Faculty Publications

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    Comparative analysis of steady state heat transfer in a TBC and functionally graded air cooled gas turbine blade
    (2010) Coomar, N.; Kadoli, R.
    Internal cooling passages and thermal barrier coatings (TBCs) are presently used to control metal temperatures in gas turbine blades. Functionally graded materials (FGMs), which are typically mixtures of ceramic and metal, have been proposed for use in turbine blades because they possess smooth property gradients thereby rendering them more durable under thermal loads. In the present work, a functionally graded model of an air-cooled turbine blade with airfoil geometry conforming to the NACA0012 is developed which is then used in a finite element algorithm to obtain a non-linear steady state solution to the heat equation for the blade under convection and radiation boundary conditions. The effects of external gas temperature, coolant temperature, surface emissivity changes and different average ceramic/metal content of the blade on the temperature distributions are examined. Simulations are also carried out to compare cooling effectiveness of functionally graded blades with that of blades having TBC. The results highlight the effect of including radiation in the simulation and also indicate that external gas temperature influences the blade heat transfer more strongly. It is also seen that graded blades with about 70% ceramic content can deliver better cooling effectiveness than conventional blades with TBC. © 2010 Indian Academy of Sciences.
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    Validation of an integral sliding mode control for optimal control of a three blade variable speed variable pitch wind turbine
    (Elsevier Ltd, 2015) RAJENDRAN, S.; Jena, D.
    Reduction in cost of wind energy requires most efficient control technology which can able to extract optimum power from the wind. This paper mainly focuses on the control of variable speed variable pitch wind turbine (VSVPWT) for maximization of extracted power at below rated wind speed (region 2) and regulation of extracted power when operating at above rated wind speed (region 3). To extract maximum power at below rated wind speed torque control is used whereas to regulate rated power at above rated wind speed pitch control is used. In this paper a nonlinear control i.e. integral sliding mode control (ISMC) is proposed for region 2 whereas a conventional proportional-integral (PI) control is adapted for region 3 of a VSVPWT. The proposed controller is combined with modified Newton Raphson (MNR) wind speed estimator to estimate the wind speed. The stability of the proposed ISMC is analyzed using Lyapunov stability criterion and the control law is derived for region 2 which is also adapted for the transition period between region 2 and region 3 (region 2.5). The dynamic simulations are tested with nonlinear FAST (Fatigue, Aerodynamics, Structures, and Turbulence) wind turbine (WT). The simulation results of ISMC are presented and the control performance is compared with conventional SMC and existing controllers such as aerodynamic torque feed forward control (ATF) and Indirect speed control (ISC). It is seen that especially in region 2.5, ISMC gives better performance compared to all other controllers. © 2015 Elsevier Ltd.
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    Computational study of pressure side film cooling—effect of density ratio with combination of holes
    (Springer Heidelberg, 2017) Radheesh, D.; Pugazhendhi, P.; Gnanasekaran, N.; Panda, R.K.
    Film cooling is a proven cooling technique for gas turbine blades. The temperature distribution and flow phenomena vary with the suction and pressure sides. A computational investigation is carried out to understand the film cooling effectiveness and flow phenomenon on pressure side of a gas turbine aerofoil. A specific turbine blade profile is considered with combination of cylindrical and shaped holes in staggered fashion, oriented at different angles. Computations are carried out using the k-? Realizable model available in the commercial code FLUENT 6.3. Meshing of the present model is done by using GAMBIT. The parameter variation considered for the present study is the blowing ratio (0.5–1.25) with an interval of 0.25 and three different density ratios (DR) 1.25, 1.5 and 2. The film cooling performance is discussed with effectiveness distribution on the interface wall. It is inferred that the film cooling performance enhances with increasing density ratio values. Also the optimum value of blowing ratio lies close to 0.75 for higher density ratio values of 2. © Springer India 2017.
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    Effect of RANS-Type Turbulence Models on Adiabatic Film Cooling Effectiveness over a Scaled Up Gas Turbine Blade Leading Edge Surface
    (Springer, 2018) Yepuri, G.B.; Talanki Puttarangasetty, A.B.; Kolke, D.K.; Jesuraj, F.
    Increasing the gas turbine inlet temperature is one of the key technologies in raising gas turbine engine power output. Film cooling is one of the efficient cooling techniques to cool the hot section components of a gas turbine engines in turn the turbine inlet temperature can be increased. This study aims at investigating the effect of RANS-type turbulence models on adiabatic film cooling effectiveness over a scaled up gas turbine blade leading edge surfaces. For the evaluation, five different two equation RANS-type turbulent models have been taken in consideration, which are available in the ANSYS-Fluent. For this analysis, the gas turbine blade leading edge configuration is generated using Solid Works. The meshing is done using ANSYS-Workbench Mesh and ANSYS-Fluent is used as a solver to solve the flow field. The considered gas turbine blade leading edge model is having five rows of film cooling circular holes, one at stagnation line and the two each on either side of stagnation line at 30° and 60° respectively. Each row has the five holes with the hole diameter of 4 mm, pitch of 21 mm arranged in staggered manner and has the hole injection angle of 30° in span wise direction. The experiments are carried in a subsonic cascade tunnel facility at heat transfer lab of CSIR-National Aerospace Laboratory with a Reynolds number of 1,00,000 based on leading edge diameter. From the Computational Fluid Dynamics (CFD) evaluation it is found that K–? Realizable model gives more acceptable results with the experimental values, compared to the other considered turbulence models for this type of geometries. Further the CFD evaluated results, using K–? Realizable model at different blowing ratios are compared with the experimental results. © 2016, The Institution of Engineers (India).
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    Plasma sprayed Cr3C2-NiCr/fly ash cenosphere coating: Cyclic oxidation behavior at elevated temperature
    (Institute of Physics Publishing helen.craven@iop.org, 2018) Doddamani, M.; Mathapati, M.; Ramesh, M.R.
    Oxidation is one of the major degradation phenomena observed in components subjected to higher temperatures like in thermal power plants (boiler tubes), steam and gas turbines blades etc. Developing protective coatings for such components mitigate oxidation. In the present study, plasma spray technique is utilized to deposit the Cr3C2-NiCr/Cenospheres coating on MDN 321 steel substrate. Thermo cyclic oxidation test is conducted at 600 °C (20 cycles) on both the coating and MDN 321 steel substrate. The thermogravimetric methodology is employed to estimate the oxidation kinetics. Energy Dispersive Spectroscopy (EDS), x-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and x-ray mapping technique is employed to characterize the oxidized samples. Cr3C2-NiCr/Cenosphere coating displayed lower rate of oxidation as compared to substrate implying its suitability in high-temperature applications. Protective oxides like Al2O3, Cr2O3, and NiCr2O4 are observed on the uppermost layer of the coating lowering the oxidation rate in the developed coating. © 2018 IOP Publishing Ltd.
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    Enhancement of surface integrity by cryogenic diamond burnishing toward the improved functional performance of the components
    (Springer Verlag service@springer.de, 2019) Sachin, B.; Narendranath, S.; Dupadu, D.
    17-4 precipitation-hardenable (PH) stainless steel is one of the widely used materials in various applications of engineering practices owing to their excellent corrosion resistance and high strength. The components such as automotive body, aerospace compressor blades, turbine blades and molds demand higher load carrying capacity and improved fatigue strength, which is possible to achieve by surface severe plastic deformation. Diamond burnishing process is an appropriate technique to produce such components which improves the surface integrity characteristics of the material. This article presents a comprehensive examination of the surface integrity of cryogenic diamond burnished 17-4 PH stainless steel using a novel diamond burnishing tool. The impact of diamond burnishing control factors on subsurface microhardness, surface roughness, surface hardness, surface topography, residual stress and surface morphology has been analyzed. The optimal control factor setting ensures the least surface roughness of 0.03 µm by the application of one factor at a time approach. Cryogenic diamond burnished surface achieves the exceptional surface finish and the surface hardness in tool-tip of 8 mm and 6 mm, respectively. The maximum surface hardness of 413 HV was attained using 6-mm tool-tip diameter. The subsurface microhardness improvement of 2% and 4% has been observed while using a tool-tip diameter of 6 mm in contrast to 8 mm and 10 mm. Compressive residual stresses have been generated at the top surface layer of the specimen. The attained experimental results prove that cryogenic diamond burnishing can be successfully applied to 17-4 PH stainless steel to enhance its surface integrity characteristics. © 2019, The Brazilian Society of Mechanical Sciences and Engineering.
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    Transient analysis of upstream wake inside turbine blade passage with purge flow
    (Elsevier Masson SAS 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2020) Babu, B.; Anish, S.
    Secondary air bled from the compressor which bypasses the combustion chamber is used to seal the turbine components from incoming hot gas. Interaction of this secondary air (also known as purge flow) with the mainstream flow can alter the flow characteristics of turbine blade passage. This paper presents numerical investigation of interaction between ejected purge flow and mainstream flow in the presence of upstream disturbances/wakes. Steady as well as unsteady simulations are carried out using Reynolds Averaged Navier Stokes equations and SST turbulence model. The numerical results are validated with experimental measurements obtained at the blade exit region using an L shaped 5 hole probe and Scanivalve. Upstream wakes are generated by a circular cylinder, kept upstream of blade leading edge at different pitch-wise positions. For transient analysis cylinders are kept at stagnation line (STW) and middle of the blade passage (MW). The analysis reveals the interaction effects of two more additional vortices, viz. the cylinder vortex (Vc) and the purge vortex (Vp). Steady state analysis shows an increase in the underturning at blade exit due to the squeezing of the pressure side leg (PSL) of horse shoe vortex towards the pressure surface by the cylinder vortices (Vp). The unsteady analysis reveals the formation of filament shaped wake structures which breaks into smaller vortical structures at the blade leading edge for STW configuration. These filaments lead to the formation of additional pressure surface vortices. On the contrary, in MW configuration, the obstruction created by the purge flow causes the upper portion of cylinder vortices bend forward, creating a shearing action along the spanwise direction. In MW configuration, the horse shoe vortices generated from the upstream cylinder are broken by the purge vortex whereas in the STW configuration it slides over the purge vortex and move towards the suction surface under the influence of the pitchwise pressure gradient. © 2019 Elsevier Masson SAS
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    Aerodynamic performance of profiled endwalls with upstream slot purge flow in a linear turbine cascade having pressure side separation
    (American Institute of Physics Inc., 2021) Babu, S.; Anish, S.
    In aeroengines, purge flow directly fed from the compressor (which bypasses the combustor) is introduced through the disk space between blade rows to prevent the hot ingress. Higher quantity of purge gas fed through the wheel space can provide additional thermal protection to the passage endwall and blade surfaces. However, the interaction of purge flow with the mainstream flow leads to higher secondary losses. Secondary losses inside a turbine blade passage can be reduced effectively by endwall contouring. This paper presents computational investigation on the influence of non-axisymmetric endwall contouring over endwall secondary flow modification in the presence of purge flow with the pressure side bubble (PSB). The experimental analysis was conducted for the base case without purge and base case with purge (BCP) configurations having flat endwalls. The total pressure loss coefficient and exit yaw angle deviation were measured with the help of a five-hole pressure probe. Static pressure distribution over the blade midspan was obtained by 16 channel Scanivalve. Aerodynamic performances of three different profiled endwalls are numerically analyzed and are compared against the BCP configuration. The effects of different contoured endwall geometries on endwall static pressure distribution and secondary kinetic energy were also discussed. Analysis shows that in the first contoured endwall configuration (EC1), the formation of stagnation zones at a contour valley close to the suction surface causes the exit total pressure loss coefficient to increase. The shifting of the contour valley near to the pressure surface (EC2 configuration) has resulted in local acceleration of the diverted pressure side leg of the horseshoe vortex over the hump toward the end of the passage. In the third configuration (EC3 configuration), reduced valley depth and optimum hump height have effectively redistributed the endwall pitchwise pressure gradient. The increased static pressure coefficient at the endwall near to the pressure surface has eliminated the PSB formation. In addition, computational results of unsteady Reynolds averaged Navier-Stokes simulations are obtained for analyzing transient behavior of PSB, with more emphasis on its migration on the pressure surface and transport across the blade passage. The additional work done by the mainstream fluid to transport the low momentum PSB fluid has caused higher aerodynamic penalty at the blade exit region. In this viewpoint, the implementation of contoured endwalls has shown beneficial effects by eliminating the PSB and related secondary vortices. At 27% of axial chord downstream of the blade trailing edge, a 4.1% reduction in the total pressure loss coefficient was achieved with endwall contouring. © 2021 Author(s).
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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
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    Experimental and numerical investigation of novel V-shaped rotor for hydropower utilization
    (Elsevier Ltd, 2021) Shashikumar, S.; Honnasiddaiah, R.; Hindasageri, V.; Madav, V.
    Hydrokinetic technologies harvest renewable power by harnessing the kinetic energy of water from free-flowing rivers, streams, dam head/tailrace and irrigation channels. Savonius rotor is one of the simple and low-cost vertical axis drag type devices used for the extraction of hydrokinetic power. The main limitation of Savonius hydrokinetic turbine is its low efficiency due to negative torque developed by the returning blade without augmentation techniques. In this paper, an experimental investigation is carried out in a multipurpose tilting water flume using V-shaped rotor blade profiles by maintaining a fixed V-angle of 90°, varying length of V-edges, arc radius and with a constant aspect ratio of 0.7. The simulations were carried out using commercial software, ANSYS Fluent. From the experimental and numerical results, it was found that, the optimum blade profile (V4) has developed a maximum coefficient of power 0.22 and 0.21 respectively, at a tip speed ratio 0.87. It was found that, the maximum coefficient of power of optimal V-shaped blade profile (V4) is 19.3% higher than the semi-circular blade profile. © 2021 Elsevier Ltd