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

Experiments are carried out in the IISc hypersonic shock tunnel, to understand the gasdynamic phenomenon associated with the presence of a thermal bump in a hypersonic flow field over a flat plate with sharp leading edge. A region (27mm × 4 mm) of high temperature (1200 K) within the thermal boundary layer located 42 mm from leading edge of the flat plate is generated using heating element mounted in flush with the surface and this region is referred here as 'thermal bump". Surface heat transfer rate measurements using platinum thin film sensors and surface static pressure measurements using miniature pressure sensors are carried out to understand effect of 2-D thermal hot spot on the flat plate flow field at Mach 7.4 (with air as test gas) and 12.6 (with argon as test gas) in the shock tunnel. A commercially available glow plug (DC 10 V, 10 A, temperature of 1200 K) has been used to generate a high temperature zone near the leading edge of the flat plate. Although there are local variations (∼ 10-15%) in the measured values of static pressure and surface convective heating rates because of thermal bump on an average the distribution of flow parameters on the flat plate remains unaltered within the measurement uncertainties. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

Department of Aerospace Engineering

World University root node

Department of Mechanical Engineering

47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition

Experimental Investigations on the Effect of a Thermal Bump in the Hypersonic Flow Around a Flat Plate

An experimental investigation of aerodynamic drag reduction by counter flow plasma jet injection from the stagnation region of a hemispherical blunt cylinder model flying at hypersonic Mach numbers are presented. Experiments are carried out in a hypersonic shock tunnel at four different jet- to-pitot pressure ratio and different supply powers. The flow fields around the test model are visualized using high speed schlieren technique. Direct force measurement is also performed using a single component accelerometer balance. The weakly ionized argon plasma jet has an electron temperature around 6400K and electron number density ∼4.9×1015 cm-3. With plasma jet at pressure ratio 72.5 and 1.8 KW supply power the reduction in drag is found to be ∼28% (more than its cold jet counter part) although the plasma jet momentum is less than its cold jet counter part. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

Shock tunnel studies on drag reduction of a blunt body using argon plasmajet

An experimental investigation of aerodynamic drag reduction by counter flow plasma jet injection from the stagnation region of a hemispherical blunt cylinder model flying at hypersonic Mach numbers are presented. Experiments are carried out in a hypersonic shock tunnel at four different jet-to-pitot pressure ratios namely 15·3, 24·52, 72·5 and 96·67 and three supply powers, namely 1·8KW, 2·7KW and 3·6KW. The flow fields around the test model are visualised using high speed schlieren technique. Direct force measurement is also performed using a single component accelerometer balance. The weakly ionised argon plasma jet has an electron temperature around 6,400K and electron number density ∼1.64 × 10 15cm-3. With plasma jet at pressure ratio 72·5 and 1·8KW supply power the reduction in drag is found to be ∼28% (more than its cold jet counter part) although the plasma jet momentum is less than its cold jet counter part.

Aeronautical Journal

Effect of counterflow argon plasma jet on aerodynamic drag of a blunt body at hypersonic Mach numbers

A simple acceleration of convergence technique known as the 'ε-convergence algorithm' (ea) is applied to determine the critical temperatures and exponents. Several illustrations involving well-known series expansions appropriate to two- and three-dimensional Ising models, three-dimensional Heisenberg models, etc., are given. Apart from this, a few recently studied ferrimagnetic systems have also been analysed to emphasise the generality of the approach. Where exact solutions are available, our estimates obtained from this procedure are in excellent agreement. In the case of other models, the critical parameters we have obtained are consistent with other estimates such as those of the Padé approximants and group theoretic methods. The same procedure is applied to the partial virial series for hard spheres and hard discs and it is demonstrated that the divergence of pressure occurs when the close-packing density is reached. The asymptotic form for the virial equation of state is found to be P/ρkT ∼ (1 -ρ/ρc-1 for hard spheres and hard discs. Apart from the estimation of 'critical parameters', we have applied the ea and the parametrised Euler transformation to sum the partial, truncated virial series for hard spheres and hard discs. The resulting values of pressure so obtained, compare favourably with the molecular dynamics results. © 1984 Indian Academy of Sciences.

Department Of Chemistry

Pramana

Perturbation expansions and series acceleration procedures. Part I. ε-convergence and critical parameters

A lattice formalism using "spin variables" is employed to analyse multi-state models for the adsorption of neutral dipoles. In particular, a spin-1/2 (two-state) model incorporating permanent and induced dipole moments of the solvent and the organic adsorbate, substrate interactions, and discreteness of charge effects is analysed. The resulting Generalized Ising Hamiltonian is solved under mean field approximation (MFA) in order to derive the adsorption isotherm for organic molecules. A few spin-1 (three-state) models are also analysed under MFA to describe the competitive adsorption of multi-state solvent and organic dipoles, and the appropriate equilibrium relations are derived. The unification and isomorphosm existing at the Hamiltonian level for several diverse realizations, such as adsorption of ions and solvent/organic molecules, is indicated. The possibility of analysing phase transitions using this generalized approach is briefly indicated. © 1984 Elsevier Sequoia S.A.

Journal of Electroanalytical Chemistry

Adsorption isotherms-Microscopic modelling. Part II

A simple three-state model permitting two different configurational states for the solvent, together with one for the organic adsorbate, is analysed to derive the adsorption isotherm. The implications of this model regarding pseudo-two-state and pseudo-Frumkin adsorption isotherms are indicated. A critique of the earlier theory of Bockris, Devanathan and Müller is presented in brief. © 1984 Elsevier Sequoia S.A.

Adsorption isotherms for neutral organic compounds-A hierarchy in modelling. Part III

A two-state model allowing for size disparity between the solvent and the adsorbate is analysed to derive the adsorption isotherm for electrosorption of organic compounds. Explicity, the organic adsorbate is assumed to occupy "n" lattice sites at the interface as compared to "one" by the solvent. The model parameters are the respective permanent and induced dipole moments apart from the nearest neighbour distance. The coulombic interactions due to permanent and induced dipole moments, discreteness of charge effects, and short-range and specific substrate interactions have all been incorporated. The adsorption isotherm is then derived using mean field approximation (MFA) and is found to be more general than the earlier multi-site versions of Bockris and Swinkels, Mohilner et al., and Bennes, as far as the entropy contributions are concerned. The role of electrostatic forces is explicity reflected in the adsorption isotherm via the Gibbs energy of adsorption term which itself is a quadratic function of the electrode charge-density. The approximation implicit in the adsorption isotherm of Mohilner et al. or Bennes is indicated briefly. © 1984 Elsevier Sequoia S.A.

Adsorption isotherms for neutral organic compounds-A hierarchy in modelling. Part II

The relations for the inner layer potential difference (E) in the presence of adsorbed organic molecules are derived for three hierarchical models, in terms of molecular constants like permanent dipole moments, polarizabilities, etc. It is shown how the experimentally observed patterns of the E vs. θ plots (linear in all ranges of σM, non-linear in one or both regions of σM, etc.) can be understood in a semi-quantitative manner from the simplest model in our hierarchy, viz. the two-state site parity version. Two-state multi-site and three-state (site parity) models are also analysed and the slope (∂E/∂θ)σM tabulated for these also. The results for the Esin-Markov effect are derived for all the models and compared with the earlier result of Parsons. A comparison with the GSL phenomenological equation is presented and its molecular basis, as well as the limitations, is analysed. In particular, two-state multi-site and three-state (site parity) models yield E-σM relations that are more general than the "unified" GSL equation. The possibility of viewing the compact layer as a "composite medium" with an "effective dielectric constant" and obtaining novel phenomenological descriptions is also indicated. © 1984 Elsevier Sequoia S.A.

Adsorption isotherms for neutral organic compounds-A hierarchy in modelling. Part V. Models for the inner layer potential difference in the presence of dipolar adsorption

Three new procedures for the extrapolation of series coefficients from a given power series expansion are proposed. They are based on (i) a novel resummation identity, (ii) parametrised Euler transformation (pet) and (iii) a modified pet. Several examples taken from the Ising model series expansions, ferrimagnetic systems, etc., are illustrated. Apart from these applications, the higher order virial coefficients for hard spheres and hard discs have also been evaluated using the new techniques and these are compared with the estimates obtained by other methods. A satisfactory agreement is revealed between the two. © 1984 the Indian Academy of Sciences.

Perturbation expansions and series acceleration procedures: Part-II. Extrapolation techniques

The charge at which adsorption of organic compounds attains a maximum (σmaxM) at an electrochemical interface is analysed using several multi-state models in a hierarchical manner. The analysis is based on statistical mechanical results for the following models: (A) two-state site parity, (B) two-state multi-site, and (C) three-state site parity. The coulombic interactions due to permanent and induced dipole effects (using mean field approximation), electrostatic field effects and specific substrate interactions have been taken into account. The simplest model in the hierarchy (two-state site parity) yields the explicit dependence of σmaxM on the permanent dipole moment, polarizability of the solvent and the adsorbate, lattice spacing, effective coordination number, etc. Other models in the hierarchy bring to light the influence of the solvent structure and the role of substrate interactions, etc. As a result of this approach, the "composition" of σmaxM in terms of the fundamental molecular constants becomes clear. With a view to use these molecular results to maximum advantage, the derived results for σmaxM have been converted into those involving experimentally observable parameters like C0, C1, EN, etc. Wherever possible, some of the earlier phenomenological relations reported for σmaxM, notably by Parsons, Damaskin and Frumkin, and Trasatti, are shown to have a certain molecular basis, viz. a simple two-state site parity model. As a corollary to the hierarchical modelling, σmaxM and the potential corresponding to it (Emax) are shown to be constants independent of θmax or corg for all models. The implication of our analysis for σmaxM with respect to that predicted by the generalized surface layer equation (which postulates σmax and Emax variation with θ) is discussed in detail. Finally we discuss in passing σminM and the electrosorption valency in this context. © 1984 Elsevier Sequoia S.A.

Adsorption isitherms for neutral organic compounds-A hierarchy in modelling. Part IV. Charge of maximum adsorption-Statistical mechanical basis

A simple two-state statistical mechanical model ascribing one configurational state each to the solvent and the adsorbate and site parity between them is analysed and solved under mean field approximation. The input parameters of the model are: (i) the permanent dipole moments of the solvent and the adsorbate; (ii) the respective polarizabilities; and (iii) the nearest neighbour distance. The interactions taken into account are: (a) the coulombic interactions due to permanent and induced dipole effects: (b) the discreteness of the charge effects; and (c) the specific substrate interactions. The resulting adsorption isotherm is non-congruent and more general than the classical Frumkin isotherm thereby providing a molecular basis for the latter. It is shown how a pseudo-Frumkin interaction constant that quadratically depends on the electrical variable can arise purely from polarizability differences between the solvent and the adsorbate. Many equivalent forms of the adsorption isotherm are also reported and the criteria for charge congruence and the potential congruence are analysed in the light of this new isotherm. © 1984 Elsevier Sequoia S.A.

Adsorption isotherms for neutral organic compounds-A hierarchy in modelling. Part I

Three new procedures - in the context of estimation of virial coefficients and summation of the partial virial series for hard discs and hard spheres - are proposed. They are based on the parametrised Euler transformation, a novel resummation, identity and the εlunate-convergence methods respectively. A comparison with other estimates (molecular dynamics, graph theory and empirical methods) reveals satisfactory agreement. © 1983.

Physics Letters A

Extrapolation and series acceleration procedures: Hard spheres and discs as illustrations

A simple ε-convergence technique is applied to obtain accurate estimates of critical temperatures and critical exponents of a few two- and three-dimensional Ising models. When applied to the virial series for hard spheres and hard discs, this method predicts a divergence of the equation-of-state at the density of closest packing. © 1983.