Faculty Publications
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Item Modeling duration of lateral shifts in mixed traffic conditions(American Society of Civil Engineers (ASCE) onlinejls@asce.org, 2018) Asaithambi, G.; Joseph, J.Traffic on urban roads in developing countries is characterized by wide mix of vehicles with loose lane discipline, which results in parallel movement of vehicles in the same lane. Hence, vehicles not only interact longitudinally with the vehicles ahead but also laterally with vehicles to the sides. Lateral movements have a significant impact on the characteristics of traffic flow and therefore are of great importance in microscopic traffic simulation models. Existing simulation models for mixed traffic conditions model lateral shifts (lateral movements) as an instantaneous process but neglects detailed modeling. However, the duration for lateral shifts is generally in the range of 0.5-15 s. The omission of lateral shift duration from simulation models may have a significant impact on simulation outputs. Also, different vehicle types may have different lateral shift durations due to variations in their physical and operational characteristics. This paper attempts to develop a vehicle-specific lateral shift duration model by considering different explanatory variables such as direction of lateral shift, available space gaps, speeds of subject vehicle and surrounding vehicles, vehicle types, and clearance. The models were estimated using trajectory data collected during medium-flow conditions from an urban arterial in Chennai city, India. The findings from this study have direct implications on modeling lateral shifts in microscopic traffic simulations to be developed specifically for mixed traffic conditions. © 2018 American Society of Civil Engineers.Item 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 Implementation of tubercles on Vertical Axis Wind Turbines (VAWTs): An Aerodynamic Perspective(Elsevier Ltd, 2022) Sridhar, S.; Joseph, J.; Radhakrishnan, J.In recent days, enhancement of Vertical Axis Wind Turbines (VAWTs) by mitigating flow deteriorating effects like dynamic stalling, unsteady wake is given great importance. The following article focuses on implementing four different tubercles on the blades’ leading edge and studying its performance and flow characteristics using CFD techniques. Results indicate that the addition of tubercles generated counter-rotating vortices and delayed flow separation and helped control dynamic stalling. Between azimuth angles 70°–160°, the flow was seen to separate only along the trough regions of the blade and remained attached along the peak regions, thus providing more torque and power. In addition to the enhancements in the flow characteristics, a 28% increase in power coefficient was observed for the optimal configuration at the optimal tip speed ratio. Additionally, a 14% increase in maximum lift generated by the blade was observed. Preliminary aeroacoustics analysis revealed a 12% and 20% decrease in the noise emissions along the blade tip and mid-plane of the turbine, respectively. Hence, it can be shown that tubercles effectively control dynamic stall, reduce noise emissions, and increase the power output of VAWTs. © 2022 Elsevier LtdItem Experimental Study on the Effect of Tubercle on Aerodynamic Characteristics of Swept Wings at low Reynolds Number(Springer Science and Business Media Deutschland GmbH, 2022) Joseph, J.; Sathyabhama, A.Inspired from the Humpback whale flipper, airfoils and wings incorporated with sinusoidal leading edge are much studied for their improved aerodynamic characteristics like delayed stall and higher lift in post-stall region. In this work, the performance of different swept wings equipped with leading edge tubercles is studied by comparing with their baseline models at a low Reynolds number of 100,000. Tubercles on swept wings can either be placed normal to leading edge or parallel to flow direction. First part of the study involves selecting the swept wing configuration which has superior aerodynamic performance from the two possible configurations based on the tubercle alignment on it. Wind tunnel experiment is conducted for the above-mentioned configuration of tubercles on different swept wings as well as unswept wing and compared to corresponding baseline wings. The orientation of tubercle relative to flow has a significance in aerodynamic performance. Aerodynamic efficiency is maximum when the tubercles are aligned with the flow direction. It is seen that tubercles on high swept wing are not as effective as it is on a unswept wing. On unswept and low swept, wing tubercles improve the stall characteristics by preventing abrupt stall and maintaining high lift in post-stall regime. The lift-to-drag ratio for these wings is improved when tubercles are introduced. However, for high swept, wing tubercles do not change the aerodynamic characteristics significantly. © 2021, Shiraz University.Item 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.Item 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