Wind tunnel study: is turbulent intensity a good candidate to help in bypassing low Reynolds number effects on 2d blade sections?

Abstract

Wind turbines operate in the turbulent atmospheric boundary layer and can be additionally exposed to the wakes of upstream wind turbines. Hence the inflow encountered by wind turbine rotor blades is turbulent. One way to gain more knowledge on the impact of the turbulence on the airfoil aerodynamics is by studying a 2d airfoil section of a real wind turbine blade against inflows of various turbulence intensities and Reynolds numbers. Therefore, for the purpose of this paper, experiments were performed and aerodynamic coefficients were calculated for chord based Reynolds numbers between 1.3 × 105 and 3 × 105 and angles of attack between -10° and 24° for inflows of three different averaged turbulence intensities, 0.3%, 3% and 5.5%. Results were compared with the already available result of measurements done at a higher chord based Reynolds number of 4.7×106 for the same airfoil type. The results show that, for a given Reynolds number, an increase in turbulence intensity suppresses the flow separation. It was also found that an increase in the turbulence intensity of the inflow does reduce the dependence of aerodynamic coefficients on the Reynolds number. The Comparison between experimental results for lower chord-based Reynolds numbers and high chord-based Reynolds numbers shows differences which implies that an increase of the turbulence intensity is not enough to bypass the low Reynolds number effect completely.

Reynolds effects on wall pressure fluctuations at stall inception of a wind turbine blade section

“…However the region of pressure gradient varies with the Reynolds number. For Re c = 5.10 5 , this region ends at x c = 0.55 and it moves towards the leading edge with the increase of Re c reaching x c = 0.47 at Re c = 3.4×10 6 . This indicates that increasing the Reynolds number moves the mean separation point towards the leading edge.…”

Developing a Digital Twin Framework for Wind Tunnel Testing: Validation of Turbulent Inflow and Airfoil Load Applications

“…These steps were significantly improved manually to an accuracy of less than 0.45mm, which was sufficient to match simulation results. It should be noted that for this inflow velocity, a TI of at least 3% was necessary to avoid low Reynolds number effects found in previous investigations (see Mishra et al (2022)).…”

“…To study their effects, field experiments can be carried out, but they are complex, time-consuming, and costly. Alternatively, experiments can be conducted in a wind tunnel by subjecting a Reynolds-scaled wind turbine rotor or a blade section from a real wind turbine blade to turbulent inflow under different inflow conditions, such as homogeneous inflow or gust inflow (see e.g., Wei et al (2019); Wester et al (2022); Mishra et al (2022); Nietiedt et al (2022) and Neunaber and Braud (2020a)). However, wind turbines have grown to become the largest flexible, rotating machines in the world, with blade lengths approaching now 120m.…”

Control of flow separation over an aerofoil by external acoustic excitation at a high Reynolds number

“…The current angle of attack of the aerofoil under investigation is in the transition-to-stall region where the flow separation, shear layer and aerofoil wake are the most susceptible to freestream turbulence intensity (TI) 38 . As the focus of the current work is the investigation of acoustic excitation effects on turbulent flow separation, a range of freestream turbulent intensity levels are explored for the effectiveness of acoustic excitation.…”