N. Asok Kumar

Bio: N. Asok Kumar is an academic researcher from College of Engineering, Trivandrum. The author has contributed to research in topics: Shock tube & Mach number. The author has an hindex of 2, co-authored 8 publications receiving 40 citations.

Reacting Flow Simulation of Rocket Nozzles

Abstract: Reacting flow simulation of high area ratio rocket nozzles is done using an indigenously developed Point Implicit Unstructured Finite Volume Solver. A numerical solution procedure to solve turbulent-reacting nozzle flow field is developed, which is based on the implicit treatment of chemical source terms by preconditioning and then explicitly solved along with unsteady turbulent Navier-Stokes equations. Chemical equilibrium was assumed in the nozzle inlet and the properties of combustion products and species concentration resulting in thrust chamber are obtained using chemical equilibrium composition code. Using this equilibrium composition as boundary conditions at inlet and ambient pressure conditions at exit, the present turbulent—reacting flow solver was able to successfully simulate nozzle flow field and predicted the delivered specific impulse.

Application of the Point Stress Criterion to Assess the Bond Strength of a Single-Lap Joint

Abstract: Finite element analysis has been carried out to obtain the interfacial stresses in a single lap joint using a special 6-node isoparametric element for adhesive layer. The analysis results are found to be in good agreement with the closed-form solution of Goland and Reissner. The peak normal and shear stresses found in the adhesive layer at the edges of the joint are due to stress singularity. The bond strength of the single-lap joint is estimated considering one of the stress fracture criteria known as the point stress criterion. Bond strength estimates are found to be reasonably in good agreement with existing test results.

Performance evaluation of shock tube with helium and carbon dioxide using numerical simulation

Abstract: This work deals with the performance of the shock tube with helium and carbon dioxide as working fluids at different diaphragm pressure ratios using numerical simulation. A two-dimensional planar geometry of the shock tube is considered for the study. An inviscid time accurate model is developed to find the effects of diaphragm pressure ratios on the shock Mach number, temperature behind the incident and reflected shocks.. This numerical model is validated analytically as well as experimentally with air as working gas. Simulations were conducted for same and different driver/driven gas combinations with helium and carbon dioxide test gases using this model. Simulations were carried out using CFD solver FLUENT. Adaptive Mesh Refinement (AMR) technique was applied to accurately capture and resolve shock and contact discontinuities. At lower pressure ratios the different gas model is able to produce 20.4% and at higher diaphragm pressure ratios up to 33% increase in shock Mach number when compared to the similar driver-driven gas model.

Energy-exergy analysis and modernization suggestions for a combined-cycle power plant

Abstract: Energy and exergy analysis were carried out for a combined-cycle power plant by using the data taken from its units in operation to analyse a complex energy system more thoroughly and to identify the potential for improving efficiency of the system In this context, energy and exergy fluxes at the inlet and the exit of the devices in one of the power plant main units as well as the energy and exergy losses were determined The results show that combustion chambers, gas turbines and heat recovery steam generators (HRSG) are the main sources of irreversibilities representing more than 85% of the overall exergy losses Some constructive and thermal suggestions for these devices have been made to improve the efficiency of the system Copyright © 2005 John Wiley & Sons, Ltd

Determination of Scattering and Absorption Coefficients for Plasma‐Sprayed Yttria‐Stabilized Zirconia Thermal Barrier Coatings

Abstract: Prediction of radiative transport through translucent thermal barrier coatings (TBCs) can only be performed if the scattering and absorption coefficients and index of refraction of the TBC are known. To date, very limited information on these coefficients, which depend on both the coating composition and the microstructure, has been available for the very commonly utilized plasma-sprayed 8 wt% yttria-stabilized zirconia (8YSZ) TBCs. In this work, the scattering and absorption coefficients of freestanding plasma-sprayed 8YSZ coatings were determined from room-temperature normal-incidence directional-hemispherical reflectance and transmittance spectra over the wavelength range from 0.8 to 7.5 μm. Spectra were collected over a wide range of coating thickness from 60 to almost 900 μm. From the reflectance and transmittance spectra, the scattering and absorption coefficients as a function of wavelength were obtained by fitting the reflectance and transmittance values predicted by a four flux model to the experimentally measured values at all measured 8YSZ thicknesses. While the combined effects of absorption and scattering were shown in general to exhibit a nonexponential dependence of transmittance on specimen thickness, it was shown that for sufficiently high absorption and optical thickness, an exponential dependence becomes a good approximation. In addition, the implications of the wavelength dependence of the plasma-sprayed 8YSZ scattering and absorption coefficients on (1) obtaining accurate surface-temperature pyrometer measurements and on (2) applying mid-infrared reflectance to monitor TBC delamination are discussed.

Thermophysical properties of matter - the TPRC data series. Volume 8. Thermal radiative properties - nonmetallic solids. (Reannouncement). Data book

Abstract: Abstract : The TPRC Data Series published in 13 volumes plus a Master Index volume constitutes a permanent and valuable contribution to science and technology. This 17,000 page Data Series should form a necessary acquisition to all scientific and technological libraries and laboratories. These volumes contain an enormous amount of data and information for thermophysical properties on more than 5,000 different materials of interest to researchers in government laboratories and the defense industrial establishment. Volume 8 in this 14 volume TPRC Data Series covers seven nonmetallic elements (including 18 varieties of graphite), 46 simple oxides, six groups of mixtures of simple oxides, 59 complex oxides and salts, 185 nonmetallic compounds, 19 groups of intermetallic compounds, 13 groups of cermets, nine groups of pressed nonmetal- metal powder mixtures, 14 groups of miscellaneous mixtures, 14 kinds of glasses, nine kinds of minerals and rocks, and 10 groups of polymers. Data for some of the materials have been critically evaluated and analyzed data graphs are presented in addition to the original experimental data.

Literature Survey of Numerical Heat Transfer (2000–2009): Part II

Abstract: A comprehensive survey of the literature in the area of numerical heat transfer (NHT) published between 2000 and 2009 has been conducted Due to the immenseness of the literature volume, the survey