Journal Articles
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Item Combating corrosion degradation of turbine materials using HVOF sprayed 25% (Cr3C2-25(Ni20Cr)) + NiCrAlY coating(2013) Jegadeeswaran, N.; Ramesh, M.R.; Bhat, K.High velocity oxy fuel process (HVOF) is an advanced coating process for thermal spraying of coatings on to components used in turbines. HVOF process is a thermal spray coating method and is widely used to apply wear, erosion, and corrosion protective coatings to the components used in industrial turbines. 25% (Cr3C2-25(Ni20Cr)) + NiCrAlY based coatings have been sprayed on to three turbine materials, namely, Ti-31, Superco-605, and MDN-121. Coated and uncoated substrates were subjected to hot corrosion study under cyclic conditions. Each cycle consisted of 1 hour heating at 800°C followed by 20 minutes air cooling. Gravimetric measurements were done after each cycle and a plot of weight gain as a function of number of cycles is drawn. Parabolic rate constants were estimated for the understanding of corrosion behaviour. It was observed that coated Ti-31 and MDN-121 were more resistant compared to the uncoated ones. Uncoated superco-605 was undergoing sputtering during corrosion study and hence comparison between coated and uncoated superco-605 was difficult. The cross-sectional analysis of the corroded, coated samples indicated the presence of a thin layer of chromium oxide scale on the top of the coating and it imparted better corrosion resistance. Parabolic rate constants also indicated that coating is more beneficial to Ti-31 than to MDN-121. © 2013 N. Jegadeeswaran et al.Item Effect of Wire Material on Productivity and Surface Integrity of WEDM-Processed Inconel 706 for Aircraft Application(Springer New York LLC barbara.b.bertram@gsk.com, 2016) Sharma, P.; Dupadu, D.; Narendranath, S.Inconel 706 is a recently developed superalloy for aircraft application, particularly in turbine disk which is among the most critical components in the gas turbine engines. Recently, wire electrical discharge machining (WEDM) attained success in machining of gas turbine components which require complex shape profiles with high precision. To achieve the feasibility in machining of these components, the research work has been conducted on Inconel 706 superalloy using WEDM process. And, the effect of different wire materials (i.e., hard brass wire, diffused wire, and zinc-coated wire) on WEDM performance characteristics such as cutting speed, surface topography, surface roughness, recast layer formation, residual stresses, and microstructural and metallurgical alterations have been investigated. Even though, zinc-coated wire exhibits improved productivity, hard brass wire was found to be beneficial in terms of improved surface quality of the machined parts. Additionally, lower tensile residual stresses were obtained with hard brass wire. However, diffused wire has a moderate effect on productivity and surface quality. Under high discharge energy, higher elemental changes were observed and also the white layer was detected. © 2016, ASM International.Item 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.Item 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).Item 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.Item 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 SASItem 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 LtdItem Numerical and experimental investigation of modified V-shaped turbine blades for hydrokinetic energy generation(Elsevier Ltd, 2021) Shashikumar, S.; Madav, V.The Savonius rotor is one of the simple and cost-effective vertical axis drag type devices for hydropower generation. The main drawback of the Savonius hydrokinetic turbine is its low performance due to negative torque developed by returning blade profile. In this paper, the performance of modified V-shaped rotor blades with different V-angles ranging from 90° to 40°, by maintaining fixed edge length, arc radius and aspect ratio of 0.7 is investigated. The numerical analysis is carried out to estimate the optimum V-angle by maintaining 70 mm depth of water with an inlet velocity of 0.3090 m/s. The numerical study revealed that, for 80° V-angle rotor blade profile, the maximum coefficient of power was found to be 0.2279 at a tip speed ratio of 0.9. This optimum V-angle model was used for experimental analysis to study the effect of aspect ratio ranging from 0.7 to 1.75 using top, middle and bottom plates by maintaining 140 mm depth of water and inlet velocity of 0.513 m/s. The rotor blade with two endplates and one middle plate with an aspect ratio of 1.75 has shown a significant increase of performance by 86.13% at a tip speed ratio of 0.86 as compared to turbine blade with two endplates. © 2021 Elsevier LtdItem Leading edge tubercle on wind turbine blade to mitigate problems of stall, hysteresis, and laminar separation bubble(Elsevier Ltd, 2022) Joseph, J.; Sathyabhama, A.Low Reynolds number flows may encounter some phenomena like stall, hysteresis, laminar separation bubble. etc., which can deteriorate the performance or efficiency of aerodynamic devices, including wind turbines. This study investigates the effect of the Humpback whale inspired leading edge tubercle on these characteristics, especially stall and hysteresis by comparing a tubercle blade with its baseline counterpart. Surface pressure measurements on various span wise locations of the blades as well as force measurement are done at Reynolds number ranging from 2.5×105 to 6.5×105. For all Reynolds numbers studied, there is a deterioration in stall angle when tubercles are introduced on the blade. The baseline blade experiences abrupt single step deep stall whereas tubercle blade experiences soft stall in multiple steps. From the surface pressure analysis, it is seen that the baseline blade stalls initially at the middle section which further progresses to the tips with increase in angle of attack. However, the stall progression to the tips is drastically inhibited for tubercle blade. It is also seen that there exists significant hysteresis loop for baseline model at all the studied Reynolds numbers. The extent or size of the hysteresis loop is dependent on the Reynolds number. This phenomenon of hysteresis is absent for tubercle blade. Surface pressure over baseline blade for a specific post stall angle of attack shows two distinct pressure distributions- one for increasing branch of angle of attack and one for the decreasing branch. Identical pressure distribution is obtained for tubercle blade irrespective of the direction of movement of blade. Clear regions of laminar separation bubble can be seen for baseline, whereas it is absent for tubercle blade. © 2022Item Performance analysis of novel V-shaped turbine blade profile by three-dimensional numerical investigations with varying overlap ratios for hydropower application(Elsevier Ltd, 2022) Shashikumar, C.M.; Madav, V.In the present paper, three-dimensional numerical simulations were carried out to examine the influence of the overlap ratio between the two straight edges on the advancing and returning blades of the novel V-shaped rotor blade profiles using the sliding mesh technique. The performance parameters were computed with respect to the tip speed ratio. The findings show that the coefficient of torque and power for the novel V-shaped turbine blade is maximum for the zero-overlap ratio compared to the turbine blade, with an overlap ratio ranging from 0.05 to 0.3. The blade profiles' flow field was visualized at different angular positions, and various significant zones developed during the turbine blade rotation were captured and analyzed. The new overlapping jet developed between the two straight edges of the advancing and returning blade profiles as the overlap ratio varies from 0.05 to 0.3. Therefore, the turbine's performance is reduced due to the development of an overlap jet as it travels parallel to the straight edges of the blade profile and does not impact the rear side of the returning blade profile. © 2022 Elsevier Ltd