Numerical Study on the Aerodynamic Characteristics of the NACA 0018 Airfoil at Low Reynolds Number for Darrieus Wind Turbines Using the Transition SST Model

Abstract

A symmetrical NACA 0018 airfoil is often used in such applications as small-to-medium scale vertical-axis wind turbines and aerial vehicles. A review of the literature indicates a large gap in experimental studies of this airfoil at low and moderate Reynolds numbers in the previous century. This gap has limited the potential development of classical turbulence models, which in this range of Reynolds numbers predict the lift coefficients with insufficiently accurate results in comparison to contemporary experimental studies. Therefore, this paper validates the aerodynamic performance of the NACA 0018 airfoil and the characteristics of the laminar separation bubble formed on its suction side using the standard uncalibrated four-equation Transition SST turbulence model and the unsteady Reynolds-averaged Navier-Stokes (URANS) equations. A numerical study was conducted for the chord Reynolds number of 160,000, angles of attack between 0 and 11 degrees, as well as for the free-stream turbulence intensity of 0.05%. The calculated lift and drag coefficients, aerodynamic derivatives, as well as the location and length of the laminar bubble quite well agree with the results of experimental measurements taken from the literature for validation. A sensitivity study of the numerical model was performed in this paper to examine the effects of the time-step size, geometrical parameters and mesh distribution around the airfoil on the simulation results. The airfoil data sets obtained in this work using the Transition SST and the k-ω SST turbulence models were used in the improved double multiple streamtube (IDMS) to calculate aerodynamic blade loads of a vertical-axis wind turbine. The characteristics of the normal component of the aerodynamic blade load obtained by the Transition SST approach are much better suited to the experimental data compared to the k-ω SST turbulence model.

Plunging Airfoil: Reynolds Number and Angle of Attack Effects

“…Moreover, the model has been offering satisfactory results with high fidelity boundarylayer resolution over the years in flapping airfoils [30]. The same turbulence model coupled with a transition model also has shown its potential at low to moderate Reynolds numbers analysis [31].…”

Interaction Mechanism and Loss Analysis of Mixing between Film Cooling Jet and Passage Vortex

“…The steady RANS (Reynolds Averaged Navier-Stokes) equations are employed in the current study. The numerical simulations are solved using ANSYS Fluent 19.2, where the “Coupled” pressure velocity coupling scheme and second-order discretization for all variables are adopted [ 30 ]. For the grid independence analysis, the film cooling over a flat plate is considered.…”

Accuracy of the Gamma Re-Theta Transition Model for Simulating the DU-91-W2-250 Airfoil at High Reynolds Numbers

“…The reliability of the airfoil polars is an essential factor for the prediction accuracy of aerodynamic blade loads using BEM approaches [7][8][9][10][11]. These polars can be obtained in various ways, e.g., from wind tunnel measurements [12,13], from CFD analyzes [14][15][16], using the XFOIL code [17][18][19], or also from flight tests [20,21].…”

“…Transitional boundary layer flows are especially significant in many CFD applications of engineering interest such as airfoils, wind turbines, vehicles, or turbomachinery blade rows [25][26][27]. In many cases, the transition effects are so important for pressure distributions that classic one or two-equation turbulence models give inaccurate aerodynamic forces results [9]. Various mechanisms of the transition formation, depending on the flow regime, the free-stream turbulence intensity, and the geometry of the flowing objects, make it extremely difficult for 2D CFD models.…”