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Effects of solidity on the vibrational characteristics of the LEP VAWT

WIND AND STRUCTURES 2025年第1期40卷 13-28页

作者： Elangovan, Karthik Vel Pillai, S. Nadaraja SASTRA Deemed Be Univ Turbulence & Flow Control Lab Thanjavur 613041 Tamil Nadu India

The primary goal of this research is to explore the influence of structural responses brought about by alterations in aerodynamic characteristics resulting from the incorporation of leading-edge protuberance (LEP) blades in vertical-axis wind turbines (VAWTs). A scaled-down straight-blade VAWT was utilized and subjected to operational wind speeds at a fixed pitch angle and various blade configurations to carry out this investigation. The study specifically aimed to investigate the unsteady structural excitation caused by the decay of vortices due to different aerodynamic loads and their effects on the VAWT structure. The results demonstrated that counter-rotating vortices in the LEP profile enhanced the aerodynamics of the blades at higher angles of attack. Understanding the structural characteristics resulting from aerodynamic changes is essential for developing VAWTs. The current research analyzes the effects of LEP on the structural excitation of a VAWT by examining the acceleration and displacement data obtained from a static-structure VAWT for various solidity ratios and LEP profiles. The results indicated that the VAWT with LEP blades resulted in decreased acceleration and displacement amplitudes for a low solidity ratio, which increased with an increase in the solidity ratio. Significant aerodynamic and structural damping were observed in the VAWT with LEP blades. These results were in close agreement with the time and frequency domains of the measured displacement and acceleration of the structure. The average bi-directional vibration damping of approximately 35% was observed by substituting the straight blade with the LEP blades for the operation of VAWT.

关键词： aerodynamic damping dynamic stall experimental study leading edge protuberance passive flow control solidity ratio VAWT

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Effect of Pitch Angle on Structural and Aerodynamic Characteristics of Vertical-Axis Wind Turbines (VAWTs) Using Leading-Edge Protuberance Blades

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ENERGIES 2025年第2期18卷 286-286页

作者： Elangovan, Karthikvel Pillai, S. Nadaraja SASTRA Deemed Univ Sch Mech Engn Turbulence & Flow Control Lab Thanjavur 613401 Tamil Nadu India

An experimental investigation was carried out to understand the effects of LEP (leading-edge protuberance) blades on the structural characteristics of VAWTs. A series of experiments were performed on VAWTs with straight and LEP blades for a wide range of wind velocity (6 m/s to 20 m/s) and pitch angles (-20 degrees to 20 degrees), and the structural excitations on the VAWT structure were measured using a triaxial accelerometer in each case. The raw acceleration data were extensively processed in the time and frequency domains to identify the variation in structural excitation caused by the unsteady wind and aerodynamic loads on the VAWT structure. Understanding the aerodynamic changes and their impact on structural characteristics is essential. The current study examines how LEP influences the structural excitation of VAWTs. However, a great deal of aerodynamic variation was observed for the LEP blades, so the straight blades of the VAWT were replaced with various modified LEP blades, for which a similar set of experiments was carried out. The study presents a better performance (self-starting, stall-mitigating) for VAWTs with LEP 3 and 2 blades, with a significant reduction in the excitation of loads due to wind load and the changes in aerodynamics observed in the along- and across-wind directions.

关键词： dynamic stall VAWT (vertical-axis wind turbine) leading-edge protuberance energy reduction index vibration passive flow control condition monitoring dynamic testing

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Downstream characteristics of extended flat plate trailing edge on S809 wind turbine blade under various turbulent intensities

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Aircraft Engineering and Aerospace Technology 2023年第10期95卷 1678-1693页

作者： Mano, S. Nadaraja Pillai, S. Turbulence and Flow Control Lab School of Mechanical Engineering SASTRA Deemed University Thanjavur India

Purpose: This study aims to investigate the effect of downstream characteristics of S809 wind turbine blade with various extended flat plate (EFP) configuration. Wind farms are recently modified to improve the power production through placing number of wind turbines and locations. Design/methodology/approach: A series of wind tunnel experiments were carried out to evaluate the downstream wake characteristics of the S809 airfoil attached with various EFP (EFP, A = 0.1C, 0.2C and 0.3C) at various angles of attack corresponding to free stream velocity Reynolds number (Re) = 2.11 × 105 and various turbulence intensity (TI = 5%, 7%, 10% and 12%). Findings: For the S809 wind turbine blade attached with EFP, the downstream velocity ratio decreases with increasing in angle of attack and the velocity deficit decrease with increasing turbulence intensity (TI) up to TI = 10%. The wake intensity for the S809 wind turbine blade and S809 airfoil with 10% of chord EFP performs the same for each downstream location. Practical implications: Placing the wind turbine in the wind park next to another wind turbine poses a potential challenge for the park power performance. This research addresses the characteristics of the downstream turbulence intensity profile modified with the EFP in the wind turbine blade which improves the downstream characteristics of the turbine in the wind park. Originality/value: The downstream velocity ratio decreases with increasing angle of attack and the velocity deficit decrease with increasing turbulence intensity (TI) up to TI = 10%. © 2023, Emerald Publishing Limited.

关键词： Angle of attack

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Experimental Investigation of Trailing Edge Surface Roughness on the Aerodynamic Characteristics of the Wind Turbine Blades 9th

Experimental Investigation of Trailing Edge Surface Roughnes...

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9th International and 49th National Conference on Fluid Mechanics and Fluid Power, FMFP 2022

作者： Vel, E Karthik Vandish, Sanchay Ramesh, Mugil Rai, Samar Pratap Pillai, S Nadaraja Turbulence & Flow Control Lab SchoolofMechanicalEngineering SASTRA Deemed to Be University Thanjavur613401 India

ISBN: (纸本)9789819710324

Numerous research studies have been conducted on the effects of aerodynamic characteristics of airfoils with leading-edge modifications such as adding roughness, undulations, and so on, which have resulted in favourable changes in aerodynamic characteristics as a successful passive flow control method, thereby increasing the repository of scientific data for the corresponding research. This led to the present study, which deals with a new passive flow control technique that has a distributed roughness element in the form of an emery sheet, placed on the suction side of the airfoil with an area covering about 50% chord from the trailing edge of the airfoil. An experimental analysis of the modified NACA 0015 airfoil was performed in the low subsonic wind tunnel situated at SASTRA Deemed to Be University for the free stream Reynolds number of 2.04 × 105 at angles of attack ranging from 0° to 45°. A multichannel Ethernet-Based Simultaneous Pressure Scanner was used to measure the surface pressure of the airfoil, which was further processed for aerodynamic characteristics. The investigation has revealed exceptional aerodynamic characteristics in the pre-stall region with a decrease in the coefficient of drag, thereby increasing the aerodynamic efficiency. The stall behaviour has also been altered by the addition of a roughness element at the flow transition region on the airfoil surface. This in turn reduces the effects of the adverse pressure gradient at critical and post-critical angles of attack, inducing turbulence kinetic energy at the transitional boundary layer, enhancing an attached flow and a delay in the stall. The addition of the roughness element at the trailing surface of the airfoil has predominantly affected the aerodynamic characteristics, which may reduce the effects of dynamic stalls, thus paving the way for the design of an efficient wind turbine blade. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.

关键词： Airfoils

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Effect of stall delay characteristics of symmetrical aerofoil using lateral circular ridges

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WIND AND STRUCTURES 2022年第4期34卷 385-394页

作者： Raatan, V. S. Ramaswami, S. Mano, S. Pillai, S. Nadaraja SASTRA Sch Mech Engn Turbulence & Flow Control Lab Thanjavur 613401 India

Global Warming has been driven majorly by the consumption of fossil fuels. Harnessing energy from wind is viable solution towards reducing carbon footprint created due to burning such fuels, However, wind turbines have their problems of flow separation and aerodynamic stall to tackle with. In an attempt to delay the stall angle and improve the aerodynamic characteristics of the NACA 0015 symmetrical aerofoil, lateral cylindrical ridges were attached to its suction surface, at chord positions ranging from 0.1c to 0.5c. The characteristics of the original and ridged aerofoils were obtained using simultaneous pressure readings taken in a wind tunnel, at a free stream Reynolds number of R-e = 2.81 x 10(5) for a wide range of free stream angles of attack ranging from -45 degrees to 45 degrees. Depending on the ridge size, a delay in stall angle varying from 5 degrees to 20 degrees was achieved together with the maximum increase in lift in the post-stall phases. Additionally, efforts were made to identify the optimum position for each ridge.

关键词： cylindrical/circular ridges flow separation separation bubble

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Effect of turbulence intensity on aerodynamic characteristics of extended trailing edge airfoil

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AIRCRAFT ENGINEERING AND AEROSPACE TECHNOLOGY 2022年第10期94卷 1780-1791页

作者： Livya, E. Pillai, S. Nadaraja SASTRA Deemed Univ Sch Mech Engn Turbulence & Flow Control Lab Thanjavur India

Purpose This paper aims to study the extended trailing edge airfoil for a range of angle of attack at different intensities of turbulence. Design/methodology/approach In this paper, an experimental study on NACA 0020 airfoil with thin extended trailing edge modification of amplitude of h = 0.1c, 0.2c and 0.3c at the Reynolds number of 2.14 x 10(5) are tested. The research was carried out for an angle of attack ranging from 0 degrees = alpha = 35 degrees for the turbulence intensity of 0.3%, 3%, 5%, 7% and 12%. From the experimental readings, the surface pressures are scanned using a Scanivalve (MPS2464) pressure scanner for a sampling frequency of 700 Hz. The scanned pressures are converted to aerodynamic force coefficient and the results are combined and discussed. Findings The airfoil with the extended trailing edge will convert the adverse pressure gradient to a plateau pressure zone, indicating the delayed flow separation. The CL value at higher turbulence intensity (TI = 12%) for the extended trailing edge over perform the base airfoil at the post-stall region. The maintenance of flow stability is observed from the spectral graph. Practical implications A thin elongated trailing edge attached to the conventional airfoil serves as a flow control device by delaying the stall and improving the lift characteristics. Additionally, extending the airfoil's trailing edge helps to manage the performance of the airfoil even at a high level of turbulence. Originality/value Distinct from existing studies, the presented results reveals how the extended trailing edge attached to the airfoil performs in the turbulence zone ranging from 0.3% to 12% of TI. The displayed pressure distribution explains the need for increasing trailing edge amplitude (h) and its impact on flow behaviour. The observation is that extended trailing edge airfoil bears to maintain the performance even at higher turbulence region.

关键词： Extended trailing edge airfoil turbulence intensity Wind tunnel experiment Surface pressure measurement Lift coefficient

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Aerodynamic Analysis of Stretched Trailing Edge Over NACA 0020 Airfoil at Various turbulence Intensities 9th

Aerodynamic Analysis of Stretched Trailing Edge Over NACA 00...

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9th International and 49th National Conference on Fluid Mechanics and Fluid Power, FMFP 2022

作者： Livya, E. Pillai, S. Nadaraja Turbulence and Flow Control Lab School of Mechanical Engineering SASTRA Deemed University Thanjavur613401 India

ISBN: (纸本)9789819957514

To understand how the stretched trailing edge customizes the airfoil aerodynamics in an experimental approach, the present work studied the symmetrical NACA 0020 airfoil subjects to the incoming airflow at higher intensities of freestream turbulence (i.e. 12%). The Reynolds number was fixed as Re = 2.4 × 105, the airfoil was tested under various turbulence intensities of 0.3, 7 and 12%. The trailing edge of the airfoil has been stretched for the extension (h) of 10%, 20% and 30% of chord (c) and the test carried for the angle of attack varies from 0° to 35°. It has been realized that stretching the airfoil trailing edge can augment the lift with a less significant increment in drag. The stretched trailing edge is simply an add-on thin plate fixed together with the airfoil at the trailing edge without altering the elemental structure of the conventional airfoil benefits to advance the aerodynamic performance. The obtained results direct that revising the airfoil trailing edge revises the flow pattern over the airfoil. The modification in terms of stretching the trailing edge acts as a flow control tool and aids to maintain the performance even operating at higher freestream turbulence. © 2024, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

关键词： Airfoils

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Influence of trailing edge serration in the wake characteristics of S809 airfoil

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WIND AND STRUCTURES 2023年第1期37卷 15-23页

作者： Sekar, Mano Pasha, Amjad Ali Subramania, Nadaraja Pillai SASTRA Deemed Univ Turbulence Flow Control Lab Thanjavur Tamil Nadu India King Abdulaziz Univ Dept Aerosp Engn Jeddah 21589 Saudi Arabia

The wake behavior of extended flat plate and serration in the trailing edge of S809 airfoil is presented in this experimental study using wind tunnel testing. The clustering of wind turbines in wind parks has recently been a pressing issue, due to the expected increase in power output and deciding the number of wind turbines to be installed. One of the prominent factors which influence the performance of the subsequent wind turbines is the downstream wake characteristics. A series of wind tunnel investigations were performed to assess the downstream near wake characteristics of the S809 airfoil at various angles of attack corresponding to the Reynolds Number Re = 2.02 x 105. These experimental results revealed the complex nature of the downstream near wake characteristics featuring substantial asymmetry arising out of the incoherent flow separations prevailing over the suction and the pressure sides of the airfoil. Based on the experimental results, it is found that the wake width and the downstream velocity ratio decrease with an increase in the angle of attack. Nonetheless, the dissipation length and downstream velocity ratio increases proportionally in the downstream direction. Additionally, attempts were made to understand the physical nature of the near wake characteristics at 1C, 2C, 3C and 4C downstream locations.

关键词： downstream velocity ratio downstream wake velocity Extended Flat Plate (EFP) trailing-edge serrations wake intensity

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The Influence of Serrated Trailing-Edge Over NACA 0020 Airfoil at Different turbulence Intensities 1

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48th National Conference on Fluid Mechanics and Fluid Power, FMFP 2021

作者： Livya, E. Nadaraja Pillai, S. Turbulence & Flow Control Lab School of Mechanical Engineering SASTRA Deemed University Thanjavur613401 India

ISBN: (数字)9789811969706

ISBN: (纸本)9789811969690

To realize the intuition on how serrated trailing edge modifies the airfoil aerodynamics in a standardized manner, the current experimental work considers a NACA 0020 symmetrical airfoil exposed to the approaching flow with different turbulent intensity. The Reynolds number was adhered at Re = 3.4 × 105, whereas the turbulent intensity ranges from 0 to 5% is consider in this study. It is noticed that a thin serrated trailing edge can boost the lift, although it appears no series rise in drag. The serrated trailing edge is a mechanism that joined together to the wing at the trailing edge without changing the basic geometry favours ability to progress vast aerodynamic improvement. In addition, seeding turbulence to the flow shows an effect on delaying the stall angle to the extent of 5°. An increment in lift co-efficient along the linear region is also observed with an increase in turbulence intensity. At higher turbulence intensity, additional kinetic energy develops on the boundary layer along the suction side of the airfoil. This results to suppress the pressure fluctuation and in turn, a rise in lift to considerable extent, thus the serration on the trailing edge works as a flow control device. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

关键词： Airfoils

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A CFD analysis on the effects of design modifications on flow characteristics in a directional control valve 1

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48th National Conference on Fluid Mechanics and Fluid Power, FMFP 2021

作者： Datta, Aluru V. Siva Charana Sudarshan, G. Pranav, D.S. Ramaswami, S. Pillai, S. Nadaraja Turbulence & Flow Control Lab School of Mechanical Engineering SASTRA Deemed University Thanjavur613401 India

ISBN: (数字)9789811962707

ISBN: (纸本)9789811962691

This paper aims to study the characteristics of a directional control valve of spool-type to determine the relation among inlet pressure, outlet pressure, and mass flow rate;to study the effect of geometrical modifications on the pressure drop and to reduce the pressure drop. Initially, the spool valve model was simplified to make it easier to conduct a study. The steadystate analysis of spool valve characteristics was conducted. In this analysis, the valve was opened fully and the mass flow rate subsequently changed. The graph between outlet pressure and mass flow rate was plotted. Finally, geometrical modifications have been made to reduce the pressure drop caused by the sudden change in flow area due to spool geometry. This was verified through analysis, the results of which were compared with those obtained during the initial analysis. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

关键词： Pressure drop

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