The present disclosure relates to nacelle assemblies for wind turbines having a nacelle and a wind flow deflector system and wind turbines comprising such nacelle assemblies.

BACKGROUND

Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation generates a torque that is normally transmitted through a rotor shaft to an electrical generator, either directly (“directly driven”) or through the use of a gearbox. This way, the electrical generator produces electricity which can be supplied to the electrical grid.

Most wind turbines comprise a yaw system used for orienting the rotor of the wind turbine in the prevailing wind direction. Normally, when the rotor is aligned with the wind direction, the yaw system maintains the position by means of brakes (e.g. hydraulic brake calipers and/or electro-brakes of the yaw motors). When the rotor is misaligned from the wind direction, the yaw system rotates the nacelle to reach an appropriate alignment with the wind. The nacelle can thus be rotated around the tower's longitudinal axis in or out of the wind direction. The rotatable connection between the wind turbine tower and the nacelle is called a yaw bearing.

The nacelle may house a generator and/or a converter and several electrical components controlling the operation of the generator. For example, in direct drive wind turbines the electrical generator may be positioned within the nacelle or forming part of the nacelle. In examples of wind turbines having a gearbox, the nacelle may house an electrical generator and the drive train including a gearbox.

The length of wind turbine blades and the height of wind turbines are continuously increasing with the aim of capturing as much kinetic energy as possible from the wind and, thereby, generating more electrical energy. This may consequently require increasing the size of wind turbine components within the nacelle, e.g. an electrical generator, a converter, a transformer or a gearbox. Larger nacelles to house these larger wind turbine components may thus be required. Nacelles are normally transported by truck, railway or boat from the manufacturing facility to the erection site to be lifted on top of a wind turbine tower. Depending on the shape and the size of the nacelle, transporting the nacelle from the manufacturing factory to the wind turbine farm may be difficult.

Larger nacelles may also increase the area of the nacelle facing the wind. In some events, e.g. in high wind speeds or in storm events, power cannot be supplied to the yaw system and, consequently, the nacelle cannot be aligned with respect to the predominant wind direction. During these events, wind direction may vary causing a misalignment of the nacelle with respect to the predominant wind direction. When the nacelle is misaligned, a lateral side of the nacelle may be subjected to wind flow. The lateral side may thus offer a drag or an aerodynamic resistance with respect to the wind flow. Wind flow acting on the lateral side of the nacelle may cause high bending loads on the wind turbine tower, in particular in high wind turbine towers. Towers and tower connections with the foundations may have to be designed to withstand a misaligned nacelle subjected to high wind speeds. Otherwise, the maximum wind speed able to be withstood by the wind turbine may have to be reduced.

Substantially oval nacelles may be used to reduce the aerodynamic resistance or the drag coefficient of the nacelle. This oval shape may reduce loads on the wind turbine. However, due to this specific shape, these types of nacelles are generally difficult to be manufactured and transported and a rounded or oval shape does not allow for an efficient use of the space inside the nacelle housing different components.

The present disclosure provides examples of systems and methods that at least partially resolve some of the aforementioned disadvantages.

SUMMARY

In one aspect, a nacelle assembly for a wind turbine is provided. The nacelle assembly is connected to a wind turbine tower through a yaw system and has a front region coupled to a rotor comprising a rotor hub and at least one rotor blade is provided. The nacelle assembly comprises a nacelle having a cover structure to house wind turbine components. The cover structure comprises a front side arranged at the front region; a rear side opposite to the front side; a first and a second lateral side; and a top side and a bottom side. The cover structure extends from the front side to the rear side along a longitudinal axis. The nacelle assembly further comprises an add-on wind flow deflector system coupled to an outside of the cover structure to guide wind flowing to the nacelle for reducing a drag of the nacelle when a wind direction is misaligned with respect to the longitudinal axis in a yaw system failure event.

In this disclosure, a yaw system failure event refers to an event during the operation of a wind turbine in which the yaw system cannot rotate the nacelle. This may occur when one or a plurality of yaw drives are broken so that not enough torque may be provided to rotate the nacelle. A yaw system failure event may comprise a yaw system power failure event in which there is no power or not enough power supplied to the yaw system to make the nacelle rotate to follow the predominant wind direction.

A yaw system power failure event may be caused by grid loss event or by insufficient backup power to rotate the nacelle or by broken yaw drive. During some grid loss events, blades cannot be pitched, so that loads cannot be reduced by pitching the blades. A grid loss event may be caused by an extreme storm such as hurricanes or typhoons. During an extreme storm high winds and a grid loss may occur at the same time.

In this disclosure, an add-on wind deflector system refers to an aerodynamic profile that may be coupled to a nacelle to modify the aerodynamics of the nacelle.

In this disclosure, a misalignment of the nacelle or of the longitudinal axis of the nacelle with respect to the wind direction refers that the direction of the wind speed is not substantially parallel to the longitudinal axis of the nacelle. For example, a nacelle may be misaligned with respect to the wind direction when the angle between the wind direction and the longitudinal axis of the nacelle is greater than 10°, specifically greater than 20°, and more specifically greater than 30°.

The add-on wind deflector system may modify the aerodynamic profile of the nacelle to reduce the drag of the nacelle when the wind direction is misaligned with respect to the longitudinal axis of the nacelle. The aerodynamic resistance of the nacelle may consequently be reduced. Loads acting on the wind turbine for a given wind speed when the nacelle is misaligned may thus be reduced when compared with a nacelle without an add-on wind flow deflector system. Accordingly, the tower or the connection of the tower with the foundation may be optimized or more optimally used. In addition, expensive backup power system to power the yaw system during a grid loss event may be avoided. Costs of the wind turbine may thus be reduced without adversely affecting the structural integrity of the wind turbine.

The add-on wind deflector system may be coupled to the outside of the cover structure after transporting the nacelle to the erection site. Accordingly, the add-on wind flow deflector system does not adversely affect the shape and the size of the nacelle during transport. In addition, as the add-on wind flow deflector system is coupled to the outside of the cover structure, the space inside the nacelle for housing wind turbine components may be maintained as small as possible to house the components for not increasing the overall size of the nacelle. Accordingly, a compact nacelle housing wind turbine components such as an electrical converter or an electrical generator may be provided.

