Appraisal of Straight Bladed Vertical and Horizontal Windmills

摘要

Vertical (VA) and horizontal axis (HA) windmills were compared in uniform wind and free air tests. Free air performance for both types is similar. The absence of yaw control mechanism is a significant factor in favor of the VA type. Pitch control over the entire blade allows both types to operate in high winds. Cyclic stall in high wind speeds makes extensive (whole blade) pitch control essential for VA machines, and incurs an unquantified penalty in terms of rotor complexity and tower head weight. There is no favored output shaft arrangement. The simple blade shape of VA machines should result in cost savings. The dynamic characteristics of VA machines are uncertain, in contrast to a well developed and validated analysis for the HA type. If light weight rotors can be built for VA machines (using advanced, high specific strength materials), their development to large sizes is attractive.