A review of momentum models for the actuator disk in yaw

Abstract

BEM (Bladed Element Momentum) models have shown to be inaccurate in predicting loads in the case of yawed flow [1-3]. Actuator disk momentum theory is the basis for BEM codes, following Glauert’s auto-gyro theory [4]. Therefore, a first step to improve BEM in yawed flow is to assess momentum models for the actuator disk in yaw and investigate possibilities for improvement. In the past, several models have been developed for an actuator disc under yawed conditions, but they are subject to various assumptions. In this paper, different yaw models for the actuator disk will be reviewed and compared against higher fidelity models: fixed and free [5] wake vortex models so that the earlier made assumptions can be assessed. The comparison considers the case of a uniformly loaded actuator disk at varying yaw angle (0°~90°) and thrust coefficient (0.1~0.9). From the models which have been assessed, Øye’s correction [6] performs best, however, this model too suffers from deficiencies. This indicates that an improved momentum model for yawed flow is necessary.