Journal Articles
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/123456789/19884
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Item Critical review of ribbed solar air heater and performance evaluation of various V-rib configuration(Elsevier Ltd, 2021) Nidhul, K.; Yadav, A.K.; Anish, S.; Kumar, S.The low heat transfer rate in a flat plate solar air heater (SAH) is due to the development of a laminar sub-layer near the heated absorber plate. Owing to this, the plate temperature rises substantially, instigating losses and thus reducing the efficiency. Extensive research has been carried out to mitigate this problem, of which passive technique emerged to be a promising solution. The passive method involves the application of fins/turbulators/ribs on the surface where the boundary layer develops so that it breaks the same. Various profiles and configurations of the ribs ranging from transverse to inclined and continuous to discrete have been presented concisely. Correlations on Nusselt number (Nu) and friction factor (f) for different rib configurations have been summarized in order so that it can be accessed for future research. 3-D CFD analysis is carried out to gain insight into the flow pattern of various V-ribbed SAH, and with the help of streamlines and contours, the findings are established. Furthermore, various exergy destruction has been studied in detail for different V-rib configurations, namely– V-rib, multiple V-rib, and multiple V-rib with the gap, and analyzed in detail for prospective studies. Exergetic performance study of these rib configurations indicates that the multiple ribs and the multiple rib-gap combinations enhance exergetic efficiency (ηex) by 12% and 31.6%, respectively, in comparison to V-rib SAH. © 2021 Elsevier LtdItem Machine learning approach for optimization and performance prediction of triangular duct solar air heater: A comprehensive review(Elsevier Ltd, 2023) Nidhul, K.; Thummar, D.; Yadav, A.K.; Anish, S.This paper presents a comprehensive review of various kinds of distinct artificial roughness employed in rectangular and triangular duct solar air heaters to aid prospective researchers in finding a critical gap in the domain of solar air heaters. A Machine Learning (ML) model is developed using 72 distinct rib combinations compiled to 454 datasets and trained using an Artificial Neural Network (ANN) to predict the performance of ribbed triangular duct Solar Air Heater (SAH). The developed ML model predicts the data with an average deviation of <3%. Owing to reasonably accurate predictions, the same could be increased when more cases (geometric or operating parameters) are added to the databases by retraining the ANN. Further, a second law analysis of the rib configurations features collector efficiency and entropy generation variation with Re for various rib parameters. For the Re range of 4000 to 18000, optimum parameters such as rib height, pitch, chamfer angle, and inclinations are obtained for triangular duct SAH. This could help design engineers obtain the performance parameters of ribbed triangular duct SAH with other artificial roughness designs, possibly with a combination of different geometrical and operating parameters, without having to perform tests. © 2023 International Solar Energy SocietyItem Wall shear stress and oscillatory shear index distribution in carotid artery with varying degree of stenosis: A hemodynamic study(World Scientific Publishing Co. Pte Ltd wspc@wspc.com.sg, 2017) Basavaraja, P.; Anish, S.; Gupta, A.; Saba, L.; Laird, J.R.; Nicolaïdes, A.; Mtui, E.E.; Baradaran, H.; Lavra, F.; Suri, J.S.A significant proportion of cerebral stroke is a consequence of the arterial stenotic plaque rupture causing local thrombosis or distal embolization. The formation and subsequent rupture of the plaque depends on wall shear stress (WSS) and oscillatory shear index (OSI). The purpose of the present study was to understand the effect of hemodynamics on the spatial and temporal variations of WSS and OSI using realistic models with varying degree of carotid artery stenosis (DOS). Multiple CT volumes were obtained from subjects in the carotid bifurcation zone and the 3D models were generated. A finite volume-based computational fluid dynamics (CFD) method was utilized to understand the hemodynamics in pulsatile flow conditions. It was observed that high stenosis models occupied a large value of normalized WSS in the internal carotid artery (ICA) whereas they had smaller values of normalized WSS in the common carotid artery (CCA). For clinical use, the authors recommend using the spatial average value of oscillatory shear rather than the maximum value for an accurate knowledge about the severity of stenosis. The resultant vorticity changes the direction of spin after the bifurcation zone. Additionally, we propose the use of limiting streamlines as a novel and convenient method to identify the disturbed flow regions that are prone to atherogenesis. © 2017 World Scientific Publishing Company.Item Computational study of radial gap effect between impeller and diffuser on the unsteadiness of vaned diffuser in a centrifugal compressor(Korean Society of Mechanical Engineers, 2017) Anish, S.; Sitaram, N.Understanding the unsteady fluid dynamics inside the diffuser holds the key to improve the performance of centrifugal compressor. A detailed computational study has been conducted in a low-speed centrifugal compressor to understand the unsteady flow mechanisms that govern the static pressure recovery inside the vaned diffusers. Simulations are carried out for three different leading edge locations at design and off-design conditions. The study is carried out using Reynolds-averaged Navier-Stokes simulations. This study revealed that the unsteady fluctuations exhibit contrasting behavior at different radial gaps and flow coefficients. An optimum radial gap is strictly a function of the stage loading. A high radial gap helps contain the fluctuations at low flow coefficients, but it enhances the fluctuations at high flow coefficients. If the leading edge is kept close to the impeller blade, then the above design flow coefficient of the vaned passage facilitates a reduction in the unsteady fluctuations. On the contrary, keeping the leading edge close to the impeller blade can accelerate the unsteady fluctuations at low flow coefficients. © 2017, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature.Item An investigation on the effect of pitchwise endwall design in a turbine cascade at different incidence angles(Elsevier Masson SAS 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2017) Kiran, K.N.; Anish, S.This paper describes the effects of non-axisymmetric endwall profiling on the aerodynamic performance of a linear turbine cascade at different incidence angles. The sinusoidal profiling is carried out with constant profile curvature along the mean streamline path. Three different profiles, with varying hump to dip height, are analyzed numerically and the performances are compared with the planar profile. Reynolds Averaged Navier Stokes (RANS) equations are solved in their conservative form using Finite Volume Method with SST turbulence model. The calculated results indicate that the profiled endwall minimizes the lateral movement of weaker boundary layer fluid from the hub-pressure side corner. In comparison with planar case, the flow deviations are largely contained with endwall profiling but closer to the endwall it enhances the overturning and secondary flow kinetic energy. The reduction in loss coefficient is estimated to be 1.3%, 8.7% and 38% for incidence angles of ?10°, nominal and +15° respectively. The sinusoidal profiling has brought down the pitch averaged flow deviation and secondary flow kinetic energy at nominal and positive incidence angles but the impact is insignificant at negative incidence. Profiling minimizes the rolling up of the passage vortex and makes the passage vortex to migrate closer to the endwall. This flow modification brings down the losses in the core flow but enhances the losses near the endwall. © 2017 Elsevier Masson SASItem An aerothermal investigation of purge flow behaviour in a linear turbine cascade with upstream wakes(Bentham Science Publishers, 2018) Babu, S.; Anish, S.Background: Over all efficiency of a turbofan engine can be improved by increasing turbine inlet temperature. To withstand the high turbine inlet temperatures advanced cooling techniques and robust materials are required. Air supplied from compressor can be used to purge turbine components and disk cavities from the incoming hot gas. Objective: In the present study, an attempt is made to understand the aerodynamic and thermal effects caused by the purge flow in the presence of stationary upstream wakes. Methods: Reynolds Averaged Navier Stokes Equation coupled with SST turbulence model is used for computational study. Base case experimental data conducted on a 5 blade linear cascade is used for numerical validation. The coolant to mainstream blowing ratio is varied from 0.2 to 1.2 with a step size of 0.2. Results: It is observed that with an increase in the blowing ratio, the mass averaged total pressure losses also increase. Purge flow shifts the passage vortex away from the endwall and causes significant overturning up to a span of 30-40mm, before they exhibit underturning up to midspan. In an effort to reduce the losses, purge ejection angle is reduced to 45° from 90°. Significant loss reduction and improved endwall protection are observed at 45° ejection angle. This ejection angle provides enough acceleration and momentum to the fluid inside the endwall boundary layer. But the upstream secondary wakes and secondary flows enhanced the mixing losses within the blade passage. Conclusion: The turbulent mixing generated by upstream wakes reduced the film cooling effectiveness over the endwall. The numerical results show that film cooling effectiveness can be improved by reducing the purge ejection angle. Various patents have been discussed in this article. © 2018 Bentham Science Publishers.Item Computational investigation on secondary flows in a linear turbine cascade with tapered dual fence(Korean Society of Mechanical Engineers, 2019) Kiran, K.N.; Babu, B.; Anish, S.The focus of the present work is to minimize the secondary flow losses inside a linear turbine cascade by means of a novel design of streamwise dual fence. The leading edge and trailing edge of the fences have been modified so as to reduce the total pressure loss coefficient in the passage. The study has been carried out computationally based on RANS simulations with SST turbulence model. Numerous simulations have been undertaken with single fence and dual fence models and compared with the base case model. The dual fence model with tapered trailing edge exhibits significant loss reduction compared to the base case. A suitable fence height ratio (FHR) has been identified for the dual fence model. The FHR = 2 configuration reduces the secondary flow kinetic energy by 78 % within the blade passage and it reduces the exit angle deviation significantly throughout the span. Detailed flow field analysis has been carried out to understand the physical mechanism behind the loss reduction with dual fence models. It is observed that fence-1 breaks the pressure side leg of the horse shoe vortex at the beginning of their formation itself. The radial penetration of the suction side leg of the horse shoe vortex is restrained by fence-2. These combined effects prevent the formation and mixing of two prominent loss core regions thereby avoiding the accumulation of low energy fluid near the suction side of blade. © 2019, KSME & Springer.Item Discrete-Phase Modelling of an Asymmetric Stenosis Artery Under Different Womersley Numbers(Springer Verlag, 2019) Prashantha, B.; Anish, S.Understanding the hemodynamics in the post-stenotic region of an asymmetric stenosis is of paramount importance in the study of atherosclerosis progression. Numerically, the analysis becomes more complex when a discrete phase is added to the continuous phase in order to understand the behaviour of atherogenic particles in a pulsatile flow environment. In the present study, discrete-phase modelling (DPM) of an asymmetric and symmetric stenosed artery models has been carried out at different Womersley numbers. The objective is to understand the correlation between the discrete-phase (atherogenic) particle behaviour with the characteristics of continuous phase (blood) under varying pulse frequencies. Continuous phase is modelled by time-averaged Navier–Stokes equations and solved by means of pressure implicit splitting of operators algorithm. DPM has been carried out with one-way coupling. The transport equations are solved in the Eulerian frame of reference, and the discrete phase is simulated in Lagrangian frame of reference. The study brings out the importance of helicity in the atherosclerosis progression. Result shows that the asymmetric stenosis model exhibits less helical flow structure and the vortical structures are not getting transported to the downstream. Consequently, the average particle residence time (PRT) of the atherogenic particles is one order higher than the symmetric stenosis model. Low PRT leads to enhanced mass transport in the arterial flow and triggers further occlusion/plaque build-up at the post-stenotic region. The extent of asymmetry in a diseased artery may be considered as a useful parameter in understanding the rate of progression of atherosclerosis. © 2018, King Fahd University of Petroleum & Minerals.Item Computational investigations on the hemodynamic performance of a new swirl generator in bifurcated arteries(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2019) Prashantha, B.; Anish, S.Hemodynamic behaviour of blood in the bifurcated arteries are closely related to the development of cardiovascular disease. The secondary flows generated at the bifurcation zone promotes the deposition of atherogenic particles on the outer walls. The present study aims at suppressing the development of atherosclerosis plaque by inducing helical flow structure in the arterial passage. To realize this objective a novel swirl generator (stent like structure with an internal groove) has been developed to induce helicity in the bifurcated passage. The functional requirement of the swirl generator is to minimize the relative residence time (RRT) of the fluid layer near the endothelial wall without generating any additional pressure drop. Different configurations of the swirl generator have been tested computationally using large eddy simulation (LES) model. It is observed that the induced helical flow redistributes the kinetic energy from the centre to the periphery. A single rib swirl flow generator proximal to the stent treated passage can generate sufficient helicity to bring down the RRT by 36% without generating any additional pressure drop. The swirl flow adds azimuthal instability which increase vortex formations in the passage. The induced helical flow in the domain provokes more linked vortices, which may act as self-cleaning mechanism to the arterial wall. © 2018, © 2019 Informa UK Limited, trading as Taylor & Francis Group.Item Numerical investigation on the effect of dry and wet compression on a linear low speed compressor cascade(Isfahan University of Technology secretary@jafmonline.net, 2020) Narayanan, D.; Anand, S.; Anish, S.Several techniques are implemented to reduce the temperature rise in multistage compressors, which leads to the noticeable improvement in specific power output of a gas turbine. The objective of the present investigation intends to understand the effect of incidence angles on the aerodynamic performance of the compressor cascade under wet compression. Using large eddy simulations (LES) the effects of wet compression on compressor flow separation and wake formation are investigated. Experimental investigation was performed to validate the numerical results. The study reveals notable flow modifications in the separated flow region under the influence of wet compression and the total loss coefficient reduces significantly at the downstream side of the compressor for positive incidence angles. On the other hand, for negative incidence angles the wet compression enhances the total pressure losses inside the blade passage. Also, in the present investigation, particular emphasis has been given to understand the water film formation at negative and positive incidence angles. © Isfahan University of Technology.
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