The Effect of Flat Plate Theory Assumption in Post-Stall Lift and Drag Coefficients Extrapolation with Viterna Method

In employing blade element momentum (BEM) method to compute the performance of a turbine propeller, the lift and drag coefficients of propeller element/airfoil are needed. The coefficients are usually obtained from model experiment. Unfortunately, the model experiment can only be conducted for small angle of attack until stall mode. Beyond stall mode, Viterna extrapolation method is commonly used. The method is used to predict the lift and drag coefficients from stall angle to 90o. Beyond that range, besides Viterna method, original flat plate theory assumption can also be adopted. The present study compares the lift and drag coefficients extrapolation using Viterna method and flat plat theory. NACA2415 airfoil shape is used for computation. The computation formulas and procedures are presented and important parameter effect to the coefficients are shown and explained