An investigation of unsteady 3-D effects on trailing edge flaps

Abstract

Abstract. The present study investigates the impact of unsteady 3-D aerodynamic effects on a wind turbine blade with trailing edge flap by means of computational fluid dynamics (CFD). Harmonic oscillations are simulated on the DTU 10 MW rotor with a morphing flap of 10 % chord extent ranging from 70 to 80 % blade radius. The deflection frequency is varied in the range between 1 and 6 p. To quantify 3-D effects, rotor simulations are compared to 2-D airfoil computations and the 2-D theory by Theodorsen. It was found that the deflection of the flap on the 3-D rotor causes a complex wake development and induction which influences the loads over large parts of the blade. In particular, the rotor near wake with its trailing and shed vortex structures revealed a great impact. Trailing vorticity, a 3-D phenomenon, is caused by the gradient of bound circulation along the blade span. Shed vorticity originates from the temporal bound circulation gradient and is thus also apparent in 2-D. Both lead to an amplitude reduction and shed vorticity additionally to a hysteresis of the lift response with regard to the deflection signal in the flap section. A greater amplitude reduction and a less pronounced hysteresis is observed on the 3-D rotor compared to the 2-D airfoil case. Blade sections neighboring the flap experience, however, an opposing impact and hence partly compensate for the negative effect of trailing vortices in the flap section with respect to integral loads. Comparisons to steady flap deflections at the 3-D rotor revealed the high influence of dynamic inflow effects.

Simulation of oscillating trailing edge flaps on wind turbine blades using ranging fidelity tools

“…This is apparently due to the induced downwash/upwash velocities within the span of the flap section, which results in reduced lift with respect to that of the 2D like analysis when the flap moves downwards, and increased lift when it moves upwards (see Figure 9). CFD predictions indicate that the flap effect due to the influence of the trailing vortices also extends outside the flap region (the above effect is not seen in the BEM‐based simulation results), being in‐line with earlier findings 19,21 . The lift force developing on the sections outside the flap range (near the two edges) is higher/lower than the one predicted by the BEM models.…”

Extracting the angle of attack on rotor blades from CFD simulations

“…To assess the methods in 2D, the required degree of accuracy in the AoA calculation has to be determined beforehand. As reported for the rated conditions of the DTU 10‐MW turbine, a variation of the extracted AoA ( α e x ) from a 3D simulation of about 1° only has minor influence on the lift coefficient ( c l ) but a strong impact on the drag coefficient ( c d ). Since a sound AoA extraction method should be able to predict both aerodynamic coefficients correctly, c d is the decisive value.…”

“…The main part constitutes the CFD code FLOWer, which originates from the German Aerospace Center (DLR) . Grid generation and postprocessing is widely automated, and it is referred to Jost et al for further information.…”

“…At the blade root, which is of cylindrical shape, unsteady flow separation is dominant. 20 First, the RAV-AA method is analyzed using varying AE distances. To ensure that the AE do not intersect the blade, the definition of the AE distance is changed in the 3D case.…”

Pengaruh Desain Interior Diffuser Terhadap Peningkatan Performa Diffuser Augmented Wind Turbine (DAWT)

“…Model tersebut terdiri atas kombinasi dari model standard k-ε [9] di daerah freestream dan Wilcox k-ω model [10] untuk aliran di dekat dinding. SST k-ω merupakan model turbulensi yang baik dalam hal memprediksi aliran dengan pengaruh adverse pressure gradient yang kuat sebagaimana telah digunakan pada simulasi numerik terdahulu Hu dan Wang [6], Bangga dan Sasongko [11], Bangga et al [12], Pape and Lecanu [13], Sørensen et al [14], Weihing et al [15], Jost et al [16], dan Klistafani [17,18]. Gambar Terlihat pada gambar 6 bahwa tidak ada perbedaan peningkatan kecepatan rata-rata yang dihasilkan oleh flat diffuser dengan curved diffuser pada daerah upstream hingga inlet diffuser (x/L = 0).…”