Patent Description:
The present disclosure relates to an airfoil performance monitor, and more specifically, such a monitor that senses conditions at the working surface of an airfoil.

Aircraft are equipped with various sensors for providing real-time feedback of various operator controls. For example, sensors may be surface mounted to a wing of an aircraft in order to measure and provide data indicative of lift and drag across and over an airfoil of the wing. Measurements taken by sensors may account for contamination effects in any environmental conditions that the aircraft, and specifically the wing, may be experiencing. The sensors disposed on the wing of the aircraft allow actionable decisions to be made to improve performance of the airfoil of the wing. These airfoil performance sensors are designed and certified for aircraft wings to operate as a critical, life-saving sensor for icing impact quantification.

In addition to fixed wing aircraft, airfoils are used in a number of other applications for various purposes. For example, the blade of a wind turbine is essentially an airfoil. Air flowing past the airfoil causes a lift force on that blade which in turn causes the wind turbine to rotate, thereby ultimately driving a generator from which electrical power is derived. Currently, the overall performance of a wind turbine is typically monitored using a "power curve" which is a measure of the electrical power produced by the turbine and is often related to environmental sensors such as the local wind speed. This method provides a gross overview of the performance of the entire wind turbine, but it yields little insight into the specific cause of any performance losses, which might arise from aerodynamic, mechanical, electrical, or control systems issues, among others. Furthermore, the power curve yields no direct information about the possible aerodynamic degradation being experienced by one or more of the rotor blades individually. Such degradation can arise from numerous causes, including but not limited to manufacturing defects, leading-edge erosion (caused by sand, water or debris), acute damage (caused by hail, lightning or bird strike), or contamination by heavy rain, sleet, or accumulated ice deposits. Icing is a particularly serious problem, because its aerodynamic effects depend on so many factors (e.g. ice thickness, chordwise extent, vertical extent, spanwise extent, roughness, etc.), that they are essentially impossible to predict. The current state of the art includes the use of icing detectors, and even some icing thickness sensors, but none of these can predict the effect of the measured ice on the performance of the airfoils. Similar limitations apply to theoretical efforts to determine the impact of icing, such as Computational Fluid Dynamics techniques. As a result, the common approach to operation in icing conditions is to shut down the wind turbine, which has serious operational and financial consequences, because entire wind farms can be simultaneously impacted and shut down due to severe icing conditions. All of these factors can have an immediately deleterious effect on an individual wind turbine's performance, but they can also lead to reduced longevity, significantly increased maintenance costs, and higher operating costs for an entire wind farm because these problems are extremely difficult to isolate and address with the prior art. Some examples of prior art solutions are available in the following documents : <CIT>, <CIT> and <CIT>.

The present invention is directed toward an airfoil performance monitor that is designed to overcome the deficiencies in the related art. Thus, one embodiment of the airfoil performance monitor of the present invention includes a housing that may be mounted on a low-pressure face of an airfoil. The housing includes at least one pitot pressure orifice used to determine the total pressure at the airfoil performance monitor and at least one static pressure orifice used to determine the static pressure at the airfoil performance monitor. The airfoil performance monitor includes at least one airspeed-dependent sensor that senses the total pressure at the airfoil performance monitor via the pitot pressure orifice and generates a digital airflow signal indicative of the dynamic pressure at the airfoil performance monitor. A controller derives a turbulence intensity ratio by processing and filtering turbulence values calculated from the digital airflow signal.

The present invention is also directed toward an airfoil performance monitor system that includes at least one airspeed-dependent sensor disposed on a low-pressure face of an airfoil. The air foil performance monitor system includes at least one pitot pressure sensing orifice used to determine the total pressure at the airfoil performance monitor and at least one static pressure orifice disposed on a low-pressure face of an airfoil used to determine the static pressure at the airfoil performance monitor. At least one airspeed-dependent sensor measures the total pressure at the pitot pressure orifice and generates a digital airflow signal indicative of the dynamic pressure measured at the at least one pitot pressure orifice.

The signal generated from an airspeed-dependent sensor is processed into a digital airflow signal indicative of turbulence of the airflow. Additionally, the airfoil performance monitor system of the present invention includes one or more inertial sensors that measure acceleration, or other motions, in up to three orientations in relation to the mounting point. A controller derives a turbulence intensity by normalizing the measured turbulence intensity using the steady-state airflow signal, thereby generating a non-dimensional turbulence intensity ratio of the turbulent to steady state signal components. The controller also filters the signals from the airflow- dependent sensors using the frequencies obtained from the inertial sensors to eliminate the unwanted blade vibration effects on the turbulence intensity calculations.

A controller uses the processed turbulence intensity signal to monitor the aerodynamic performance of the airfoil, and to prevent a pre-set turbulence intensity threshold being exceeded which would be indicative of an airfoil "stall" as discussed below.

In addition, the present invention is directed toward an airfoil performance monitor system for use with a wind turbine. The system includes a housing mounted on a low-pressure face of an airfoil. The housing defines at least one pitot and one static pressure orifice. At least one airspeed-dependent sensor is disposed on a low-pressure face of an airfoil. The signal generated from the airspeed-dependent sensor as a result of airflow measured via the pitot-static orifices is processed into a digital signal indicative of the turbulence of the airflow. One or more inertial sensors measure a blade pitch angle, and motion in up to three orientations from their mounting location based on mechanical motion of the airfoil transmitted mechanically to the housing. A controller derives a turbulence intensity ratio by filtering turbulence values with the acceleration in response to the blade pitch angle and the frequency and amplitude of the acceleration from the one or more inertial sensors and relating the filtered airflow turbulence signal to the steady state airflow signal, and generates data upon which commands are based to adjust the blade pitch angle using a rotor control system.

The present invention is also directed toward a wind turbine that includes one or more blades that turn a shaft, a generator, which may be connected via a gearbox to the shaft, that converts and stores energy, and a housing mounted on a low-pressure face of an airfoil. The housing defines at least one pitot pressure orifice used to measure the total pressure at the airfoil performance monitor and at least one static pressure orifice used to measure the static pressure at the airfoil performance monitor. At least one airspeed-dependent sensor is in fluid communication with the at least one pitot pressure orifice that converts airflow measured via the pitot orifice and generates a digital airflow signal indicative of turbulence of the airflow. One or more inertial sensors are disposed on a low pressure face of an airfoil of one of the blades that may measure a blade pitch angle, and acceleration, which is frequency and amplitude data measured in up to three orientations from the mounted location on one or more of the blades. A controller derives a turbulence intensity ratio by relating the filtered turbulence signal to the steady state airflow signal and generates commands to adjust the blade pitch angle using a rotor control system.

Other objects, features and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description taken in connection with the accompanying drawings.

As described in greater detail below, the present invention is directed toward an airfoil performance monitor. As a means of illustrating the inventive features of the present invention, the performance monitor is described with respect to use in connection with wind turbines. However, those having ordinary skill in the art will appreciate from the description that follows that this is only one representative example of how the performance monitor of the present invention may be employed to monitor and track environmental and operational performance conditions at an airfoil used in any number of applications.

With this representative, environmental application in mind, <FIG> depicts one representative perspective view of a wind farm <NUM> having a plurality of wind turbines <NUM>. The wind turbines <NUM> are arranged in an array <NUM>. The wind turbines <NUM> convert kinetic energy from wind into electrical energy, by way of an electro-mechanical system. As will be described in more detail below, wind flows across each wind turbine <NUM> within the array <NUM>, which causes blades <NUM> of each of the wind turbines <NUM> to turn. Turning the blades <NUM> transfers kinetic energy from wind into the mechanical power, which can be used to rotate a generator that produces electricity that can be stored or transmitted to an electrical grid as electrical energy from the wind turbine <NUM>. Therefore, each of the plurality of wind turbines <NUM> may be disposed in an array <NUM> arranged based on wind patterns to enhance and maximize energy conversion within the wind turbines <NUM>.

As shown, the array <NUM> of plurality of wind turbines <NUM> is oriented such that each of the wind turbines <NUM> has adequate spacing to allow the blades <NUM> to turn, while maximizing an amount of individual wind turbines <NUM> within the array <NUM>. Stated differently, a distance <NUM> between each of the turbines <NUM> may be set to maximize a number of wind turbines <NUM> disposed within the array <NUM> of the plurality of wind turbines <NUM>. Additionally, in order to cause the blades <NUM> of the wind turbines <NUM> to rotate, the wind turbines <NUM> planes of rotation need to be oriented in a direction substantially perpendicular to the direction of the wind. While described as substantially perpendicular, the orientation of each of the wind turbines <NUM> may be within a range of angles dependent on the direction and patterns of wind that flows through the wind farm <NUM> to allow the blades <NUM> to turn with optimal efficiency.

The array <NUM> of wind turbines <NUM> may be arranged in a shape designed to optimize an amount of wind turbines <NUM> in the plurality of wind turbines <NUM> disposed within the array <NUM> of the wind farm <NUM>. The shape of the array <NUM> of wind turbines <NUM> disposed and arranged on the wind farm <NUM> may be based, at least in part, on the distance <NUM> needed between each of the other wind turbines <NUM> to allow the blades <NUM> full rotation, as described above, and a pattern and direction of wind as it passes through the wind farm <NUM>. Additionally, a fore and aft distance <NUM> between each turbine <NUM> within the plurality of turbines <NUM> may impact the shape and orientation of the array <NUM> of the plurality of wind turbines <NUM>. For example, minimizing the fore and aft distance <NUM>, as well as the distance <NUM> between each of the wind turbines <NUM> may maximize a number of wind turbines <NUM> disposed within the array <NUM>.

Likewise, an optimized fore and aft distance <NUM> and distance <NUM> between each of the wind turbines <NUM> may impact the shape of the array <NUM> to maximize efficiency of the wind farm <NUM>. Optimizing the fore and aft distance <NUM> between each of the wind turbines <NUM> may also consider a strength, direction and pattern of wind across the wind farm <NUM>. Stated differently, the direction and pattern of wind blowing across the array <NUM> of wind turbines <NUM> may further provided data indicative of an optimal fore and aft distance <NUM> between each of the wind turbines <NUM> within the array <NUM> to maximize an efficiency of each of the wind turbines <NUM> in the array <NUM>.

Referring to <FIG>, a side view of an individual wind turbine <NUM> is depicted. The wind turbine <NUM> may include a generally vertical tower <NUM> that supports a housing, sometimes referred to as a nacelle, <NUM> which, in turn, supports internal components of the turbine, such as a generator <NUM>, gearbox <NUM>, associated shafts, yaw drive, yaw motor and the like. The housing <NUM> includes a rotor <NUM> that comprises a hub <NUM> to which are mounted wind turbine blades <NUM>. The wind turbine <NUM> depicted in <FIG> is shown having individual blades <NUM>. Each turbine <NUM> may include a plurality of blades <NUM> based on an optimal number of blades <NUM> to maximize efficiency of energy generation by the wind turbine <NUM>. The number of blades <NUM> arranged on the wind turbines <NUM> may also be determined based on the direction and pattern of wind blowing across the wind farm <NUM> to maximize efficiency of energy generation by the wind turbines <NUM> across the array <NUM> of wind turbines <NUM>. The blades <NUM> are arranged on the wind turbine <NUM> such that, in response to wind flowing through the wind turbine <NUM>, the blades <NUM> rotate around a horizontal axis <NUM> that intersects a centerline <NUM> of the rotor <NUM> of the wind turbine <NUM>.

Specifically, wind flowing across each blade <NUM> is separated such that the blades <NUM> define high and low pressure sides <NUM>, <NUM>. The blades <NUM> turn in response to the pressure difference between the high and low pressure sides <NUM>, <NUM>. For example, the pressure difference from the high pressure side <NUM> to the low pressure side <NUM> provides a force necessary to accelerate the blades <NUM> on the rotor <NUM> to turn a shaft <NUM> that converts a mechanical torque from the wind energy into electrical energy by a generator <NUM>, as will be described in more detail below. The rotor <NUM> may be controlled by a rotor control system <NUM> that is adapted to adjust a position and orientation of the blades <NUM> relative to the centerline <NUM> of the rotor <NUM>. For example, the rotor control system <NUM> may adjust a pitch angle <NUM> of the blades <NUM> to optimize performance of the wind turbine <NUM>.

The rotor <NUM> rotates the shaft <NUM> disposed within the housing <NUM> of the wind turbine <NUM>. The shaft <NUM> may transfer torque from the rotor <NUM> through a gearbox <NUM> connected to the generator <NUM> or may be directly connected to the generator <NUM>. The generator <NUM> converts torque into electrical energy, which can be stored for later use or transmitted to an electrical grid. Therefore, as wind flows across the wind turbine <NUM> and causes the blades <NUM> to rotate, as described, the rotor <NUM> rotates the shaft <NUM> to transfer power to the generator <NUM>, which produces electrical energy for use. The more revolutions of the shaft <NUM> by the blades <NUM> turning the rotor <NUM>, the more electrical energy that is produced by the generator <NUM>. Stated differently, performance of the blades <NUM> dictate an amount of electrical energy converted by the generator <NUM>, and providing adjustment to an orientation <NUM> of the blades <NUM> and a pitch angle <NUM> of each blade <NUM> may further aid to improve performance of each of the blades <NUM>. Additionally, in at least one other embodiment, a coning angle <NUM> between each blade <NUM> may be based on optimal parameters from the strength, direction and pattern of wind blowing across the wind turbine <NUM>.

The pitch angle <NUM> of each blade <NUM> aids the blade <NUM> in turning the rotor <NUM>. The inventors have found that monitoring the pitch angle <NUM> of each blade <NUM> and providing adjustments to maximize efficiency is advantageous. For example, as wind flows past the wind turbine <NUM> and across the blades <NUM> of the wind turbine <NUM>, the pitch angle <NUM> of the blade <NUM> forces air to travel around an airfoil <NUM> of the blade <NUM>, as previously described. The movement of air around the airfoil <NUM> of the blade <NUM> propels the blade <NUM> around the rotor <NUM>. Therefore, the pitch angle <NUM> of the blade <NUM> aids in determining efficiency and production of mechanical power transfer through the rotor <NUM> and shaft <NUM> into electrical energy converted by the generator <NUM>.

Each blade <NUM> includes a span length <NUM> as well as a chord length <NUM>. The chord length <NUM> is a length of a cross-section of the blade <NUM>, as measured from the leading edge <NUM> to the trailing edge <NUM> of the blade <NUM> cross-section. As wind flows across the blades, the resulting forces on the blade cause a torque to be applied to the rotor <NUM> which spins the shaft <NUM> connected to the generator. The wind turbine control system adjusts the pitch angle <NUM> of the blades <NUM> to optimize the performance of the wind turbine for the extant wind conditions, while keeping the wind turbine within its design operating limits (e.g. RPM, structural loads, etc.). As will be discussed in more detail below, the airfoil performance monitor and system of the present invention disposed on the blade <NUM> aids the control system in improving the overall performance of the wind turbine <NUM> under a broad range of operating conditions, including the presence of airfoil degradations such as those caused by leading edge erosion or icing, generally indicated at <NUM> in <FIG>.

<FIG> depict a perspective view of the blade <NUM> detached from the rotor <NUM> and wind turbine <NUM>. <FIG> depicts one operative embodiment where the blade <NUM> has four airfoil performance monitors <NUM> disposed between the blade root and blade tip <NUM>, <NUM>, and wherein the blade <NUM> attaches to the rotor <NUM> at the root <NUM>. The blade <NUM> attaches to the rotor <NUM> at the root <NUM> using one or more fasteners (not shown). Alternatively, the blade <NUM> may attach to the rotor <NUM> at the root <NUM> using any known mechanical fastening technique. The airfoil performance monitor <NUM> may also be referred to as an airfoil performance monitor system <NUM>. As will be described in more detail below, the airfoil performance monitor <NUM> may be mounted on a low-pressure face <NUM> of the airfoil <NUM>. Securing the airfoil performance monitor <NUM> on a low-pressure face <NUM> of the airfoil <NUM> allows the airfoil performance monitor <NUM> to provide data indicative of a performance of the blade <NUM> of the wind turbine <NUM>.

As shown, the airfoil performance monitor <NUM> may be spaced along the blade <NUM> between the blade root and blade tip <NUM>, <NUM>. The airfoil performance monitor <NUM> may be secured to the blade <NUM> at distinct, predetermined positions <NUM>, or may be spaced according to a set, predetermined pattern (not shown). For example, depending on the shape and design of the wind turbine blade <NUM> or on wind patterns, direction and strength, as well as a design of the array <NUM> of wind turbines <NUM>, the airfoil performance monitors <NUM> may be secured at the predetermined position <NUM> indicative of providing the airfoil performance monitor <NUM> a data set, that may be utilized to optimize the performance of the blade <NUM> and wind turbine <NUM>. The predetermined position <NUM> of the airfoil performance monitor <NUM> may be determined by computational fluid dynamics analysis and/or by experimentation during initial setup to ensure the predetermined position <NUM> provides the best available data to the airfoil performance monitor <NUM> to optimize a performance of the wind turbine <NUM>.

Alternatively, the airfoil performance monitor <NUM> may be evenly spaced between the root and tip <NUM>, <NUM> of the blade <NUM>. For example, the airfoil performance monitors <NUM> may define an equal distance <NUM> between centers <NUM> of each of the airfoil performance monitors <NUM> disposed on the blade <NUM>. Providing equal distance <NUM> between centers <NUM> of each of the airfoil performance monitors <NUM> allows the airfoil performance monitor <NUM> to collect data in evenly distributed sections <NUM> across the blade <NUM>. Collecting data in distributed sections <NUM> provides performance information of the airfoil <NUM> of the blade <NUM> as wind acts to rotate the blades <NUM> about the rotor <NUM>. This data indicative of performance of the blade <NUM> at each section <NUM> allows the airfoil performance monitor <NUM> to provide accurate analysis of the interaction between the blade <NUM> and wind acting across the blade <NUM>, and likewise aid to optimize performance and efficiency of each individual blade <NUM> on the wind turbine <NUM> for greater production of electrical energy from the wind farm <NUM>.

As noted above, the embodiment shown in <FIG> includes four airfoil performance monitors <NUM> secured to the blade <NUM>. However, this is merely exemplary. The blade <NUM> may employ any number of airfoil performance monitors <NUM> secured between the root and tip <NUM>, <NUM> of the blade <NUM>. The number of airfoil performance monitors <NUM> secured to the blade <NUM> may be dependent on the shape and design of the wind turbine blade <NUM>, and/or the direction, pattern and strength of wind that interacts with the blade <NUM>. The number of airfoil performance monitors <NUM> may also be dependent on an amount of data necessary to calculate and optimize a performance of the blade <NUM> and wind turbine <NUM>. For example, a single airfoil performance monitor <NUM> may provide enough data and processing power to effectively calculate and adjust a performance of the blade <NUM> such that production of wind energy is optimized. Likewise, multiple airfoil performance monitors <NUM>, as shown, may provide additional data to increase a sensitivity of the overall performance of the airfoil performance monitor system <NUM>.

Referring to <FIG>, a schematic view of one embodiment of the airfoil performance monitor <NUM> is depicted. As shown in <FIG>, the airfoil performance monitor <NUM> includes a housing or mast <NUM>. The mast <NUM> defines a fin portion <NUM> and a base portion <NUM>. The fin portion <NUM> extends in a direction perpendicular from the airfoil <NUM> from the base portion <NUM>. The base portion <NUM> attaches to the airfoil using mechanical fasteners (not shown) extending through a plurality of holes <NUM> defined through the base portion <NUM>. However, those having ordinary skill in the art will appreciate that the base portion <NUM> may be mounted to the airfoil using any conventional fastening mechanism. The fin portion <NUM> attaches to the base portion <NUM> through welding, forming, adhesion or any other known mechanical joining technique such that the fin portion <NUM> is sealed to the base portion <NUM>. Alternatively, the fin and base portions may be formed as an integral, one-piece component. The base portion <NUM> may be substantially solid and formed to provide as much surface area contact between the base portion <NUM> and the airfoil <NUM> to ensure greater stability of the mast <NUM> on the blade <NUM>. The fin portion <NUM> is formed as substantially hollow, and may be of a streamlined airfoil shape such that air flows on each side <NUM> of the fin portion <NUM>, as shown in <FIG> Alternatively, the fin may be manufactured as an integral part of the wind turbine blade <NUM>, in which case the fin portion <NUM> would be integrated into the wind turbine blade <NUM> foregoing the need for the base portion <NUM> attachment.

<FIG> depicts a perspective view of the fin housing or mast <NUM> of an airfoil performance monitor <NUM> that includes fin <NUM> and base portions <NUM>. The fin portion <NUM> is designed to house components of the airfoil performance monitor <NUM>. For example, <FIG> depicts a schematic, perspective, cross-sectional view of one embodiment of the airfoil performance monitor <NUM> as a single combined unit that houses all of the necessary electronics in the mast. Specifically, <FIG> depicts an interior <NUM> of the combined airfoil performance monitor <NUM>. And as will be described in more detail below with respect to <FIG>, the fin portion <NUM> is designed to house at least one or more inertial sensors <NUM>, such as accelerometers, one or more airspeed-dependent sensors <NUM>, a controller <NUM> and associated electronics to provide data indicative of a performance and efficiency of the airfoil <NUM> for the blade <NUM> of the wind turbine <NUM>.

In one embodiment shown in <FIG>, the fin portion <NUM> defines at least one pitot pressure orifice <NUM> and at least one static pressure orifice <NUM>. However, the airfoil performance monitor <NUM> of the present invention may include a plurality of pitot orifices <NUM> and a plurality of static pressure orifice <NUM>. For example, in the embodiment shown in <FIG>, the pitot pressure orifice <NUM> is disposed on the front or leading edge <NUM> of the fin portion <NUM> and the static pressure orifice <NUM> is located on the trailing edge <NUM> of the fin portion <NUM>. On the other hand, and as shown in <FIG>, the airfoil performance monitor <NUM> may include a plurality of static pressure orifices <NUM>. One of the static pressure orifices may be located on the side <NUM> of the fin portion <NUM> and another may be located on the trailing edge <NUM> of the fin portion <NUM>. These embodiments are merely exemplary, and the amount and location of pitot and static orifices <NUM>, <NUM> may vary between depending, for example, on airflow strength, pattern and direction at a location of the mast <NUM>. The size and shape of the pitot and static orifices <NUM>, <NUM> may be adjusted to adjust the exposure of the airflow dependent sensor and tune the sensitivity necessary to calculate a performance and efficiency of the blade <NUM> of the wind turbine <NUM>. The pitot and static pressure orifices <NUM>, <NUM> may also be disposed at a <NUM> degree angle relative to a horizontal plane passing through the fin portion <NUM> to facilitate drainage of any liquid, such as water from rain or melting snow or ice, from the mast <NUM>.

Each of the pitot pressure orifices <NUM> is in fluid communication with at least one airspeed-dependent sensor <NUM>. The static pressure orifices <NUM> may also be in fluid communication with at least one airspeed-dependent sensor <NUM> as well. Alternatively, the static pressure orifice <NUM> may be in fluid communication with the interior <NUM> of the mast <NUM> such that the pressure of the interior of the mast <NUM> reflects the external static pressure. In this configuration, the static pressure orifices are simply open to the interior <NUM> of the mast <NUM> to equalize the internal and static external pressure. The pitot orifice <NUM> and its associated airspeed-dependent sensor <NUM> is used to measure total pressure that impinges upon the pitot orifice <NUM>. The static pressure orifice <NUM> is used to measure the static pressure that impinges on the static orifice <NUM>. As will be discussed in greater detail below, the static pressure measured at the static pressure orifice <NUM> is subtracted from the total pressure measured at the pitot pressure orifice <NUM> to arrive at the dynamic pressure.

With continuing reference to <FIG>, one or more inertial sensors <NUM>, and one or more airspeed-dependent sensors <NUM> are shown stacked above the controller <NUM> within the interior <NUM> of the fin portion <NUM> of the mast <NUM>. In the embodiment shown in <FIG>, the inertial sensors <NUM> may be accelerometers. However, those having ordinary skill in the art will appreciate that any type of inertial sensor suitable for the purposes disclosed herein are acceptable. Stacking the inertial sensors <NUM>, the airspeed-dependent sensors <NUM>, and the controller <NUM> allows the mast <NUM> to efficiently package electronics necessary to optimize a performance and efficiency of the wind turbine <NUM>.

The inertial sensors in the form of accelerometers <NUM> may be disposed above the airspeed-dependent sensors <NUM>, which are located above the controller <NUM> in the embodiment illustrated in the figures. As noted above, however, those having ordinary skill in the art will appreciate that these components may be arranged relative to each other in any number of configurations without departing from the scope of the present invention. This arrangement is merely exemplary. In at least one other embodiment, the airspeed-dependent sensors <NUM> may be disposed above the accelerometers <NUM>, which are located above the controller <NUM>. Likewise, the controller <NUM> may be stacked above both the accelerometers <NUM> and the airspeed-dependent sensors <NUM>. The combination and orientation of the accelerometers <NUM>, airspeed-dependent sensors <NUM>, and controller <NUM> may be optimized by sensor type, efficiency and performance requirements. For example, the airspeed-dependent sensors <NUM> may be disposed in an orientation and stacked within the interior <NUM> of the mast <NUM> such that airflow measured via pitot orifices <NUM> in the mast <NUM> provide airspeed-dependent data accurately sensed by the airspeed-dependent sensors <NUM>. In the same way, the accelerometers <NUM> may be disposed in an orientation and stacked within the interior <NUM> of the mast <NUM> such that an angle, or pitch of the airfoil performance monitor <NUM> provides acceleration data of the blade <NUM> accurately sensed by the accelerometers <NUM>. Similarly, the controller <NUM> may be disposed and stacked within the interior <NUM> of the mast <NUM> in an orientation that provides efficient data processing and transfer.

The airspeed-dependent sensors <NUM> may be pressure sensors. The pressure sensors used as airspeed-dependent sensors <NUM> may be sensors with a high frequency response, such as, but not limited to, piezo-resistive, thin film sensors. Any other type of pressure sensor, for example sealed and unsealed, that is adapted to measure differential airflow pressure or velocity may also be contemplated by one having ordinary skill in the art. Likewise, the inertial sensors, such as accelerometers <NUM>, may be sensors that measure vibration of the blade <NUM>. The accelerometers <NUM> may be either high or low impedance piezoelectric sensors. As noted above, he accelerometers <NUM> may be substituted with, or supplemented by, alternative inertial measurement sensors to also include <NUM>-axis or <NUM>-axis gyroscopes adapted to measure vibration from the blade <NUM> through the mast <NUM>. Operation of the inertial sensors <NUM>, airspeed-dependent sensors <NUM> and controller <NUM> will be explained in more detail with reference to the other Figures.

The airfoil performance monitor illustrated in <FIG> also includes heater elements <NUM>. Heater elements <NUM> may be supported within the interior <NUM> of the mast <NUM> on either side of the accelerometers <NUM>, the airspeed-dependent sensors <NUM> and the controller <NUM>. While shown and described as being disposed on either side of the accelerometers <NUM>, the airspeed-dependent sensors <NUM> and the controller <NUM>, the heater elements <NUM> may be a single heater element <NUM> disposed on a single side from the accelerometers <NUM>, the airspeed-dependent sensors <NUM> and the controller <NUM>. The heater elements <NUM> may be any element adapted to radiate heat into the mast <NUM>, such as, but not limited to, a resistive heating element <NUM> that produces heat in response to electrical current. The heater elements <NUM> are configured to keep the mast <NUM>, the accelerometers <NUM>, the airspeed-dependent sensors <NUM>, and controller <NUM> from accumulating ice on the mast <NUM> and obstructing the pitot and static orifices <NUM>, <NUM> during adverse weather conditions.

The mast <NUM> may also include a power supply <NUM> disposed within the interior <NUM> of the mast <NUM>. The power supply <NUM> may be on a single side of the interior <NUM> of the mast <NUM> or disposed on either side of the interior <NUM> of the mast <NUM>, depending on an amount of power needed. The power supply <NUM> is adapted to provide electrical power to the accelerometers <NUM>, the airspeed-dependent sensors <NUM> and the controller <NUM> depending on required power use of the accelerometers <NUM>, airspeed-dependent sensors <NUM>, the controller <NUM> and the heaters <NUM>. Power provided by the power supply <NUM> may be optimized based on a type of accelerometer <NUM>, airspeed-dependent sensors <NUM>, heaters <NUM> and processing requirements of the controller <NUM>.

<FIG> depicts another embodiment of the airfoil performance monitor <NUM> wherein the controller <NUM> is separated from the accelerometers <NUM> and airspeed-dependent sensors <NUM>. By separating the controller <NUM> from the accelerometers <NUM> and airspeed-dependent sensors <NUM>, a smaller footprint for the mast <NUM> may be achieved. Additionally, with the controller <NUM> separated from the accelerometers <NUM> and airspeed-dependent sensors <NUM>, the mast <NUM> has greater mounting flexibility on the blade <NUM> of the wind turbine <NUM> based on this smaller footprint. Specifically, in the embodiment shown in <FIG>, the mast <NUM> may include the pitot and static orifices <NUM>, <NUM>, the accelerometers <NUM> and the airspeed-dependent sensors <NUM>. The controller <NUM> may be disposed remote from the mast <NUM> shown in <FIG>. As shown, the controller <NUM> is disposed beneath the mast <NUM>. This is merely exemplary, and indicative of the controller <NUM> being remote from the mast <NUM>. Again, <FIG> depicts a further embodiment of the airfoil performance monitor <NUM> that allows for a mast <NUM> with a smaller footprint, providing ease of installation for the mast <NUM> on the blade <NUM>.

Referring to <FIG>, a functional block diagram of operation of the airfoil performance monitor <NUM> is depicted. The functional block diagram shown in <FIG> depicts interaction between the accelerometers <NUM>, airspeed-dependent sensors <NUM> disposed within the mast <NUM>, the controller <NUM>, and a display <NUM>. As can be seen in the embodiment depicted in <FIG>, the mast <NUM> includes the airspeed-dependent sensors <NUM>, the accelerometers <NUM>, and the heater elements <NUM>. As will be described in more detail with reference to the other Figures, the heater elements <NUM> may be operated as a closed loop with a switch <NUM> such that the switch <NUM> is used to regulate heat from the heater elements <NUM>. As shown, for example, the heater elements <NUM> receive approximately <NUM> volts of direct current to operate. This is merely exemplary, however, and the required volts to operate the heater elements <NUM> may be more or less than <NUM> volts depending on the type and arrangement of the heater elements <NUM>.

<FIG> also depicts the accelerometers <NUM> and airspeed-dependent sensors <NUM> in communication with the controller <NUM>. As shown, the airspeed-dependent sensors <NUM> send sensor voltage data produced by, and indicative of an airflow pressure and velocity measured via the pitot pressure orifice <NUM> and possibly the static pressure orifices <NUM>. The inertial sensors <NUM>, such as accelerometers, provide acceleration data indicative of the mechanical motion of the blade <NUM> and can be used to infer the pitch angle <NUM> of the blade <NUM> of the wind turbine <NUM>. Both the acceleration data from the inertial sensors <NUM> and the sensor voltage data from airspeed-dependent sensors <NUM> are used by the controller <NUM> to calculate a turbulence value of airflow across the blade <NUM>. Specifically, the acceleration data, as will be described in more detail below, from the inertial sensors <NUM> is used to filter vibratory noise detected by the airfoil performance monitor <NUM>, and the sensor voltage data from the airspeed-dependent sensors <NUM> is used to calculate the dynamic pressure at the blade <NUM> of the wind turbine <NUM>. Again, as can be seen in <FIG>, the power supply <NUM> connects to the sensors in the mast <NUM>, and specifically the airspeed-dependent sensors <NUM> to provide power to the mast <NUM>. As shown, the power supply <NUM> supplies <NUM> volts of direct current to the airspeed-dependent sensors <NUM>. The airspeed-dependent sensors <NUM> may also be adapted to be powered on any amount of voltage from the power supply <NUM>.

The controller <NUM> is also in communication with the inertial sensors <NUM>, airspeed-dependent sensors <NUM> and power supply <NUM>. The power supply <NUM> is adapted to supply power to the controller <NUM> to allow the controller <NUM> sufficient processing power to compute a digital airflow signal. Ultimately, the controller <NUM> is configured to calculate a filtered turbulence airflow signal. The turbulence airflow signal is used to calculate an airflow, turbulence intensity ratio, as will be described in greater detail with reference to the other figures. Specifically, the airspeed-dependent sensors <NUM> provide data indicative of the total pressure at the blade <NUM> as measured at the pitot orifices <NUM> of the airfoil performance monitor <NUM>. The static pressure orifices <NUM> are used to measure the static pressure at the airfoil performance monitor <NUM>. The measured static pressure is subtracted from the total pressure to arrive at the dynamic pressure at the airfoil performance monitor <NUM>. The inertial sensors <NUM> provide data indicative of vibration frequency and amplitude of vibrations on the blade <NUM> through the mast <NUM> to the controller <NUM> to calculate the turbulence intensity ratio. Additionally, data from the inertial sensors <NUM> is corrected for an orientation of the blade <NUM> by a blade incidence angle (not shown), if necessary, such that a characteristic, vibration frequency and amplitude are extracted from the filtered turbulence signal using the controller <NUM>. To account for the blade pitch angle <NUM>, a gain is set in the controller <NUM> since the blade pitch angle <NUM> may be set at an arbitrary pitch angle independent of the local airspeed.

The vibration frequency and amplitude data from the inertial sensors <NUM> is used to filter the digital airflow signal derived from data indicative of turbulent airflow from the airspeed-dependent sensors <NUM> to eliminate noise caused by vibration of the mast <NUM> on the blade <NUM> of the wind turbine <NUM>. Specifically, as air impinges on the pitot and static orifices <NUM>, <NUM> the airspeed-dependent sensors <NUM> are excited by an increase in turbulence as an angle-of-attack of the blade <NUM> increases to generate an alternating current (hereinafter "AC") signal being data indicative of turbulent airflow. A change in the blade <NUM> aerodynamics from contamination, damage, defect, or other airflow modifying cause(s) may also increase the turbulence of the airflow. The airspeed-dependent sensors <NUM> are excited by this increase in turbulence to generate an AC signal being data indicative of turbulent airflow. In the absence of mechanical vibration, the inertial sensors <NUM> provide a relatively small or zero oscillatory signal due the lack of mechanical motion of the blade <NUM>, and the AC signal can be determined to be accurately indicative of an increase in turbulence.

Conversely, if mechanical motion, such as vibrations, are induced on the blade <NUM>, the mechanical motion relative to the airflow measured at the pitot and static orifices <NUM>, <NUM> generates an AC signal falsely indicative of increased turbulence. The inertial sensors <NUM> are adapted to register, as frequency and amplitude data, mechanical motion during vibratory oscillations in order that the frequency of these spurious vibration-induced turbulence signals can be determined and filtered out from the airflow signal. As described, the controller <NUM> is configured to identify and filter the frequency and amplitude data indicative of mechanical motion on the blade <NUM> from the AC signal such that the filtered digital airflow signal can be determined to be accurately indicative of an increase in turbulence. The controller <NUM> may include a filter that can employ Fast Fourier Transform methods to identify the characteristic frequencies induced by mechanical vibrations. The filters may include notch, band-pass, high-pass, low-pass, low-pass parabolic or any other filter(s) to filter the undesired vibration-induced signals from the digital airflow signal to arrive at a correct measure of the airflow turbulence. More specifically, the controller <NUM> may apply Fast Fourier methods to the accelerometer signals to determine the fundamental vibratory frequencies of the unwanted noise induced by mechanical vibrations of the airfoil performance monitor <NUM> at the mast <NUM>. The controller <NUM> then uses filtering techniques which could include, but are not limited to, one or more of a notch, band-pass, high-pass, low-pass, or low-pass parabolic filters to eliminate the unwanted vibration-induced noise from the desired air turbulence signal. During steady-state conditions, in which airflow measured via the pitot and static orifices <NUM>, <NUM> is laminar and the blade <NUM> is not vibrating, both signals provide minimal signals of turbulence or motion, which is indicated by the smooth direct current (hereinafter "DC") component of the digital airflow signal.

The controller <NUM> normalizes the filtered frequency and amplitude AC signal by dividing by a DC component of the frequency and amplitude data from the airspeed-dependent sensors <NUM>. The controller <NUM> also normalizes the inputs from the one or more inertial sensors <NUM>, such as accelerometers, into acceleration components parallel to and perpendicular to the plane of rotation of the rotor <NUM> in response to a blade pitch angle <NUM>. The controller <NUM> calculates a turbulence intensity ratio R by dividing an alternating airflow component, the AC signal, by a steady-state component, the DC signal. Each airfoil performance monitor <NUM>, therefore, generates a turbulence intensity ratio R at a position of the mast <NUM> on the blade <NUM>. The controller <NUM> compares the turbulence intensity ratios R from each of the masts <NUM> disposed along the blade <NUM> to a threshold turbulence intensity ratio R', which is specific to the location of each airfoil performance monitor and airspeed-dependent sensor associated with a given pitot pressure orifice, that represents the desired stall warning threshold for the blade section at that location. The wholesale separation of the airflow from the low pressure side <NUM> of the affected section of the airfoil which leads to a rapid reduction in blade propulsive force accompanied by a rapid increase in blade drag that can have a severe effect on the operation of the wind turbine. The unsteady airflow characteristics that usually accompany a stall may also lead to severe vibrations that can jeopardize the integrity of the wind turbine, and which certainly would impact the wear and tear experienced by the drive components.

A stall may be caused by operation at too high a blade pitch angle <NUM>, or due to environmental factors such as icing, which degrades the airflow over the airfoil leading to a premature stall at an otherwise "safe" blade pitch angle <NUM>. The stall is always accompanied by an increase in the relative turbulence seen on the low-pressure side <NUM> as the lift on the blade begins to decrease. The stall phenomenon for rotating airfoils is complex. Different spanwise portions of a wind turbine airfoil may be stalled at different times; one blade may be stalled while another is not (for example if ice is shed asymmetrically from different blades); and the stall phenomenon may be cyclic - for example each blade might stall as it rotates past the wind turbine tower. It is exactly these phenomena that the proposed invention addresses.

In the case of the wind turbine <NUM>, stall conditions that reduce the blade <NUM> lift reduce rotational efficiency as the blade <NUM> turns around the rotor <NUM>. Stated differently, the term stall refers to the reduction of lift and increased drag created by the collapsing pressure differential between the low pressure side <NUM> and the high pressure side <NUM> of the blade <NUM>, due to excessive angle-of-attack of the blade <NUM>, which causes significantly increased turbulence on the low pressure side <NUM> of the blade <NUM>. In extreme cases, these conditions may cause the blade <NUM> rotational efficiency to drop below the level required to keep the rotation of the wind turbine self-sustaining. The controller <NUM> may be further configured to adjust the threshold R' to account for varying circumstances. For example, the controller <NUM> may use a blade pitch angle <NUM> measured with the accelerometers <NUM> to scale the turbulence intensity ratio R to adjust the threshold R' as a function of an angle of the blade <NUM>.

The controller <NUM> may also be configured to transfer data indicative of the turbulence intensity ratio R through a variety of interfaces. As shown in <FIG>, the controller <NUM> may communicate with a memory card <NUM> to transfer the digital airflow signal, including the frequency and amplitude data, the steady-state component, and the turbulence intensity ratio R into a file management system (not shown). The memory card <NUM> may be removable or secured with the controller <NUM> to allow the turbulence intensity ratio R to be transferred and used in various control systems of the wind turbine <NUM> or for data analytic purposes. For example, the controller <NUM> may communicate the turbulence intensity ratio R as feedback input to the rotor control <NUM> system to optimize an aerodynamic efficiency of the rotor <NUM> for the rotor control system <NUM>. Additionally, the controller <NUM> may communicate the vibration frequency and amplitude data as feedback input to the rotor control system <NUM> to minimize vibration of the rotor <NUM> for the rotor control system <NUM>.

The controller <NUM> may communicate with the rotor control system <NUM> through a network interface <NUM>. The network interface <NUM> may be a wireless network interface, a local area network interface, or any other data transmission interface that is configured to receive the turbulence intensity ratio R, the accelerometer frequency and amplitude data, the airflow data and any other data generated by the airfoil performance monitor. As can be seen in <FIG>, the rotor control system <NUM> includes a corresponding network interface <NUM> to receive communications from the controller <NUM>. Additionally, the rotor control system <NUM> may be adapted to store user-defined preferences and calibration coefficients, receive and decode the turbulence intensity ratio R and associated data, and display the turbulence intensity ratio R and associated data for each of the airspeed-dependent sensors <NUM>. The rotor control system <NUM> may also include a log file to register the turbulence intensity ratio R and associated data.

<FIG> depicts a flow chart indicative of control logic used by the controller <NUM> to calculate the turbulence intensity ratio R from the airspeed-dependent sensors <NUM> and the inertial sensors <NUM>. As described, the controller <NUM> receives airflow data generated by the airspeed-dependent sensors <NUM> at <NUM>, and blade vibration and rotation speed data at <NUM>, <NUM> generated by the inertial sensors <NUM>, such as accelerometers or provided from an existing wind turbine <NUM> control system. The controller <NUM> filters rotation speed noise, indicated by the rotation speed data at <NUM> which may be provided from the accelerometers <NUM>, from the digital airflow signal at <NUM>. The controller <NUM> also filters vibration noise, indicated by the blade vibration noise at <NUM> measured from the accelerometers <NUM>, from the digital airflow signal at <NUM>. As described above, the filters at <NUM>, <NUM> may be any type of filter configured to process vibration and rotation speed data, such as, but not limited to, a notch, band-pass, high-pass, low-pass, or low-pass parabolic filters, and may use Fast Fourier methods to determine the fundamental vibratory frequencies from the accelerometer signals.

Filtering the blade vibrations and rotation speed at <NUM>, <NUM> allows the controller <NUM> to calculate the turbulence intensity ratio R from the AC and steady-state signals (DC) of the digital airflow signal at <NUM>. The controller <NUM> calculates the turbulence intensity ratio R at <NUM> as described. Again, this allows the controller <NUM> to communicate with the rotor control system <NUM> to optimize blade pitch for maximum power and efficiency, this optimization may be with the objective to improve the lift/drag ratio of the blade for the prevailing wind conditions. Also, the controller may communicate with the rotor control system <NUM> to optimize blade pitch with an objective to minimize vibrations that be damaging, or, in the worst case, cause blade-tower collisions. The controller <NUM> may also use the turbulence intensity ratio R, and accompanying data to identify contamination incidences such as icing and activate the heaters <NUM> or other deicing systems on the wind turbine airfoil (not shown). Specifically, the controller <NUM> may use the turbulence intensity ratio R to optimize use of the de-icing system to avoid shutdown of the wind turbine <NUM>. The controller <NUM> outputs the turbulence intensity ratio R to the rotor control system <NUM> for optimization of the rotor control system <NUM> at <NUM>. Additionally, the controller <NUM> may also output the turbulence intensity ratio R to a display (not shown), as previously described.

Referring to <FIG>, a flow chart depicting control logic for a de-icing system <NUM> in communication with the controller <NUM> is shown. For illustrative purposes, the de-icing system <NUM> is configured to maintain a temperature of the mast <NUM> between <NUM>°F and <NUM>°F. At <NUM>, the de-icing system <NUM> reads a temperature supplied by the controller <NUM>. At <NUM>, the de-icing system decides if the temperature is greater or less than <NUM>°F. If, at <NUM>, the temperature is greater than <NUM>°F, the de-icing system <NUM> continues to monitor the temperature from the controller at <NUM>. If, at <NUM>, the temperature is less than <NUM>°F, the de-icing system <NUM> starts the heater elements <NUM> at <NUM>. At <NUM>, the de-icing system reads the temperature from the controller <NUM>. At <NUM>, the de-icing system determines if the temperature is greater or less than <NUM>°F. If, at <NUM>, the temperature is less than <NUM>°F, the de-icing system <NUM> continues to monitor the temperature from the controller at <NUM>. If, at <NUM>, the temperature is greater than <NUM>°F, the de-icing system <NUM> stops the heater elements <NUM> at <NUM>. Activation of the mast de-icing system <NUM> may be used in parallel to trigger the activation of the blade de-icing system, if installed, to prevent ice accumulation on the blade <NUM> of the wind turbine <NUM>. Again, operation of the de-icing system <NUM> prevents the wind turbine <NUM> from being shut down due to ice accumulation on the blades <NUM>. In addition to facilitating de-icing of any blade, the airfoil performance monitor of the present invention can also be used to detect contamination or any type of environmental condition that leads to degradation of the performance of the airfoil, which, in the representative example described herein, would also translate to a degradation in the performance of the wind turbine. This information may be used to improve efficiencies, schedule maintenance, or for any other purpose deemed advantageous by the end user.

Claim 1:
An airfoil performance monitor (<NUM>) comprising:
a housing (<NUM>) mounted on a low-pressure face (<NUM>) of an airfoil (<NUM>), and including at least one pitot pressure orifice (<NUM>) used to determine the total pressure at the airfoil performance monitor (<NUM>) and at least one static pressure orifice (<NUM>) used to determine the static pressure at the airfoil performance monitor (<NUM>);
at least one airspeed-dependent sensor (<NUM>) that senses the total pressure at the airfoil performance monitor (<NUM>) via the pitot pressure orifice (<NUM>) and generates a digital airflow signal indicative of the dynamic pressure at the airfoil performance monitor (<NUM>) and
one or more inertial sensors (<NUM>) adapted to register, as frequency and amplitude data, mechanical motion during vibratory oscillations of the airfoil (<NUM>); and
a controller (<NUM>) adapted to derive a turbulence intensity ratio (R) by normalizing turbulence values using a steady-state airflow signal calculated from the digital airflow signal, and to filter the turbulence values from the digital airflow signal with the frequency and amplitude data from the one or more inertial sensors (<NUM>) to eliminate unwanted airfoil vibration effects on the turbulence intensity calculations.