Department of Mechanical Engineering

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Micro shock tubes are widely employed in many micro instruments which require high speed and high temperature flow field. The small flow dimension introduces additional flow physics such as rarefaction effects, viscous effects etc, which makes the micro shock tube different from conventional macro shock tubes. In the present study, a numerical investigation of the flow physics associated with shock propagation and reflection inside micro shock tubes was carried out using unsteady Navier Stokes equations. Maxwell's slip boundary conditions were incorporated to simulate the rarefaction effects produced due to low pressure and very small length scale. The effect of initial pressures on the shock propagation was investigated keeping the pressure ratio constant. The dependency of the shock tube diameter on shock propagation was also investigated. The results show that shock strength attenuates drastically in a micro shock tube compared to macro shock tubes. The viscous boundary layer becomes a governing parameter in controlling micro shock tube wave propagations. The implementation of slip velocity to model rarefaction effects increases the shock strength and aids in shock wave propagation. The simulation with slip wall exhibits a wider hot zone (shock-contact distance) compared to no-slip simulation. The contact surface propagation distance reduces under the slip effects. A drastic attenuation in shock propagation distance was observed with reduction in diameter. The shock wave when reflected from the end wall inhibits the rarefaction effects, generally happening at very low pressure micro shock tubes, and the associated slip effect vanishes for the post reflected shock flow field. © 2013 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

World University root node

Journal of Mechanical Science and Technology

Computational study of the unsteady flow characteristics of a micro shock tube

We experimentally study the effect of having hinged leaflets at the jet exit on the formation of a two-dimensional counter-rotating vortex pair. A piston-cylinder mechanism is used to generate a starting jet from a high-aspect-ratio channel into a quiescent medium. For a rigid exit, with no leaflets at the channel exit, the measurements at a central plane show that the trailing jet in the present case is never detached from the vortex pair, and keeps feeding into the latter, unlike in the axisymmetric case. Passive flexibility is introduced in the form of rigid leaflets or flaps that are hinged at the exit of the channel, with the flaps initially parallel to the channel walls. The experimental arrangement closely approximates the limiting case of a free-to-rotate rigid flap with negligible structural stiffness, damping and flap inertia, as these limiting structural properties permit the largest flap openings. Using this arrangement, we start the flow and measure the flap kinematics and the vorticity fields for different flap lengths and piston velocity programs. The typical motion of the flaps involves a rapid opening and a subsequent more gradual return to its initial position, both of which occur when the piston is still moving. The initial opening of the flaps can be attributed to an excess pressure that develops in the channel when the flow starts, due to the acceleration that has to be imparted to the fluid slug between the flaps. In the case with flaps, two additional pairs of vortices are formed because of the motion of the flaps, leading to the ejection of a total of up to three vortex pairs from the hinged exit. The flaps' length (Lf) is found to significantly affect flap motions when plotted using the conventional time scale L/d, where L is the piston stroke and d is the channel width. However, with a newly defined time scale based on the flap length (L/Lf), we find a good collapse of all the measured flap motions irrespective of flap length and piston velocity for an impulsively started piston motion. The maximum opening angle in all these impulsive velocity program cases, irrespective of the flap length, is found to be close to 15°. Even though the flap kinematics collapses well with L/Lf, there are differences in the distribution of the ejected vorticity even for the same L/Lf. Such a redistribution of vorticity can lead to important changes in the overall properties of the flow, and it gives us a better understanding of the importance of exit flexibility in such flows. © 2013 Cambridge University Press.

Journal of Fluid Mechanics

Effect of hinged leaflets on vortex pair generation

Buoyant jets in natural ventilation of a model room with water as the fluid medium have been studied. A constant heat flux has been maintained on the bottom surface of the room. The buoyancy causes flow to enter through the bottom opening and leave through the top opening. The shadowgraph technique is used for visualization. At the inlet, a negatively buoyant jet is observed, whereas a positively buoyant jet is observed at the outlet. The theoretical results for the centerline trajectories of these buoyant jets using both Gaussian and top-hat profiles are discussed considering the variation of the entrainment coefficient with the local Froude number and the variation of the spreading ratio of buoyancy to velocity profile with the distance from the source. The shape of the profiles is found to evolve from top-hat to Gaussian geometry. © 2013 Elsevier Ltd. All rights reserved.

International Journal of Heat and Mass Transfer

Study of buoyant jets in natural ventilation of a model room

The flow produced by a rigid symmetric NACA0015 airfoil purely pitching at a fixed location in quiescent fluid (the limiting case of infinite Strouhal number) is studied using visualizations and particle image velocimetry. A weak jet is generated whose inclination changes continually with time. This meandering is observed to be random and independent of the initial conditions, over a wide range of pitching parameters. © 2013 American Institute of Physics.

Physics of Fluids

Jet meandering by a foil pitching in quiescent fluid

International Syposium of Infromation and Production Systems 2013, Fukuoka

Identification of Industrial Robot Using Vision

This paper presents dynamics algorithms for multibody systems using the concepts of kinematic modules and Decoupled Natural Orthogonal Complement (DeNOC) matrices. A multibody system is treated as open-loop serial- or tree-type consisting of several modules, where each module consists of one or more than one serially connected links. In fact, it is shown how the knowledge for a serial system can be extended to a module of a tree-type system. The resulting equations are used to obtain recursive inverse and forward dynamics algorithms at inter- and intra-modular levels The methodology is illustrated using a tree-type four Degrees-of-Freedom (DoF) robotic gripper and 100-DOF serial-type rope system. It is also shown how efficiency of the proposed algorithm benefits as the DOF of a system becomes very large. © KRISHTEL eMAGING SOLUTIONS PRIVATE LIMITED.

Advances in Vibration Engineering

Dynamics algorithms for multibody systems

Based on the recursive algorithms presented in Chaps. 6 and 7, a Recursive Dynamics Simulator (ReDySim) is developed in MatLab (2009) platform for analyses of fixed- and floating-base tree-type, and closed-loop systems. Its usage is shown in this chapter. © 2013, Springer Science+Business Media Dordrecht.

Intelligent Systems, Control and Automation: Science and Engineering

Recursive Dynamics Simulator (ReDySim)

In this chapter, dynamic analyses of fixed-base robotic systems are presented using the dynamic modeling presented in Chap. 5. For this, recursive inverse and forward dynamics algorithms are developed. The algorithms take care of the multiple-DOF joints in an efficient manner, as explained in Sect. 4.2.1; in contrast to treating them as a combination of several 1-DOF joints by taking into account the total number of links equal to number of 1-DOF joints or joint variables. In the presence of many multiple-DOF joints in a robotic system the latter approach is relatively inefficient due to the burden of unnecessary computations with zeros. The improvement in the computational efficiency in the presence of multiple-DOF joints are addressed in this chapter. Dynamic analyses, namely, the inverse and forward dynamics, of several systems are performed in this chapter. © 2013, Springer Science+Business Media Dordrecht.

Recursive Dynamics for Fixed-Base Robotic Systems

Fluxes in submerged arc welding of high-strength low-alloy steels are not readily available, flux compositions are not clear and compositions are patented. This study aims at the design, development and optimization of flux for submerged arc welding of high-strength low-alloy steel. Extreme vertices design suggested by McLean and Anderson is used to formulate twenty-one fluxes to study the effect of flux constituents on tensile strength, percentage elongation, impact strength, diffusible hydrogen content and microstructure of the weld metal. Mathematical models for ultimate tensile strength, percentage elongation, impact strength and diffusible hydrogen content for welded specimens versus flux constituents have been developed. From the experiments, it is found that tensile strength and elongation are affected the most with Al 2O3 content, whereas CaO and CaF2 contents have significant effect on impact strength. Synergic binary effect of CaO·CaF2, CaO·MgO and Al2O 3·CaF2 mixtures is more than other binary mixtures on the mechanical properties. Developed regression models have been checked for adequacy using t-test for regression coefficients and analysis of variance (F-test) for whole regression equation. Finally, optimum flux composition giving optimum mechanical and microstructural characteristics is suggested. © 2013 IMechE.

Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture

Investigation on flux design for submerged arc welding of high-strength low-alloy steel

High carbon steels are more difficult to weld than low and medium carbon steels due to its high hardness because of the presence of the high carbon content in it which results in crack formation during the cold working. The present work aims at studying the mechanical behavior of high carbon steel welds with a variation of welding parameters and surface heat treatment processes and relating their effects on the mechanical properties of the material In this work, high carbon steel with 0.90 wt pet C is used as the specimen material. The specimens are prepared using different arc welding parameters followed by heat treatment in the furnace for 700°C, 800°C for 60 and 120 minutes. The mechanical properties of these specimens are measured and analyzed to estimate the effect of variation of process parameters.