Laminar-turbulent transition characteristics of a 3-D wind turbine rotor blade based on experiments and computations

Abstract

Abstract. Laminar-turbulent transition behaviour of a wind turbine blade section is investigated in this study by means of field experiments and 3-D computational fluid dynamics (CFD) rotor simulations. The power spectral density (PSD) integrals of the pressure fluctuations obtained from the high frequency microphones mounted on a blade section are analyzed to detect laminar-turbulent transition locations from the experiments. The atmospheric boundary layer (ABL) velocities and the turbulence intensities (T.I.) measured from the field experiments are used to create several inflow scenarios for the CFD simulations. Results from the natural and the bypass transition models of the in-house CFD EllipSys code are compared with the experiments. It is seen that the bypass transition model results fit well with experiments at the azimuthal positions where the turbine is under wake and high turbulence, while the results from other cases show agreement with the natural transition model. Furthermore, the influence of inflow turbulence, wake of an upstream turbine and angle of attack (AOA) on the transition behaviour is investigated through the field experiments. On the pressure side of the blade section, at high AOA values and wake conditions, variation of the transition location covers up to 44 % of the chord during one revolution, while for the no wake cases and lower AOA values, variation occurs along a region that covers only 5 % of the chord. The effect of the inflow turbulence on the effective angle of attack as well as its direct effect on transition is observed. Transition locations for the wind tunnel conditions and field experiments are compared together with 2D and 3D CFD simulations. In contrast to the suction side, significant difference in the transition locations is observed between wind tunnel and field experiments on the pressure side for the same airfoil geometry. It is seen that the natural and bypass transition models of EllipSys3D can be used for transition prediction of a wind turbine blade section for high Reynolds number flows by applying various inflow scenarios separately to cover the whole range of atmospheric occurrences.

Analysis of the DANAERO wind turbine field database to assess the importance of different state‐of‐the‐art blade element momentum (BEM) correction models

“…In their work, Ozçakmak et al 26,39 performed the analysis of field transition measurements for the tip section, focusing on the boundary layer transition laminar to turbulent. They showed that the turbulent inflow and surface roughness were the main contributors in the boundary layer transition.…”

“…The tangential force measurement, F t , is also impacting the lift force F L through the projection of the rotor forces onto the local aerofoil reference frame (see Figure 5). The relationship is made through the inflow angle , and looking at Equation (26), it is then apparent that a tangential force measurement error will influence both the lift and drag. Albeit, the C L is less impacted than the C D at low values of inflow angle ( ) thanks to the C t sin in the C L transfer formulae: In order to estimate the impact on the results due to tangential force uncertainty, a 2D CFD unsteady simulation using an in-house solver ISIS-CFD 50 was run.…”

“…This important database was available through the IEA group Task 29 Phase IV led by G. Schepers since 2010 and used in many studies. 7,[15][16][17][18][19][20][21][22][23][24][25][26] The focus of IEA Task29 Phase IV Work Package 3 was the validation, improvement, and understanding of aerodynamic models as implemented in wind turbine design codes by analyzing detailed aerodynamic measurements from the DANAERO experiment. Different phenomena were targeted: the impact of the turbulent inflow, the yawed conditions, the wake inflow, 2D/3D aerofoil characteristics, aeroelastic effects, the transition, and acoustics.…”

Wind tunnel investigations of DU97‐W‐300‐mod equipped with riblets

“…Possibility (1) is restricted as the inflow turbulence in the real atmosphere is rarely low enough to prevent premature transition 10–13 …”

Characterization of a Fast Response Probe for Inflow Turbulence Measurements on Wind Turbine Blades

“…For the inflow characterization, on the other hand, it is found that integrating the spectra of pressure fluctuations obtained from the leading edge microphone in the frequency range from 100 Hz to 300 Hz represents characteristics of the inflow turbulence (11). It was seen that data captured by the microphones placed on the leading edge can be used for showing the trend for the effect of the atmospheric turbulence on boundary layer transition (3). However, microphones could only be used to show a trend.…”