Patent Publication Number: US-11029323-B2

Title: Sailing ship comprising an aerodynamic profile and a system for determining characteristics of an airflow incident on a leading edge of the aerodynamic profile

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of the French patent application No. 1761483 filed on Nov. 30, 2017, the entire disclosures of which are incorporated herein by way of reference. 
     TECHNICAL FIELD 
     The present invention relates to a sailing ship comprising an aerodynamic profile and to a system for determining characteristics of an airflow incident on a leading edge of the aerodynamic profile. 
     BACKGROUND OF THE INVENTION 
     The determination of speed and orientation characteristics of an airflow incident on the leading edge of a sail of a sailing ship is conventionally based on the use of wind indicators and anemometers, and on the use of meteorological data. 
     These instruments and data deliver only overarching information, and, in particular, do not allow the direction and speed of the airflow at various points on the leading edge to be known. 
     Such information would however be useful, on the one hand, for detailed a posteriori analysis of the performance and behavior of the sail, and, on the other hand, in order to allow the precision of automatic or assisted piloting devices to be improved. 
     SUMMARY OF THE INVENTION 
     An aim of the invention is especially to provide a simple, economical and effective solution to this problem. 
     To this end the invention proposes a sailing ship comprising an aerodynamic profile forming a sail of the sailing ship, and a system for determining characteristics of an airflow incident on a leading edge of the aerodynamic profile, the system comprising: 
     a series of pressure sensors, which pressure sensors are arranged on a surface of the aerodynamic profile, the pressure sensors of each series being distributed on either side of the leading edge of the aerodynamic profile, the series of pressure sensors virtually forming respective patterns that are spaced apart from one another, each of the patterns being a simple polygonal line; and 
     a computer connected to the pressure sensors so as to receive local pressure values respectively originating from the pressure sensors. 
     The computer is configured to determine, along each of the patterns, a respective stagnation-point position defined by a curvilinear abscissa defined along the pattern in question and for which a pressure P* interpolated from pressure measurements delivered by the pressure sensors of the corresponding series is maximal along the pattern in question, and by an altitude evaluated from respective altitude data of the pressure sensors of the corresponding series. 
     The respective altitude data of the pressure sensors are determined from respective altitudes of the pressure sensors in a frame of reference that is fixed with respect to the sailing ship, and from a variable component determined, for each of the pressure sensors, from measurements of the orientation of the ship. 
     The system allows the position of the stagnation point in various zones along the leading edge of the aerodynamic profile to be precisely determined. 
     Knowledge of the position of the stagnation point is particularly advantageous in that it may allow the modulus of the speed of the incident flow and its direction at various points along the leading edge to be determined, as will become more clearly apparent below. 
     In preferred embodiments of the invention, the patterns lie in respective pattern planes that are distinct from one another and such that each of the pattern planes is orthogonal to the osculating plane at the point of intersection of the leading edge and of the pattern plane in question. 
     Preferably, the pattern planes are parallel to one another. 
     In preferred embodiments of the invention, the system furthermore comprises a memory containing a map relating the stagnation-point positions respectively determined along each of the patterns and operational parameters of the aerodynamic profile to a direction profile of the airflow. 
     In preferred embodiments of the invention, the computer is furthermore configured to determine, along each of the patterns, a respective stagnation pressure, defined as the value of the pressure P* at the corresponding stagnation-point position. 
     Preferably, the system furthermore comprises a reference-pressure sensor placed in a sheltered zone away from the aerodynamic profile and connected to the computer, and the computer is furthermore configured to determine a speed profile of the airflow from a reference pressure delivered by the reference-pressure sensor and from the stagnation pressures respectively determined along each of the patterns. 
     As a variant, the system furthermore comprises an anemometer connected to the computer, and the computer is furthermore configured to determine a speed profile of the airflow by equating an airflow speed value delivered by the anemometer to a speed value of the airflow incident on one of the patterns, and from the stagnation pressures respectively determined along each of the patterns. 
     In preferred embodiments of the invention, the sailing ship comprises an automatic or assisted piloting device configured to control at least one operational parameter of the aerodynamic profile on the basis of the stagnation-point positions respectively determined along each of the patterns. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and other details, advantages and features thereof will become apparent on reading the following description, which is given by way of non-limiting example with reference to the appended drawings, in which: 
         FIG. 1  is a schematic perspective view of a sailing ship according to one preferred embodiment of the invention, in the present case a sailing yacht, comprising an aerodynamic profile and a system for determining characteristics of an airflow incident on a leading edge of the aerodynamic profile; 
         FIG. 2  is a view similar to  FIG. 1  and at larger scale of the sailing yacht of  FIG. 1 , illustrating a front portion of a rigid sail of this sailing yacht; 
         FIG. 3  is a schematic view of a cross (i.e., horizontal) section of the aerodynamic profile; 
         FIG. 4  is a graph showing a quantity P*=pgz+P (ordinate axis), as a function of the normalized curvilinear position along a pattern formed by a series of pressure sensors placed on either side of the leading edge (abscissa axis); 
         FIG. 5  is a view at larger scale of the detail V of  FIG. 3 , illustrating a stagnation-point position along the pattern; 
         FIG. 6  is a graph showing the stagnation-point position (abscissa axis) of various heights (ordinate axis); 
         FIG. 7  is a graph showing the direction profile of the airflow along the leading edge; 
         FIG. 8  is a graph showing the stagnation pressure (abscissa axis) for various heights (ordinate axis); 
         FIG. 9  is a graph showing the speed profile of the airflow along the leading edge. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention generally relates to a sailing ship or yacht  10  comprising an aerodynamic profile  12  forming a sail of the sailing ship and to a system for determining characteristics of an airflow incident on a leading edge of the aerodynamic profile. 
     The described example more particularly relates to a sailing yacht with a rigid sail (sometimes referred to as a “rigid wing”). The rigid sail typically replaces the mainsail of a conventional sailing yacht, and is in general composed of a front element  12 A forming the leading edge  14  of the profile, and of a rear element  12 B, called the “flap,” forming the trailing edge  15  of the profile and making an adjustable angle θ with respect to the front element  12 A, which angle is sometimes called the camber angle (shown in  FIG. 3 ). The front element  12 A in general comprises a structural front portion, which plays the role of mast insofar as it is via this front portion that the sail is rotatably mounted on the yacht. The front element  12 A in general includes a bottom panel  12 AA and a top panel  12 AB ( FIG. 1 ) that make therebetween an adjustable angle, called the twist angle. 
     In the sailing yacht of the present description, the longitudinal direction X is defined as the general direction of advance of the sailing yacht or even as the direction extending from the stern to the bow, the transverse direction Y is the direction orthogonal to the longitudinal direction X, i.e., the direction extending from starboard to port, and the vertical direction Z is the direction orthogonal to the directions X and Y. 
     The system intended to determine characteristics of the incident airflow comprises pressure sensors  16  ( FIG. 2 ) that are arranged on the surface of the aerodynamic profile. These sensors form, generally, series S 1 -S 5  ( FIG. 2 ), which are, for example, five in number and which are defined, physically or not, such that the sensors of each series are distributed on either side of the leading edge  14  of the aerodynamic profile  12 , and such that the sensors of each series form virtually respective patterns M 1 -M 5  that are spaced apart from one another. Each of the patterns M 1 -M 5  is defined by virtually connecting pairwise the sensors of a given series so as to form a simple polygonal line, i.e., a geometric figure that is formed by a sequence of straight-line segments connecting a sequence of points corresponding to the sensors, in which figure the intersection of two distinct segments belonging to the polygonal line is either empty, or reduced to their common apex in the case of two successive segments. The fact that the patterns are spaced apart from one another in particular implies that the patterns do not intersect one another. 
     The series S 1 -S 5  of pressure sensors are thus distributed along the leading edge  14 . 
     In preferred embodiments of the invention, the series S 1 -S 5  of pressure sensors are arranged so that the patterns M 1 -M 5  lie in respective pattern planes P 1 -P 5  that are distinct from one another and such that each of the pattern planes is orthogonal to the osculating plane O 1 -O 5  at the point of intersection I 1 -I 5  of the leading edge  14  and of the pattern plane in question ( FIG. 2 ). 
     Furthermore, the series S 1 -S 5  of pressure sensors are advantageously arranged so that the pattern planes P 1 -P 5  are locally orthogonal to the leading edge  14 . 
     Generally, the arrangement of the pressure sensors is preferably designed to minimize the angle between each pattern plane and an airflow that is standard or average for the type of envisioned application. 
     In practice, the series S 1 -S 5  of pressure sensors are thus preferably arranged so that the pattern planes P 1 -P 5  are substantially parallel to the incident wind. In proximity to sea level, the wind generally blows substantially parallel to the horizontal direction. Therefore, the pattern planes P 1 -P 5  are advantageously substantially horizontal, when the yacht adopts an orientation devoid of list and pitch. 
     Moreover, within each series S 1 -S 5 , the sensors  16  are preferably equidistant pairwise along the corresponding pattern M 1 -M 5 . 
     In preferred embodiments of the invention, the series of pressure sensors S 1 -S 5  are physically defined. In particular, the series of sensors are preferably strips B 1 -B 5  that are fastened to the surface of the aerodynamic profile  12 . Documents WO2015091994A1, WO2015091996A1, and EP3144684A1 describe an example of a strip of MEMS (microelectromechanical systems) sensors that could be used in the context of the present invention. Such a strip of sensors, in particular, makes it possible to obtain a high density of sensors, able to achieve a high spatial sampling rate. The MEMS sensors may be clocked internally at high speeds, for example at a frequency of 64 Hz, and are thus capable of delivering data in real-time at a rate suitable for the processing operations carried out downstream on the data, for example at a frequency of 16 Hz. 
     The pressure sensors  16  are configured to measure the static pressure of the laminar airflow moving past the aerodynamic profile. To this end, these sensors  16  have respective sensing surfaces that are locally parallel to the surface of the aerodynamic profile  12 , and that are therefore locally parallel to the airflow in the immediate vicinity of the aerodynamic profile. 
     The system furthermore comprises a computer  20  connected to the pressure sensors  16  so as to receive local pressure values respectively originating from these pressure sensors. 
     The computer is configured to determine, along each of the patterns M 1 -M 5 , a respective stagnation-point position, defined by a pair of coordinates (ai, zi) comprising a curvilinear abscissa a 1 -a 5  defined along the pattern M 1 -M 5  in question, and an altitude z 1 -z 5 . 
     The curvilinear abscissa a 1 -a 5  is determined so as to define a point, on the pattern in question, for which a pressure P*, interpolated from pressure measurements delivered by the pressure sensors of the corresponding series S 1 -S 5 , is maximal. 
     The altitude z 1 -z 5  is the altitude of the aforementioned point of the pattern, which altitude is evaluated from respective altitude data of the pressure sensors  16  of the corresponding series S 1 -S 5 . 
     Each stagnation-point position thus defines the position of the stagnation point of the incident airflow, in the corresponding pattern plane P 1 -P 5 , i.e., the position of the point where the incident airflow separates into two flows that move past the aerodynamic profile  12  on each side thereof. 
     The stagnation-point positions are referenced PT 1  to PT 5  in  FIG. 2 . 
     To a first approximation, the altitude data may simply consist of the respective altitudes of the pressure sensors  16  in a frame of reference that is fixed with respect to the yacht. These respective altitude data relative to the yacht are fixed preset data related to the arrangement of the sensors  16 . 
     Preferably, the altitude data furthermore comprise a variable component determined, for each of the sensors  16 , from measurements of the orientation (list, longitudinal trim) of the yacht, these measurements, for example, being delivered by gyroscopic sensors. 
     The stagnation-point positions are thus determined with an optimal precision. 
     The system furthermore comprises a memory  22  containing a map relating the stagnation-point positions respectively determined along each of the patterns M 1 -M 5  and operational parameters of the aerodynamic profile to a direction profile of the airflow. Such a map is established beforehand from an aerodynamic model of the aerodynamic profile. 
     In the described example, the operational parameters of the aerodynamic profile preferably comprise the angle of rotation of the mast, and the camber angle and twist angle of the aerodynamic profile. 
     In the preferred embodiment of the invention, the computer  20  is furthermore configured to determine, along each of the patterns M 1 -M 5 , a respective stagnation pressure PS 1 , PS 5 , defined as the value of the pressure at the corresponding stagnation-point position. 
     The system furthermore comprises a reference-pressure sensor  24  placed in a sheltered zone, away from the aerodynamic profile  12 . What must be understood by this is that the reference-pressure sensor  24  is positioned in a zone that is normally not subjected to the airflow. The reference-pressure sensor  24  thus allows a reference pressure P ref  equal to the atmospheric pressure at the altitude z ref  of the sensor  24  to be measured. 
     The reference-pressure sensor  24  is connected to the computer  20 . 
     This computer  20  is furthermore configured to determine a speed profile of the airflow from the reference pressure P ref  delivered by the reference-pressure sensor  24  and from the stagnation pressures PS 1 -PS 5  respectively determined along each of the patterns M 1 -M 5 . 
     In the preferred embodiment of the invention, the determination of the speed profile is based on the application of Bernoulli&#39;s theorem, the following being considered to be true for each pattern Mi (i being comprised between 1 and 5 in the illustrated example): 
     the total pressure at the stagnation point is equal to the stagnation pressure PSi; 
     this total pressure is also equal to P ref +ρg(zi−z ref )+½ρ vi 2 , where: 
     vi is the speed of the airflow incident on the pattern Mi, 
     zi is the altitude of the corresponding stagnation-point position, 
     ρ is the density of air, which is considered to be constant and calculated at a reference point, 
     g is the gravitational acceleration. 
     Hence the value of the corresponding speed is: 
     
       
         
           
             vi 
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                   ρ 
                 
                 ⁡ 
                 
                   [ 
                   
                     PSi 
                     - 
                     
                       P 
                       ref 
                     
                     - 
                     
                       ρ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         g 
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                           ( 
                           
                             zi 
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                               z 
                               ref 
                             
                           
                           ) 
                         
                       
                     
                   
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     As a variant, instead of using the reference pressure delivered by the reference sensor  24 , the computer may be configured to determine a speed profile of the airflow from a reference speed delivered by an anemometer arranged close enough to one of the patterns Mj (j being, in the described example, comprised between 1 and 5) and to the leading edge for the speed of the airflow incident on the pattern Mj to be equatable to the reference speed. 
     The pressure within the airflow incident on the pattern Mj may then be determined by means of Bernoulli&#39;s theorem, by once again equating the total pressure at the stagnation point to the stagnation pressure PSj. The speed of the airflow incident on the other patterns may then be deduced in an analogous way to the one described above, with P ref  and z ref  replaced by PSj and zj. 
     The system may obviously combine these two techniques for determining the speed profile, i.e., reference-pressure measurement and correlation respectively, in order for example to deliver speed values obtained by averaging the results delivered by the two determining techniques. 
     Lastly, the sailing yacht  10  furthermore includes an automatic or assisted piloting device  26  configured to control at least one operational parameter of the aerodynamic profile on the basis of the stagnation-point positions respectively determined along each of the patterns M 1 -M 5 . 
     The operational parameters controlled by the device  26  preferably comprise the camber angle and the twist angle. 
     The operation of a sailing ship according to the invention, for example the sailing yacht  10 , will now be described with reference to  FIGS. 3-9 . 
       FIG. 3  shows a cross section of the aerodynamic profile  12 , for example in the plane P 1  of the series of sensors S 1 . 
       FIG. 3 , in particular, shows an airflow F incident on the leading edge  14 , the airflow becoming separated into two flows FA and FB that respectively move past the aerodynamic profile  12  on each side thereof. The flows FA and FB are separated from each other by a stagnation line FS that meets the leading edge at a corresponding stagnation point PT 1 . The angle of incidence of the flow F on the leading edge  14 , and therefore the position of the stagnation point, is liable to vary along the leading edge  14  (i.e., as a function of altitude). 
     The computer  20  receives at high frequency (for example 64 Hz) the local values of the pressure P*, which respectively originate from the pressure sensors  16 . The computer preferably carries out temporal filtering on these local pressure values in order to remove insignificant fluctuations. 
       FIG. 4  is a graph showing, in the form of points, the local value of the pressure P* in pascals (ordinate axis) for each of the sensors  16  of one of the series, for example the series S 1 . The abscissa axis corresponds to the curvilinear abscissa of the sensors along the corresponding pattern M 1 , which abscissa has, for the sake of simplicity, been normalized by the chord of the aerodynamic profile. 
     For each series of sensors S 1 -S 5 , the computer carries out an interpolation of the local values of the pressure P*, resulting in the curve connecting the points of  FIG. 4 ; then the computer determines the position of the maximum of the pressure P* on the curve, which defines the abscissa a 1 -a 5  of the corresponding stagnation-point position. 
     The computer also determines the altitude z 1 -z 5  of the corresponding stagnation-point position, preferably by interpolation of altitude data relating to the pressure sensors  16 . These data are determined from the location of each of the sensors on the aerodynamic profile, which location is recorded in the memory  22 , and these data are, in the preferred embodiment of the invention, refined by means of measurements of the orientation of the yacht, which are for example delivered to the computer at a lower frequency (for example 10 Hz). 
       FIG. 5  is a view at larger scale of the portion V of  FIG. 3 , in which the thickness of a strip of sensors B 1  and the dimensions of each sensor  16  have been exaggerated whereas the number of sensors shown has been greatly decreased, for the sake of clarity. This figure shows the abscissa a 1  of the stagnation-point position along the pattern M 1 , which for example substantially coincides with the position of a sensor  16 . 
       FIG. 6  is a graph showing the stagnation-point positions (a 1 ; z 1 )-(a 5 ; z 5 ) respectively determined for the various series of sensors S 1 -S 5 . The abscissa axis indicates the curvilinear abscissa normalized by the chord of the aerodynamic profile, whereas the ordinate axis indicates the altitude in millimeters. 
     From the stagnation-point positions and from the map stored in the memory  22 , the computer determines a direction profile of the airflow along the leading edge  14 , which is illustrated by  FIG. 7 , in which the abscissa axis indicates the orientation of the airflow in degrees, whereas the ordinate axis indicates the altitude in millimeters. 
     In addition, the computer determines, along each of the patterns M 1 -M 5 , the respective stagnation pressure PS 1 -PS 5 , which, as explained above, is defined as the value of the pressure at the corresponding stagnation-point position. 
       FIG. 8  is a graph showing the stagnation pressures PS 1 -PS 5  in pascals (abscissa axis) respectively determined for the various series of sensors S 1 -S 5 , which are identified by the altitude of the respective stagnation-point position in millimeters (ordinate axis). 
     The computer  20  furthermore determines a speed profile of the airflow, using at least one of the methods described above.  FIG. 9  illustrates an example of a speed profile thus obtained. The abscissa axis indicates the speed in km/h, whereas the ordinate axis indicates the altitude in millimeters. 
     As a variant, the invention is also applicable to a flexible sail, in which case the aerodynamic profile, on which the series of pressure sensors are placed, comprises a rigid profiled mast arranged at the front end of the sail. 
     While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.