions, the propose...

We present a comprehensive investigation of Partially-Saturated-Cells method (PSC) for the simulations of incompressible thermal flows. The methodology comprises an additional collision operator introduced into the conventional simplified thermal lattice-Boltzmann (STLBM) method that offers a unified evolution equation for solid and fluid media present...

Present work introduces a novel solid collision operator for the Partially Saturated Cells (PSC) approach within the immersed boundary lattice-Boltzmann (IB-LB) framework. This operator is designed to accurately simulate thermal flows and offers a unified evolution equation for all media within the computational domain. Primary Focus of the Study:...

Turbulent flow past an equilateral triangular cylinder with splitter plate inserted downstream is numerically tested for different gap ratios (0, 0.5, 1, 1.5, 2) and plate dimensions (0, 1, 1.5) on the flow field and heat transfer characteristics. Unsteady flow simulations are carried out at Re=22,000 in a finite volume based collocated framework,...

In the present work, we investigate the accuracy and robustness of our in-house OpenMP parallelized direct-forcing immersed boundary–lattice Boltzmann (DF-IB-LB) solver by undertaking studies on accuracy, discrete conservation, Galilean invariance and quantification of spurious force oscillations (SFO). Our study reveals that DF-IB-LB exhibits firs...

We revisit the Partially-Saturated-Cells method (PSC) in the context of incompressible single-phase flows past stationary and moving bodies. This methodology adds a solid collision operator to the Lattice Boltzmann Equation, resulting in a unified evolution equation everywhere in the domain that suitably accounts for the boundary conditions. The un...

This work discusses the development of a sharp interface immersed boundary (IB) method for viscous compressible flows and its assessment for accurate computations of wall shear and heat fluxes in hypersonic flows. The IB method is implemented in an unstructured Cartesian finite-volume (FV) framework and resolves the geometric interface sharply on t...

In this article, we focus towards the utility and demerits of low-fidelity approaches for the design of mixed compression scramjet inlets. Gas dynamic relations are cast into low- fidelity framework for design which are then tested using high-fidelity numerical simulations. Simply yet carefully designed numerical experiments are performed which hig...

In a recently published work (Sheng, 2020), Sheng identified inconsistencies in the concepts and principles leading to the Navier–Stokes equations and proposed a new asymmetric “friction tensor” to resolve these inconsistencies. We show that this friction tensor can be interpreted as the non-isotropic part of a vorticity-influenced viscous stress t...

Numerical simulation of hypersonic flows is important owing to their applications to the design of launch vehicles and re-entry capsules. We describe the development and application of a hybrid Cartesian–immersed boundary (HCIB) approach in a finite volume (FV) framework for inviscid and viscous compressible flows with a focus on the hypersonic reg...

Computer simulations of a wide range of applications like materials processing, thermal energy storage and conversion systems, nuclear reactors, solar energy, and pollution control, etc. are of high importance in this era. In many of these applications, strong thermo-fluidic interactions between fluid and structures exist. Efficient and accurate nu...

In this work, a detailed investigation on the effects of particle diameter on the fluidization characteristics of gas–particle flows inside a bubbling gas–solid fluidized bed has been carried out. The studies are performed using an in-house flow solver developed employing the Eulerian–Eulerian two-fluid model. Simulations carried out using the solv...

A novel diffuse interface immersed boundary (IB) approach in the finite volume framework is developed for non-Boussinesq flows with heat transfer. These flows are characterized by variable density, large temperature differences, nonzero velocity divergence, and low Mach numbers. The present IB methodology assumes that the solid body immersed in the...

In a very recent article, Trautmann et al.1 proposed a modified gradient computation technique for problems involving conductivity jumps. Referred to as the Flux Conservative Divergence Theorem (FC-DT), the modified approach computes the face values of electric potential by accounting for the nonlinear behavior in cells across which the conductivit...

A monolithic solver based on a diffuse-interface immersed-boundary (IB) approach for conjugate-heat-transfer (CHT) problems is presented. The IB strategy assumes that the solid which is “immersed” into the computational grid is occupied by a “virtual” fluid to facilitate construction of “unified” governing equations that are solved everywhere in th...

The focus of the present work is a comparative numerical study of various immersed boundary lattice-Boltzmann (IB-LB) methods viz. direct forcing IB-LB and partially saturated method (PSM) in lattice-Boltzmann (LB) framework. An OpenMP parallelized IB-LB code is developed to analyze the performance of different methods in terms of order of accuracy...

Purpose The purpose of this paper is to numerically investigate the effect of various parameters such as density ratio, surface wettabilities and Weber number on the droplet dripping and detachment process. Design/methodology/approach By using algebraic volume of fluid method, the governing equations are solved using a collocated finite volume a...

We propose a hybrid sharp/diffuse interface immersed boundary framework to solve fluid flows and heat transfer in complex geometries. The key idea of the work is to combine the benefits of sharp and diffuse interface immersed boundary approaches while mitigating their deficiencies particularly in flows with heat transfer. We therefore adopt a volum...

The present study investigates three different algorithms for the numerical simulation of non-Boussinesq convection with thermal radiative heat transfer based on a low-Mach number formulation. The solution methodology employs a fractional step approach based on the finite-volume method on arbitrary polyhedral meshes. The three algorithms compute th...

The development of a non-Boussinesq flow solver for simulating combined radiative-convective heat transfer is presented on arbitrary polygonal meshes using the ideas of low-Mach number asymptotics. A segregated approach for solving the governing equations using a fractional step methodology on finite-volume method is adapted to handle the low-Mach...

We describe a new and simple strategy based on the Gauss divergence theorem for obtaining centroidal gradients on unstructured meshes. Unlike the standard Green–Gauss (SGG) reconstruction which requires face values of quantities whose gradients are sought, the proposed approach reconstructs the gradients using the normal derivative(s) at the faces....

The focus of the present work is a comparative numerical study of various immersed boundary lattice-Boltzmann (IB-LB) methods viz. direct forcing IB-LB and partially saturated method (PSM) in lattice-Boltzmann (LB) framework. An OpenMP parallelized IB-LB code is developed to analyze the performance of different methods in terms of order of accuracy...

We present a simple and cost‐effective curvature calculation approach for simulations of interfacial flows on structured as well as unstructured grids. The interface is defined using volume fractions and the interface curvature is obtained as a function of the gradients of volume fractions. The gradient computation is based on a recently proposed g...

We numerically investigate the effects of restitution and specularity coefficients on the characteristics of dispersed gas-particle flows through a sudden expansion. The studies are carried out using an indigenous finite volume flow solver in a collocated framework with two-fluid model. Parametric studies are performed to gain insights into the dif...

We propose both monolithic and partitioned approach to solve conjugate heat transfer in an immersed boundary framework for complex geometries. The present framework is based on the staggered/non-staggered finite volume framework for incom-pressible flows which is extended to handle conjugate heat transfer. The key difference in the monolithic frame...

The present work elucidates the design and performance analysis of a three-dimensional microchannel for its capability in mixing two different liquids. Present studies are based on cross-T micromixer in which obstacles are introduced in the form of three-dimensional curved ribs. The mixing efficiency, quantified by the mixing index (M), has been ca...

We present an interpolation-free diffuse interface immersed boundary method for multiphase flows with moving bodies. A single fluid formalism using the volume-of-fluid approach is adopted to handle multiple immiscible fluids which are distinguished using the volume fractions, while the rigid bodies are tracked using an analogous volume-of-solid app...

Binary fluid flows distinguished by high-density ratio are of practical importance to many of the engineering applications. Numerical simulations of such flows having sharp discontinuities across the interface is a challenging task and may lead to the generation of spurious velocities if proper care is not taken during discretization. In this regar...

The present study considers a measure for enhancing mixing capability in micromixers. It incorporates a new design of obstacle, in the form of thin curved ribs, inside the micromixer and explored numerically for its mixing capabilities. The ribs can be uniquely defined by its chord length (l) and its thickness (\(t_o\)). An in-house three-dimension...

In [1], the authors proposed a charge-conservative numerical framework for simulating electrohydrodynamic two-phase flows where the electric force was discretely treated as the divergence of Maxwell stress tensor because the use of volume–averaged electric force was found to be inaccurate. In this letter, we show that this framework still suffers f...

The present work numerically investigates the influence of partitions on buoyancy induced convectionwith thermal radiation in a differentially heated cubical enclosure. Four distinct arrangements of parti-tions from the top-bottom and front-back walls are examined by adopting a symmetric (inline) andasymmetric (offset) configuration of partitions. An...

The present study considers the mixing characteristics of gaseous species in a channel with wavy walls. Waviness imparted along the walls are uniquely defined by the wavelength (λ), amplitude (a) and phase difference (PD). A quasi-incompressible formulation in a three-dimensional collocated finite volume framework is employed for the numerical simu...

Specularity coefficient (ϕ) and particle-particle restitution coefficient (e) are two important parameters governing the flow physics of dispersed gas-particle flows. In this work, a detailed numerical analysis is carried out to get an insight into the effects of these two parameters in the flow hydrodynamics of dispersed gas-particle flows through...

Particle diameter, particle phase material density and inlet particle volume fraction are three important parameters governing the flow physics of dispersed gas-particle flows. In this work, an inhouse numerical solver is developed to investigate the effects of particle diameter (Stokes number), particle phase material density, inlet particle volum...

A new Hybrid Cartesian Immersed Boundary method based compressible fluid solver is developed for simulating flow past immersed bodies for high-speed flows. A simple reconstruction scheme is devised to interpolate the centroidal fluid properties at fluid-solid interface, subjected to both Dirichlet and Neumann boundary condition. The key aspect lead...

The present work discusses the development and validation cases of turbulent axisymmetric flow simulations over a hybrid unstructured grid. The governing equations are discretized following the finite volume methodology in a collocated framework. RANS based solver is developed upon implementing a SIMPLE-like algorithm to handle pressure-velocity de...

We discuss the development and assessment of a robust numerical algorithm for simulating multiphase flows with complex interfaces and high density ratios on arbitrary polygonal meshes. The algorithm combines the volume-of-fluid method with an incremental projection approach for incompressible multiphase flows in a novel hybrid staggered/non-stagger...

A new finite–volume flow solver based on the hybrid Cartesian immersed boundary (HCIB) framework is developed for the solution of high–speed inviscid compressible flows. The immersed boundary method adopts a sharp interface approach, wherein the boundary conditions are enforced on the body geometry itself. A key component of the present solver is a...

The study of dispersed laminar gas-particle flow in a horizontal channel is carried out using finite volume method on unstructured grid. In this context, Eulerian-Eulerian two-fluid model is employed to analyze the flow behaviour of both the phases inside the flow domain. The interaction between the gas phase and the particle phase is taken care by...

In the present work for numerically investigating the interfacial flows, an algebraic Volume of Fluid technique has been implemented over hybrid unstructured meshes. Following the work of Dalal et al. (Numer Heat Transf Part B 54(2):238?259, 2008 [2]), the governing equations are discretised by cell centered finite volume method wherein pressure-ve...

The focus of the present work is to develop a robust algorithm for simulation of stationary/moving rigid solid object(s) in free surface flows. The algorithm is based on incompressible finite volume hybrid staggered/non-staggered framework and captures the fluid–fluid interface using the Volume-of-Fluid (VOF) method by solving advection equation fo...

We propose an unified formulation for thermobuoyant flows an arbitrary mesh topologies. Unlike incompressible flow, the pressure correction equation is derived from the energy equation. The resulting Poisson’s equation reduces to continuity constraint \( \nabla \cdot \varvec{u} = 0 \), only in absence of thermal gradient and compressibility effects...

Variable density flows are basically those in which density variations cannot be neglected and hence the density is treated as a variable. This formidable change in density may be caused by either of three variables of the ideal gas equation (when dealing with gases) namely pressure, temperature and molar-mass. When pressure causes considerable cha...

A generalised three-dimensional solver based on unstructured grid methodology has been developed for electrohydrodynamic flows. The Navier-Stokes equations with electrical field source term are solved in conjunction with the coupled electrical potential and ion charge density equations in a finite volume framework. An iterative boundary condition f...

A meshfree framework for numerical simulations of magnetohydrodynamic flows is proposed. The framework is based on the Least-Squares-Based Upwind Finite Difference method (LSFD-U) and is capable of handling arbitrary point distributions. The approach is based on the least-squares method of error minimisation to compute the inviscid flux derivatives...

The present work elucidates a comparative analysis to investigate the discrepancies between the incompressible and low Mach number approximations for numerically solving combined natural convection with radiative heat transfer in participating medium. The motivation behind the study is to quantify the physical differences concerning fluid flow and...

A unique hybrid Aerodynamic Shape Optimization (ASO) framework is devised for axisymmetric bodies with minimum drag coefficient in hypersonic inviscid flow at zero angle of attack. The hybrid ASO framework that has been developed in this paper makes use of a combination of low fidelity framework and high fidelity framework, with the intention to re...

Present investigations are centered on passive control of shock wave boundary layer interaction (SWBLI) for double cone and double wedge configurations with leading edge bluntness. This study seeks the differences in the flow physics of SWBLI in case of two dimensional (2D) and axisymmetric flow fields. In-house developed second order accurate fini...

The focus of the present numerical investigation is the development of an in-house Hybrid Cartesian Immersed Boundary (HCIB) method based flow solver, which is a sharp interface variant of IB method. Both 2d planar and 2d axisymmetric bodies are considered for the present study, where the former translates under the influence of force exerted upon...

We propose an immersed boundary method to solve mixed convection flows in enclosures with large temperature differences. The present algorithm is based on a staggered/non–staggered finite volume framework for in-compressible flows which is modified to capture the fluid-solid interface by Volume-of-Solid method for flows with heat transfer. The fram...

A hybrid Cartesian Immersed Boundary Method is constructed which is a variant of sharp interface method, to simulate inviscid compressible flows, that allows the use of Cartesian grid for complex geometries. The solid boundary of the body in consideration is composed of sharp interfaces and boundary conditions are enforced precisely at the interfac...

full conservative three dimensional mathematical framework has been developed for the numerical simulation of quasi-incompressible flows in open domains. In the present work a low Mach number formulation has been adopted to simulate the flow physics associated with the flows where density can’t be assumed to be constant. This variation in density i...

The report focuses on the development of a finite volume solver over 3D hybrid un- structured meshes to simulate gas-droplet flows with evaporation which has many engineering applications like spray cooling, IC Engine etc. To develop the solver, the work is being divided into two parts as validation of the evaporation model and coupling of the evap...

The report focuses on the development of a finite volume solver over 3D hybrid un-structured meshes to simulate gas-droplet flows with evaporation which has many engineering applications like spray cooling, IC Engine etc. To develop the solver, the work is being divided into two parts as validation of evaporation model and coupling of evaporation m...

A new flux splitting scheme based on wave-particle behaviour is developed for one-dimensional ideal magnetohydrodynamics. We exploit the idea that while ideal magnetohydrodynamics equations are non-convex with non-homogeneous fluxes as opposed to their hydrodynamic counterparts, they exhibit an overall wave-like structure. The proposed approach spl...

The present work is a numerical investigation of optimum value of power-effectiveness for localized energy emission method, to reduce wave drag for hypersonic flow past blunt bodies. Use of an in-house developed Immersed Boundary Method based compressible flow solver is made whose validation test cases are also provided. The flow solver is coupled...

The present computational work is an amalgamation of active and passive wave drag reduction technique for axisymmetric bodies at hypersonic inviscid flow. The methodologies adopted incorporate the use of classical minimum wave drag body for the class of power-law bodies and localized energy addition technique, to further reduce wave drag. An in-hou...

Magnetohydrodynamics (MHD) is the study of flow of electrically conducting fluids interacting with a magnetic field. A novel flux splitting scheme for numerically solving ideal MHD equations is presented. The flux vector is split into three distinct parts based on the wave-particle splitting philosophy: the transport part, the pressure part and the...

A full conservative mathematical framework for numerical simulation of laminar non-reactive variable density flows is carried out using finite volume method (FVM) on unstructured grid. In this work low Mach number formulation has been adopted to simulate the flow physics associated with the variation in density encountered in closed as well as open...

The study of axisymmetric flows is carried out using finite volume method on hybrid unstructured grids. In this context, a numerical solver has been developed to take into account the flow characteristics of axisymmetric, swirl and heat transfer phenomena. For discretizing the governing equations, a cell-centered finite volume methodology has been...

A meshfree framework for numerical simulations of magnetohydrodynamic (MHD) ows is proposed. The framework is based on the Upwind Least-Squares Finite Dierence Method (LSFD-U) and is capable of handling arbitrary point distributions. The ux derivatives at every point require the uxes at the point as well as those in ctitious interfaces in a neighbo...

A novel heuristic approach to resource estimation and target determination in interrupted and shortened Twenty20 cricket matches is presented. The present approach mimics Kleiber’s allometric relation to define the effective resources for a team. Unlike existing methods, the present methodology computes the resources using a simple non-statistical...

We propose a consistent, mass preserving algorithm to solve mixed convection flows in enclosures with large temperature differences. The present algorithm is based on a staggered/nonstaggered finite volume framework to handle variable density fluid flows with heat transfer. The framework solves a single equation for normal momentum as opposed to th...

Development of unified solver for thermobuoyant flows that can work on arbitrary mesh topologies is discussed. Unlike incompressible flow, in the present approach energy equation is used to derive a pressure correction equation. The resulting equation reduces to the continuity equation for incompressible flows, only when the thermal gradients and c...

A unique hybrid Aerodynamic Shape Optimization (ASO) frame-work is devised for axisymmetric bodies with minimum drag coefficient in hy-personic inviscid flow at zero angle of attack. The hybrid ASO framework that has been developed in this paper makes use of a combination of low fidelity framework and high fidelity framework, with the intention to...

In the present work for numerically investigating the interfacial flows, an algebraic Volume of Fluid technique has been implemented over hybrid unstructured meshes. Following the work of Dalal et al., the governing equations are discretised by cell centered finite volume method wherein pressure-velocity coupling has been achieved by momentum inter...

Variable density flows are basically those in which density variations cannot be neglected and hence the density is treated as a variable. This formidable change in density may be caused by either of three variables of the ideal gas equation (when dealing with gases) namely pressure, temperature and molar-mass. When pressure causes considerable cha...

A new algorithm to recover centroidal velocities from face-normal data on two-dimensional unstructured staggered meshes is presented. The proposed approach uses iterative defect correction in conjunction with a lower-order accurate Gauss reconstruction to obtain second-order accurate centroidal velocities. We derive the conditions that guarantee th...

The importance of fineness ratio in determining the aerodynamic shapes of minimum-drag, zero-lift axisymmetric bodies in inviscid hypersonic flows is investigated using a shape optimization framework. The framework employs modified Newtonian theory for surface pressure computation, Bezier curves for geometric parameterization and a steepest-descent...

Shock-wave boundary layer interaction (SWBLI) and associated changes in wall properties for ramp induced flow breakdown have been considered in the present studies. A two dimensional finite volume based CFD solver has been developed and implemented successfully to study the SWBLI. Pressure measurements are invariantly considered in the literature f...

Numerical investigations to assess the performance of different flux schemes for the spatial discretisation of the Euler equations have been performed. The schemes employed in the study include flux vector and flux difference splitting schemes as well as hybrid schemes. The schemes are cast in an unstructured high-order finite volume framework and...

In this work, a simple and efficient numerical approach to determine the shape of the minimum-drag axisymmetric forebody in inviscid supersonic flow with an attached shock constraint has been described. Taylor–Maccoll equation in conjunction with the tangent cone method is employed to estimate the pressure drag coefficient which is also chosen as t...

The present work includes the development of generalized incompressible three-dimensional Navier-Stokes solver using finite volume method over a hybrid unstructured grid. A collocated arrangement of variables has been followed and the pressure-velocity coupling is achieved by momentum interpolation. The diffusive terms are calculated in a natural w...

Algorithms for adaptive mesh refinement using a residual error estimator are proposed for fluid flow problems in a finite volume framework. The residual error estimator, referred to as the R-parameter is used to derive refinement and coarsening criteria for the adaptive algorithms. An adaptive strategy based on the R-parameter is proposed for conti...

We propose a novel algorithm for velocity reconstruction from staggered data on arbitrary polygonal staggered meshes. The formulation of the new algorithm is based on a constant polynomial reconstruction approach in conjunction with an iterative defect correction method and is referred to as the IDeC(k) reconstruction. The algorithm is designed for...

In this paper, we propose a novel algorithm for transient mesh adaptation based on residual error estimation. The error estimator, known as the K-parameter is a reliable measure of the local truncation error and is used to derive local length scales that guide refinement and derefinement. In order to efficiently handle moving fronts, a Refinement L...

We propose a generalisation of the CURVIB methodology (Ge & Sotiropoulos, JCP 2007) for the solution of the unsteady incompressible Navier--Stokes equations on arbitrary polygonal meshes in domains containing arbitrarily complex, moving immersed bodies. The new finite volume flow solver employs the hybrid staggered/non--staggered approach of Ge & S...

We generalize the curvilinear/immersed boundary method to incorporate overset grids to enable the simulation of more complicated geometries and increase grid resolution locally near complex immersed boundary. The new method has been applied to carry out high resolution simulations of wind and hydrokinetic turbine rotors. An interior fine mesh conta...

A residual-based strategy to estimate the local truncation error in a finite volume framework for steady compressible flows is proposed. This estimator, referred to as the R-parameter, is derived from the imbalance arising from the use of an exact operator on the numerical solution for conservation laws. The behaviour of the residual estimator for...