EP2622316A1

EP2622316A1 - Method and device for non-destructive testing of wind turbine blades

Info

Publication number: EP2622316A1
Application number: EP11760793.7A
Authority: EP
Inventors: Jacques Bouteyre; Pascal Jouan
Original assignee: Astrium SAS
Current assignee: ArianeGroup SAS
Priority date: 2010-09-28
Filing date: 2011-09-27
Publication date: 2013-08-07
Also published as: US20130235897A1; WO2012041848A1; US9562870B2; CN103154697A; FR2965353A1; CN103154697B; JP2013542360A; JP6001540B2; BR112013007550A2; FR2965353B1

Abstract

The method CND (200) of non-destructive testing of a wind turbine blade (10), comprises a step (201) of stressing the structure of the blade through a modification of a physical characteristic of a fluid filling the hollow interior volume (18) of the blade, a step (202) of observing zones to be tested of the exterior surface (19) of the blade, with the contactless measurement of a physical parameter on points of the exterior surface (19) of the blade and a step (203) of comparing the map of the values of the physical parameter measured with a reference map. A system CND for checking the structural integrity of a wind turbine blade (10) according to the method CND comprises an aerothermic device (40) for modifying the physical conditions, temperature or pressure, of a fluid filling the hollow interior volume (18) of the blade, a device for contactless measurement (50) of a physical parameter, temperature or dimensions, of the exterior surface (19) of the blade, and a device for processing the measurements.

Description

NON-DESTRUCTIVE CONTROL METHOD AND DEVICE

OF WOLF BLADES

The present invention belongs to the field of wind turbines.

More particularly, the invention relates to the non-destructive control of the integrity of wind turbine blades, especially large wind turbines, which must be controlled as much as possible without the need to deposit the blades.

The sector of energy generation, especially electrical energy, by means of wind turbines is growing rapidly. The search for economies of scale and the interest of capturing the maximum energy per wind turbine lead to the design of increasingly large machines with blades of great lengths depending on the span and masts carrying high-altitude nacelles .

Wind turbine blades are currently larger than 50 m wingspan and more than 75 m prototypes are under construction. These blades are subject to many constraints that lead to realize these blades of metal materials and or composite materials.

The composite materials used are of the type comprising organic fibers such as Kevlar® fibers or mineral fibers such as glass or carbon fibers which are held in a hard organic resin matrix in stacked layers to form the various assembled elements. blades.

Various known technologies can be implemented to manufacture such blades, but when the blade is in use on a wind turbine it is subjected to strong mechanical constraints that require regular checks to ensure its integrity and its integrity. good aging. The dimensions of the blades of large wind turbines do not allow, for economic reasons, to consider depositing or transporting the blade for frequent checks and these must be carried out on the wind turbine itself when the weather conditions allow it.

The quality of the controls and their frequencies are then essential to detect the presence of defects, such as cracks, detachments or delaminations, at the earliest stages of their appearance and to repair the blades before damage to the structure. imposes major repairs, or even the integrity of the blade and the wind turbine at risk.

To carry out the control of the blade structure the various known techniques of non-destructive testing (NDT) applied to metal structures or composite materials can be used on a wind turbine blade, in particular the visual control of the surface of the associated blade or not to bleeding and fluorescence techniques, control of material and assemblies by X-ray or ultrasound. Such techniques are in particular implemented in the factory to control the blades during their manufacture and before assembly.

Whatever the CND technique implemented, a problem that arises in the case of wind turbine blades in service is due to the difficulties encountered in accessing all the points of the outer surface of the blade to perform the control operations.

Various solutions have been devised to solve the problem of access to the different locations of the blades.

A known solution for example WO2009 / 121792 and WO

2009/155918 is to use a mobile platform along the mast that supports the wind turbine so that when a blade is held vertically downward and thus parallel to the carrier mast, each point of the blade surface can be inspected at all the heights along the blade by operators working from the platform to perform visual or ultrasonic checks, for example.

When a blade has been inspected, the platform is lowered and the wind turbine is turned to place another of the blades vertically which is inspected in turn and the operation is repeated until all the blades are checked.

A major difficulty of this type of non-destructive testing method comes from the fact that control operations are carried out by operators located on a platform that rises from necessity to several tens of meters above the ground in difficult conditions. which requires a long period of stopping of the wind turbine to carry out the inspection, limits the quality of the controls and presents potential risks for the operators whose control is binding.

In addition, such nacelles themselves require numerous security checks to be able to be used in compliance with the standards in force.

US 2010/0132137 discloses another type of device which implements an autonomous robot moving on the blade. In this case, the blade to be controlled is placed in a horizontal position with its leading edge facing upwards and the robot comprises rolling means bearing on the leading edge of the blade to move along the span of the blade. the blade.

The capabilities of this type of robot however are limited by the fact that only areas near the leading edge of the blade can be controlled and that the position of the robot can be unstable.

In addition the movement of the robot in contact with the blade requires taking precautions to ensure that the blade is not likely to be damaged during nominal operation or not the robot.

Moreover, the visual inspection techniques only make it possible to detect visible defects from outside the blade and of sufficient size to be observed, that is to say, most often at a very advanced stage of the defect and the techniques ultrasonic testing that can detect internal defects are long to implement.

The present invention simplifies the control of wind turbine blades and improves the quality of their maintenance by offering the possibility of carrying out quality checks at short intervals without prolonged immobilization of the wind turbine in order to detect as soon as possible any damage to a wind turbine. blade. For this, the CND method of the invention for non-destructive testing of a wind turbine blade, in which the structure comprises a skin which determines an outer surface of the blade and an interior volume of the hollow blade, at least partially in view of structural or non-structural elements that may be inside the blade, includes:

a first step of biasing the structure of the blade by modifying at least one physical characteristic of a fluid, in particular air if the internal volume of the blade is left in relation with the atmosphere, filling the hollow interior volume of the blade; a second step of observing zones to be controlled on the outer surface of the blade, this observation comprising the making of non-contact measurements, by means of one or more sensors kept at a distance from the outer surface, of at least one physical parameter, sensitive to the solicitation of the first step, on points of the outer surface of the blade so as to establish a measured map of the values of the physical parameter measured for the areas to be controlled; a third step of detecting anomalies by comparing values measured during the second step with nominal values expected for a blade without significant defect, that is to say corresponding to values of a healthy blade.

In a first implementation of the CND process, the mainly modified physical characteristic corresponds to the temperature of the fluid in the inner hollow volume of the blade. This temperature of the fluid is brought to a different value, higher or lower, of the temperature outside the blade during the first step and the physical parameter measured during the second step corresponds to a temperature of the outer surface. of the blade.

The change in temperature is obtained either by heating or by cooling the fluid by conventional heating or cooling means and by ensuring a circulation of the fluid in the hollow volume of the blade. In this embodiment, a rapid measurement is accurate and is advantageously achieved by infrared thermography measurement without physical contact of a measurement sensor which is maintained during measurement at a distance from the outer surface of the blade.

In another implementation of the CND method, the mainly modified physical characteristic corresponds to a pressure of the fluid in the inner hollow volume of the blade.

This pressure of the fluid is brought to a value different from the pressure outside the blade, either at a lower pressure or at a higher pressure, during the first step and the physical parameter measured during the second step. corresponds to a geometrical dimension of the outer surface of the blade which characterizes the geometrical shape of this external surface or to a modification of dimension corresponding to the deformation of this outer surface under the effect of the modification of the pressure.

According to this application of the method the generation of a differential pressure is achieved by means of a pump sealingly connected to the hollow volume of the blade which, at least during the control, is not directly connected to the ambient atmosphere.

In this embodiment, the geometrical dimensions of the outer surface of the blade or its deformations are advantageously measured without contact by a laser telemetry method, by a digital photogrammetry method, by a laser interferometry method or by a shearography method.

In one embodiment, the anomaly detection performed in the third step comprises a step of comparing the value measured at each point with values measured at points close to the point considered so as to establish a map of the contrasts of the points. values of the measured parameter and comprises a step of correlation of the said contrast map with internal structures of the blade, which makes it possible to detect the anomalies without the need to have a comparison reference other than the measured values on the blade under control.

In another embodiment, the measured map is compared with a reference map of the values of the measured parameter which is advantageously a reference map established by measurement according to the first and second process steps on one, if applicable on the blade subjected to the CND control and checked before it is put into service, or several blades considered flawless, thus making it possible to produce a card mean reference representative of all the blades of the same model, or is a theoretical reference map established by numerical simulation of the process on a digital blade model, making it possible to produce a reference map free from any artifact related to manufacturing problems. or an undetected defect of a measured blade, which also makes it possible to simulate defects to obtain a representation of the measurement according to the method, or is a reference map established by hybridizing measured values and values obtained by simulation.

In order to facilitate the interpretation of the anomalies observable with respect to the reference map, the CND method advantageously comprises a fourth step of fault characterization by comparing the characteristics of the identified anomalies, in real time during the measurement or in deferred time, of each anomaly observed with known anomalies whose characteristics are stored in an anomaly database.

The invention also relates to a non-destructive NDT control system adapted to the implementation of the CND method of the invention for verifying the structural integrity of a wind turbine blade, comprising a skin determining an outer surface of the wind turbine blade. blade and an interior hollow volume of the blade, which comprises:

an aerothermic device for modifying the physical conditions of a fluid filling the hollow interior volume of the blade;

a measuring device implementing one or more non-contact sensors of at least one physical parameter of the outer surface of the blade;

a measurement processing device configured to establish a map of the measured values of the at least one parameter on the outer surface of the blade and to identify the anomalies of the map of the measured values. According to a first embodiment of the CND system corresponding to the first mode of implementation of the method, the aerothermal device is a heating device, for example comprising electric heating or cooling resistors, for example a refrigeration compressor unit, modifying the temperature of a fluid in the inner hollow volume of the blade to bring this temperature to a value different from the outside temperature of the blade, by positive value or by negative value, and the non-contact measurement device sets implementing a thermal camera measuring the temperature of the outer surface of the blade or any other sensor for measuring without contact a value representative of the temperature of the outer surface of the blade.

In one embodiment, which makes it possible to have pre-equipped blades for which the introduction of the CND system for carrying out a control is simplified, the heating means of the heating device modifying the temperature of the fluid in the hollow volume of the blade are fixed in the hollow volume, inside the blade, these heating means comprising one or more heating electrical resistances and or means for maintaining fluid circulation in the hollow volume. According to another embodiment, the aerothermal device is a pressure generating device, for example a gas pump, and modifying the pressure of a fluid, for example air, in the inner hollow volume of the blade and now during the control operations this pressure at a controlled value different from a pressure outside the blade of a predefined difference, positive or negative.

For the purposes of this embodiment of the CND system, the non-contact measuring device in a first embodiment implements one or more devices for measuring the geometry of the outer surface of the blade under control by digital photogrammetry or in another embodiment uses a scanning range finder to measure the geometry of the outer surface of the blade being controlled by telemetry.

Other non-contact measuring device of the sensor such as a laser interferometer or a shearography device are also usable for measuring the deformations of the outer surface of the blade under the effect of the modification of the fluid pressure in the blade.

These devices implemented in the CND system have the advantage of being industrially available and relatively inexpensive, which makes it possible to consider the possibility of installing a permanent aerothermal device in each wind turbine to facilitate the installation of the CND system at the moment. to carry out control operations.

The choice of a measuring device with a non-contact sensor and a sensor support enabling the blade to be swept advantageously takes into account the speed and precision of the measurements sought and also the environmental conditions which may be very different. depending on the location of the wind turbine.

Depending on the accessibility conditions of the wind turbine and depending on whether it is preferred over the speed of the control or another condition, the non-contact measuring device can be during measurements fixed at a distance from the wind turbine, typically from the wind turbine. order of the height of the wind turbine, on the ground or on a land vehicle or on a surface vessel or be attached to an airborne platform movable along the blade in the vicinity of said blade to perform measurements at a reduced distance, typically from the order of magnitude of the rope of the profiles of the blade, or close to the surface of the blade, carried by a robot moving on the blade bearing on the blade.

The airborne platform is, for example, supported by a rotary-wing drone or micro-drone, controlled in position relative to the blade, or is supported by a balloon lighter than air and captive, controlled in position relative to the blade. to control.

Other features and advantages of the invention will be better understood on reading the following description of embodiments of the invention which are not limiting with reference to the drawings which represent:

FIG. 1: An overall perspective view of an example of a large three-dimensional wind turbine; Figure 2a: A perspective view of a blade section showing the internal structure of a blade having a box type spar with two cores;

FIGS. 2b: A perspective view of a blade section showing the internal structure of a blade comprising a spar comprising a single core separating a leading edge box from a trailing edge box;

FIG. 3: a schematic example of arrangement of an aerothermal device of the CND system of the invention

FIG. 4a: an illustration of a first embodiment of an airborne platform of the device for measuring the CND system of the invention by means of a rotary wing drone or micro-drone, FIG. 4b: an illustration of a second embodiment of an airborne platform of the device for measuring the CND system of the invention by means of a captive balloon,

FIG. 5: a simplified synoptic presentation of the method of the invention.

The present method of non-destructive testing, referred to as CND, of a blade 10 of a wind turbine 100, as shown in FIG. 1, is based on the implementation of a transmission measurement technique with a remote observation. of the blade, ie without contact of measurement sensors.

In this document the term "non-contact measurement" means that a measurement is made without the sensor (s) used to perform the measurement being in physical contact with a controlled surface of the blade, the support systems of the or sensors that can however rely on the blade to keep the sensor or sensors away from the surface.

The wind turbine blade 10 is a bearing aerodynamic shape of large elongation of which an outer surface 19 is determined geometrically by a succession of aerodynamic profiles 1 1 each corresponding to the geometry of a surface coating 1 1 1 1 and a coating of intrados 1 12 between a leading edge 1 13 and a trailing edge 1 14 and which determine the outer surface 19 of the blade as shown in Figures 2a and 2b.

The blade 10 is fixed on a rotating shaft integral with a technical nacelle 30 located in an upper part of a carrier mat 20 and which groups functional elements of the wind turbine: power generator, gearbox, pitch control blades. .. not detailed here.

The blade 10, like most large wind turbine blades in general, is hollow, for reasons of maximum relief of its mass and to save the material in which it is made.

To ensure its aerodynamic functions and the transmission of aerodynamic forces generated during its operation, the blade 10 is made in the form of a box-like structure more or less complex but most often as shown in Figure 2a a longitudinal box forming a spar 12 of the blade according to its wingspan.

Such a spar 12 is for example of substantially rectangular section, that is to say comprising at least two cores, a front core 121a and a rear core 121b, connected by flanges 122a, 122b and is covered with a skin 13 giving the blade its aerodynamic profiles, which vary according to the position along a span of the blade.

The skin 13 may be formed of several elements to reconstitute the surfaces of intrados 1 12 and extrados 1 1 1 of the blade both on the side of its leading edge 1 13 that its trailing edge 1 14 which are assembled between them and the spar 12 according to known methods such as reported fasteners and or collages.

According to this embodiment of the blade 10, said blade has a hollow volume 18 of the blade inside the skin 13 with an overall multi-box structure, in the case illustrated in FIG. 2a a leading edge box 14 between the edge 1 13 and the front soul 121a of the spar 12, a trailing edge box 15 between the rear core 121b of the spar 12 and the trailing edge 1 14 and a spar box 16 between the front webs 121a and rear 121b of the spar.

It should be noted that the spar 12 may also comprise only one core 121a as illustrated in FIG. 2b, and in this case the torsional stiffness of the blade is provided by the leading edge caissons 14 and trailing edge 15 in the absence of a spar box, or on the contrary may comprise a spar with more than two cores and delimiting a plurality of spar boxes, not shown solution.

The structural elements of the blade that are in the volume determined by the outer surface 19 are here grouped in part or in full as appropriate under the term "internal structure".

According to the method CND 200 of the invention, presented in a block diagram in FIG. 5, the blade 10 is subjected to a stressing of its structure by a modification of at least one physical characteristic of a fluid filling the hollow volume 18 of the blade and the effects of this internal stress are observed at the outer surface 19 of the blade by measuring at least one physical parameter, sensitive to the internal stress, at different points of said outer surface to detect, by comparison to a reference value of the physical parameter at each point, anomalies in the measured parameter value that may correspond to structural defects of the blade.

In a first mode of implementation of the method 200, the loading of the structure is carried out by a modification of the temperature of the fluid, a priori of the air at ambient pressure or, if appropriate, any other fluid used to fill the volume. hollow 18 and used as heat transfer fluid in this first mode, occupying the hollow volume 18 and the effects of this temperature change on the structure are observed from the outside of said blade by thermography means so that the consequences of the modification internal temperature and the resulting temperature gradient between the inside of the blade and its outside are observed by their thermal effects at the outer surface 19 of the skin 12, 13 to which the energy in the form of heat.

In a first step 201, the temperature of the fluid inside the blade is modified relative to a temperature of the air outside the blade.

This modification of the internal fluid temperature induces a heat flux in the structure between the inside of the blade and the outside of the blade, which in each point depends on the local characteristics of the structure traversed by this heat flow. effects are observable on the outer surface of the 10 from the outside of the blade where they result in temperature differences that are a function of irregularities of the internal structure.

It should be noted that the temperature inside the blade can be brought to a higher value or a value lower than the outside temperature to induce the desired heat flow, the effects then being reflected in the outer surface 19 of the blade. blade by more or less hot locations or more or less cold points depending on the location of the surface of the blade relative to the external ambient temperature depending on whether the temperature of the internal fluid is increased or decreased.

In a second step 202, the outer surface 19 of the blade is observed in order to establish a thermal map of said outer surface, in practice a map of the temperatures measured at different points of zones of the outer surface of the blade subjected to the control where each point of the measured surface is associated with the measured temperature.

In a third step 203 the map of the measured temperatures established during the second step 202 is analyzed to identify thermal anomalies, that is to say temperature differences on the surface of the blade that do not reflect the temperature differences expected at the surface of the blade.

In one embodiment of this third step 203, the identification of the thermal anomalies comprises a step of identifying thermal contrast on the thermal map that does not correspond to the effects expected by the presence of elements of the inner structure, more particularly which do not correspond to the thermal contrasts expected due to the presence of the internal structure when the observed area corresponds to the known presence of such structural elements inside the blade.

The thermal anomalies are identified in particular by the sign of a difference between the measured temperature and the expected temperature, and or by a contrast reflecting the intensity between the thermal anomaly, ie an absolute value of a difference between the measured temperature and the expected temperature, and or by an extent of the area having a thermal anomaly.

In a method of implementing this third step, the thermal anomalies are detected by a contrasts analysis of the thermal map resulting from the measurement, that is to say that each point of the surface of the The blade for which the temperature is measured is compared with measured temperatures of neighboring points so as to identify temperature gradients at the surface of the blade which do not correspond to features of elements of the inner structure.

In another method of implementing this third step, the map of the measured temperatures, translated if necessary into a thermal contrast map, that is to say brought back to a reference temperature in order to neutralize the influence of the temperature. external during the measurement, is compared to a reference map of temperatures or thermal contrasts, called reference map, previously obtained 210 on a healthy blade of similar structure, so as to extract a map of thermal anomalies corresponding in any point of measure at the difference of temperature or intensity of thermal contrast between these two cards.

It should be noted here that a blade has many "accidents" of normal structure, consequences of its internal structure and blade manufacturing processes that lead to a complex reference map on which the effects of minor structural defects are difficult to observe directly.

The reference card is for example obtained 210 by tests carried out, a priori in the factory, on one or preferably several blades checked healthy, if necessary by tests 21 1 on the blade subjected to the control in use, by any technique CND adapted, for example by ultrasound to establish a reference map established by the measurement.

Another method for producing the reference map is to produce a detailed numerical model of the blade structure and to determine by numerical simulation one or more reference maps theoretically established.

In a fourth step 204, the thermal anomalies map is analyzed to identify the type and importance of the defects corresponding to these thermal anomalies.

The type and importance of a defect are determined in practice according to the extent of the observed thermal anomaly, the location of the anomaly, especially depending on the size of the underlying interior structure, and the intensity of the thermal anomaly.

By way of nonlimiting examples, a thermal anomaly corresponding to an increased thermal contrast with respect to the expected contrast, of the same sign as the temperature difference between the fluid inside the blade and the outside of the blade, and delimited by a narrow and elongated zone translates with a high probability a crack in a wall, and a diffuse thermal anomaly and extended having a thermal contrast whose evolution is of sign reversed with respect to the temperature difference between the fluid to the The inside of the blade and the outside of the blade translate with a high probability a local delamination zone of the skin 13 of the blade or a detachment of elements of the inner structure.

Advantageously, a databank 220 presenting the characteristics of the anomalies that can be observed makes it possible to characterize the defects more rapidly.

Such a databank 220 is advantageously made by digital fault simulation on a digital blade model so as to characterize at least the defects considered to be the most critical during a safety analysis of the wind turbine.

Preferably, this databank 220 is enriched according to the observations made which show, during the lifetime of the wind turbines which may exceed 15 years, defects detected by the method of the invention and then characterized in the context of maintenance of the blades.

Once a defect detected and characterized, conventionally it is carried out the maintenance operations 205 adapted: enhanced monitoring of the defect and its evolution, repair on site or removal of the blade for repair.

An advantage of the method is that it allows early and accurate detection of defects and thus reduce monitoring and maintenance costs and reduce the risk of unavailability of the wind turbine.

In another mode of implementation of the method, the stress 201 of the blade structure is achieved by the application of a differential pressure, positive or negative, between the fluid occupying the hollow volume 18 of the blade and the air outside the blade.

In this embodiment, the differential pressure, limited to values that are compatible with the resistance of the blade structure, causes deformations of the structure of the blade that can be observed at the level of the outer surface 19 by means of measurement methods. geometric shapes of an object.

For non-contact measurement of the geometrical shape of the outer surface 19 of the blade, it is for example implemented a measurement method by laser telemetry or by digital photogrammetry or laser interferometry or by shearography.

Similarly to the first embodiment described, a map of the outer surface 19, here a map of the geometric deformations of said surface under the effect of the differential pressure is performed 202 and analyzed 203 to identify the geometric anomalies of the blade 10 subjected to the differential pressure, that is to say the deformations of the outer surface 19 which do not correspond to geometric deformation expected given the internal structure.

The identification of the geometrical anomalies results in an embodiment of the third step 203 of the identification of deformations which relative to areas adjacent to the surface of the blade do not correspond to elements of internal structure due to the positions of the deformations on the blade surface and / or their shapes and / or amplitudes.

In another embodiment, the anomaly map is obtained by performing a subtraction between the geometry of the outer surface 19 of the blade 10 under control subjected to the differential pressure and the geometry of the outer surface of a similar blade. considered healthy also subjected to a differential pressure, the latter geometry of the outer surface 19 corresponding to a reference map in this case geometric shapes obtained with the differential pressure, possibly corrected for the effects of differences between the pressures implemented between the two trials. Thus, the anomaly map shows the areas of the blade whose deformations are not expected with information on the position of said zones and on the amplitude of said deformations.

The shape of the healthy blade subjected to a differential pressure and serving as a reference for the determination of the anomalies can be obtained 210 by numerical simulations or by physical tests on blades previously verified and considered as healthy, if necessary obtained 21 1 by physical tests on the blade subjected to the control in service. The anomalies are then compared 220 to a defect bank giving the characteristics of known anomalies, characteristics established by simulation or by experience.

The invention also relates to a CND system for non-destructive testing of a wind turbine blade according to the CND method of the invention.

For the implementation of the first described mode of the CND process, the CND system comprises a first aerothermal device 40 for modifying the temperature of the fluid inside the blade 10 as illustrated in FIG.

The aerothermal device 40 comprises a generator 41 which modifies the temperature of the fluid, advantageously air, and generates in this example an interior air 43 at a temperature different from the outside air, hotter or colder than the outside air to the blade 10.

The temperature difference is on the one hand sufficient to cause thermal gradients in the blade structure 10 leading to detectable temperature variations on the outer surface 19 of the blade and, on the other hand, limited to compatible temperature values. with the materials and assembly methods implemented in the blade.

In an exemplary embodiment implementing a superheated fluid sent inside the blade, the temperature of the fluid is for example between 70 degrees centigrade and 120 degrees centigrade, acceptable temperature according to these two criteria given the means of detection of conventional temperature differences that can be implemented and current technologies for wind turbine blades. Although the smallest dimensions of the theoretically detectable defects depend on the minimum value of the temperature differences measurable by the means implemented, it is advantageous to consider detectable temperature differences on the surface of the blade of the order of 0, 01 ° C to avoid the use of complex and expensive measurement means whose implementation in the environment of a wind turbine would be economically too penalizing. A thermal camera compatible with the detection of temperature differences of this order is able with a suitable optics to provide a resolution better than one centimeter at a distance of ten meters.

In a preferred embodiment, the air generator 41 is installed in the nacelle technique 30 where it is mounted fixed and dedicated to the wind turbine to allow control operations without the requirement of special logistics to manipulate said generator.

The aerothermal device 40 also comprises a distributor 42 of the air produced by the air generator 41.

Such a distributor 42 consists mainly of one or more flexible or rigid injection pipes, which channel the hot or cold air of the air generator 41 towards the inside of the blade 10 at the level of a blade root. so that hot or cold air is injected into the hollow volume 18 of the blade through an axial opening of said blade root.

In this case, it takes advantage of the general structure of the wind turbine blades whose blade root 17 corresponding to the end located on the side fixed to the nacelle 30 is accessible.

In the case of the invention the air 43 is injected into the hollow volume 18 of the blade 10 in order to follow a predetermined circuit such that the entire hollow volume of the blade, or at least the desired volumes, are crossed. by a continuous flow of hot or cold air 43 from the air generator 41.

To guarantee such a result, it is advantageously made use of the internal structure of the blade 10, adapted if necessary, so that the air 43 injected by the blade root 17 traverses the entire blade according to its wingspan close to the end of the blade, opposite the span of the blade at the blade root, by at least one of the boxes 14, 15, 16 and follows a reverse path from the end to the blade root by the other boxes . In the example of a blade whose section is illustrated in FIG. 2a, the air is for example injected into the spar box 16 and follows a reverse path through formed trailing edge and trailing edge caissons 15. by the skin of the blade.

The souls 121a, 121b of the spar have openings that allow air to flow from the box in which the air is injected to the caissons through which the air follows a reverse path.

These openings are arranged close to the end of the blade and, where appropriate, are distributed along the span to distribute the injected air at different points of the other caissons and to ensure rapid homogenous heating of the fluid in the hollow volume 18.

To ensure the flow of air, the injected air 43 spring 44 of the blade also at the blade root 17.

The air leaving the blade 44 can be released to the outside by circulating around the injection pipe, but advantageously the air is kept in a closed circuit for better efficiency of its heating or cooling and the air outgoing 44 of the blade is returned to the air generator 41 to be recirculated. In this case, the outgoing air can be released into the nacelle 30 where it is taken by the air generator 41 or back from the blade root 17 to the air generator 41 by means of one or more outlet pipes. dedicated, solution not shown.

The arrangement of injection and outlet piping does not present any particular problem but, in view of the rotation of the blades of the wind turbine in operation, the pipes are preferably dismountable to avoid complex rotating joints.

Advantageously, the blades 10 of the wind turbine 100 are controlled one after the other and the removable pipes allow to connect the air generator 41 successively to each of the blades to perform the controls.

In an alternative embodiment, a heating means such as one or more electrical resistors is installed, permanently or during a control, inside the blade so as to heat the air inside the blade. air which is advantageously put into forced circulation inside the blade by one or more fans or turbines themselves also permanently installed or not in the blade.

For the implementation of the first described mode of the method, the system also comprises a second device 50 for measuring the temperature of the surface outside the blade.

The measuring device 50 produces a thermal map of the blade 10 on each of these faces, at least in areas of the blade 10 to be subjected to a control by the method.

In a preferred embodiment, the second device is a thermography system implementing a non-contact sensor 51 such as a thermal camera.

The thermal camera is in itself a thermal camera of a conventional model implementing an infrared sensor and whose performance of both temperature detection and resolution are chosen according to the accuracy sought in the detection of defects.

The sensor 51 is carried by a support that allows the field of a camera lens to scan the entire outer surface to control the blade.

Such a support is for example a terrestrial support, ie placed on the ground or on a land vehicle or on a surface vessel, for the cases of wind turbines implanted on the marine environment, during the measurement, such as a articulated support supporting the sensor 51 to perform measurements on the different areas of the outer surface of the blade.

The movement of the support, stabilized if necessary, can be manual or automatic and advantageously the non-contact measuring device comprises locating means for associating each measurement with the measured area of the surface of the blade.

Such locating means may comprise one or more position sensors indicating the position and the orientation of the support, corresponding in practice to a zone 52 of the surface of the blade being measured by the sensor so that each image produced by the sensor may be associated with the portion of the surface of the blade 10 to which it corresponds. Such locating means may also comprise identification means carried by the blade of the wind turbine, for example a scale graduated according to the span on the outer surface (19) of the blade is which is read or recorded simultaneously with the measurements. performed by the sensor (51).

In another embodiment, the support is an airborne platform supported by a flying device such as a drone or a rotary wing micro-drone 53a, as illustrated in FIG. 4a, or even such as an inflated 53b captive balloon. by means of a gas lighter than air, as shown in Figure 4b, which carries the sensor 51 and which is moved along the blade 10 at a selected distance from the surface of the blade.

In these exemplary embodiments, the piloting of the airborne platform 53a, 53b can be carried out by an operator on the ground or by an automatic pilot.

In this embodiment advantageously position sensors of the airborne platform in space, for example by laser telemetry, and if necessary orientation of the sensor 51 on said airborne platform, and or by the detection of markers such as targets visible on the outer surface (19) of the blade, used to control the airborne platform and associate each image made by the sensor to the portion 52 of the surface of the corresponding blade.

The use of an airborne platform 53a, 53b makes it possible to produce with economic sensors closer measurements of greater resolution and precision than when the images are taken at a distance.

In another embodiment of the support, not illustrated, a robot is movably mounted on the blade 10 so as to be able to move along the entire span under the control of said blade bearing on the blade itself. The robot carries at least one non-contact sensor, advantageously a plurality of sensors making measurements on different parts of the outer surface of the blade, for example the intrados and or the extrados and the zone of the edge of the blade. the attack, so as to carry out the measurements on an extended surface of the blade in a single course according to the span or a return trip depending on the span.

According to the embodiment of the support of the one or more sensors, said sensors are adapted to the distances from the surface of the blade 10 to which the measurements must be made. For example, in the case of a camera type sensor, the camera will be provided with a focal lens of varying length depending on whether the observation will be carried out remotely from the ground or an airborne platform with a narrow-field objective or from a robot, necessarily at a close distance with a wide-field objective. For the implementation of the second described mode of the process, the first aerothermal device 40 is a pressure generator connected by the distributor 42 in a sealed manner to the hollow inner volume 18 of the blade 10 in order to bring the fluid, for example from the air, in this interior volume at a pressure higher or lower than the pressure of the outside air by maintaining the pressure difference, or differential pressure, at a predefined desired value substantially constant.

In this case the different casings 14, 15, 16 of the blade communicate with each other via openings in the webs 121a, 121b of the spar to allow the pressure to be uniform inside the blade .

The differential pressure to be maintained between the inside of the blade and the outside during the measurements is a function of the structure of the blade and the sensitivity of the means for measuring the deformations of the outer surface of the blade.

In practice, for known blades, a differential pressure of 10 to 100 millibar is generally sufficient to produce measurable deformations without risk of damaging the blade subjected to this differential pressure.

In this embodiment, the second measuring device 50 performs geometric measurements of the surface outside the blade by means of a non-contact sensor 51 restoring the geometry of the zone 52 of the surface observed by said sensor.

Such a sensor 51 may consist, for example, of a scanning laser rangefinder, which makes it possible to obtain a measurement accuracy of the order of 0.01 mm, or of a digital photogrammetry device, or a laser interferometer or a scanning device. shearography, devices which make it possible to obtain neighboring accuracies which, as in the first embodiment described, can be placed on the ground, fixed to an airborne platform 53a, 53b or carried by a robot intended to move along the following blade the precision sought and the performance of the sensors used. In addition, the CND system also includes a device for processing measurements.

Such a measurement processing device advantageously comprises a computer with calculation units, memories and digital data storage means for receiving, in real time or in deferred time, the measurements made, for storing the reference cards and the anomaly databases and display means for presenting the results to an operator in charge of the control.

The calculation units are programmed to construct the map of the measured values representative of the parameter measured on the surface of the blade and to display the maps obtained and preferably to construct and display the anomaly maps which are for example displayed on a screen and or printed by visualizing the anomalies on a graphical representation of the blade by means of color code reflecting the intensity of the anomaly at each point of the blade considered.

Claims

R E V E N D I C A T IO N S

- CND method (200) for non-destructive testing of a wind turbine blade (10), a structure of said blade having a skin (13) defining an outer surface (19) of the blade and an inner hollow space (18) of the blade, said CND process comprising:

a first step (201) for biasing the blade structure by modifying at least one physical characteristic of a fluid filling the hollow volume (18) of the blade;

a second step (202) for observing zones to be checked on the outer surface (19), said observation comprising the non-contact measurement of a sensor for measuring at least one physical parameter, responsive to the solicitation of the first step (201), on points of the outer surface (19) so as to establish a measured map of the values of the measured physical parameter for said areas to be controlled;

a third anomaly detection step (203) by comparing values measured in the second step with expected values for a blade without significant defect. - CND method according to claim 1 wherein the at least one modified physical characteristic corresponds to the fluid temperature in the hollow volume (18), said temperature of said fluid being brought to a different value of the temperature outside the blade during the first step (201), and wherein the physical parameter measured during the second step (202) corresponds to a temperature of the outer surface (19) of the blade. - CND method according to claim 2 wherein the temperature of the outer surface (19) of the blade is measured without contact by infrared thermography. - CND method according to claim 1 wherein the at least one modified physical characteristic corresponds to a pressure of the fluid in the hollow volume (18), said pressure of said fluid being brought to a different value from the pressure outside the blade during the first step (201), and wherein the physical parameter measured during the second step (202) corresponds to a geometric dimension of the outer surface (19) characterizing the geometric shape of said outer surface.

The CND method of claim 4 wherein the geometric dimension of the outer surface (19) is measured by one of laser ranging, digital photogrammetry, laser interferometry or shearography methods.

- CND method according to one of claims 1 to 5 wherein the detection of anomalies made in the third step (203) comprises a step of comparing the measured value at each point with values measured at points adjacent to the point considered so as to establish a map of the contrasts of the values of the measured parameter and comprises a step of correlating said contrast map with internal structures of the blade (10).

- CND method according to one of claims 1 to 5 wherein the detection of anomalies performed in the third step (203) comprises a step of comparing the measured map with a reference map, said reference map being a map of reference of the values of the measured parameter established by measurement according to the first and second steps (201, 202) of the method on one or more blades considered flawless, or a reference card established by digital simulation of the method on a digital blade model, or is a hybrid map obtained by hybridization of all or part of reference maps established by measurement or by numerical simulation. - CND method according to one of Claims 1 to 7, comprising a fourth defect characterization step (204) by comparing the anomalies identified during the third step (203), in real time during the measurement or in deferred time, of each anomaly observed with known anomalies whose characteristics are stored in an anomaly database. CND non-destructive testing system for verifying the structural integrity of a wind turbine blade (10) according to the method of one of claims 1 to 8, said blade having a skin (13) defining an outer surface ( 19) of the blade and a hollow volume (18) of the blade, characterized in that it comprises:

an aerothermal device (40) for modifying the physical conditions of a fluid filling the hollow interior volume (18) of the blade;

- a measuring device implementing at least one non-contact sensor (50) of at least one physical parameter of the outer surface (19) of the blade;

a measurement processing device configured to establish a map of the measured values of the at least one parameter on the outer surface (19) of the blade and to identify anomalies of said map of the measured values. - CND system according to claim 9 wherein the aerothermal device (40) is a heating or cooling device modifying the temperature of a fluid in the hollow volume (18) of the blade to a value different from a temperature to the outside of the blade. - CND system according to claim 10 wherein heating means of the heating device changing the temperature of the fluid in the hollow volume (18) of the blade (10) are fixed in said hollow volume inside the pale ladit, the said heating means having one or electrical heating resistors and or fluid circulation holding means in the hollow volume (18).

12- CND system according to claim 10 or claim 1 1 wherein the non-contact sensor measuring device (50) implements a thermal camera measuring the temperature of the outer surface (19) of the blade.

13 - CND system according to claim 10 wherein the aerothermal device (40) is a pressure generating device and modifying the pressure of a fluid in the hollow volume (18) of the blade and now during the control operations said pressure at a controlled value different from a pressure outside the blade of a predefined difference. The CND system according to claim 13 wherein the non-contact measuring device (50) implements one or a plurality of devices for measuring the geometry of the outer surface (19) of the blade by laser ranging or digital photogrammetry or by laser interferometry or shearography.

The CND system according to claim 12 or claim 14 wherein the non-contact measuring device (50) is attached to the ground, or to a land vehicle, or to a surface ship, away from the blade to be controlled during the measures.

The CND system of claim 12 or claim 14 wherein the non-contact measuring device (50) is attached to an airborne platform (50) movable along the blade (10) in proximity to said blade.

17 - CND system according to claim 16 wherein the airborne platform (50) is supported by a drone or micro-UAV rotary wing (53a) and controlled in position relative to the blade (10) to control. - CND system according to claim 16 wherein the airborne platform (50) is supported by a balloon (53b) lighter than air and captive and controlled in position relative to the blade (10) to be controlled. - CND system according to claim 12 or claim 14 wherein the non-contact measuring device (50) is attached to a mobile robot along the blade (10) and bearing on said blade.