Design, analysis and test of a model turbine blade for a wave basin test of floating wind turbines

Abstract

a b s t r a c tFroude scaling is a generally reliable way to design models of floating wind turbines for wave basin testing. However, the resulting rotor thrust of the model is far lower than the Froude-scaled value of a full-size turbine, because the reduction in Reynolds number decreases the lift coefficients and increases the drag coefficients (the Reynolds number scaling effect). A 1/50th scale model wind turbine based on a NREL-5MW reference turbine is examined here. To mitigate the Reynolds number scaling effect in the model, the original aerofoils of the reference turbine (DU series and NACA 64-618) were replaced by an aerofoil at a low Reynolds number (NACA 4412). Such a model with aerofoil-adjusted blades was used in the mathematical optimization of rotor thrust. The design objective was to guarantee that while the rotor thrust of the model equalled the Froude-scaled rotor thrust of the reference, the smallest chord lengths were achieved, considering the weight control in building the model blade. The distribution of chord lengths fitted a fourth-order polynomial curve, and the distribution of twist angles along the blade fitted a second-order polynomial curve. The eight coefficients of the two curves were chosen as optimization variables, and pattern search method was used to solve the optimization model. The model blade was designed at zero pitch angle and further tested in FAST, a fully coupled simulation tool. A model test was conducted using the optimized blade geometry in the State Key Laboratory of Ocean Engineering in Shanghai, China, and the thrusts were compared with the predicted values.

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

“…The linear wake grow rate systematically decreases with Reynolds number, except for the transient area. Therefore, one can expect that this airfoil produces a smaller total wake area, including the unobserved downstream development at higher Reynolds numbers, which physically supports the observation of Du et al [38] that this airfoil has a good performance at higher Re. The wake width, which is affected less in the transition regime, seems to be the wake width based on stream-wise fluctuations; this width displays the largest grow a.…”

Effect of Manufacturing Inaccuracies on the Wake Past Asymmetric Airfoil by PIV

“…The coordinates of the NACA 64-618 airfoil were obtained from the public database Airfoiltools.com [3]. This airfoil is frequently used at the tips of the wind turbines [17] and has a reasonable lift even at high angles of attack (which is valid only for larger Reynolds numbers, as shown later). The trailing edge of this airfoil is sharp, and it points towards the high pressure side; see the black line in Figure 1.…”

How Manufacturing Inaccuracies Affect Vortices in an Airfoil Wake

“…This profile is used at the tip of wind turbine blades. Du et al [25] used computational fluid dynamics (CFD) to investigate the performance of several airfoil profiles including NACA 64-618 at angles of attack up to 40 • at Reynolds number 1.15 • 10 7 and 3.3 • 10 4 .…”