Faculty Publications

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Publications by NITK Faculty

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Analyzing dynamic stall on tubercle mounted VAWT blades: A simplistic experimental approach using an oscillating rig
(Elsevier Ltd, 2024) Joseph, J.; Sridhar, S.; A, S.; Radhakrishnan, J.
Leading-edge tubercles, inspired by the flippers of humpback whales, are widely adopted passive flow control devices to enhance the aerodynamic performance of various lifting surfaces. This experimental study investigates the implementation of sinusoidal and triangular tubercles on H-type Vertical Axis Wind Turbine blades to analyze their effects on dynamic stall characteristics. Experimental tests were conducted using a specially designed oscillating rig to replicate blade motion at different reduced frequencies. The results reveal that tubercle blades exhibit a lower stall angle and maximum normal force compared to the baseline configuration. Moreover, the dynamic stall characteristics of tubercle blades are notably smoother, leading to reduced hysteresis losses. A variation in the tubercle amplitude-wavelength ratio further decreases hysteresis, albeit at the cost of reduced normal force generation. At the highest tested reduced frequency of 0.065, tubercles reduce hysteresis by up to 38%. Despite the reduction in normal force, tubercles effectively mitigate the effects of dynamic stall vortices, resulting in smoother stall behavior. The observed reduction in hysteresis can contribute to enhancing the turbine's lifespan and increasing power production efficiency. This experimental approach provides a cost-effective alternative to more expensive methods for studying dynamic stall characteristics. © 2024 The Authors
Deep learning ensemble method for classification of satellite hyperspectral images
(Elsevier B.V., 2021) Iyer, P.; A, S.; Lal, S.
Classification of hyperspectral image(HSI) is extensively utilized for the study of remotely sensed satellite images for various real-life applications. Convolutional Neural Networks (CNNs) are a commonly used deep learning technique for image data processing. The utilization of 2D CNNs and 3D CNNs have gained popularity in recent years for classification of hyperspectral image, and a lot of architectures with the combination of two have been proposed some of which include residual network based architectures. So, far individual models have been proposed and ensembling has not been explored much. In this paper, we propose an inception inspired architecture (IIA) and ensembled it with existing architectures HybridSN and inception residual network. The proposed IIA has 3D and 2D inception blocks which enable better spectral-spatial learning features. The Experiments are conducted on three well known publicly available HSI datasets and the results are compared to the state-of-the-art techniques. Experimental results yield that proposed deep learning ensemble method provides enhanced performance as compared to the state-of-the-art techniques. The python source code of the proposed method is available at https://github.com/shyamfec/DL-Ensemble-Method. © 2021 Elsevier B.V.
Experimental and numerical analysis of humpback whale inspired tubercles on swept wings
(Emerald Publishing, 2022) Joseph, J.; A, S.; Sridhar, S.
Purpose: With aims to increase the aerodynamic efficiency of aerodynamic surfaces, study on flow control over these surfaces has gained importance. With the addition of flow control devices such as synthetic jets and vortex generators, the flow characteristics can be modified over the surface and, at the same time, enhance the performance of the body. One such flow control device is the tubercle. Inspired by the humpback whale’s flippers, these leading-edge serrations have improved the aerodynamic efficiency and the lift characteristics of airfoils and wings. This paper aims to discusses in detail the flow physics associated with tubercles and their effect on swept wings. Design/methodology/approach: This study involves a series of experimental and numerical analyses that have been performed on four different wing configurations, with four different sweep angles corresponding to 0°, 10°, 20° and 30° at a low Reynolds number corresponding to Rec=100,000. Findings: Results indicate that the effect of tubercles diminishes with an increase in wing sweep. A significant performance enhancement was observed in the stall and post-stall regions. The addition of tubercles led to a smooth post-stall lift characteristic compared to the sudden loss in the lift with regular wings. Among the four different wings under observation, it was found that tubercles were most effective on the 0° configuration (no sweep), showing a 10.8% increment in maximum lift and a 38.5% increase in the average lift generated in the post-stall region. Tubercles were least effective on 30° configuration. Furthermore, with an increase in wing sweep, co-rotating vortices were distinctly observed rather than counter-rotating vortices. Originality/value: While extensive numerical and experimental studies have been performed on straight wings with tubercles, studies on the tubercle effect on swept wings at low Reynolds number are minimal and mainly experimental in nature. This study uses numerical methods to explore the complex flow physics associated with tubercles and their implementation on swept wings. This study can be used as an introductory study to implement passive flow control devices in the low Reynolds number regime. © 2022, Emerald Publishing Limited.
Liquid-infused surfaces for mitigation of corrosion and inorganic scaling
(Elsevier Ltd, 2024) Yandapalli, A.V.V.R.P.; A, S.; Kuravi, S.; Kota, K.
In this study, the effectiveness of a binary surface (BiS), a type of liquid-infused surface, in enhancing corrosion resistance and mitigating inorganic fouling without compromising heat exchange efficiency is demonstrated. An Ultra-Omniphilic Surface (UOS) was initially prepared from a plain aluminum alloy surface (PS) using a bulk micro-manufacturing approach. Subsequently, the sub-surface micro/nanocavities of UOS were infused with a liquid lubricant to create BiS, characterized by two distinct superficial phases — solid islands and liquid puddles. Lab-scale experiments in a simulated brackish water environment revealed that BiS outperformed both PS and UOS in inhibiting scaling and corrosion. The BiS exhibited nearly 50% less mass gain due to mineral deposition than PS and UOS. Moreover, corrosion rates obtained from electrochemical and immersion tests indicated significantly slower metal degradation on BiS compared to PS and UOS. Furthermore, BiS displayed superior heat exchange capabilities, collecting approximately 73% and 44% more condensate than PS and UOS, respectively. This enhancement is attributed to well-distributed liquid puddles on BiS, promoting a smooth, defect-free surface that reduces foulant adhesion and shields the underlying metal from corrosion, while also enhancing two-phase heat transfer activity. © 2024 Elsevier Ltd