Horizontal axis wind turbines (HAWTs) experience yaw misalignments due to the physical limitations of yaw controllers and various novel active yaw controls. Moreover, the motion of floating offshore wind turbines (FOWTs) accelerates yaw misalignment. The blade element momentum (BEM) method is widely used due to its computational efficiency for the design of HAWTs. Momentum theory, the basis of BEM, assumes steady flow and uniform induction field at the disc. Those assumptions are relaxed by engineering models to capture yaw and unsteady effects. Current yaw engineering models, however, are inaccurate since they do not capture the asymmetric wake expansion effect. Dynamic inflow models have been developed for non-yawed flow. Furthermore, the AVATAR project shows that BEM using fully coupled engineering models, the current yaw, dynamic inflow and various engineering models, suffers from significant deficiencies. This purpose of this paper, therefore, is to investigate dynamic effects for yawed flow, and determine if current dynamic inflow models are applicable in yawed conditions. The Glauert’s modified momentum theory is applied to dynamic inflow models to couple the two models. Among all coupled models, Øye, Yu PWVM and Yu FWVM DIM can capture asymmetric trends. However, the results show the significant deficiencies in phase delay on the actuator disc. @en

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. @en

Nine research teams organized a round-robin measurement campaign of the wake of two porous discs in a homogeneous and "low-turbulent' flow. Mean streamwise velocity and turbulence intensity profiles at four diameters downstream of the discs were measured and compared through such metrics as the maximum of velocity deficit, the maximum of turbulence intensity, the wake width and the thrust coefficient. The dependence of these metrics on the inflow conditions (freestream turbulence intensity and Reynolds number based on the disc diameter) is discussed.

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