Challenging low Reynolds - SWT blade aerodynamics

Abstract

One of the main issues related to the design and development of small wind turbines (SWTs) is the low Reynolds number. Operation in the transitory regime makes the rotor aerodynamic analysis a challenging task. Project GUST (Generative Urban Small Turbine) realized currently at the Institute of Turbomachinery (Lodz University of Technology, Poland) is devoted to the development of SWT (D = 1.6 m) for low-Reynolds number (low wind speed) flow conditions. The emphasis is on the blade design, aiming at improving the rotor aerodynamic efficiency. The paper will highlight the rotor design process, based on contemporary methods of experiment-simulation integration approach and use of rapid manufacturing techniques. In-house wind tunnel measurements of a scaled model performance were executed. A numerical analysis using dedicated software (QBlade) was conducted in parallel. A comparison between the obtained results indicated that the chosen numerical tools are capable of providing a reliable output, even in complex, transitional flow conditions. Bearing in mind the above observations, QBlade was incorporated into the development process of a completely new blade geometry which would increase rotor performance. The selected design has indeed prove to show better power outcome in an additional experimental campaign.

Experimental investigation of the effects of the Reynolds number on the performance and near wake of a wind turbine

“…The authors reported that the C p vs. λ curves's dependence on Reynold's number was caused by variations in the rotor's aerodynamic lift and drag coefficients with the Reynolds number. Another experimental study carried out by Kadrowski et al reveals that higher Reynolds numbers allow the turbine to reach higher maximum power coefficients C p,max but at lower optimum tip-speed ratios λ opt [9]. Similar studies have also been conducted with micro-scale vertical axis wind turbines [10,11].…”

Design and Economic Analysis of a Hydrokinetic Turbine for Household Applications

“…The gray patches indicate the 𝜆 ranges where the numerical solution is more problematic (see, e.g., [42,47]) due to the appearance of high angle of attacks (i.e., stall) at low tip speed ratios (high 𝛼, low 𝜆) and negative angle of attacks (nearly zero and negative 𝐶 𝐿 ) at high tip speed ratios (low 𝛼, high 𝜆). 𝐶 𝑃 strongly decreases when 𝐶 𝐿 ∕𝐶 𝐷 drops [48,49], so the analysis of these regions is not relevant under the steady-state conditions considered here.…”

Fluid–Structure Interaction Numerical Analysis of a Small, Urban Wind Turbine Blade

“…This small wind turbine has a nominal power 350 W at a wind velocity of 8.4 m/s [20]. The blades are of variable chord and twist angle ( Figure 1) and are constructed upon NREL S826 and S834 airfoils [21]. The examined rotor radius R is equal to 0.8 m, which is the same as that used in experimental investigation used as a reference.…”