Department of Applied Mechanics

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

Atomization of a jet in air cross flow has numerous applications in industrial and natural systems. In this study, spray characteristics (i.e., droplet mean diameter, Sauter mean diameter, and volume flux distribution) generated from perpendicularly interacting air jet of 7.5-mm diameter and water jet of 0.8-mm diameter are characterized using a phase Doppler particle analyzer (PDPA) in a forward scattering mode. The investigation is done for seven momentum ratios (q), where the momentum ratios are varied by varying the jet flow rate while keeping air flow rate constant. The jet Weber number is calculated to be 42.56, which is constant for all the cases and falls under the multimode breakup regime. PDPA measurements are done at different spatial locations, 40 mm below the tip of the injector to avoid ligaments and to ensure stable droplets. From the experimental results, it is found that for all flow conditions, volume flux is maximum near the geometric center of the spray and decreases towards the edges indicating the solid cone structure of the spray. The volume flux also increases with increase in q. The maximum of mean droplet diameter (D10) and Sauter mean diameter (SMD or D32) is found at the geometric center of the spray in the x direction, whereas in the y direction the maximum D10 and D32 are shifted towards the windward side of the jet. The diameter–velocity correlation is negative at the center of the spray and positive at the edges for both x and y directions. The correlation model for volume flux is found to be in accordance with the experimental data, while a few outliers are found in the diameter model due to the presence of large droplets that skew the data. © 2020 by Begell House, Inc.

World University root node

Journal of Flow Visualization and Image Processing

Phase doppler particle analyser (PDPA) characterization and modeling of sprays from orthogonally interacting water and air jets

Uni-axial compressive failure of silica-epoxy based heterogeneous honeycombs is investigated in detail for a range of volume fractions. Introduction of heterogeneity in compression of staggered-square honeycomb is seen to result in damage initiation at multiple locations and subsequent damage growth to be more stable compared to pure epoxy in which damage was observed to be localized until peak load when catastrophic failure of the honeycomb specimen occurs. The increase in stiffness and comparative stability of the response is accompanied with reduction in strength, however, between 0 and 5% the total work of compressive failure is comparable. From the elastic-plastic analysis it is evident that the non-linearity in the response of pure honeycombs, prior to peak load, is largely due to formation of plastic hinges near corners of cells, whereas in case of heterogeneous honeycomb the non-linearity is mostly due to debonding of hard filler particles and matrix cracking leading to damage growth in cell walls. © 2020 Elsevier Ltd

Department of Ocean Engineering

Composite Structures

Effect of heterogeneity on crushing failure of disordered staggered-square honeycombs

A large Magnetoelectric (ME) response at room temperature in CoFe2O4 - BaTiO3 core shell composite is crucial for the biomedical application because of its biocompatibility. Good ME response of coreâ€“shell system is directly related to synthesis conditions as it determines extent of coupling between core and shell structures. In this work, CoFe2O4 - BaTiO3 core shell structures with improved ME response were prepared through hydrothermal and citric gel synthesis. Reitveld refinement analysis and microscopic images confirmed the successful formation of CoFe2O4 - BaTiO3 core shell structure. The core shell sample is composed of tetragonal BaTiO3 and cubic spinel CoFe2O4 phases. CoFe2O4 was found to exhibit both positive and negative magnetostriction at room temperature. ME coefficient of 12.38 mV/cm Oe was observed at room temperature, which is quite high and can enhance the efficiency of targeted drug delivery. Â© 2020 Elsevier B.V.

Materials Letters

Improved room temperature magnetoelectric response in CoFe2O4-BaTiO3 core shell and bipolar magnetostrictive properties in CoFe2O4

In the last three decades of developments, the technique of Digital Photoelasticity (DP) has been stabilized and the methodology has been successfully applied to a wide range of problems in Engineering and science. This review succinctly summarizes both the techniques and their applications. Sufficient attention is paid to bring out the problem-solving capability of photoelasticity in each of the domains so as to motivate the reader to extrapolate these ideas to the uncharted territory of new problems they may come across in their domains. © 2020 Elsevier Ltd

Optics and Lasers in Engineering

Digital photoelasticity: Recent developments and diverse applications

The surface of a rectangular wing is morphed numerically at high angles of attack such that it still operates at the reduced coefficient of lift at which the baseline wing operates but while the flow is separated on the baseline wing, it remains attached on the morphed wing. The aerodynamic characteristics of the baseline wing are obtained experimentally and that of the morphed wing is obtained numerically. The morphed surface at high angles of attack is obtained using a novel ‘decambering’ technique, which accounts for the deviation of the coefficients of lift and pitching moment from that predicted by the potential flow. Two wings with different airfoil sections, N ACA0012 and N ACA4415 are tested and compared at high α. Numerical morphing of wing surface for design coefficient of lift (CL ) (in terms of percentage increment) is presented at angles of attack 50 and 150 . This concept of design CL of a morphing wing is one of the possible solutions to fly at different flight conditions with corresponding targets and maneuvering requirements. A significant addition to the present numerical approach is to provide some comparison of the flow separation behavior with CFD at the root section of both the wing sections. The effects of morphed surfaces on drag penalty, coefficient of lift and post-stall angles of attack are studied and compared in terms of aerodynamic performance. © 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

AIAA Scitech 2020 Forum

Numerical morphing of a rectangular wing to prevent flow separation

This paper uses a numerical post-stall predictive tool based on ‘decambering’ approach to study the aerodynamic characteristics of a lead-trail formation in pre and post-stall flow conditions. A basic lead-trail formation consisting of 2 wings and an extended formation consisting of 5 wings are studied with a view to the possibility of fuel savings, increase in range of operation, delayed flow separation and efficient positioning of the wings with respect to each other. Whether increasing the number of wings in a configuration is more useful is also looked into. The optimum operational angles of attack for maximum advantage in terms of fuel efficiency of all wings is studied including post-stall angles of attack. Numerical results for CL, CDi, section Cl distribution and their dependence on vertical offsets and angle of attack are reported. © 2019 Elsevier Masson SAS

Fulltext

European Journal of Mechanics, B/Fluids

Aerodynamic analysis of basic and extended lead-trail formation using numerical technique

Carbon capture and sequestration (CCS) is necessary to mitigate global warming caused by anthropogenic CO 2 emissions in the atmosphere. However, due to very high storage cost, it is difficult to sustain the CCS industry. The hot sedimentary and dry rock reservoirs with very high temperature can support both geothermal energy production, and carbon geosequestration economically, provided the CO 2 is used as a heat-carrying fluid with proper optimization of injection parameters according to reservoir conditions. In this paper we have reviewed past studies discussing the working mechanisms, pressure management strategies and various advantages of energy extraction from hydrothermal reservoirs by CO 2 plume geothermal technology and hot dry rock— enhanced geothermal system (EGS) technology. Past studies highlighted that due to very high thermal expansivity and mobility, supercritical CO 2 can produce more heat than water-EGS. For low enthalpy (around 50 ∘C) and shallow (0.5–1.5 km) reservoirs, CO 2 can fetch more heat than water because of higher heat capacity. Other advantages of CCS and EGS are (i) the production of brine or CO 2 assisting to manage the reservoir pressure and restrict the fluid interference with neighboring reservoirs, (ii) the fluid loss, which is a significant concern in a water-EGS but for CO 2-EGS it is environmentally friendly, and (iii) higher pressure and cold fluid injection induced geological deformation and microseismicity are relatively less for CO 2-EGS than water-EGS. In this paper, we have also discussed various challenges of CO 2-EGS to enable CCS in hydrothermal reservoir and hot dry rock system. © 2020, Springer Nature Switzerland AG.

GENERAL

Geomechanics and Geophysics for Geo-Energy and Geo-Resources

Potential of CO 2 based geothermal energy extraction from hot sedimentary and dry rock reservoirs, and enabling carbon geo-sequestration

Surfactant and polymer are used to improve oil recovery. The micro-emulsion phase composition, viscosity and interfacial tension vary with salinity and injection concentration of chemicals. The viscosity contrast which is very large for heavy oil reservoirs, results in various types of viscous instabilities. There is no comprehensive field-scale modelling on the viscous fingering affecting the oil recovery for different types of surfactant-polymer (SP) flooding. We numerically simulated the above phenomena for different types of SP flooding in five-spot wells setup for both water-wet and oil-wet reservoirs. We have observed that many saturation shocks and banks of micro-emulsion, water and polymer are formed. The viscous fingering at the interface of these banks depend on the reservoir wettability, micro-emulsion phase behaviour and injection concentration of chemicals. Fingering can be suppressed by changing the duration of injection and concentration of surfactant and polymer. We have shown that Type II(+) flooding produces more oil than Type II(−) and Type III. But the oil production by Type II(−) can be increased by adopting better injection strategies. We have made a quantitative comparison of output, i.e., oil recovery vs inputs such as injected mass of chemicals, injection duration and pumping energy, which is of interest to industry. The pumping energy requirement is higher for Type II(−) flooding irrespective of wettability. Our results show that short duration injection of surfactant with multistep reduction of polymer concentration suppresses viscous instabilities and produce more than 90% OOIP. © 2019, Springer Nature Switzerland AG.

Numerical analysis of viscous fingering and oil recovery by surfactant and polymer flooding in five-spot setup for water and oil-wet reservoirs

We study the expansion of a vortex ring generated due to the spreading of ethanol-water droplets, with ethanol concentration range of 20%≤Ce ≤ 100%, on the surface of a 50-mm-deep water layer. Once deposited on the water layer, the surface tension difference leads to some part of the lighter ethanol droplet spreading as a thin film over the water layer. We observe an expanding vortex ring below the radially spreading film front. We visualize the film spreading from top using aluminum particles, while the vortex is visualized from the side using polyamide particles with laser induced fluorescence (LIF) from the dyed drop used to distinguish the alcohol from the water. Particle image velocimetry (PIV) is used to obtain the velocity and the vorticity fields below the spreading film. Vortex regions and their centers, identified by the λ2 method from the velocity fields, are tracked to determine the vortex expansion. We show that the vortex ring expands with the same velocity of expansion as that of the spreading ethanol film at the free surface, possibly since the vortex ring is created due to the surface tension difference across the film front. Using dimensional arguments, we also propose a scaling for the upward velocity,uΓ, induced by this expanding vortex ring and show that uΓ ∼ t−1/2. © 2020 by Begell House, Inc.

Vortex ring below a spreading alcohol film on water

Fluid flow and heat transfer characteristics past four elliptic cylinders arranged in square configuration are numerically investigated in this study. An in-house finite element method code based on streamline upwind Petrov - Galerkin algorithm has been used for simulations of two-dimensional, incompressible and laminar flow of air. Analyses are carried out by changing geometric parameters such as spacing ratio, axis ratio and incident angle. Results in terms of vorticity and temperature contours, Strouhal number, drag and lift coefficients and Nusselt number are studied for all cases. These results show that fluid flow patterns are strongly influenced by geometric parameters, based on which flow can be categorized into different types. A critical spacing ratio is found for some of the configurations, where a steep increase in drag coefficient is encountered. From this study, it is observed that incident angle 22.5 degree gives a higher heat transfer rate compared to the other two configurations (0 and 45 degree). Also, elliptic cylinders (axis ratio of 0.8 and 0.5) have similar Nusselt number value with less drag force compared to circular cylinders (axis ratio of 1.0) which justifies the utilization of elliptic cylinders as an alternative for circular ones. © 2020 Taylor &amp; Francis Group, LLC.