Department of Mechanical Engineering

Indian Institute of Technology Palakkad&nbsp;(IIT Palakkad or IIT PKD) is a public autonomous&nbsp;engineering&nbsp;and&nbsp;research&nbsp;institute located in&nbsp;Palakkad,&nbsp;Kerala. It was&nbsp;one of the five new&nbsp;IITs&nbsp;proposed in the&nbsp;2014 Union budget of India. The campus was inaugurated on 3 August 2015. The institute has 94 faculty, 978 students, and 63 non-teaching staffs.

IT Palakkad currently offers four-year Bachelor of Technology (B.Tech) and two years MS programmes in 8 different engineering disciplines including&nbsp;Computer Science, Electrical, Mechanical, Civil among others.

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IIT Palakkad

The present work proposes a design procedure along with guidelines for the choice of initial clearance of a typical rotating gas turbine seal in a secondary air system. The basis for the design is to prevent seal rubbing against stator, by ensuring that the centrifugal and thermal growths of the seal are within the safe operating limits. As a case study, a six-tooth straight-through rotating labyrinth seal configuration is considered with wide ranging seal parameters, namely the seal inner radius (25-700 mm), speed (1000-5000 rad/s), temperature (200-650 °C) and pressure ratio (1.1-2.5). By means of an iterative process, which involves computational fluid dynamics and finite element analysis techniques, and with a choice of initial clearance, an extensive database is generated. The results are presented in terms of non-dimensional variables, namely seal clearance ratio, centrifugal growth ratio, thermal growth ratio, operating clearance ratio due to centrifugal growth and operating clearance ratio due to thermal growth. It is found that the value of clearance ratio depends significantly on the dimensionless radial position. For a seal clearance ratio of 0.01, at 3000 rad/s, the leakage flow rate gets reduced by 18 and 4%, respectively for pressure ratios of 1.1 and 2.5, when the centrifugal growth alone is considered. When both centrifugal and thermal growths are considered, the percentage reduction becomes about 70% for the same seal operating at 3000 rad/s and 204 °C, and it is as high as 95% at 426 °C. © 2016 Institution of Mechanical Engineers.

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Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

On the choice of initial clearance and prediction of leakage flow rate for a rotating gas turbine seal

A major part of the domestic and the industrial thermal energy requirement for the heating purpose is achieved by the combustion of hydrocarbon fuels using burners. The present study reveals that thermal characterisation of impinging flame jets can be performed with a steady state technique similar to thin metal foil technique used for impinging air jets. The target surface impinged by the premixed methane-air flame jet is simultaneously cooled from the rear side by impinging air jets at different Reynolds number. One dimensional energy balance across the thickness of the plate is performed. The Nusselt number and the effectiveness distributions for a tube burner with the present technique matched reasonably well with the two-equation technique proposed in our previous work. Maximum deviations of 12% and 15% are observed for Nu and η respectively. Correlations are developed for the local Nusselt number and effectiveness in terms of flame jet parameters. The burner is analysed for the thermal efficiency. For premixed cone flames, it is observed that the thermal efficiency increases with the Reynolds number and equivalence ratio and decreases with the burner tip to plate spacing. © 2016 Elsevier Ltd. All rights reserved.

Applied Thermal Engineering

Air jet impingement technique for thermal characterisation of premixed methane-air impinging flame jets

The jet impingement heat transfer is a well-established technique for obtaining high heat transfer rates for many cooling and heating applications. Impingement heat transfer methods are widely used in domestic and industrial appliances. The impinging isothermal gas jets are used for both heating and cooling. However, premixed flame jets are used for heating the target surface. Present study is an attempt to compare the heat transfer characteristics of the isothermal air jets and premixed flame jets. The isothermal air jet having jet temperature of 30 °C (cold jet or ambient temperature jet), 100 °C (hot jet), and premixed methane-air flame jet (stoichiometric mixture) with Reynolds numbers of 500, 750, 1000, 1250 and 1500 and nozzle or burner to plate spacings of 2d, 4d and 6d are experimentally investigated for heat transfer characterisation. Thin metal foil technique is used for characterising isothermal air jets. For a fixed jet Reynolds number, the Nusselt number of isothermal air jet is found independent of the temperature difference between jet and surrounding fluid. A steady state technique is proposed for characterisation of premixed flame jets. The outcome of the present study reveals that the heat transfer characteristics of isothermal air jet and the premixed flame jet are almost same. The higher thermal entrainment in premixed flame jet in comparison with isothermal air jet results in a lower effectiveness. The present heat transfer data can be directly utilised for many practical applications. © 2015 Elsevier Masson SAS.

International Journal of Thermal Sciences

Isothermal air jet and premixed flame jet impingement: Heat transfer characterisation and comparison

Faults such as misalignment, rotor cracks and rotor to stator rub can exist collectively in rotor bearing systems. It is an important task for rotor dynamic personnel to monitor and detect faults in rotating machinery. In this paper, the rotor startup vibrations are utilized to solve the fault identification problem using time frequency techniques. Numerical simulations are performed through finite element analysis of the rotor bearing system with individual and collective combinations of faults as mentioned above. Three signal processing tools namely Short Time Fourier Transform (STFT), Continuous Wavelet Transform (CWT) and Hilbert Huang Transform (HHT) are compared to evaluate their detection performance. The effect of addition of Signal to Noise ratio (SNR) on three time frequency techniques is presented. The comparative study is focused towards detecting the least possible level of the fault induced and the computational time consumed. The computation time consumed by HHT is very less when compared to CWT based diagnosis. However, for noisy data CWT is more preferred over HHT. To identify fault characteristics using wavelets a procedure to adjust resolution of the mother wavelet is presented in detail. Experiments are conducted to obtain the run-up data of a rotor bearing setup for diagnosis of shaft misalignment and rotor stator rubbing faults. © 2015 Elsevier Ltd. All rights reserved.

Mechanical Systems and Signal Processing

Fault detection in rotor bearing systems using time frequency techniques

Laser-light diffusers are used in conjunction with pulsed lasers to generate bright, spatially uniform background illumination for imaging and particle sizing applications. The present paper describes a cost effective way of fabricating a fluorescent laser-light diffuser. The procedure to obtain a uniform background using laser illumination is explained. To characterize the diffuser, images are acquired using a CCD camera with the illumination provided using the diffuser and the variations of pixel intensity values along the centerline of the images are plotted. It is observed that the standard deviation of pixel intensity values is fairly small. Hence, these diffusers are suitable for experiments that need a uniform background. © 2016 IOP Publishing Ltd.

Measurement Science and Technology

A fluorescent laser-diffuser arrangement for uniform backlighting

Underwater vehicles are usually designed with additional degrees of freedom than those required to accomplish given manipulator tasks. A robot platform should be effective to maintain its position and orientation in order to attain diverse underwater tasks. This study addresses the dynamic modeling of an autonomous underwater vehicle (AUV) which consists of tilting thrusters for hovering motion to oppose reaction force of the manipulator and ocean current. The suggested system consists of four tilting thrusters with six degrees-of-freedom (DOF). The tilting movements of the thrusters make the system unstable due to complex coupling. A robust position tracking controller is designed based on redundancy resolution scheme has been posited. The trajectory tracking potentiality of the manipulator has been analyzed. The numerical results of the proposed redundancy resolution scheme indicate that this approach shows a significantly revamped outcome when compared with the conventional counterpart. © 2016 IEEE.

OCEANS 2016 - Shanghai

Task space position tracking control of an autonomous underwater vehicle with four tilting thrusters

Currently, the manufacturing sector is adapting sustainable techniques to minimise the damage to the environment. Minimum quantity lubrication (MQL) is one of the sustainable techniques to address the ecological and economic issues. In MQL atomised mixture of cutting fluid and compressed air is injected into the machining zone. The effectiveness of MQL technique primarily depends on the quality of the mixture which mainly depends upon the droplet quality. In this work, a combination of microscopy and image processing techniques has been used to ascertain the quality of droplets. The raw droplet features captured with a stereo-zoom microscope and analysed by measuring the average droplets size and number of droplets per unit area. To ensure the enhanced effectiveness of MQL parameters like droplets quality, air pressure, flow rate and nozzle positions have been optimised experimentally. Further, obtained optimal MQL parameters have been used in the grindability study of Inconel 718. © Copyright 2016 Inderscience Enterprises Ltd.

International Journal of Machining and Machinability of Materials

An alternate method for optimisation of minimum quantity lubrication parameters in surface grinding

Fatigue failure occurs in components subjected to cyclic loading in various applications. To reduce the fatigue failure of components compressive residual stresses in the material plays an important role. There are mechanical surface treatment processes to induce compressive residual stress in the materials up to certain depth by which fatigue life of the component can be increased. Among that, Laser shock processing (LSP) is one of the surface treatment processes that improve fatigue life of the component. In LSP, a target component coated with a sacrificial layer is subjected to high power laser short duration pulse. This causes shock waves which induce compressive residual stresses in the component. For optimising the LSP process parameters simulation is widely used with complex physics model of the process and predict its outcome. This paper discusses the various input parameters required for LSP simulation and the commonly used mesh representations and material models. It also reviews the different simulation procedures used to simulate single as well as multiple laser impacts. © 2016 Elsevier Ltd. All rights reserved.

Materials Today: Proceedings

Modeling and Strategies for Laser Shock Processing

Inconel 706 superalloy has established itself in the field of gas turbine industry because of its easy fabricability combined with high mechanical strength. Due to its high stress rupture and tensile yield strength, conventional machining of this superalloy exhibits poor surface and low dimensional accuracy of the machined components. It is well known that most of the gas turbine components include complex shaped profile with high precision and hence, wire electrical discharge machining (WEDM) of Inconel 706 has been performed to achieve the feasibility in manufacturing of complex shaped components for gas turbine application. In the current investigation, the effect of wire diameter on WEDM performance characteristics such as cutting speed, surface roughness, surface topography, recast layer formation, microhardness, microstructural and metallurgical changes have been evaluated. It was investigated that smaller diameter wire is advantageous over the larger diameter wire since it improves productivity as well as surface quality of the machined components under the same settings of control parameters. In addition, smaller diameter wire has shown comparatively lower recast layer thickness, minimum hardness alteration and shorter manufacturing time. The XRD result has confirmed the presence of residual stress within WED machined component. © 2016 The Society of Manufacturing Engineers

Journal of Manufacturing Processes

Effect of wire diameter on surface integrity of wire electrical discharge machined Inconel 706 for gas turbine application

Gasketed flange joints are usually subjected to internal pressure at high temperature. The most important requirement of flange joint is to provide leak-free joint under operating condition. In the present study, temperature-dependent nonlinear gasket properties of spiral-wound gasket at elevated temperatures are obtained experimentally and included in the analysis. The relaxation of gasket contact stress in both single and twin-gasketed joints at elevated temperatures is compared. It is observed that the ability to withstand internal pressure decreases with increase in temperature in both single and twin-gasketed flange joints. But, the twin-gasketed flange joint is found to withstand higher internal pressure than single-gasketed joint at a given bolt preload and temperature. The influence of gasket seating surface rotation on the distribution of gasket radial contact stress at elevated temperature is studied. The effect of elevated temperature on flange stresses of twin-gasketed joint is also examined. © Institution of Mechanical Engineers.