Patent Publication Number: US-2022235666-A1

Title: Method for coating a turbomachine guide vane, associated guide vane

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention pertains to the general field of turbomachines. 
     The invention more particularly relates to a method for coating a turbomachine guide vane making it possible to optimise the aerodynamic performances of said vane. The invention also pertains to a guide vane provided with a coating. 
     TECHNOLOGICAL BACKGROUND OF THE INVENTION 
     A bypass turbomachine comprises, at its upstream end, an air inlet supplying a fan that delivers an annular air flow splitting into two flows. 
     One part of the flow, called primary flow, is injected into a compressor that supplies a turbine driving the fan. The other part of the flow, called secondary flow, is injected to the atmosphere to provide a part of the thrust of the turbomachine, after having passed through a fixed blade ring arranged downstream of the fan. 
     The fixed blade ring, also known by the acronym OGV (outlet guide vane), makes it possible to guide the flow of air at the outlet of the fan into the secondary flow. The guide vanes, made of composite materials, are manufactured using a known so-called RTM (resin transfer moulding) method. 
     The RTM method consists in injecting a liquid resin into layers of dry reinforcement fibres preformed beforehand to the shape of the vane and arranged in a vacuum sealed mould. After the moulding step, it is known to deposit a metal reinforcement, in the form of a foil, on the leading edge of the vane in order to protect it from erosion and/or potential impacts (birds, gravel, ice, sand, etc.). Alternatively, the metal reinforcement is arranged on the preformed layers of reinforcement fibres during the resin injection step. 
     Further, a polymer coating provided with grooves is applied on the surfaces exposed to air flows. These grooves are oriented in the direction of travel of the air flow and make it possible to reduce the friction generated by the turbulent limit layers on the surface of the vanes exposed to the secondary flow. 
     If the presence of grooves makes it possible to reduce between 5 and 10% of the friction drag generated by the turbulent limit layers, they can also lead to an increase in friction when it involves laminar limit layers. In addition, the grooves can generate considerable aerodynamic losses if they involve unbonded limit layers or more generally non-oriented chaotic flows. 
     SUMMARY OF THE INVENTION 
     The invention offers a solution to the aforementioned problems, making it possible to limit the friction of the air flow on the surface of a guide vane. 
     A first aspect of the invention relates to a method for coating a turbomachine guide vane comprising a root and a tip, an extrados face and an intrados face connected to one another by a leading edge and a trailing edge. 
     The method for coating according to the first aspect comprises the following steps:
         completely covering one of the faces of the vane with a polymer coating provided with grooves,   removing the grooves from a part of the polymer coating so that the polymer coating comprises a grooved zone of thickness e1 and a non-grooved zone of thickness e2,   coating the non-grooved zone with a coat of paint of thickness e3 such that the thickness of the coat of paint superimposed on the non-grooved zone is substantially equal to the thickness e1 of the grooved zone.       

     Thanks to the method for coating according to the invention, the aerodynamic performances of the vane are improved. 
     Indeed, the method for coating according to the invention makes it possible to obtain a guide vane having a grooved zone on the surfaces exposed to turbulent flow and a substantially flat zone, i.e. the coat of paint, on the surfaces exposed to laminar flow. The presence of said zones on one of the surfaces of the vane make it possible to reduce the friction drag generated by the secondary flow during its passage on the exposed surfaces of the vane. In addition, the fact that the coat of paint is in the continuity of the grooved zone makes it possible to limit steps in surface transitions and thus to limit aerodynamic losses associated with the presence of such steps. 
     Further, the steps consisting in completely covering the face of the vane with a polymer coating provided with grooves and then removing the grooves on a determined zone of the polymer coating make it possible to simplify the integration of the polymer coating on the vane. In addition, the fact of keeping a part of the polymer coating, i.e. the non-grooved zone, on a zone where the grooves are not desired makes it possible to limit the amount of paint required to fill the thickness of polymer coating removed beforehand. Thus, this makes it possible to reduce the manufacturing costs and risks of non-compliance due to the presence of the coat of paint. 
     Apart from the characteristics that have been set out in the preceding paragraph, the method for coating according to the first aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations thereof. 
     According to a non-limiting embodiment, the step of removal of the grooves is carried out by a sanding operation on a part of the polymer coating intended to form the non-grooved zone. 
     According to a non-limiting embodiment, the sanding operation is carried out at a pressure greater than 2.5 bars. 
     According to a non-limiting embodiment, prior to the removal step, the method for coating comprises a step of deposition of a protective film on a part of the polymer coating intended to form the grooved zone. 
     A second aspect of the invention relates to a turbomachine guide vane comprising a root and a tip, an extrados face and an intrados face connected to one another by a leading edge and a trailing edge. 
     The vane according to the second aspect being characterised in that:
         at least one of its faces is completely covered with a polymer coating comprising:
           a grooved zone of thickness e1,   a non-grooved zone of thickness e2 less than the thickness e1 of the grooved zone,   
           a coat of paint, of thickness e3, covers the non-grooved zone such that the thickness of the coat of paint superimposed on the non-grooved zone is substantially equal to the thickness e1 of the grooved zone.       

     Apart from the characteristics that have been set out in the preceding paragraph, the guide vane according to the second aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations thereof. 
     According to a non-limiting embodiment, the polymer coating is made of polyurethane. 
     According to a non-limiting embodiment, the coat of paint is made of polyurethane. 
     According to a non-limiting embodiment, the coat of paint extends onto the extrados face, along the root of the vane. 
     According to a non-limiting embodiment, the coat of paint extends onto the extrados face, along the leading edge. 
     The invention according to a third aspect relates to a turbomachine guide comprising at least one vane according to the second aspect of the invention. 
     The invention and the different applications thereof will be better understood on reading the description that follows and by examining the figures that accompany it. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The figures are presented for indicative purposes and in no way limit the invention. 
       a  FIG. 1  illustrates a longitudinal sectional view of a bypass turbomachine, 
         FIG. 2  illustrates a turbomachine guide vane according to a first embodiment of the invention, 
         FIG. 3 a    is a block diagram illustrating the steps of the method for coating according to an embodiment of the invention, 
         FIG. 3 b   , illustrates a part of the steps of the method for coating shown schematically in  FIG. 3   a,    
         FIG. 4  illustrates a turbomachine guide vane according to a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The figures are presented for indicative purposes and in no way limit the invention. 
     Unless stated otherwise, a same element appearing in the different figures has a single reference. 
       FIG. 1  shows a schematic representation in longitudinal section of a bypass turbomachine  1 . 
     In the remainder of the description, the terms “inner” and “outer”, “axial and “radial”, and derivatives thereof, are defined with respect to the longitudinal axis A of the turbomachine  1 . 
     With reference to  FIG. 1 , a bypass turbomachine  1  has a longitudinal axis A and comprises an outer casing  10  inside of which are arranged, from upstream to downstream, a fan  12 , a low pressure compressor  14 , a high pressure compressor  16 , a combustion chamber  18 , a high pressure turbine  20 , a low pressure turbine  22  and an exhaust cone  24 . An inner casing  28  is arranged in the outer casing  10 , around the compressors  14  and  16 , of the combustion chamber  18  and the turbines  20  and  22 . Further, a guide  30  extends downstream of the fan  12 , between the inner  28  and outer  10  casings, in the region of the compressors  14  and  16 . 
     In operation, the inner casing  28  divides the air flow accelerated by the fan  12  between a primary flow Fp which supplies the compressors  14  and  16 , and a secondary flow Fs which flows between the inner  28  and outer  10  casings and is thus ejected from the turbomachine  1  after having crossed the guide  30  to supply a part of the thrust. 
     The guide  30 , also designated by the acronym OGV for “outlet guide vane”, makes it possible to guide the secondary flow Fs at the outlet of the fan  12  and comprises a plurality of fixed vanes  100  arranged in a crown around a ring  32  borne by the inner casing  28 . 
       FIG. 2  illustrates a guide  30  vane  100  according to a first embodiment of the invention. 
     With reference to  FIG. 2 , the vane  100  of the guide  30  has a leading edge  101 , and a trailing edge  102 , extending between a radially inner end  103 , called root of the vane  100 , and a radially outer end  104 , called tip of the vane  100 . The leading edge  101  and the trailing edge  102  delimit an extrados face  105  and an intrados face  106 . 
     The vane  100  is for example manufactured using a moulding method called resin transfer moulding (RTM) during which a liquid resin, preferentially of epoxy type, is injected into layers of dry reinforcement fibres, notably made of carbon, preformed beforehand substantially in the shape of the vane  100  and arranged in a vacuum sealed mould. 
     Furthermore, in order to protect the leading edge  101  from erosion and/or potential impacts, it is covered with a metal reinforcement  112 , for example made of nickel-cobalt alloy. The metal reinforcement  112  is preferably injected onto the preform made of layers of reinforcement fibres during the injection of the liquid resin. Advantageously, a film of adhesive is positioned between the metal reinforcement  112  and the preform in order to ensure the maintaining of the metal reinforcement  112  on the leading edge  101 . 
     Further, the extrados face  105  is completely covered with a polymer coating  107 , for example made of polyurethane. Advantageously, the polymer coating  107  is fixed to the extrados face by means of an adhesive applied on the leading edge  101 . 
     A part  109  of the polymer coating  107 , which will be called grooved zone, comprises a plurality of grooves  108  provided at the level of the part of the vane  100  intended to be exposed to turbulent flow. The grooved zone  109 , of overall rectangular shape, is delimited by the tip  104  of the vane  100  and the trailing edge  102  so as to cover around 75% of the extrados face  105 . The grooves  108 , also called riblets, have a shape, for example a U or V shaped section, and dimensions suited to the flow conditions of said secondary flow Fs. Advantageously, the grooved zone  109  of the polymer coating  107  has a thickness e1 comprised between 200 and 300 μm. 
     The other part  110  of the polymer coating  107 , which will be called non-grooved zone, is substantially flat and covers around 25% of the extrados face  105 . In particular, the non-grooved zone  110  extends along the root  103  of the vane  100  and along the metal reinforcement  112  so as to form an L. In this configuration, the non-grooved zone  110  extends along the direction of travel of the secondary flow Fs, i.e. for the portion which extends along the root  103  of the vane  100 , and along a direction perpendicular to the direction of travel of the secondary flow Fs, i.e. for the portion that extends along the metal reinforcement  112 . Advantageously, the non-grooved zone  110  has a thickness e2 comprised between 100 and 200 μm. 
     In addition, the non-grooved zone  110  is covered with a coat of paint  111 , for example made of polyurethane, intended to be exposed to laminar flow. The coat of paint  111  has a thickness e3 such that when the coat of paint  111  is applied on the non-grooved zone  110 , the thickness of the coat of paint  111  superimposed on the non-grooved zone  110  of the polymer coating  107  is substantially equal to the thickness e1 of the grooved zone  109  of the polymer coating  107 . Advantageously, the coat of paint  111  has a thickness e3 comprised between 80 and 120 μm. 
     Advantageously, the intrados face  106  is also covered with a polymer coating  107  and with a coat of paint  111  arranged on the surface of the vane  100  according to the flow conditions of the secondary flow Fs on the intrados face  106 . 
       FIG. 3 a    is a block diagram illustrating the steps of the method for coating  200  the guide  30  vane  100  according to an embodiment of the invention. It should be noted that the method for coating  200  according to the invention takes place after the manufacture of the vane  100  and the deposition of the metal reinforcement  112 . 
       FIG. 3 b    illustrates a part of the steps of the method for coating shown schematically in  FIG. 3   a.    
     In a first step  201 , a polymer coating  107 , of thickness e1, having grooves  108  is applied on the entire extrados face  105 . Advantageously, a film of adhesive is used to maintain the polymer coating  107  on the extrados face  105  of the vane  100 . 
     In a second step  202 , a part  109  of the polymer coating  107  is covered with a protective film, for example made of polymer material. 
     In a third step  203 , the grooves  108  present on the other part of the polymer coating  107 , i.e. which is not covered by the protective film, are removed so as to obtain a non-grooved zone  110 , of thickness e2, and a grooved zone  109 . Advantageously, the removal of the grooves  108  is carried out by a sanding operation, preferably at a pressure greater than 2.5 bars. 
     In a fourth step  204 , the protective film is removed from the part  109  of the polymer coating  107 . 
     In a fifth step  205 , the non-grooved zone  110  is coated with a coat of paint  111  of thickness e3 such that the thickness of the coat of paint  111  superimposed on the non-grooved zone  110  is substantially equal to the thickness e1 of the grooved zone  109 . It should be noted that the coat of paint  111  of thickness e3 may be obtained by the application of one or more layers of paint on the non-grooved zone  110 . 
       FIG. 4  illustrates a guide  30  vane  100  according to a second embodiment of the invention. 
     The vane  100  according to the second embodiment is identical to the vane  100  according to the first embodiment, with the difference that the grooved  109  and non-grooved  110  zones are arranged in another manner on the extrados face  105  of the vane  100 . 
     As may be seen in  FIG. 4 , the grooved zone  109  has an overall rectangular shape and is delimited by the tip  104  of the vane  100 , the trailing edge  102  and the metal reinforcement  112  so as to cover around 75% of the extrados face  105 . Advantageously, the grooved zone  109  of the polymer coating  107  has a thickness e1 comprised between 200 and 300 μm. 
     The non-grooved zone  110  of overall rectangular shape extends uniquely along the root  103  of the vane  100  so as to cover around 20% of the extrados face  105 . In this configuration, the non-grooved zone  110  extends uniquely along the direction of travel of the secondary flow Fs. Advantageously, the non-grooved zone  110  has a thickness e2 comprised between 100 and 200 μm. 
     The non-grooved zone  110  is also covered with a coat of paint  111  of thickness e3 such that the coat of paint  111  superimposed on the non-grooved zone  110  has a thickness substantially equal to the thickness e1 of the grooved zone  109 . Advantageously, the coat of paint  111  has a thickness e3 comprised between 80 and 120 μm. 
     The guide  30  vane  100  according to the second embodiment is produced using the method for coating  200  described previously.