Faculty Publications

Now showing 1 - 3 of 3

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. © 2022
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 Ltd
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.

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