Faculty Publications

Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736

Publications by NITK Faculty

Browse

Has files: NoSubject: search.filters.subject.Vortex flow

Search Results

Now showing 1 - 10 of 23
  • No Thumbnail Available
    Item
    Numerical simulation of laminar flow past a circular cylinder
    (2009) Rajani, B.N.; Kandasamy, A.; Majumdar, S.
    The present paper focuses on the analysis of two- and three-dimensional flow past a circular cylinder in different laminar flow regimes. In this simulation, an implicit pressure-based finite volume method is used for time-accurate computation of incompressible flow using second order accurate convective flux discretisation schemes. The computation results are validated against measurement data for mean surface pressure, skin friction coefficients, the size and strength of the recirculating wake for the steady flow regime and also for the Strouhal frequency of vortex shedding and the mean and RMS amplitude of the fluctuating aerodynamic coefficients for the unsteady periodic flow regime. The complex three dimensional flow structure of the cylinder wake is also reasonably captured by the present prediction procedure. © 2008 Elsevier Inc. All rights reserved.
  • No Thumbnail Available
    Item
    Simulation of laminar flow in a three-dimensional lid-driven cavity by lattice Boltzmann method
    (2009) De, S.; Nagendra, K.; Lakshmisha, K.N.
    Purpose: The purpose of this paper is to apply lattice Boltzmann equation method (LBM) with multiple relaxation time (MRT) model, to investigate lid-driven flow in a three-dimensional (3D), rectangular cavity, and compare the results with flow in an equivalent two-dimensional (2D) cavity. Design/methodology/approach: The second-order MRT model is implemented in a 3D LBM code. The flow structure in cavities of different aspect ratios (0.25-4) and Reynolds numbers (0.01- 1000) is investigated. The LBM simulation results are compared with those from numerical solution of Navier-Stokes (NS) equations and with available experimental data. Findings: The 3D simulations demonstrate that 2D models may predict the flow structure reasonably well at low Reynolds numbers, but significant differences with experimental data appear at high Reynolds numbers. Such discrepancy between 2D and 3D results are attributed to the effect of boundary layers near the side-walls in transverse direction (in 3D), due to which the vorticity in the core-region is weakened in general. Secondly, owing to the vortex stretching effect present in 3D flow, the vorticity in the transverse plane intensifies whereas that in the lateral plane decays, with increase in Reynolds number. However, on the symmetry-plane, the flow structure variation with respect to cavity aspect ratio is found to be qualitatively consistent with results of 2D simulations. Secondary flow vortices whose axis is in the direction of the lid-motion are observed; these are weak at low Reynolds numbers, but become quite strong at high Reynolds numbers. Originality/value: The findings will be useful in the study of variety of enclosed fluid flows.© Emerald Group Publishing Limited.
  • No Thumbnail Available
    Item
    Computational investigation of the temperature separation in vortex chamber
    (Korean Society of Mechanical Engineers, 2014) Anish, A.; Setoguchi, T.; Kim, H.D.
    The vortex chamber is a mechanical device, without any moving parts that separates compressed gas into a high temperature region and a low temperature region. Functionally vortex chamber is similar to a Ranque-Hilsch vortex tube (RVHT), but it is a simpler and compact structure. The objective of the present study is to investigate computationally the physical reasoning behind the energy separation mechanism inside a vortex chamber. A computational analysis has been performed using three-dimensional compressible Navier-Stokes equations. A fully implicit finite volume scheme was used to solve the governing equations. A commercial software ANSYS CFX is used for this purpose. The computational predictions were validated with existing experimental data. The results obtained show that the vortex chamber contains a large free vortex zone and a comparatively smaller forced vortex region. The physical mechanism that causes the heating towards periphery of the vortex chamber is identified as the work done by the viscous force. The cooling at the center may be due to expansion of the flow. The extent of temperature separation greatly depends on the outer diameter of the vortex chamber. A small amount of compression is observed towards the periphery of the vortex chamber when the outer diameter is reduced. © 2014 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
  • No Thumbnail Available
    Item
    Axis switching in impinging premixed methane-air flame jets
    (Elsevier Ltd, 2016) Hindasageri, V.; Kuntikana, P.; Tajik, A.R.; Vedula, R.P.; Prabhu, S.V.
    Axis switching in non-circular tube burner flame jets is studied. Experimental data of heat flux is obtained for square and rectangular burners of different aspect ratios: 1, 1.55, 2.1 and 3.73. A three dimensional CFD simulation is carried out to explain the phenomenon of axis switching in premixed flame jets. From the CFD simulations it is observed that the vortices formed near the corner of the tube exit are responsible for the axis switching phenomenon. These vortices control the spreading (in a preferential manner) of the flame jet along the tube axis. This preferential spreading of the flame jet is responsible for switching of contours of heat flux on the impingement plate. Furthermore, for the rectangular burner, elliptical lobes of heat flux distribution on the impingement plate are observed and this is again attributed to vortex structures. © 2016 Elsevier Ltd
  • No Thumbnail Available
    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 SAS
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    Shape induced magnetic vortex state in hexagonal ordered cofe nanodot arrays using ultrathin alumina shadow mask
    (Elsevier B.V., 2018) Boominathasellarajan, B.; Saravanan, P.; Ghosh, S.K.; Nagaraja, H.S.; Barshilia, H.C.; Chowdhury, P.
    The magnetization reversal process of hexagonal ordered CoFe nanodot arrays was investigated as a function of nanodot thickness (td) varying from 10 to 30 nm with fixed diameter. For this purpose, ordered CoFe nanodots with a diameter of 80 ± 4 nm were grown by sputtering using ultra-thin alumina mask. The vortex annihilation and the dynamic spin configuration in the ordered CoFe nanodots were analyzed by means of magnetic hysteresis loops in complement with the micromagnetic simulation studies. A highly pinched hysteresis loop observed at 20 nm thickness suggests the occurrence of vortex state in these nanodots. With increase in dot thickness from 10 to 30 nm, the estimated coercivity values tend to increase from 80 to 175 Oe, indicating irreversible change in the nucleation/annihilation field of vortex state. The measured magnetic properties were then corroborated with the change in the shape of the nanodots from disk to hemisphere through micromagnetic simulation. © 2017 Elsevier B.V.
  • No Thumbnail Available
    Item
    Fluid flow characteristics in double-sided lid-driven microcavity using lattice boltzmann method
    (Begell House Inc. orders@begellhouse.com, 2019) Rajan, I.; Arumuga Perumal, D.A.; Yadav, A.K.
    In this study, we analyze the fluid flow characteristic of rarefied gas flows in double-sided lid-driven microcavity subjected to various combinations of boundary conditions that simulate the slip at the walls using lattice Boltzmann method (LBM) constituting a single relaxation time (SRT) model. The fluid motion inside a closed square container with two rigid walls and two moving walls constitutes an exemplar for internal vortex flows. First, a complicated geometry, namely, the single-sided lid-driven microcavity is studied using the LBM-SRT model. Next, this code is extended to simulate flows in a double-sided microcavity flow. Numerical computation of fluid flow incorporating various slip boundary conditions as bounce-back and specular boundary condition (BSBC) for different values of tangential accommodation momentum coefficient (TMAC) has been investigated. Various values of Knudsen number in the slip and transition regime (Kn = 0.01, 0.05, 0.10, 0.135, and 0.15) along with different aspect ratios of 0.33, 0.50, 1.0, 2.0, and 3.0 have been considered in this study. The streamline patterns and velocity profiles were obtained for different Knudsen numbers. The formation and movement of primary vortices have been well captured with the variation of Knudsen numbers for different aspect ratios of microcavity. © 2019 by Begell House, Inc.
  • No Thumbnail Available
    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.
  • No Thumbnail Available
    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.