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

This paper reports an experimental study of spray characteristics in rotary slinger atomizers using different laser diagnostic tools. The main objective of the present study is to investigate the effect of size of the slinger orifices on liquid breakup dynamics and droplet size distribution over a wide range of rotational speed (5000–45,000 rpm) and liquid flow rates (0.2–2 lpm). Three different slinger discs having the same number of orifices but different sizes (d0 = 1, 1.5, and 2 mm) are considered. The primary liquid breakup visualization is achieved using volumetric laser-induced fluorescence (VLIF) technique; whereas, the droplet size is measured by interferometric laser imaging for droplet sizing (ILIDS) technique. The results demonstrate critical role of orifice size on liquid breakup mode and droplet size up to rotational speed about 30,000 rpm, beyond which the aerodynamic force dominates the atomization process such that neither the orifice size nor rate of rotation has strong influence. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

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Lecture Notes in Mechanical Engineering

A Parametric Study on Rotary Slinger Spray Characteristics Using Laser Diagnostics

The present investigation focuses on the effect of heat treatment parameters on the hardening and fracture behavior of 17-4 PH stainless steel, thereby assessing the susceptibility to failure at intense loading conditions. The tensile tests were conducted at an effective strain rate of 47 s−1 on a GleebleTM 3800 thermo-mechanical simulator at room temperature and 75 °C. X-ray diffraction (XRD) analyses revealed the presence of a predominant martensitic phase with significant reverted austenite content at higher aging times in the 480 °C condition, thereby resulting in the softening phenomenon and lower strength values. Peak hardness and superior strength values were obtained for higher aging times in the 450 °C condition and lower aging times in the 480 °C condition due to precipitate-particle segregation at packet junctions and finer lath microstructure. Consequently, the fractographic observations from scanning electron microscopy (SEM) exhibited a semi-brittle mode of failure. In the over-aged conditions, a transition toward ductile fracture mode with dimple morphology was depicted. The higher testing temperature produced a uniform set of failure strain values compared to the scattered strains at ambient conditions. © 2022, ASM International.

Journal of Materials Engineering and Performance

Microstructure-Induced High-Strain-Rate Deformation Behavior of Heat-Treated 17-4 PH Stainless Steel

Two-dimensional numerical computations were carried out on flow past a heated circular cylinder undergoing vortex-induced vibrations (VIVs). The cylinder was elastically mounted on springs and allowed to oscillate in streamwise and transverse directions. The C++ library in the finite-volume–based OpenFOAM software program was used for the simulations. The solver was modified to consider thermal effects, and an energy equation was added to the existing solver. The flow and thermal characteristics were examined for different values of the reduced velocity (Ur) ranging from 1 to 8. Three different mass ratio (m*) values (i.e., 2.5, 5, and 10) were considered at Reynolds number (Re) = 200. The effects of the Ur and m* values on the cylinder response and frequency ratio were disclosed. Higher oscillation amplitudes, i.e., the synchronous regime, were found to change with a change in the m* value. With a change in the Ur value, different modes of vortex shedding and their effects on the temperature field were examined, corresponding to each value of m*. The heat transfer coefficient of the cylinder undergoing VIVs was found to be higher than that observed for the stationary cylinder at the same Re value. The mean drag coefficient and root-mean-square value of the lift coefficient were also reported with a change in the Ur value for each value of m*. © 2023 by Begell House, Inc.

Journal of Flow Visualization and Image Processing

VORTEX-INDUCED VIBRATION OF A HEATED CIRCULAR CYLINDER AT LOW REYNOLDS NUMBER: FLOW AND THERMAL CHARACTERISTICS

During simultaneous impacts in linkages connected by joints, there can be several sequences of pair-wise impulse propagation and the choice of the most accurate sequence involves a combinatorial evaluation of all possible impulse sequences.In this paper, a simultaneous impact algorithm for planar frictionless constrained multibody systems is proposed that does not require an impulse propagation sequence to be determined.The formulation is developed by extending the generalized Newtonian restitution model for simultaneous impacts in unconstrained rigid bodies presented in [1] to planar linkages connected by frictionless joints.The algorithm is a computationally efficient alternative to the modeling of collisions in force-based continuous-time domains [2, 3], never results in an increase in kinetic energy (K.E.) [1] and predicts contact separation between bodies having zero pre-impact relative velocity of approach.Results using the proposed algorithm showing various collision scenarios in constrained linkages are included in the paper.Furthermore, the solutions are compared with linear complementarity (LCP) [4]-based approach and simulation results from ADAMS software. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

A New Method for Solving Simultaneous Impact Problems in Constrained Multibody Systems

This work presents a numerical study on axisymmetric inverse coflow flames fueled by synthetic gases. The simulations are carried out using ANSYS-FLUENT. The numerical model includes variable thermo-physical properties, detailed chemical kinetic mechanism, multi-component diffusion and radiation sub-model to model reactive flow. Four typical synthetic gases obtained from different gasification processes are chosen from literature. Inverse coflow burner is reported to produce lower emissions, and is chosen as the burner configuration. Characteristics of flames from inverse coflow burner are presented. Hydrogen or carbon monoxide content in the mixture is varied individually by keeping the other constituents at their average values. The power rating is chosen as 250 W. Air flow rate is also varied to study its effects on flame structure. Hydrogen and CO contents affect the formation of OH, H, heat release rate and flame stability. The maximum temperature increases with increasing hydrogen and CO. Flow, thermal and species fields are discussed in detail. Increase in hydrogen content increases the flame stability, extent of reaction zone and increases the flame temperature. The profiles of net reaction rate of several species and kinetic rate of important reactions have been discussed to explain the characteristics of these flames. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Effect of Addition of Carbon Monoxide and Hydrogen in Syngas Inverse Diffusion Flames

Ultrasonic SHM approaches using bulk or guided waves has been well documented. Here the waves are generate using PZT transduction that requires excitation inputs using either high voltage or high current or both. Several critical applications such as component in explosion susceptible environment, extreme temperature condition, etc. have limitations in deployment of high voltage/current excitation. In this paper, the use of wave-guide-based excitation is explored for plate and pipe like geometries. The waveguide help isolate the excitation part of the ultrasound generation, away from the component that may be in a hostile condition. The ultrasound wave modes excited in the waveguide is coupled to the structure and optimized to generate the desired guided wave modes in the geometry of the structures using Finite Element Wave Propagation models. The reception of these modes are also explored using similar ultrasonic waveguides. The detection of defects, in an SHM mode, using this remote generation approach is also demonstrated on a plate geometry component. This article demonstrates the detection of fundamental symmetric wave mode (S0), shear horizontal waves (SH0) and antisymmetric wave mode (A0) in an steel plate by placing a thin wire-like stainless steel waveguide sensor. In order to uniquely identify the three-fundamental plate-guided modes, we map the experimentally measured group velocities as detected by the waveguide sensor to theoretically obtained group velocity dispersion curves. The analytically obtained FEM results are evaluated experimentally using time-of-flight measurements. In future, this sensor arrangement may be utilized in areas like high-temperature furnaces, engines and aircrafts for detecting cracks. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.

Lecture Notes in Civil Engineering

Remote Excitation Ultrasonic Waveguide-Based SHM for Critical Applications

We propose a simple 3D nonlinear rate-type constitutive relation with just three parameters for elastomeric dampers capable of emulating double-shear data in frequency and strain sweep mode. The nonlinear relation derived using two scalar functions, namely Helmholtz free energy and the rate of dissipation function [1], result in a partitioned constitutive relation: Cauchy stress tensor is described in terms of the left Cauchy-Green stretch tensor and a tensor describing instantaneous elastic response, and the evolution equation for the instantaneous elastic response is derived by maximizing the rate of dissipation function. A compressible version of this model is implemented in Abaqus® The constitutive relation and the implementation are validated by comparing with known semi-inverse solutions obtained by specializing rate-type relation to special deformations. Material parameters are obtained for dampers made of synthetic and natural rubber by fitting the predictions of the model with that of double shear data. By using the same parameters, three dimensional simulations of a cylindrical damper subjected to sinusoidal force akin to that of an unbalanced machinery predict different hysteresis curves in compression/tension and shear. To that end, we show that the non-linear 3 parameter model is one of the simple models that can be formulated within the thermodynamic framework which can predict the inherent non-linearity of the damper operating under combined harmonic loading situations. A robust implementation (VUMAT) of the developed model is included with the article. We believe that this can aid engineers in tailoring dampers for its controlled dissipation across multiple modes of deformation as well as academicians in adding more value by building and implementing sophisticated models within this framework. © 2021 Taylor & Francis Group, LLC.

Mechanics of Advanced Materials and Structures

On the explicit dynamics implementation and validation of partitioned rate-type constitutive relation for dampers

This paper proposes a Phononic crystal (PnC) device formed by embedding spheres in a polymer matrix for energy harvesting, an application that has drawn much research interest recently. A parametric study is performed to evaluate the optimal radius to lattice parameter ratio r/a = 0.4 to obtain a large bandgap as well as gap to mid-gap ratio. By removing a sphere from the central lattice point, a defect is created within an otherwise perfect PnC. The supercell technique is employed to compute defect modes and band structure of defect PnC. These defect bands show strong vibrational modes within the spatial arrangement of the defect point and these defect frequencies appear to be flat (dω/dk = 0) in the band structure confirming energy localization at these modes. Also, while varying the radius of the defect sphere rd in the range of [0.1a–0.5a], the number of defect modes within the bandgap tend to decrease, vanishing when rd equals 0.4a and 0.5a. To utilize the defect mode for energy harvesting, a small patch made of a piezoelectric material is attached onto the PnC device exactly above the defect. Introduction of this patch renders the band structure and defect modes to shift upwards compared to the defect PnC without the patch. A highly localized vibrational eigen mode is observed around 662 kHz in the band structure for the defect PnC with patch. The voltage response of this device is simulated by connecting a high resistance (open-circuit) to the patch and sweeping frequencies around the defect mode. This process produced a voltage of 2.8 V at 656.7 kHz for a 0.3 µm displacement excitation, thus demonstrating the usefulness of the proposed concept. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.

Department of Metallurgical and Materials Engineering

Spherical Inclusions Based Defect Modes in a Phononic Crystal for Piezoelectric Energy Harvesting

Biogas is primarily composed of methane, carbon dioxide and other gases in trace amounts. The amount of CO2 present in biogas varies with the source of biomass and the method of production. The CO2 content in biogas significantly affects the flame stability. In the present work, comprehensive numerical study of structure, stability and characteristics of confined coflow biogas diffusion flames are presented. A short reaction mechanism with 25 species participating in 121 reactions is used to model reactive flow. Numerical simulations are carried out using OpenFOAM. Fick’s diffusion, thermal diffusion and variable thermophysical properties are incorporated in the model. Biogas with 55% methane (rest carbon dioxide) is considered in the present study. The burner is operated at 250 W. The primary air is systematically increased from 5 to 40% of the stoichiometric air requirement. The rate of coflow air is fixed as the stoichiometric value in one set of cases. Subsequently, the rate of coflow air is varied such that the total air supplied is equal to the stoichiometric value. Results indicate that the flame stability increase with an increase in the amount of primary air flow rate in the fuel stream. The stability is seen to be better in cases where total airflow to the burner is equal to the stoichiometric value. Entropy generation during processes such as chemical reactions, mass diffusion, heat transfer and coupled heat and mass transfer are discussed in detail. Results in terms of velocity, temperature, species and entropy fields are used to describe the stability and flame characteristics of confined coflow biogas flames. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

A Study of Structure and Entropy Generation in Confined Biogas Coflow Diffusion Flames

Integrated thermodynamic system for multiple products such as polygeneration systems utilizes the resource energy efficiently. In this research paper, an advanced absorption cycle based on renewable source heat driven polygeneration is proposed for multiple products to rural communities. This cycle is an ammonia-water absorption cycle with parallel evaporators for different cooling options and the power production. Net power output is increased either by decrease of the pumping power or increase of the pressure ratio. The two absorbers, which are incorporated in the advanced absorption cycle, provides both these advantages. The rejected heat is utilised either for fresh water production, drying or domestic hot water applications. The influence of medium pressure (MP) absorber temperature, generator temperature, condenser temperature and the refrigerant flow to cooling and power sub cycle is analysed. The maximum resource utilization efficiency and system exergy efficiency of the advanced absorption polygeneration is about 22.46% and 12.26% respectively at a typical operating condition with the generator temperature of 230 °C. © 2022