Department of Mechanical Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

The unsteady wake of a rotating and translating sphere is experimentally investigated at Reynolds numbers (Re) ranging from 115 to 550 for two rotational speeds. Non-dimensional rotational speed, Ω∗, is defined as the ratio of the maximum azimuthal speed of the sphere and the speed of translation. Motion of the sphere is generated using a specially designed mechanism in a channel, and its wake has been visualized using fluorescent dye. Unlike the steady flow past a stationary sphere where the limiting Reynolds number is 270, the flow becomes unsteady when sufficient rotation rate is introduced at much lower Reynolds number (Re = 115 , Ω∗= 0.375). The transition from one-sided to double-sided hairpin vortex occurs at one critical Re for a given rotational speed, and it switches back to one-sided hairpin vortex shedding at another critical Re. Particle image velocimetry results demonstrate the vorticity distribution in the wake and the variation of the wake width with axial distance. At very low Re, velocity profiles in the wake are nearly self-similar. The strength of the vortex rings weakens in the far wake. The decay of centerline velocity in axial direction confirms the dissipation of the vorticity in the far wake. In this unsteady flow, the time-averaged value of the separation angle is higher than that of the steady flow on the advancing side due to enhanced adverse pressure gradient. The Strouhal number calculated from the dye visualization in this range of Ω∗ and Re varies from 0.175 to 0.25, a clear increasing trend both with increasing Re and Ω∗. The coefficient of drag evaluated at the center plane remains constant at 0.94 for the present investigation up to Re = 550. The wavelength of the unstable hairpin vortices is found to scale inversely with the translational velocity of the sphere. © 2021, Springer-Verlag GmbH Austria, part of Springer Nature.

World University root node

Acta Mechanica

Wake of transversely rotating and translating sphere in quiescent water at low Reynolds number

This study is focused on investigating the dual performance of Rh/CeO2/γ-Al2O3 catalyst for steam reforming of ethanol (SRE) and thermochemical water splitting (TCWS) using a packed bed reactor. The catalyst is designed to be thermally stable containing an active phase of Rh and the redox component of CeO2 for oxygen exchange, supported on γ-Al2O3. The catalyst has been characterised by SEM, XRD, BET, TPR, TPD, XPS and TGA before testing in the reactor. The optimal temperature for SRE reaction over this catalyst is between 700 °C and 800 °C to produce high concentrations of hydrogen ( 60%), and low CO and CH4. The selectivity towards CO and CH4 is higher at low temperatures and drops with rise in reaction temperature. Further, Rh/CeO2/γ-Al2O3 is found to be active for TCWS at relatively low temperatures (≤1200 °C). At temperatures as low as 800 °C, this catalyst is especially found suitable for multiple redox cycles, producing a total of 48.9 mmol/gcat in four redox cycles. The catalyst can be employed for large number of redox cycles when the reactor is operated at lower temperatures. Finally, the reaction pathways have been proposed for both SRE and TCWS on Rh/CeO2/γ-Al2O3 catalyst. © 2021 Hydrogen Energy Publications LLC

Department Of Chemistry

International Journal of Hydrogen Energy

Thermochemical hydrogen production using Rh/CeO2/γ-Al2O3 catalyst by steam reforming of ethanol and water splitting in a packed bed reactor

Electromagnetic acoustic transducers (EMATs) can efficiently generate the shear horizontal (SH) guided wave modes. In this article, the Halbach magnet array pattern is explored as an alternate to the conventional periodic permanent magnet (PPM) structure. The magnetic field strength of a Halbach array is significantly higher on one side of the structure while it is weak on the opposite side of the array. This magnetic field distribution enables Halbach EMATs to generate ultrasonic waves with relatively large amplitude. To observe this phenomenon, this study compares the amplitude generated from multiple single-row Halbach EMATs with single-row PPM EMAT configurations using finite-element-based simulation models for SH0 ultrasonic wave generation. This article then presents the ultrasonic wave fields generated by various double-row Halbach EMAT configurations using finite-element-based simulation models and experimentally validated for guided fundamental SH0 mode generated in an aluminum plate specimen. It is observed that distinct ultrasonic guided wave beam patterns be associated and predicted for different double-row Halbach EMAT configurations. © 1986-2012 IEEE.

Department of Metallurgical and Materials Engineering

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

Characterizing Halbach EMAT Configurations for SH0 Ultrasonic Waves

Solar energy is one of the emerging technologies and the use of concentrating power technology is increasing in solar power plants. Parabolic trough collector is a concentrating solar power technology that is situated in the open terrain and subjected to wind loads. The structural stability of these devices under such loads determines the ability to accurately concentrate the rays at the absorber tube, which affects the overall optical and thermal efficiencies. A detailed numerical analysis is carried out at different wind loads and design conditions. It is observed that for a change in velocity from 5 m/s to 25 m/s, slope deviations increase from 1.21 mrad to 3.11 mrad at the surface of the reflector exceeding the shape quality of the mirror panels. Higher yaw angles and pitch angles of 60° and 120° are observed to be decisive in the design of collectors. Roof-mounted collectors experience a 40% higher drag force than ground-mounted collectors at a 0° pitch angle. For the Aluminium trough, the slope deviation at the surface of the reflector is higher by 4.62% than glass. The study will be helpful for engineers and scientists in the design of the parabolic trough collectors. © 2021 Elsevier Ltd

Department Of Civil Engineering

Renewable Energy

Wind load and structural analysis for standalone solar parabolic trough collector

A 1-D numerical modelling of the dynamics of inclined closed loop buoyancy driven heat exchangers with inclusion of the wall conduction effect at the heat exchanger is presented in the current study. A Coupled Natural Circulation Loop (CNCL) is an ideal system for studying the closed loop buoyancy driven heat exchanger. The modelling utilises a Fourier series based approach to develop a 1-D model of the Conjugate CNCL system, which is then verified with the 3-D CFD studies of the respective cases. A good agreement is observed with the 3-D CFD data, which demonstrates the suitability of the 1-D model for transient behaviour prediction. The non-dimensional numbers and thermal coupling sensitivity coefficients which govern the dynamics of the Conjugate CNCL are identified and an appropriate parametric study is conducted. Results show that the wall conduction and inclination have a significant effect on the transient behaviour of the Conjugate CNCL system. A jump in the heat transfer coefficient with variation in the inclination of the Conjugate CNCL system is observed. The 1-D model is also able to capture the flow direction reversal with change in the inclination of the Conjugate CNCL system for zero flow field initial conditions. © 2021 Elsevier Masson SAS

International Journal of Thermal Sciences

Fourier series based 1-D numerical modelling of the dynamics of inclined closed loop buoyancy driven heat exchangers with conjugate effect

In this work, we propose to replace the conventional flat stainless steel gasket in flanged bolted joints used in seawater piping with an O-ring polymer gasket to provide a leak-proof joint under bolt preload. Modeled as hyperelastic material, the polymer gasket undergoes large deformation when sandwiched between the pipe flanges. To alleviate the commonly encountered problems due to element distortion, we use a variant of the smoothed finite element, the (Formula presented.) SFEM within Abaqus standard to simulate the flanged bolted joint. A systematic study is performed to arrive at an acceptable design for leak-proof flanged bolted joints. © 2021 Taylor & Francis Group, LLC.

International Journal for Computational Methods in Engineering Science and Mechanics

Design and analysis of O-ring polymer gasket for flanged bolted joints in seawater piping using α-FEM

In this paper, one of the variants of the smoothed finite element method, α-FEM is adopted for hyperelastic material with large deformation and contact nonlinearity in two dimensions. The salient feature of the α-FEM is that it is stable and this is accomplished by using the scale factor α [0, 1] to combine the compatible finite element method and the node-based smoothed finite element method. The framework is implemented in the commercial software, Abaqus using the user element feature, UEL. The efficacy and robustness of the proposed work is demonstrated by several benchmark problems in both linear and nonlinear elasticity with and without contacts. The developed UEL and the associated files can be downloaded from https://github.com/nsundar/alphaFEM. © 2021 World Scientific Publishing Company.

International Journal of Computational Methods

α -Finite Element Method for Frictionless and Frictional Contact including Large Deformation

The microstructure attributes are responsible for the deformation mechanism of material, which induces shear instability primarily in difficult-To-machine material like Ti-6Al-4V. Consequently, the dynamic cutting force yields serrations in the chip morphology. Therefore, microstructure induced shear instability has been investigated in the present work using an analytical tool to unveiled the deformation behavior in correlation with microstructural characteristics (grain sizes, phase fractions, and microhardness) and process parameters: Temperature, strain, and strain rate. The combined effect of feed rate and high cutting speed was found to enhance the strain localization phenomena, which leads to a more pronounced cracking, inducing dynamic cutting force. Segmentation frequency and force-frequency correlation imply a significant transition exhibit from the static to dynamic nature of cutting force. The segmentation frequency of the equiaxed microstructure is lowest among the rest at lower cutting speed, revealing the shear instability dependency on the microstructure. The grain size effect restricts the dislocation movement at the higher cutting speed, which led to a larger strain in as-received microstructure followed by equiaxed and fully lamellar microstructure. © 2021 Georg Thieme Verlag. All rights reserved.

Journal of Manufacturing Science and Engineering, Transactions of the ASME

Microstructure Induced Shear Instability Criterion during High-Speed Machining of Ti-6Al-4V

Isogeometric Analysis introduced by Hughes et al.[1] has gained importance in the recent times due to its ability to capture accurate solutions and exact geometry representations. In the present study, IGA-Collocation is extended for oscillatory problems in acoustics. Numerical solutions of oscillatory problems often suffer from numerical dispersion errors, which demands use of minimum of ten nodes per wavelength or higher order bases. But employing higher order bases in IGA based on Galerkin approach (IGA-G) is computationally expensive. To overcome this issue, we employed IGA based on Collocation (IGA-C)[2] which is often regarded as a rank sufficient one-point quadrature scheme and has the potential to reduce the computational cost. In the present study, IGA-C with higher order bases is employed for solving rectangular waveguide and oscillating cylinder problems with different wave numbers. The performance of IGA-C is compared with the IGA-G in terms of efficacy and computational time. From the results, the potential of IGA-C is clearly observed in solving wave problems. © 2021, Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

Isogeometric Collocation for Time-Harmonic Waves in Acoustic Problems

TiAl4V is used widely in aerospace and biomedical application due to its high specific strength and good bio-compatibility. Its poor tribological performance restricts usage for hip implant articulation. Various surface characteristics such as surface roughness and wettability affect the tribological behaviour of Ti6Al4V sliding. Surface texturing is the recent technique to modify the surface features and improve the wettability. This study aims to compare the wettability and coefficient of friction (CoF) of discrete and continuous texture under bio-lubricated condition. Dimple and crosshatch textures are fabricated using laser surface texturing (LST) technique. The geometrical parameters such as depth, pitch and area density have been kept the same. Wettability associated with both the textures are analysed by measuring surface contact angles using goniometer. Further, friction behaviour is evaluated for all the textured and non-textured surfaces under biological environment using reciprocating pin-on-disc tribometer. Results show a significant reduction in contact angle for crosshatch texture compared to dimple and non-textured surface. Also, both the texture reduced the friction by 24% compared to non-textured surface. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.