https://libjncir.jncasr.ac.in/xmlui/handle/10572/2 2026-04-04T05:27:46Z https://libjncir.jncasr.ac.in/xmlui/handle/123456789/3510 Analysis of vortex ring collisions using Lattice Boltzmann Method Kumar B., Ganesh Vortical structures appear in a wide range of flow scenarios, including wall-bounded turbulence, boundary layer separation behind bluff bodies, and large-scale phenomena such as hurricanes. Understanding these structures is crucial for gaining insights into the overall flow behaviour. Among them, vortex rings are unique flow features characterized by vorticity concentrated around a closed circular loop. Due to the mutually induced velocity along the ring, they self propagate in a straight line. Coaxial vortex ring collisions, a topic widely studied in the literature, exhibit different mechanisms of vortex stretching and dissipation across varying Reynolds numbers. However, these cases represent idealized configurations that differ significantly from realistic flow scenarios, where vortex collisions often occur under arbitrary orientations. In the present work, we numerically investigate non-coaxial vortex ring interactions using the Lattice Boltzmann method, wherein the axes of the colliding rings are offset by a finite distance. We examine the influence of varying this offset for different Reynolds numbers. For small axial offsets, the collision plane of the rings tilts proportionally to the offset distance. In contrast, for larger offsets (of the order of ring radius), vortex stretching occurs predominantly on one side of the ring while the other side undergoes reconnection, forming secondary vortex rings. This behaviour reveals a novel breakup mechanism. Furthermore, we extend our numerical study to explore vortex ring interactions with V-shaped walls. Due to the acute angle of these walls, the rings exhibit enhanced curling, maintaining sufficient vorticity to generate secondary and even tertiary vortex rings. These complex dynamics are successfully captured in our simulations, demonstrating the capability of the numerical model to reproduce intricate reconnection processes and multiple ring formations. Open access 2025-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/123456789/3509 Combined immersed volume-phase field approach for predicting multiphase fluid structure interactions S., Guruprasad The application of numerical methods and the development of solution algorithms to solve various multi-physics scenarios are of prime importance in our modern industrialised world. This thesis deals with numerical methods to compute Fluid-Structure Interactions (FSI) oc curring with more than one fluid phase. The underlying discretisation technique used is the versatile finite volume method. The work essentially develops two different components ca pable of accurately handling the multiphase part and the FSI part. It amalgamates them to develop a formulation capable of handling complex multiphase + FSI problems. The problem’s multiphase aspect is taken care of here by developing a binary and a ternary flow phase field formulations based on the modified Cahn-Hilliard equation. The FSI part of the problem is tackled by using the immersed volume approach, which works by employing a permeability penalty term to the momentum equations. The final step is to combine both these techniques, taking the ternary phase field components to compute the interfacial dynamics and using one of the extra phases as the designated solid phase. The permeability penalty term is applied to the solid phase, thus giving us a new numerical algorithm to compute multiphase + FSI problems. A series of validations have been deployed for both the individual models and the combined approach. Open access 2025-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/123456789/3508 Thermal analysis of a modular plant growth chamber: Experiments and numerical simulation Tanagawade, Manoj Tanaji India, an agriculture-based economy, is the second-largest producer of vegetable crops globally. However, the seasonal and weather-dependent nature of these crops poses significant challenges, prompting a growing adoption of technologies like protected farming. Introduced to India in 1998 through the Indo-Israel Greenhouse Project, greenhouse farming has expanded rapidly but brought unique challenges, especially the issue of overheating during the summer months. India’s abundant sunlight, particularly in summer, often results in temperatures inside greenhouses exceeding optimal levels for plant growth. To address this, evaporative cooling systems, such as pad-and-fan setups, are commonly employed. However, these systems signifi cantly increase water consumption, contradicting one of the primary objectives of protected farming—efficient resource usage, particularly water. The focus of this work is to quantify the extent of overheating in a lab-scale greenhouse model and explore the potential of Infrared (IR) filtering to mitigate this issue. Experimental results demonstrate the effectiveness of IR filters in reducing overheating, offering a promising solution to this challenge. Additionally, this study presents a comprehensive approach to predicting bulk air temperature inside greenhouses through two methodologies: Computational Fluid Dynamics (CFD) simulations and a simplified lumped mass reduced-order model. Both models exhibit good accuracy in temperature prediction, providing valuable tools for optimizing greenhouse designs and ensuring favorable growing conditions with efficient resource usage. Restricted access up to (20-08-2026) 2025-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/123456789/3507 Experimental and numerical investigation of continuous dip-coating for wire with immiscible two-fluid system Goswami, Jishnu Dip-coating is one of the extensively used industrial coating processes. The popularity of this technique coating process is due to its ease of application, versatility in using a wide variety of substrates and coating liquids, low wastage, etc. Understanding this coating process holds economic and industrial importance in having better control of the final film thicknesses. The pioneering work in dip-coating is because of Landau-Levich [19] and subsequent improvements by Derjaguin [8]. The entrainment law given by Landau-Levich stressed the importance of the interaction of capillary and viscous forces. Several modifications and improvements were made to this theoretical work and David Quéré and his group did a voluminous amount of work in understanding the fibre/wire coating process [30]. They incorporated the effect of inertia into the film formation process and showed the possibility of various regimes within the flow. In recent years, the multiphase dip-coating processes become increasingly popular and this present work aims to extend our understanding of fibre/wire coating using a single liquid, involving a liquid-air interface to a two-fluid flow configuration, which contains an evolving fluid-fluid interface. Experimental and numerical work has been performed to study this problem. Experiments are performed by direct visualization of the coating film with varying control parameters. A numerical model is then established by solving fluid flow equations and capturing the fluid fluid interface with the help of a level-set method. The data generated upon this exercise in JNCASR and performed experiments at Universite de Lille, France, we set to discover and understand various flow regimes present in this flow problem. The results show the presence of a visco-capillary regime where the role of inertia and gravity can be assumed to have minimal importance. In this regime, the entrainment is shown to have a close resemblance with the classical LLD theory, which is being followed at higher Ca numbers. The role of inertia is manifested in providing a sharp deviation to the film thickness from the LLD thickness values and the sharpness becomes gentler as viscous, capillary, gravity and inertia all start to play important roles simultaneously. At higher inertia, the film formation is limited by the growth of the boundary layer and this gives rise to a regime solely dominated by boundary layer effects. An alternate visco-gravitational regime is also present suggesting the formation of the film primarily because of the interaction of viscous and gravity forces with negligible inertia and capillary suction. Moreover, film formation over a thin fibre/wire is often susceptible to instabilities and our numerical exercise shows the presence of them for an extensive range of control parameters and non-dimensional numbers. Open access 2025-01-01T00:00:00Z