BITS Faculty Publications

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Subject: search.filters.subject.Computational Fluid Dynamics (CFD)

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    Laser pulse dispersion in underdense plasma and associated ion acceleration by relativistic self-induced transparency
    (AIP, 2019-08) Holkundkar, Amol R.
    The propagation of laser pulses in the underdense plasma is a very crucial aspect of the laser-plasma interaction process. In this work, we explored the two regimes of laser propagation in the plasma, one with a0 < 1 and the other with ⁠. For the a0 < 1 case, we used a cold relativistic fluid model, wherein apart from immobile ions no further approximations are made. The effects of laser pulse amplitude, pulse duration, and plasma density are studied using the fluid model and compared with the expected scaling laws and also with the particle-in-cell (PIC) simulations. The agreement between the fluid model and the PIC simulations are found to be excellent. Furthermore, for the case, we used the PIC simulations alone. The delicate interplay between the conversion from the electromagnetic field energy to the longitudinal electrostatic fields results in dispersion, and so the redshift of the pump laser pulse. The dispersed pulse is then allowed to be incident on the subwavelength two-layer composite target. The underdense plasma before the target regulates the dispersion of the pulse. We observed an optimum pretarget plasma density which results in the acceleration of the ions from the secondary layer to ∼170 MeV by a ∼8 fs linearly polarized Gaussian laser pulse with ∼8.5 × 1020 W/cm2.
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    Development of Colburn j Factor and Fanning Friction Factor Correlations for Compact Surfaces of the Triangular Perforated Fins Using CFD
    (Taylor & Francis, 2015-07) Ranganayakulu, Chennu
    The necessity of increased heat transfer surface area has resulted in the development of compact heat exchangers, which are widely used in the aerospace and automobile industries. Hence perforations are made on triangular plain fins to study the effects on the heat transfer coefficient. A numerical model has been developed for the perforated fin of a triangular plate fin heat exchanger. Perforated fin performance has been analyzed with the help of computational fluid dynamics (CFD) by changing the various parameters of the fin. The Colburn j factor and the Fanning friction factor are calculated for different Reynolds numbers. The values of the Colburn j factor and the Fanning friction factor are validated for known geometric fins with available data in the literature and extended to triangular perforated fins. The correlations have been developed between Reynolds number, Colburn j factor, and Fanning friction factor by taking into account fin height, fin thickness, and fin spacing. The present numerical analysis is carried out for air media.
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    Applications of Computational Fluid Dynamics Simulation and Modeling
    (Intechopen, 2022-06) Bhattacharyya, Suvanjan
    This book provides well-balanced coverage of computational fluid dynamics analysis for thermal and flow characteristics of various thermal and flow systems. It presents the latest research work to provide insight into modern thermal engineering applications. It also discusses enhanced heat transfer and flow characteristics.
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    A novel design for solar collector used for water heating application having nanofluid as working medium: CFD modeling and simulation
    (Springer, 2022-08) Bhattacharyya, Suvanjan
    A solar collector is a simple and cheap device that converts solar radiation into valuable heat energy. The thermal performance of the solar collectors can be enhanced significantly with the suspension of nanoparticles in the base fluid. A novel design for a solar-assisted water heater (SWH) is proposed in the current study, and the effect of nanofluid has been investigated on the thermal efficiency of the SWH. The use of nanofluid is one of the prominent methods in comparison to other techniques for improving the performance of solar collectors. Therefore, the base working fluid, i.e., water is mixed with the alumina nanoparticles of average particle size of 30 nm, and they are assumed to be spherical. The flow and thermal characteristics of nanofluid through the solar water heater are simulated numerically with the help of the Eulerian–Eulerian two-phase model using the finite volume method (FVM). The commercial package ANSYS Fluent, is used for modeling the problem under transient conditions with a pressure-based solver. In comparison to a conventional flat plate collector, the proposed solar water heater consists of a corrugated absorber-plate and the effect of the radius of curvature has been investigated on the heat transfer and collector efficiency. With the proposed design, the heat transfer area available with the riser tubes increases remarkably and it leads to a 43% and 14% increase in heat transfer augmentation and collector efficiency, in comparison to the conventional solar water heater.
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    Introductory Chapter: A Brief History of and Introduction to Computational Fluid Dynamics
    (Intechopen, 2021-08) Bhattacharyya, Suvanjan
    Computational Fluid Dynamics (CFD) refers to a broad set of methods that are used to solve the coupled nonlinear equations that govern fluid motion. To our best knowledge, the first attempt to calculate fluid flow was set forth by Lewis Fry Richardson, with applications for weather prediction. He envisioned a “forecast factory” that included 64,000 human “computers”. Each “computer” was positioned at tiered elevations around a spherical globe, occupying computational cells that corresponded to map locations, as shown below for northern Europe. His method involved inputting weather observation data to the corresponding grid locations and then solving the forward-stepping equations. Based on Richardson’s description, the following image provides the imagined weather prediction system, commonly referred to as the “fantastic weather factory” of Lewis Richardson. Each of the red and white grid cells represents a human calculator. They are arranged across the surface of a sphere (which represents the Earth). In the center, a conductor uses spotlights to highlight calculated results at each grid cell. It was acknowledged that for such a system to work, each human calculator would be required to perform their calculations at the same speed. That is, if one human calculator was either faster or slower than its neighbors, it would send information to the neighbors at a faster or slower rate which would consequently cause numerical instability; a concept that is important even today as we will show. In the image, the blue spotlight identifies calculators that are operating too slowly, and the red spotlight identifies those that are too fast.
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    Computational of studies of heat transfer enhancement in turbulent channel flow with twisted strip inserts
    (Begell House, 2015) Bhattacharyya, Suvanjan
    Heat transfer behaviour in twisted strips swirl generator inserted tube are investigated numerically. This work presents the configuration optimization of a typical single-twist twisted strip in a circular tube for turbulent heat transfer in air using computational fluid dynamics (CFD) modelling. In the present paper, transition - SST model which can predict the change of flow regime from laminar through intermittent to turbulent has been used for numerical simulations. The twisted strips are inserted separately from the tube wall. The configuration parameters include the, entrance angle (α) and pitch (H). The computational results are in good agreement with experimental data. The results indicate that the larger rotated angle yields a higher heat transfer value and a greater flow resistance of Reynolds number. The optimal design of typical twisted strips in a circular tube for turbulent air flow is, α = 180°, 160° and 140° with a Reynolds number that varies from 100 to 20000. The using of single twist twisted strips supplies considerable increase on heat transfer and pressure drop when compared with the literature. The Nusselt number increases with the increase of Reynolds number. This result is useful for the design of solar thermal heaters and heat exchangers.
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    CFD Study on Thermal Hydraulic Performance of A Wavy Channel Based PCHE Model
    (Springer, 2016-09) Aneesh, A.M.
    Three dimensional CFD study is done here—using a commercial software- to propose an efficient PCHE (Printed Circuit Heat Exchanger) model; used as a recuperator in International Thermonuclear Experimental Reactor (ITER). The present work is aimed to study a wavy channel based PCHE model, with certain modifications in design to demonstrate better thermal and hydraulic performance. The waviness for the hot as compared to cold channel is in anti-phase. The study is done for various angle of bend (0° (straight), 5°, 10° and 15°) and Reynolds number (350, 700, 1400 and 2100). The inlet temperature of the hot and cold channel is taken as 1173 and 813 K, respectively; and the operating pressure of the PCHE is taken as 3 MPa. Thermal hydraulic performance parameters are presented for the various periodic sections of the wavy-channel. Power density as well as pressure drop increases with increasing Reynolds number and angle of bend. Wavy as compared to plane channel based PCHE is demonstrated here to give better thermal-hydraulic performance.
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    Thermal-hydraulic characteristics and performance of 3D wavy channel based printed circuit heat exchanger
    (Elsevier, 2015-08) Aneesh, A.M.
    CFD study is done here to propose an efficient PCHE (Printed Circuit Heat Exchanger) model; used as a recuperator in International Thermonuclear Experimental Reactor (ITER). 3D steady state conjugate heat-transfer numerical simulations are done; considering the variation of thermo-physical properties as a function of temperature. Helium is used as a working fluid and alloy 617 as solid substrate. The study is done for various angle of bend (θ = 0°(straight), 5°, 10° and 15°) and Reynolds number (Re = 350, 700, 1400 and 2100). Various types of flow patterns, within one wavy-section, are presented to analyze thermal-hydraulic characteristics. Thermal hydraulic performance parameters are presented for the various wavy-sections as well as within a section; and for the complete PCHE model. Heat transfer enhancement as compared to pressure penalty is higher for the wavy channel; and increases with increasing Re and θ. Wavy as compared to plane channel based PCHE is demonstrated here to give better thermal-hydraulic performance. A detailed characteristics as well as performance-parameters for thermal hydraulics in a 3D wavy channel based PCHE model − not found in the literature − is presented here.
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    Heat Transfer Simulation by CFD from Fins of an Air Cooled Motorcycle Engine under Varying Climatic Conditions
    (World Congress on Engineering, 2011-07) Srinivasan, P.
    An air-cooled motorcycle engine releases heat to the atmosphere through the mode of forced convection. To facilitate this, fins are provided on the outer surface of the cylinder. The heat transfer rate depends upon the velocity of the vehicle, fin geometry and the ambient temperature. Many experimental methods are available in literature to analyze the effect of these factors on the heat transfer rate. However, an attempt is made to simulate the heat transfer using CFD analysis. The heat transfer surface of the engine is modeled in GAMBIT and simulated in FLUENT software. An expression of average fin surface heat transfer coefficient in terms of wind velocity is obtained. It is observed that when the ambient temperature reduces to a very low value, it results in overcooling and poor efficiency of the engine