Designing wind turbines starts with knowledge of the aerodynamic forces acting at the wind machine. This chapter concentrates on the basic principles of the aerodynamics of conventional horizontal- and vertical-axis wind turbines (HAWTs and VAWTs). Aerodynamic theories are discussed, starting from the actuator disk model of a HAWT, extending through the Glauert optimum actuator disk model, to the strip theory, which has been the mainstay of HAWT aerodynamic design and analysis. Various corrections, including thrust coefficient modifications, tip-loss models, and gap corrections, are developed. Comparisons are made between test data, strip theory, and free vortex calculations to evaluate the accuracy of strip theory.

HAWT operational and design features are presented, including the teetered rotor, yawing and yaw stability, blade- and tip-pitch controls, ailerons, transient aerodynamics, and vortex generators. Power outputs and aerodynamic loads of medium- and large-scale HAWTs are presented and compared with theory. The aerodynamic behavior of VAWTs is examined in a parallel fashion, starting with an analysis of limiting VAWT performance and then proceeding to a development of the streamtube theory. Comparisons are made between power output predictions and test results for a medium-scale research VAWT. The effects on VAWT performance of rotor solidity, blade number, rotor shape, and Reynolds Number are presented, along with a discussion of starting and stopping. Test data are used to demonstrate the shape of rotor power curves and the effects of vortex generators.