Browsing by Author "Sathyabhama, A."

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AERODYNAMIC ANALYSIS OF WING WITH LEADING EDGE PROTUBERANCES USING PRANDTL’S LIFTING LINE THEORY
(Begell House Inc., 2022) Sathyabhama, A.; Marathe, A.; Rangapure, S.; Potadar, A.
The establishment of active or passive flow control techniques over aircraft wings has been an area of continuous effort of experimental as well as theoretical investigations. The passive flow control method of leading edge modification has proven to be effective in improving the lift performance of a wing. Extensive performance analysis of sinusoidal tubercles and the wavy wing has been conducted in the literature. This work aims to determine whether other leading edge geometric modifications like square and triangular protrusions similar to sinusoidal tubercles can provide the same effects. The aerodynamic performance of the wings with sinusoidal, square, and triangular tubercles with amplitudes of 3 mm, 5 mm, 7 mm, and 9 mm and wavelengths of 8 mm, 16 mm, 32 mm, and 64 mm is investigated using Prandtl’s lifting line theory. The effect of wavelength and amplitude variation on lift coefficient (CL) and coefficient of induced drag (CDi) is studied within the prestall regime. The results have shown that CL and CDi reduce and the ratio of these coefficients (CL/CDi) improves for the tubercled wing when compared to the baseline wing. The effect of wavelength variation is found to be negligible. In contrast, amplitude variation showed a maximum increase of CL/CDi in the wing with square tubercles, where it reached 305.15 at 1° AoA, for an amplitude of 9 mm. © 2022 by Begell House, Inc.
An efficient online sequential extreme learning machine model based on feature selection and parameter optimization using cuckoo search algorithm for multi-step wind speed forecasting
(Springer Science and Business Media Deutschland GmbH, 2021) Shetty, R.P.; Sathyabhama, A.; Pai, P.S.
Accurate wind speed forecasting (WSF) has become increasingly important to overcome the adverse effects of stochastic nature of the wind on wind power generation. This paper proposes a multi-step hybrid online WSF model by combining online sequential extreme learning machine (OSELM), optimized variational mode decomposition (OVMD) and cuckoo search optimization algorithm (CSO). OVMD decomposes the wind speed series into subseries, and CSO selects the input features for each subseries. Multi-step forecasting for each subseries is performed using OSELM model optimized by CSO. Finally, the forecasting results are obtained by the aggregate calculations. The proposed model has been examined by using 10-min average wind speed data collected in monsoon and winter seasons from a supervisory control and data acquisition system of a 1.5 MW wind turbine situated in central dry zone of Karnataka, India. The results reveal that the model proposed captures the nonlinear characteristics of the wind speed in a better manner in comparison with the batch learning approach, giving accurate wind speed forecasts. This can help wind farms to estimate the wind power in a location efficiently. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Aspen Plus simulation of NH3-H2O-NaOH and NH3-H2O-KOH ternary cycles
(Elsevier Ltd, 2022) Kolapkar, G.; Sathyabhama, A.
The NH3-H2O is the most frequently utilized refrigerant-absorbent binary mixture in the vapor absorption refrigeration system (VARS) for low-temperature applications, but this mixture has the disadvantage of rectification requirement. To overcome this disadvantage, the researchers suggested the addition of salt to the binary NH3-H2O mixture. In this paper, a simulation of the ternary NH3-H2O-salt mixtures implemented in the VARS is presented. The NaOH and KOH salts are selected in the mass fraction range of 0 to 30% with 50 and 55% NH3 massconcentrations. The Aspen Plus process tool has been used to perform the simulation study. The addition of NaOH and KOH salts to the binary NH3-H2O mixture leads to an increase in thecoefficient of performance (COP) of the VARS with a simultaneous reduction in the initial generator operating temperature. The decrease in the generator temperature is slightly higher after adding NaOH salt than that by adding the KOH salt. TheCOP of thecycle increases after adding salt up to 20% salt mass fraction and then starts decreasing. The rise in the evaporator temperature leads to a gradual rise in theCOP of the ternary NH3-H2O-saltcycles. TheCOP of the ternary NH3-H2O-NaOHcycle is greater than that of the ternary NH3-H2O-KOHcycle under the same operating conditions. © 2022
Assessment of mixture boiling heat transfer correlations for ammonia/water mixture
(2009) Sathyabhama, A.; Ashok Babu, T.P.
The aim of this work is to present a critical examination of both the available experimental data and the performance of the available mixture boiling heat transfer correlations for ammonia/water mixture. First, a selection and comparison of the experimental database found in the open literature at the mentioned working conditions is presented. Subsequently, after a short description of the most relevant heat transfer correlations, and in accordance with the selected data, a detailed analysis of the performance of each correlation is carried out. Results show a small divergence between the experimental data sets and conclude that the presently available correlations show considerable discrepancies in heat transfer coefficients within the selected conditions. © 2009 Wiley Periodicals, Inc.
Augmentation of heat transfer coefficient in pool boiling using compound enhancement techniques
(Elsevier Ltd, 2017) Sathyabhama, A.; Dinesh, A.
Modern compact electronic chip design demands more efficient and innovative cooling techniques in a limited space. One such method is the immersion cooling by pool boiling heat transfer, which is a highly efficient technique when compared with conventional cooling techniques. The boiling heat transfer coefficient can be enhanced using active and passive techniques. In the present investigation grooves as passive and surface vibration as active techniques were coupled to improve the boiling heat transfer coefficient. The forced vertical vibrations were induced on the copper grooved surface with a mechanical vibrator. The frequency of vibration was varied in the range 0–100 Hz and the amplitude of vibration was varied in the range 0–2.5 mm. The compound technique gave 62% improvement in heat transfer coefficient at 300 kW/m2 heat flux compared to the 29% enhancement due to grooves alone and 10% enhancement due to vibration alone. The experimental results were used to develop a modified Rohsenow correlation which predicts the experimental Nusselt number with an accuracy of ±25%. Boiling visualization was performed and the bubble parameters such as bubble departure diameter, bubble frequency and bubble growth were determined. The bubble departure diameter decreased by almost 36% and the bubble frequency increased by 221% for boiling on vibrated grooved surface. © 2017 Elsevier Ltd
Boiling of saturated water on grooved surface
(Serbian Society of Heat Transfer Engineers, 2019) Sathyabhama, A.
The flow patterns and pool boiling heat transfer performance of rectangular grooved surface immersed in saturated water were experimentally investigated. The effect of the aspect ratio (groove depth/fin thickness) on boiling performance was examined. The test surfaces were manufactured on a copper block with a base diameter of 19 mm with four fin thickness (0.5 mm, 1mm, 1.5 mm and 2 mm) and three groove depths (1.0 mm, 2.0 mm and 3.0 mm). All experiments were performed in the saturated state at atmospheric pressure. A plain surface was used as the reference standard and compared with the grooved surfaces. The photographic images showed different boiling flow patterns among the test surfaces at various heat fluxes. The test results indicated that closer and more number of grooves yielded a greater flow resistance against the bubble/vapor lift-off along the groove wall. At higher heat flux, numerous vapor mushrooms periodically appeared from the perimeter of the grooves. The developed correlation for Nusselt number predicts the experimental data with MAE of 7.42%. © 2018 Serbian Society of Heat Transfer Engineers.
Bubble dynamics and enhanced heat transfer during high-pressure pool boiling on rough surface
(American Institute of Aeronautics and Astronautics Inc. custserv@aiaa.org, 2019) Walunj, A.; Sathyabhama, A.
In the present study, the influence of surface roughness (Ra) on critical heat flux (CHF) of water at pressure of 1, 5, and 10 bar is investigated. The desired value of Ra is achieved by making unidirectional scratches on the flat copper surface. Surface roughness Ra varies from 0.106 to 4.03 ?m. The high-speed camera of 1000 fps is used for the boiling visualization study. The effect of surface roughness on bubble departure diameter and bubble frequency at different pressure is reported. Kim's CHF model is modified to include the contact angle as a function of surface roughness and temperature, which predicts the experimental CHF with mean absolute error (MAE) of 10.50% at pressure up to 10 bar. The correlation developed for bubble departure diameter predicts the experimental values with MAE of 17.09%. The relation between bubble departure diameter and bubble frequency is also developed, which predicts the corresponding experimental values with MAE of 25.26%. © 2019 American Institute of Aeronautics and Astronautics Inc. All rights reserved.
Bubble dynamics in pool boiling on rough surface under exponential heat supply
(Begell House Inc. orders@begellhouse.com, 2018) Walunj, A.; Sathyabhama, A.
In this paper, bubble dynamics in the pool boiling of distilled water on the horizontal copper test sample of 20 mm diameter at atmospheric pressure is studied. The experiments are carried under steady and exponential heat supply of Î³=1 to rough copper sample with Ra ranging from 0.106 Î¼m to 4.03 Î¼m. The high speed camera of 1000 fps is used to observe the bubble morphology. The effect of surface roughness on boiling heat transfer during transient heat supply is reported. The effect of surface roughness on bubble departure diameter and bubble frequency is studied. The waiting time and growth time of the bubble for different samples is also compared. The effect of steady and exponential heat supply on bubble departure diameter and bubble frequency is also reported. Â© 2018 Begell House Inc.. All rights reserved.
Bubble dynamics of water-ethanol mixture during subcooled flow boiling in a conventional channel
(Elsevier Ltd, 2017) Suhas, B.G.; Sathyabhama, A.
In this paper, bubble dynamics in subcooled flow boiling of water-ethanol mixture in horizontal rectangular channels is investigated through visualization. The subcooled flow boiling heat transfer coefficient of water ethanol mixtures are determined for various heat flux, mass flux and ethanol volume fraction. A new empirical correlation is proposed to predict the heat transfer coefficient of pure water based on the parameters like heat flux, bubble departure diameter, waiting period and the growth period. Two types of bubble behaviours are observed after nucleation: (i) Sliding for a distance along the bottom wall of the channel surface before lift-off and (ii) Lift-off from the bottom wall of the channel surface without sliding. Force balance analysis is carried out to determine the reason for bubble lift-off and bubble sliding. The bubble lift-off without sliding is observed at higher ethanol volume fraction, lower heat flux and higher channel inlet temperature. The bubble sliding and lift-off are observed at higher heat flux and lower channel inlet temperature for water and water-ethanol mixture of 25% ethanol volume fraction. However, the effect of mass flux on the bubbles sliding or bubble lift-off is not significant. © 2016 Elsevier Ltd
Comparative study of pool boiling heat transfer from various microchannel geometries
(Elsevier Ltd, 2018) Walunj, A.; Sathyabhama, A.
This paper presents the experimental investigation of pool boiling heat transfer enhancemrent using open microchannels. Rectangular, parabolic and stepped microchannels are fabricated on the 10 mm diameter circular copper test piece and their boiling characteristics are compared with that of the plain surface at saturated condition of distilled water. The effect of channel shape and geometrical parameter on the boiling heat transfer is studied. The channel top width and channel base width are varied from 250 ?m to 500 ?m and 500 ?m to 800 ?m, respectively. The fin tip thickness is varied from 200 ?m to 500 ?m. The channel height is fixed at 500 ?m. The morphology of bubble is observed by using high-speed camera. Compound study of bubble departure diameter and bubble frequency has proved the significant performance of parabolic and stepped microchannel. All the microchannel geometries enhanced the heat transfer rate. The modification of rectangular channel into parabolic and stepped microchannel resulted in the maximum of 88% and 169% enhancement, respectively at 11.7 °C wall superheat. At heat flux of 100 kW/m2, the heat transfer coefficient increased by 21.49–35.37% for different microchannels. The incipient temperature reduced by 13.72–23.18%. A semi-analytical model is developed to estimate the bubble departure diameter of the microchannel which predicts the present experimental data with mean absolute error of 5.58%. © 2017 Elsevier Ltd
Comparative study on the aerodynamic performance of airfoil with boundary layer trip of various geometrical shapes
(IOP Publishing Ltd, 2021) Sreejith, B.K.; Sathyabhama, A.; Sandeep Kumar, S.
Performance of small scale wind turbine (SSWT) and miniature aerial vehicles (MAV) is always effected with Laminar separation bubble. The problem of a laminar separation bubble on the upper surface of an E216 airfoil operated at low Reynolds number (Re=100000) is investigated numerically. Incompressible steady two-dimensional simulation is carried out with Transition Î³ - ReÎ¸ turbulence model on the airfoil with a boundary layer trip (BLT). The performance of two different types of trips, namely, isosceles triangular (IT) and right-angled triangular (RA) is compared with that of the airfoil with a rectangular (RT) trip. The trip locations used are, 17% of the chord for location-1 and 10% of the chord for location-2 from the leading edge of the airfoil, while the trip heights selected are 0.3 mm, 0.5 mm, 0.7 mm, and 1 mm. Results showed that the boundary layer trip significantly affected the laminar separation and improved the aerodynamic performance of the airfoil. Maximum improvement in drag by 17.41% and corresponding lift to drag ratio by 10.86% are obtained for the isosceles trip at location-2 for the angle of attack of 6Â°. There is no observable advantage for isosceles and right-angled triangular trips over rectangular trips. Considering the geometrical complexity in fabrication, the rectangular trip is recommended. Â© Published under licence by IOP Publishing Ltd.
Comparative Study on the Effect of Leading Edge Protuberance of Different Shapes on the Aerodynamic Performance of Two Distinct Airfoils
(Isfahan University of Technology, 2023) Reddy, C.J.; Sathyabhama, A.
This study investigated the effect of leading-edge protuberances on the aerodynamic performance of two distinct airfoils with low Reynold’s number (Re): E216 and SG6043. Three protuberance shapes, namely sinusoidal, slot, and triangular, were considered. The amplitudes (A) of protuberances considered were 0.03c, 0.06c, and 0.11c, and the wavelengths (W) were 0.11c, 0.21c, and 0.43c, where c is the chord of the airfoil. The numerical and experimental analyses were performed in the angle of attack (AoA) range of 0° to +20° at and Re of 105. The numerical investigation was performed using the commercial computational fluid dynamics package ANSYS FLUENT. The SST k-ɷ model was used to simulate turbulent flow. The experimental force measurements were conducted using a highly sensitive three-component force balance in a subsonic wind tunnel facility. The flow physics was analyzed using vorticity contours in streamwise and spanwise slices and static pressure distribution contours. The smoke flow visualization technique was used to observe flow streamlines, boundary layer separation, and reattachment over the airfoil surface. The result indicated that the triangular and slot protuberances were the most beneficial for improving poststall lift and reducing skin friction drag. The operating mechanism involved a shift in pressure distribution due to leading-edge alterations and flow energization by secondary flow emanating from the protuberances. © 2023, Journal of Applied Fluid Mechanics. All Rights Reserved.
Comparison of modeling methods for wind power prediction: a critical study
(Higher Education Press Limited Company, 2020) Shetty, R.P.; Sathyabhama, A.; Pai, P.S.
Prediction of power generation of a wind turbine is crucial, which calls for accurate and reliable models. In this work, six different models have been developed based on wind power equation, concept of power curve, response surface methodology (RSM) and artificial neural network (ANN), and the results have been compared. To develop the models based on the concept of power curve, the manufacturer’s power curve, and to develop RSM as well as ANN models, the data collected from supervisory control and data acquisition (SCADA) of a 1.5 MW turbine have been used. In addition to wind speed, the air density, blade pitch angle, rotor speed and wind direction have been considered as input variables for RSM and ANN models. Proper selection of input variables and capability of ANN to map input-output relationships have resulted in an accurate model for wind power prediction in comparison to other methods. © 2018, Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature.
Design of Small-Scale Vertical Axis Wind Turbine with Passive Blade Pitch Control
(Springer Science and Business Media Deutschland GmbH, 2025) Guhan Sidharth, M.; Sathyabhama, A.; Hegde, R.N.
The increase in global energy demand fuelled by the increase in global population along with the need for sustainable and environment-friendly methods of electricity generation has shifted the focus to renewable sources of energy. One such form of energy is the wind energy. It is important to achieve the best possible performance from wind turbines to extract maximum amount of energy from the wind flow. This research work aims at designing a small-scale Vertical Axis Wind Turbine (VAWT) with suitable blade pitch control which would be useful in improving its performance. A three-bladed H-type Darrieus VAWT is considered with the NACA0021 airfoil as the blade cross-sectional profile. The pitch angle is made to vary sinusoidally with the position of the blade with respect to the direction of wind flow. The pitch angle amplitude used is 16Â°. A four-bar mechanism in the double crank configuration has been designed to implement collective blade pitching. Computer-aided design (CAD) models for various parts of the VAWT and the four-bar mechanism have been developed. The designs of these parts were found to be safe based on finite element analysis (FEA) carried out in ANSYS. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Discrepancy in Predicted Head Loss of Non-Newtonian Aqueous Suspension of Fly Ash with Two Different Yield Stress Values Obtained from Rheological Data
(Springer Science and Business Media Deutschland GmbH, 2024) Senapati, S.; Prasad, V.; Dubey, A.; Sathyabhama, A.
The rheological behavior of aqueous suspension of fly ash in 60â€“70% concentration range by weight has been investigated using a high precision rotational rheometer. The nature of the slurry indicated non-Newtonian Bingham plastic. Using Darby et al.â€™s correlation, the combined laminar and turbulent fanning friction factors for the suspension were evaluated with the help of Bingham parameters such as yield stress (Ï„0) and Bingham viscosity (Î·p), and the head loss of fly ash suspension was predicted at weight concentrations of 60, 65, 68, 69 and 70% in a 400 NB mild steel pipe. Besides, the yield stress (Ï„0sg) of the ash suspension samples was determined by using stressâ€“growth method in the concentration range of 60â€“75% by weight. The Ï„0sg values so obtained were then again used to evaluate the head loss of the suspension with the same value of Bingham viscosity at the specified concentrations. It was observed that the head loss predicted by using Ï„0sg values from stressâ€“growth method incurred lower frictional losses as compared to head losses by using the Ï„0 values obtained from linear fit of shear stressâ€“shear rate data. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.
Effect of boiling surface vibration on heat transfer
(2017) Sathyabhama, A.
Experimental investigation of effect of forced vertical surface vibration on nucleate pool boiling heat transfer of saturated water at atmospheric pressure is presented in this paper. Vertical vibration was induced externally to the circular copper test surface on which boiling took place, using a vibration exciter. Frequency was varied in the range 0 25 Hz and amplitude of vibration was varied in the range 0 5 mm. Boiling takes place at much lower superheats for the same heat flux, slope of boiling curve decreases remarkably, when the surface is given external excitation. High frequency and high amplitude oscillations lead to more intensive heat transfer. There are some combinations of frequency and vibration amplitude, which cause up to two times increase in heat transfer coefficients. 2016, Springer-Verlag Berlin Heidelberg.
Effect of boiling surface vibration on heat transfer
(Springer Verlag service@springer.de, 2017) Sathyabhama, A.
Experimental investigation of effect of forced vertical surface vibration on nucleate pool boiling heat transfer of saturated water at atmospheric pressure is presented in this paper. Vertical vibration was induced externally to the circular copper test surface on which boiling took place, using a vibration exciter. Frequency was varied in the range 0–25 Hz and amplitude of vibration was varied in the range 0–5 mm. Boiling takes place at much lower superheats for the same heat flux, slope of boiling curve decreases remarkably, when the surface is given external excitation. High frequency and high amplitude oscillations lead to more intensive heat transfer. There are some combinations of frequency and vibration amplitude, which cause up to two times increase in heat transfer coefficients. © 2016, Springer-Verlag Berlin Heidelberg.
Effect of RIBS/FINS and Aspect Ratio on Flow Boiling Characteristics in Conventional Channels
(American Society of Mechanical Engineers (ASME), 2024) Madan, K.; Sathyabhama, A.
In this work, experiments are conducted with conventional rectangular channels of two different aspect ratios (AR =w/d) for the horizontal boiling flow conditions at atmospheric pressure. Distilled water was used as the working substance. The heat transfer coefficients (HTC) were measured for mass fluxes and heat fluxes ranging from 85.94 kg/m2-s to 343.77 kg/m2-s and 10 kW/m2 to 100 kW/m2, respectively, and at inlet subcooled temperatures of 303 K, 313 K, and 323 K. Visualization of the boiling phenomenon was done using a high-speed camera for the two channels under similar conditions. The results show that the AR has a dominant effect on the HTC. At low heat flux values, higher HTC was noticed for the channel of higher AR (AR=1.25) whereas, at high heat flux conditions, the HTC is higher for the channel of lower AR (AR =0.2). With an increase in inlet subcooled temperature, the HTC decreased for both channels due to increased thermal boundary layer thickness and reduced bubble formation. Further, the channel of AR=1.25 with ribs/fins performed better than the smooth channel due to the high bubble nucleation rate. © 2023 by ASME.
Effect of salt on the performance of ammonia absorption refrigeration cycle: A simulation study
(Elsevier Ltd, 2024) Kolapkar, G.; Sathyabhama, A.
To overcome the drawbacks associated with conventional binary mixtures (NH3-H2O and H2O-LiBr) in the vapor absorption refrigeration system (VARS), salt is added to the NH3-H2O mixture. The present simulation study analyzes the influence of adding LiBr and LiNO3 salts within a salt mass fraction range of 0 to 35% on the coefficient of performance (COP) of the NH3-H2O cycle. The simulations are conducted using Aspen Plus software. Furthermore, the influence of generator temperature on the COP and evaporator capacity of the ternary NH3-H2O-LiBr and NH3-H2O-LiNO3 cycles are also studied. The simulation results demonstrate that adding LiBr and LiNO3 salts improves the COP and reduces the initial temperature requirement in the generator of the VARS. Specifically, the NH3-H2O-LiBr cycle achieves the highest COP of 0.645 at an NH3 mass fraction of 55% and a LiBr mass fraction of 25%. This represents an 8.81% improvement compared to the COP of the NH3-H2O cycle. Similarly, the NH3-H2O-LiNO3 cycle exhibits the peak COP of 0.603 with the same NH3 mass fraction and LiNO3 mass fraction of 20%, which is 2.2% greater than the COP of the NH3-H2O cycle. Under similar operating conditions, the COP of the NH3-H2O-LiBr cycle is greater than that of the NH3-H2O-LiNO3 cycle. © 2024 Elsevier Ltd
Effect of Surface Roughness on Pool Boiling Characteristics under Variable Heat Supply
(Toronto Metropolitan University, 2019) Walunj, A.; Sathyabhama, A.
An experimental investigation of critical heat flux (CHF) for boiling heat transfer from the rough copper sample under steady and quasi-steady exponentially varying heat supply is presented in this paper. The unidirectional scratches are made on the 20 mm diameter copper sample to obtain a wide range of surface roughness, ranging from Ra=0.106 Î¼m to Ra=4.03 Î¼m. The boiling characteristics for steady and transient-state conditions are compared by considering the onset of boiling (ONB) and CHF. The effect of surface roughness on the surface wettability and CHF are also studied. The enhancement in the transient CHF for the roughest sample (Ra=4.03 Î¼m) is found to be 98.88%. The Rohsenow correlation for heat transfer coefficient (HTC) is modified, which predicts the present experimental data of HTC with mean absolute error (MAE) of 10.36%. The hydrodynamic model with capillary wicking force predicts the CHF for a wide range of Ra with a mean absolute error of 4.14%. Â© 2019, Toronto Metropolitan University. All rights reserved.