Wind Turbine Post-Stall Airfoil Performance Characteristics Guidelines for Blade-Element Momentum Methods

Abstract

The objective of this study was to provide post-stall airfoil data input guidelines for the prediction of peak and post-peak rotor power when using blade-element momentum theory. A steady-state data set from the Unsteady Aerodynamic Experiment (UAE) rotor test was used to provide guidelines for the development of a global post-stall method for the prediction of post-stall 3-D airfoil characteristics to be used with 2-D airfoil data. Based on these UAE data, methods to emulate the 3-D aerodynamics in the post-stall region were explored. Also suggested are experimental tests needed to better understand the 3-D flow physics and to quantify needed theory or empirical factors for a global post-stall approach to support blade-element momentum methods.

Experiments in Fixed-Wing UAV Perching

“…Notice that, although data from any individual trial showed time-varying coefficients due to the vortex shedding at high angles of attack (see Figure 12), the coefficient data averaged over many trials agrees incredibly well with that predicted by flat plate theory. 23 In general, the coefficients are a function of the angle-of-attack of the wings, the elevator deflection angle, the Reynolds number, and the Mach number, as well as additional fluid-related terms in the unsteady regime. In our data, although the Reynolds number (relative to the mean chord) varies characteristically during the trajectory starting around 53,000 at launch and decreasing to around 14,000 at termination, the elevator deflection angle was the more significant variable for both prediction and control.…”

Inboard Stall Delay due to Rotation

“…Further experimental studies confirmed these early results, indicating in stall-delay and post-stalled higher lift coefficient values the main effects of rotation on wings. Measurements on wind turbine blades were performed by Ronstend (Ronsten, 1992), showing the differences between rotating and non-rotating pressure coefficients and aerodynamic loads, and by Tangler and Kocurek (Tangler & Kocurek, 1993), who combined results from measurements with the classical BEM method to properly compute lift and drag coefficients and the rotor power in stalled conditions. The theoretical foundations for the analysis of the rotational effects on rotating blades come at the late 40's with Sears (Sears, 1950), who derived a set of equations for the potential flow field around a cylindrical blade of infinite span in pure rotation.…”

Nonlinear control of aerial vehicles subjected to aerodynamic forces

“…In this respect, small vehicles are advantaged over large ones. As a matter of fact, the model (17) is reminiscent of the aerodynamic coefficients of a flat plate when setting c 0 = 0 [25].…”