Performance of a High Tip Speed Ratio H-Darrieus in the Skewed Flow on a Roof

2003 ◽  
Author(s):  
Sander Mertens ◽  
Gijs van Kuik ◽  
Gerard van Bussel
Keyword(s):  
Wind Turbines ◽  
Power Output ◽  
Energy Demand ◽  
Leading Edge ◽  
Spatial Dimension ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Blade Element Theory ◽  
Excess Power ◽  
Flat Roof

Small wind turbines sited on a flat roof have good opportunities to become widespread. They operate in the accelerated wind above the roof and deliver the power where it is needed. Since the power produced offsets that which would otherwise be bought from the utility, they reduce energy demand and bills from the utility. Furthermore excess power can be sold back to the utility, thus producing income as well. Flow over a building separates at the roof leading edge at a certain angle. Wind turbines sited well above the roof thus operate in skewed flow. H-Darrieus operating at (flat) roofs just recently start to be at public interest, operation of an H-Darrieus in skewed flow is thus not discussed in literature until now. To examine this, a model of an H-Darrieus with high Tip Speed Ratio (λ) in skewed flow is developed. The model is based on multiple stream-tube theory: a combination of axial momentum and blade element theory on an actuator plate representation of the rotor, which is divided into multiple stream-tubes. The model shows that, for an H-Darrieus designed for skewed flow, the optimal power output in skewed flow can be up to two times the power output in normal - perpendicular to the H-Darrieus axis- flow. The spatial dimension of the H-Darrieus is responsible for this.

Study of Aerodynamic Performance and Power Output for Residential-Scale Wind Turbines

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Alaa S. Hasan ◽  
Mohammed Abousabae ◽  
Abdel Rahman Salem ◽  
Ryoichi S. Amano
Keyword(s):  
Wind Turbines ◽  
Power Output ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Speed Ratio ◽  
Computational Domain ◽  
Horizontal Axis Wind Turbine ◽  
Layer Transition ◽  
Baseline Design ◽  
Wind Speeds

Abstract This study presents the rotor blade airfoil analysis of residential-scale wind turbines. On this track, four new airfoils (GOE 447, GOE 446, NACA 6412, and NACA 64(3)-618) characterized by their high lift-to-drag ratios (161.3, 148.7, 142.7, and 136.3, respectively). These new airfoils are used to generate an entire 7 m long blades for three-bladed rotor horizontal axis wind turbine models tested numerically at low, medium, and rated wind speeds of 7.5, 10, and 12.5 m/s, respectively, with a design tip speed ratio of 7. The criterion to judge each model’s performance is power output. Thus, the blades of the model that produce the highest power are selected to undergo a tip modification (winglet) and leading-edge modification (tubercles), seeking power improvement. It is found that the GOE 447 airfoil outperformed the other three airfoils at all tested wind speeds. Thus, it is opted for adding winglets and tubercles. At 12.5 m/s, winglet design produced 5% more power, while tubercles produced 5.5% more power than the GOE 447 baseline design. Furthermore, the computational domain is divided into two regions: rotating (the disc that encloses the rotor) and stationary (the rest of the flow domain). Meanwhile, the numerical model is validated against the experimental velocity measurements. Since Reynolds-averaged Navier–Stokes with k–ω shear stress transport turbulence model can capture the laminar-to-turbulent boundary layer transition, it is used in the 18 simulations of the current work. However, large eddy simulation (LES) can deal successfully with the various scale eddies resulting from the rotor blades and its interactions with the surrounding flow. Thus, the LES was used in the six simulations done at the rated wind speed. LES power output calculation is 7.9% to 11.9% higher than the RANS power output calculation.

Experimental Investigation of Performance Characteristics for Savonius-Style VAWTs: A Comparative Study

2021 ◽  
Author(s):  
Diplina Paul ◽  
Abhisek Banerjee
Keyword(s):  
Wind Turbines ◽  
Coefficient Of Performance ◽  
Total Power ◽  
Speed Ratio ◽  
Mechanical Loads ◽  
Tip Speed Ratio ◽  
Ac Motor ◽  
Different Types ◽  
Laminar Air Flow ◽  
Rotor Profiles

Abstract Savonius-style wind turbines are mainly gauged by two types of coefficients namely: (i) coefficient of power (CP) and (ii) coefficient of torques (CT). Coefficient of power is defined as the ratio of power generated by the turbine to the total power available to the turbine from the free-flowing wind. This is synonymous to the operational efficiency of the wind turbine. Coefficient of torque reflects the torque generating ability of the turbine. In this manuscript, experiments have been performed using three different types of rotor profiles for Savonius-style wind turbines (SSWTs) namely, classical SSWT, Benesh type SSWT and elliptical shaped SSWT using oriented jets. Using deflector plates the orientation of jets have been varied from 20° to 70°. Addition of deflector plates to the wind turbines, assists in maximizing the utilization of wind energy. Experiments have been performed in the laminar air flow. Mechanical loads have been used to study Coefficient of performance (CP) and coefficient of torque (CT) as a function of tip speed ratio (TSRs). The velocity of the wind is adjusted by varying the rheostat that controls the AC motor for the wind tunnel systems. Experimental results indicated that optimum performance could be achieved from all three types of SSWT variants at TSR ∼ 0.70. Out of the three designs studied in this manuscript, elliptic shaped SWT yielded best coefficient of performance equal to 0.39 at TSR = 0.70.

Performance of an H-Darrieus in the Skewed Flow on a Roof1

2003 ◽  
Vol 125 (4) ◽  
pp. 433-440 ◽  
Author(s):  
Sander Mertens ◽  
Gijs van Kuik ◽  
Gerard van Bussel
Keyword(s):  
Wind Turbines ◽  
Power Output ◽  
Vertical Axis ◽  
Horizontal Wind ◽  
Energy Yield ◽  
Wind Environment ◽  
Momentum Theory ◽  
Vertical Axis Wind Turbines ◽  
Flat Roof ◽  
Blade Element

Application of wind turbines on roofs of higher buildings is a subject of increasing interest. However, the wind conditions at the roof are complex and suitable wind turbines for this application are not yet developed. This paper addresses both issues: the wind conditions on the roof and the behavior of a roof-located wind turbine with respect to optimized energy yield. Vertical Axis Wind Turbines (VAWTs) are to be preferred for operation in a complex wind environment as is found on top of a roof. Since the wind vector at a roof is not horizontal, wind turbines on a roof operate in skewed flow. Thus the behavior of an H-Darrieus (VAWT) is studied in skewed flow condition. Measurements showed that the H-Darrieus produces an increased power output in skewed flow. The measurements are compared with a model based on Blade Element Momentum theory that also shows this increased power output. This in contradiction to a HAWT in skewed flow which suffers from a power decrease. The paper thus concludes that due to this property an H-Darrieus is preferred above the HAWT for operation on a flat roof of higher buildings.

scholarly journals Wake Expansion and the Finite Blade Functions for Horizontal-Axis Wind Turbines

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7653
Author(s):  
David Wood
Keyword(s):  
Radial Velocity ◽  
Wind Turbines ◽  
Loss Factor ◽  
Axial Direction ◽  
Horizontal Axis ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Constant Pitch ◽  
Horizontal Axis Wind Turbines ◽  
Blade Element

This paper considers the effect of wake expansion on the finite blade functions in blade element/momentum theory for horizontal-axis wind turbines. For any velocity component, the function is the ratio of the streamtube average to that at the blade elements. In most cases, the functions are set by the trailing vorticity only and Prandtl’s tip loss factor can be a reasonable approximation to the axial and circumferential functions at sufficiently high tip speed ratio. Nevertheless, important cases like coned or swept rotors or shrouded turbines involve more complex blade functions than provided by the tip loss factor or its recent modifications. Even in the presence of significant wake expansion, the functions derived from the exact solution for the flow due to constant pitch and radius helical vortices provide accurate estimates for the axial and circumferential blade functions. Modifying the vortex pitch in response to the expansion improves the accuracy of the latter. The modified functions are more accurate than the tip loss factor for the test cases at high tip speed ratio that are studied here. The radial velocity is important for expanding flow as it has the magnitude of the induced axial velocity near the edge of the rotor. It is shown that the resulting angle of the flow to the axial direction is small even with significant expansion, as long is the tip speed ratio is high. This means that blade element theory does not have account for the effective blade sweep due to the radial velocity. Further, the circumferential variation of the radial velocity is lower than of the other components.

scholarly journals Design of Wind Turbine Blade with Thick Airfoils and Flatback and its Aerodynamic Characteristic

2015 ◽  
Vol 9 (1) ◽  
pp. 910-915 ◽  
Author(s):  
Lijun Xu ◽  
Lei Xu ◽  
Lei Zhang ◽  
Ke Yang
Keyword(s):  
Wind Turbine ◽  
Power Output ◽  
Aerodynamic Characteristic ◽  
Aerodynamic Performance ◽  
Parameter Design ◽  
Speed Ratio ◽  
Original Design ◽  
Tip Speed Ratio ◽  
Blade Tip ◽  
The Relationship

large-scaled blade has posed many problems related to design and production. After introducing the features of blade with thick airfoils and flatback, based on relevant parameters of Huaren 100 kW wind turbine, the paper designed blade with thick airfoils and flatback, introduced blade parameter design, and analyzed the aerodynamic performance of blades using GH bladed software, obtaining the relationship between power output of wind turbine with blade tip speed ratio Cp. Furthermore, it analyzed the aerodynamic performance of original design blades, modified blades and Huaren 100 kW blades, and assessed the aerodynamic performance of modified blade.

Experimental and Computational Investigation on Gyromill Wind Turbines Focusing on Wing Camber

2015 ◽  
Author(s):  
Eiji Ejiri ◽  
Tomoya Iwadate
Keyword(s):  
Wind Turbines ◽  
Flow Analysis ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Computational Investigation ◽  
Tip Speed Ratio ◽  
Maximum Value ◽  
Commercial Code ◽  
Volume Method ◽  
Turbine Impeller

Gyromill wind turbines with three different blade profiles were investigated experimentally and numerically in order to verify the effect of the direction of camber on aerodynamic performance. Experiments were carried out using a model turbine impeller with an axial length of 200 mm and a diameter of 200 mm. The results showed that the maximum power coefficient was higher for blades with negative camber than for ones with positive camber. On the other hand, the operating range of the tip speed ratio tended to be narrower for the blades with negative camber than for the ones with positive camber. An unsteady numerical flow analysis around the wind turbines was conducted using a commercial code employing the finite volume method. The results showed that the power coefficient of one blade had a maximum value in the second quadrant and that the blades with negative camber were advantageous for obtaining high rotational force in the position, compared with the blades with positive camber and a symmetrical blade.

Aerodynamic Design and Wind Tunnel Tests of Small-scale Horizontal-axis Wind Turbines for Low Tip Speed Ratio Applications

2022 ◽  
pp. 1-34
Author(s):  
Ojing Siram ◽  
Neha Kesharwani ◽  
Niranjan Sahoo ◽  
Ujjwal K. Saha
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Pitch Angle ◽  
Horizontal Axis ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Small Scale ◽  
Wind Tunnel Tests ◽  
Tip Speed Ratio ◽  
Horizontal Axis Wind Turbines

Abstract In recent times, the application of small-scale horizontal axis wind turbines (SHAWTs) has drawn interest in certain areas where the energy demand is minimal. These turbines, operating mostly at low Reynolds number (Re) and low tip speed ratio (λ) applications, can be used as stand-alone systems. The present study aims at the design, development, and testing of a series of SHAWT models. On the basis of aerodynamic characteristics, four SHAWT models viz., M1, M2, M3, and M4 composed of E216, SG6043, NACA63415, and NACA0012 airfoils, respectively have been developed. Initially, the rotors are designed through blade element momentum theory (BEMT), and their power coefficient have been evaluated. Thence, the developed rotors are tested in a low-speed wind tunnel to find their rotational frequency, power and power coefficient at design and off-design conditions. From BEMT analysis, M1 shows a maximum power coefficient (Cpmax) of 0.37 at λ = 2.5. The subsequent wind tunnel tests on M1, M2, M3, and M4 at 9 m/s show the Cpmax values to be 0.34, 0.30, 0.28, and 0.156, respectively. Thus, from the experiments, the M1 rotor is found to be favourable than the other three rotors, and its Cpmax value is found to be about 92% of BEMT prediction. Further, the effect of pitch angle (θp) on Cp of the model rotors is also examined, where M1 is found to produce a satisfactory performance within ±5° from the design pitch angle (θp, design).

Evaluation of the MPPT performance in small wind turbines by estimating the tip-speed ratio

2013 ◽  
Author(s):  
Louis F. M. Gevaert ◽  
Jeroen D. M. De Kooning ◽  
Tine L. Vandoorn ◽  
Jan Van de Vyver ◽  
Lieven Vandevelde
Keyword(s):  
Wind Turbines ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Small Wind Turbines
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