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

In this paper, we propose the study of optimizing the hyperparameters of deep learning Data-driven simulation-assisted-Physics learned AI (DPAI) model to simulate the ultrasonic wave propagation for extended depth with a lower error. DPAI model has layers of encoder–decoder structure with modified convolutional long short-term memory (ConvLSTM). DPAI model is trained using the finite element (FE) simulations dataset of distributed single-point to multi-point excitation sources in the 2D domain. The DPAI is the data-driven approach to apprehending the underlying physics of elastodynamic wave propagation. Six different combinations of hyperparameters (hidden dimensions, kernel size, batch size) are used in the DAPI model to study parameter optimization for lowering compounding error. The effectiveness of the trained DPAI models with varying hyperparameters is demonstrated to reduce the compounding error for modeling the deeper simulations of the single-point excitation and multi-point excitation sources. The maximum MAE on amplitude is 5.0×10-2, and MAPE is 2.64% on time of flight (TOF) between DPAI and FE simulations. © 2022 Elsevier B.V.

Ultrasonics

Optimizing hyperparameters of Data-driven simulation-assisted-Physics learned AI (DPAI) model to reduce compounding error

The combined effect of grain size variation and plastic deformation on the acoustic nonlinearity parameter has been investigated in an austenitic stainless-steel material of grade 304. The nonlinear behavior of this parameter with grain growth has deviated to linear fit with deformation. This is due to the interaction of elastic waves with the strain-induced dislocation substructure in the grains. The normalized mean square strain of the deformed specimens has been estimated through angle dispersive x-ray diffraction studies using a synchrotron source, and this has been correlated with the change in the acoustic non-linearity parameter with deformation. The nonlinearity parameter is found to be very sensitive to the plastic deformation even in the presence of grain size variations. The results infer that the variations in the nonlinearity parameter can be used to have an estimate of the extent of localized deformations often occurring during the fabrication of metallic components. © 2023 Author(s).

Review of Scientific Instruments

An experimental investigation on the combined effect of plastic deformation and grain size variation on the acoustic nonlinearity parameter

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

Wall thickness reduction, which typically results from corrosion, erosion, or operating conditions, is a significant challenge in many industries. In order to generate a broadband pure shear horizontal wave mode in plate structures, this paper proposes a magnetostrictive patch transducer called the Staircase Magnetostrictive Patch (ScaMP) Transducer. For ScaMP transduction, an optimised patch width offers a broadband frequency response is employed. The lowest remnant thickness of the sample was estimated using the wideband SH1 dispersive guided wave mode's cut-off property. The broad frequency excitation method enabled measurement over a range of wall thinning up to 80% of the nominal thickness with a single data acquisition. Experiments were carried out on an 8 mm nominal wall thickness aluminium plate with gouge defects to evaluate the proposed sensor's broad frequency response. The measurement of remnant thickness was estimated with a maximum error of 5.5%. © 2023 Elsevier Ltd

NDT and E International

Lowest remnant thickness estimation using Staircase Magnetostrictive Patch (ScaMP) Transducer

Humidification-Dehumidification (HDH) desalination technology can ensure adequate freshwater supply to the people living in water-stressed regions in remote locations. Although, HDH process can be operated by using simple and inexpensive components such as cooling tower and heat exchanger which are readily available in the market. But to achieve the desired freshwater productivity and thermal performance, it is important to carry out the detailed design of these components and choose the right operating parameters such as mass flow rate ratio, top brine temperature which significantly affects system performance. In the present study, the thermal performance of a closed-air, open-water and water-heated version of the HDH cycle has been investigated experimentally and the previously developed detailed numerical model for the similar HDH cycle has been validated with the experimental results. The HDH system has been built with a counter-flow packed-bed cooling tower and finned-tube heat exchangers which are widely utilized across all industries. The thermal performance of the system is evaluated in terms of four main parameters which are gained output ratio (GOR), distillate flow rate, and the effectiveness of the humidifier as well as the dehumidifier by varying the top brine temperature as well as the mass flow rate ratio. It is observed that the present system can produce around 125.5 L of freshwater per day, having total dissolved solids of approximately less than 15 ppm, operating at a feed temperature of only 61.7 °C and mass flow rate ratio (MR) of 2.34. At these operating conditions, energy effectiveness of the humidifier and dehumidifier were approximately 0.75 and 0.80. The gained output ratio (GOR) of the present system is quite modest (=0.81) which indicates that the system may be further improved in the future. The results of our current experimental study validated the predictions of the model developed in our prior study. Hence, the model can be utilized to design the HDH system as per the desired output of freshwater and GOR. The results from both experiments and simulations are in closer agreement with each other. The numerical analysis also showed that the integration of solar energy-driven AHT (Absorption Heat Transformer) has the potential to further increase the production rate of the HDH system. The economic performance of the system revealed the levelized cost of water production (LCOW) from such a system is approximately USD 4.0 $/m3 of fresh water but the total capital expenditure to install this system is very low (&lt;USD $1500). Overall, it was inferred that an HDH system with optimum performance can be designed and installed at a much lower cost, and using simple construction, which is a huge advantage for marginalized communities living in remote locations across the world (since the simple components of this system can be easily operated and maintained by them). © 2023 Elsevier Ltd