Figure 6 - uploaded by Anas Abdulrahim
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Turbulence intensity distribution within the wake of the turbine rotor. (from left-to-right) 1 st column: Baseline case; 2 nd column: Mie vane case; 3 rd column: R M =0.2%. (from top-to-bottom) 1 st row: 0.25D, 2 nd row: 0.5D, 3 rd row: 1D and 4 th row: 2D. Flow is coming out of the page and the circular line marks the outline of the open-jet tunnel.
Source publication
This paper presents the results of an experimental study that focuses on the tip leakage/vortex control of a model horizontal axis wind turbine rotor. The effects of Mie vanes and tip injection on the performance and wake characteristics of a model horizontal axis wind turbine rotor are investigated through experiments that are conducted by placing...
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... further downstream. However, there is a slight difference in the level of turbulence intensity especially in the region occupied by the tip vortices, it seems that the injection case (R M =0.2%) results in higher turbulence levels compared to the Mie vane case which result in lower turbulence levels as compared to the baseline case as shown in Fig. 6. Based on previous results from Abdulrahim et al. (Ref. 6 and Ref. 7), for the injection case (R M =1.3%), the effects are very substantial compared to the Mie vanes and R M =0.2% injection cases. The high momentum jet ejecting from the rotor blades seems to induce more effects on the wake region as well as the region dominated by the ...
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... shows that as the injection gets stronger diffusion of the tip vortices gets faster. Figure 6 describes the turbulence intensity variations on the same downstream planes for the cases mentioned previously. From the turbulence intensity contour plots one can clearly observe the substantial effects resulting from the Mie vanes and injection scenarios. ...
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... observations explained above can also be seen more quantitatively from Fig. 7. In this figure the values extracted along a radial line shown in Fig. 6 (top-left) are compared for all three cases at different locations downstream of the turbine rotor. Within the tip vortex region (0.8< s <1.1) for Mie-vane case, both velocity and velocity gradient levels are slightly decreased as expected. In the injection R M =0.2% case this reduction is even more pronounced. The results from the Mie vanes and ...
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Citations
... VAWT Darrieus as they appear in operation Wind turbines (Figure 1.3) can rotate about either a horizontal or a vertical axis, the former being both older and more commonn [25] . They can also include blades, or be bladeless [26] . Vertical designs produce less power and are less common. ...
... This results in more complicated tip vortices than the static wing. Mie-type tip vane and end plate have been proved to be effective in weakening the tip vortices and enhance the power performance of both HAWTs and VAWTs [26][27][28][29][30]. However, the vane results in increasing the fatigue loading and decreasing the lifetime for the VAWT [31]. ...
Wind turbines, like aircraft propeller blades, turn in the moving air and power an electric generator that supplies an electric current. Simply stated, a wind turbine is the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity.
... This results in more complicated tip vortices than the static wing. Mie-type tip vane and end plate have been proved to be effective in weakening the tip vortices and enhance the power performance of both HAWTs and VAWTs [26][27][28][29][30]. However, the vane results in increasing the fatigue loading and decreasing the lifetime for the VAWT [31]. ...
Vertical axis wind turbines (VAWTs) have been attracting an increasing attention in recent years because of their potential for effectively using wind energy. The tip vortices from the VAWT blades have a negative impact on the power efficiency. Since a winglet has been proved to be effective in decreasing the tip vortex in the aerospace field, this paper numerically studies the aerodynamic effect of appending a winglet on the blade of a VAWT. Based on the theoretical motion pattern of the VAWT blade, this paper simplifies the three-dimensional full-scale rotor simulation to a one-blade oscillating problem in order to reduce the computational cost. The full rotor model simulation is also used in validating the result. The numerical approach has been validated by the experimental data that is available in the open literature. Six parameters are applied in defining the configuration of the winglet. The orthogonal experimental design (OED) approach is adopted in this paper to determine the significance of the design parameters that affect the rotor's power coefficient. The OED results show that the twist angle of the winglet is the most significant factor that affects the winglet's performance. A range analysis of the OED results produces an optimal variable arrangement in the current scope, and the winglet's performance in this variable arrangement is compared with the blade without a winglet. For the single blade study, the comparison result shows that the optimal winglet can decrease the tip vortices and improve the blade's power performance by up to 31% at a tip speed ratio of 2.29. However, for the full VAWT case, the relative enhancement in the power coefficient is about 10.5, 6.7, and 10.0% for TSRs of 1.85, 2.29, and 2.52, respectively. The winglet assists in maintain the pressure difference between the two sides of the blade, thus weakening the tip vortex and improving the aerodynamic efficiency of the surface near the blade tip.
... This results in more complicated tip vortices than the static wing. Mie-type tip vane and end plate have been proved to be effective in weakening the tip vortices and enhance the power performance of both HAWTs and VAWTs [26][27][28][29][30]. However, the vane results in increasing the fatigue loading and decreasing the lifetime for the VAWT [31]. ...
... Their experiments showed that the winglets did not significantly change the tip-vortex strength, suggesting that the aerodynamic improvements came from a downwind shift in the tip-vortex structure rather than diminishing its magnitude. Shimizu et al. [7] and Abdulrahim et al. [8] has experimentally shown that Mie-vane type tip devices can also have positive effects on the power performance of wind turbines. Effects of winglets used in the current study on the power and thrust coefficients of the model wind turbine have been investigated asmeJoSE_SOL-17-391-0 Uzol 5 previously by the authors [9]. ...
This study presents an experimental investigation on the effects of winglets on the near wake flow around the tip region and on the tip vortex characteristics downstream of a 0.94 m diameter three-bladed horizontal axis wind turbine (HAWT) rotor. Phase-locked 2D particle image velocimetry (PIV) measurements are performed with and without winglets covering 120 deg of azimuthal progression of the rotor. The impact of using winglets on the flow field near the wake boundary as well as on the tip vortex characteristics such as the vortex convection, vortex core size, and core expansion as well as the resultant induced drag on the rotor are investigated. Results show that winglets initially generate an asymmetric co-rotating vortex pair, which eventually merge together after about ten tip chords downstream to create a single but nonuniform vortex structure. Mutual induction of the initial double vortex structure causes a faster downstream convection and a radially outward motion of tip vortices compared to the baseline case. The wake boundary is shifted radially outward, velocity gradients are diffused, and vorticity and turbulent kinetic energy levels are significantly reduced across the wake boundary. The tip vortex core sizes are three times as big compared to those of the baseline case, and within the vortex core, vorticity and turbulent kinetic energy levels are reduced more than 50%. Results show consistency with various vortex core and expansion models albeit with adjusted model coefficients for the winglet case. The estimated induced drag reduction is about 15% when winglets are implemented.
