HOW VARIATIONS IN DOWNSTREAM COMPUTATIONAL FLUID DYNAMICS TURBULENCE STUDIES CAN BE IMPACTED WHEN EMPLOYING COMMONLY USED INITIAL SET-UP CONFIGURATION PARAMETERS FOR AIRFOILS

摘要

Upstream wind turbine turbulence can negatively impact the aerodynamic performance of downstream wind turbines. It is important to understand and evaluate the characteristic nature of this inflowing turbulence. Computational Fluid Dynamics (CFD) is a foundational analytical tool used to help predict and describe both boundary layer behavior and the resulting downstream turbulence for both these upstream turbines and the impacted downstream turbines. Increasing the predication accuracy of turbulence models, particularly at the higher Reynolds number regimes, commonly encountered at the outer radius of wind turbine blades, remains a fundamental consideration in such CFD analysis. The work discussed here focuses on understanding how CFD simulations can be impacted by basic CFD approaches and configurations. Commonly use unstructured grids and incremental positive angles of attack around the well-studied NACA0012 airfoil were used to assess how these basic set-up parameters can influence CFD turbulence results. Navier-Stokes equations were solved for incompressible flow to assess downstream turbulence using the SST k-co (two equation) turbulence model within ANSYS Fluent (SIMPLE solution method). Two airfoil configurations with respect to angle of attack (a) were of interested and studied, with one configuration defined as "fixed-position" and the second configuration defined as "changed-position". Fixed-position refers to a single common airfoil/grid configuration and changing incoming u_x, v_y velocity vectors to yield different angle of attack (α) values. Changed-position refers to a utilizing a single u_x velocity vector and physically rotating the impacted airfoil in the computational field to yield different angles of attack. A two-dimensional unsteady state SST k-ω turbulence model was used at a Reynolds of 3.0 × 10~6. The resulting data from the system setup models studied here (fixed and changed-positions) were successfully validated by comparing the computed lift and drag coefficients at these varying a values to common values found in literature. Downstream pressure contours, along with U_x and V_y, and net-velocity contours at various distances from 1.5 cord lengths up to 12.0 cord lengths from the leading edge of the airfoil at incremental angles of attack were studied. The authors review how such variations in rudimentary approaches impact the CFD downstream output results.