Journal Articles

Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/123456789/19884

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Subject: search.filters.subject.Numerical investigations

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    Study on shelter effect of solid wind fences
    (2011) Umesh, U.; Prashanth, J.; Yaragal, S.C.; Nagaraj, M.K.
    In this paper the shelter effect of solid wind fence is investigated. A solid fence was considered with different bottom gap ratios (ratio of bottom gap to the height of the fence) of 0, 0.1, 0.2 and 0.3. The numerical analysis was done for different free stream velocities of 7.5 m/s, 10 m/s and 12.5 m/s. The results obtained were compared with the results of wind tunnel testing and flow visualization. Comparison between the experimental and numerical results showed a fairly good agreement. Flow visualization technique provided sufficient information for planning and conducting flow field measurements with a clear demarcation of reattachment length. The modified k- ? turbulence model predicted the flow well. From both the experimental and numerical investigation it is shown that a fence with gap ratio of 0.1 is effective in providing good shelter effect. © 2011 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.
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    A numerical investigation on heat transfer and emissions characteristics of impinging radial jet reattachment combustion (RJRC) flame
    (Elsevier Ltd, 2015) Tajik, A.R.; Hindasageri, V.
    Radial Jet Reattachment combustion (RJRC) flame jet is used in applications where the impingement surface is delicate and demands low impingement pressure. In the present study, a two dimensional axisymmetric computational fluid dynamics (CFD) simulation is carried out. The turbulence-combustion interaction in the flame field is modeled in a k-?/EDM framework. The distribution of heat flux, pressure coefficient and emissions is presented for varying Reynolds number (Re = 1000 to 30,000) and different non-dimensional nozzle tip to plate spacing (X/R = 0.5 to 3). It is found that the peak heat flux increases and pressure coefficient reduces significantly with the increase in Reynolds number. However, with the increase in the nozzle tip to plate spacing the peak heat flux and the pressure coefficient decrease. Furthermore, the concentrations of NOx and CO emissions increase with the increase in Reynolds number and the distance of the location of the nozzle tip from the impingement plate. © 2015 Elsevier Ltd. All rights reserved.
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    Numerical study of basal reinforced embankments supported on floating/end bearing piles considering pile-soil interaction
    (Elsevier Ltd, 2015) Bhasi, A.; Rajagopal, K.
    Construction sites consisting of soft soils may require ground improvement to prevent excessive settlements or bearing capacity type failures and shear movements, which results in construction delays and premature failures. Among the various ground improvement techniques, the Geosynthetic Reinforced Piled Embankment Systems (GRPES) provide a practical and efficient solution due to the low cost and short construction times. Most of the piled embankments are constructed on end bearing piles. At large depths of foundation soil, floating piles are more economical and technically feasible than the end bearing piles. The design of floating piles involves complex soil-structure interaction and there are no clear uniform guidelines available for the design of embankments supported on floating piles. This paper presents the results of numerical investigation into the performance of geosynthetic reinforced embankments supported on end bearing as well as floating piles considering the pile-soil and geosynthetic-soil interaction. 3-D Column models are employed to carry out the parametric studies on factors such as the development of arching, skin friction distribution along the pile length and axial force distribution. Full three-dimensional analyses are carried out to study the overall behavior of the GRPES system and the results obtained from the analyses were compared with those from British Standard BS8006-2010. The results indicated that the use of floating piles could considerably reduce the settlements and the embankment load transferred through the piles to the foundation soil is found to depend very much on the length of the piles. This aspect needs to be accounted for while calculating the arching factor in the empirical equations. © 2015 Elsevier Ltd.
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    Buckling and dynamic characteristics of a laminated cylindrical panel under non-uniform thermal load
    (Techno Press technop2@chollian.net, 2016) Bhagat, V.; Jeyaraj, J.; Murigendrappa, S.M.
    Buckling and free vibration behavior of a laminated cylindrical panel exposed to non-uniform thermal load is addressed in the present study. The approach comprises of three portions, in the first portion, heat transfer analysis is carried out to compute the non-uniform temperature fields, whereas second portion consists of static analysis wherein stress fields due to thermal load is obtained, and the last portion consists of buckling and prestressed modal analyzes to capture the critical buckling temperature as well as first five natural frequencies and associated mode shapes. Finite element is used to perform the numerical investigation. The detailed parametric study is carried out to analyze the effect of nature of temperature variation across the panel, laminate sequence and structural boundary constraints on the buckling and free vibration behavior. The relation between the buckling temperature of the panel under uniform temperature field and non-uniform temperature field is established using magnification factor. Among four cases considered in this study for position of heat sources, highest magnification factor is observed at the forefront curved edge of the panel where heat source is placed. It is also observed that thermal buckling strength and buckling mode shapes are highly sensitive to nature of temperature field and the effect is significant for the above-mentioned temperature field. Furthermore, it is also observed that the panel with antisymmetric laminate has better buckling strength. Free vibration frequencies and the associated mode shapes are significantly influenced by the non-uniform temperature variations. © 2016 Techno-Press, Ltd.
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    Sound transmission loss characteristics of sandwich aircraft panels: Influence of nature of core
    (SAGE Publications Ltd info@sagepub.co.uk, 2017) Arunkumar, M.P.; Jeyaraj, J.; Gangadharan, K.V.; Mailan Chinnapandi, M.C.
    Sandwich panel which has a design involving acoustic comfort is always denser and larger in size than the design involving mechanical strength. The respective short come can be solved by exploring the impact of core geometry on sound transmission characteristics of sandwich panels. In this aspect, the present work focuses on the study of influence of core geometry on sound transmission characteristics of sandwich panels which are commonly used as aircraft structures. Numerical investigation has been carried out based on a 2D model with equivalent elastic properties. The present study has found that, for a honeycomb core sandwich panel in due consideration to space constraint, better sound transmission characteristics can be achieved with lower core height. It is observed that, for a honeycomb core sandwich panel, one can select cell size as the parameter to reduce the weight with out affecting the sound transmission loss. Triangular core sandwich panel can be used for low frequency application due to its increased transmission loss. In foam core sandwich panel, it is noticed that the effect of face sheet material on sound transmission loss is significant and this can be controlled by varying the density of foam. © 2016, © The Author(s) 2016.
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    Vibro-acoustic behavior of functionally graded carbon nanotube reinforced polymer nanocomposite plates
    (SAGE Publications Ltd info@sagepub.co.uk, 2018) George, N.; Jeyaraj, P.; Murigendrappa, S.M.; Mailan Chinnapandi, M.C.
    This paper presents the numerical investigation results carried out on vibro-acoustic behavior of functionally graded carbon nanotube reinforced polymer nanocomposite plate using combined finite element method and Rayleigh integral. Parameter studies are carried out to analyze the in?uence of nature of functional grading, loading of carbon nanotube, and structural boundary conditions on free and forced vibration and sound radiation characteristics in detail. It is found that natural frequencies are significantly in?uenced by the nature of functional grading while the mode shapes are insensitive. The resonant amplitude of vibration and acoustic response are significantly in?uenced with the nature of different functional grading. This re?ects in the bandwise calculation of sound power also which recommends the carbon nanotube functional grading with X distribution along the thickness direction for lower frequency level. Similar variation in vibro-acoustic response has been observed with increase in the carbon nanotube loading also. © 2016, IMechE 2016.
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    Experimental and Numerical Investigation of Effusion Cooling Performance Over Combustor Liner Flat Plate Model
    (Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2019) Jesuraj, J.; Rajendran, R.; Kumar, G.N.; Yepuri, Y.G.; Karthik, M.K.; Ramesha, D.K.
    This article presents a study of cooling performance of combustor liner of a gas turbine, using a flat plate model. The combustion process in gas turbine engines liberates very high temperature gases, which impacts the properties of the combustor liner. Hence, cooling of liner is important and is carried out by effusion cooling method. Experiments are carried out over a flat plate with staggered effusion holes. The hot mainstream air flows at a Reynolds number of 2.325 × 105, which indicates a turbulent flow. The coolant to mainstream density ratios of 1.3 and 1.5 is maintained by varying the blowing ratios ranging from 0.5 to 2.5. Test plate surface temperature measurements are recorded by an infrared camera and the overall cooling effectiveness in the flow direction is calculated. Numerical validation for conjugate heat transfer analysis is performed using ANSYS workbench and the temperature contours obtained are compared with infrared camera images. MATLAB program is used to obtain the effectiveness contours for experimental and computational fluid dynamics results. The effectiveness contours are found to be similar, showing the increase in effectiveness with the increase in blowing ratios. Density ratios comparison shows that with the increase in density ratio, the overall cooling effectiveness marginally decreases. © 2018, © 2018 Taylor & Francis Group, LLC.
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    Numerical investigation of engulfment flow at low Reynolds numbers in a T-shaped microchannel
    (American Institute of Physics Inc. claims@aip.org, 2020) Madana, V.S.T.; Ali, B.
    Microreactors play a major role in the intensification of industrial processes. The performance of microfluidic devices depends on the flow behavior and flow regimes present in such systems. In this work, single-phase flow behavior and associated flow regimes in a T-shaped microchannel are numerically analyzed using computational fluid dynamics (CFD). To predict the single-phase flow regimes, three dimensional transient CFD simulations are performed. The critical Reynolds number (Re) at which flow regime transition and onset of engulfment occur is identified (Recritical = 300). To achieve engulfment flow at lower Re, the inlet geometry of the microchannel is modified as a convergent (C)-divergent (D) section and its effect on engulfment flow is analyzed. When the C/D ratio is 9:1, the predicted pressure drop (?p) is found to be minimum (Recritical = 75, ?p = 5.4 kPa). The understanding of the engulfment flow regime is exploited through residence time distribution (RTD). The predicted RTD profiles indicate strong recirculation among vortices. The mixing index is calculated to quantify RTD, and it is found to be minimum when the C/D ratio is 9:1. The mixing performance is further verified by introducing buoyant particles in Lagrangian manner using discrete phase modeling. The predicted dynamics are qualitatively and quantitatively analyzed through Poincaré maps and Shannon's entropy for various convergent-divergent inlets to characterize mixing. Once again, the C/D ratio of 9:1 supports in enhancing mixing in the microchannel. Hence, the proposed micromixer based on geometric modifications at the inlet helps achieve the engulfment flow regime at low Re. © 2020 Author(s).
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    Numerical investigation on the wave dissipating performance due to multiple porous structures
    (Taylor and Francis Ltd., 2021) Venkateswarlu, V.; Karmakar, D.
    Gravity wave interaction with porous structures is investigated under the assumption of linearized wave theory. Multiple porous blocks of finite thickness with finite spacing are investigated under the action of oblique ocean waves considering leeward unbounded region and confined region. The eigenfunction expansion method is employed to analyse the effect of multiple-confined regions in the trapping of oblique waves. The study outcomes are validated with numerical and experimental results available in the literature. The friction factor and the inertia effect of the porous medium are considered and different porosity conditions are adopted to determine the wave reflection coefficient, transmission coefficient, wave dissipation and wave force impact on the leeward wall. The functional efficiency of multiple fully extended porous structures is studied for different values of porosity, water chamber length, angle of incidence, friction factor and spacing between the porous blocks. The seabed is assumed to be uniform impermeable bottom and uneven bottom (step approximation is adopted). The study demonstrates that the better wave blocking is achieved with the increase in the series of porous structures and the confined regions can be used effectively for the trapping of oblique waves. The present study will be helpful in the design of porous structures for security of coastal facilities and coastal structures in offshore environment. © 2019 Indian Society for Hydraulics.
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    Numerical investigation of conventional and tapered Savonius hydrokinetic turbines for low-velocity hydropower application in an irrigation channel
    (Elsevier Ltd, 2021) Shashikumar, S.; Vijaykumar, H.; Madav, V.
    In the present work, computational fluid dynamics simulation was carried out using ANSYS Fluent to study the performance of conventional and tapered turbine blades for hydrokinetic power generation. The sliding mesh technique is used to study the influence of taper on conventional Savonius turbine using the SST k-? turbulence model and performance parameters were determined. The geometric parameters used in the present simulation for conventional and tapered turbine blades are aspect ratio and overlap ratio of 1.0 and 0.0. The inlet velocity and depth of water used for present simulation are 0.5 m/s and 103.6 mm for both conventional and tapered turbine blades. The results show that a 5% increase in the performance of a conventional turbine as compare to tapered turbine blade with a taper angle of 5°. The value of maximum coefficient of power for conventional Savonius turbine blade is 0.21 with a tip speed ratio 0.9. The flow field around the conventional and tapered turbine blades at different angular positions are analysed. It was found that there is a loss of energy at the exit side of the advancing blade for the case of tapered turbine, that leads to 5% reduction of performance as compared to the conventional turbine. © 2020 Elsevier Ltd