Abstract:
An example method of coating a surface includes rotating a sprayer about an axis and directing spray away from the axis using the sprayer. The method coats a surface with the spray. The method moves a fluid through apertures established in the surface to limit movement of spray into apertures. The apertures are configured to direct the fluid toward the axis.

Description:
BACKGROUND 
     This disclosure relates generally to applying a coating and, more particularly, to applying a coating to a perforated surface. 
     As known, gas turbine engines, and other turbomachines, include multiple sections, such as a fan section, a compressor section, a combustor section, a turbine section, and an exhaust section. Air moves into the engine through the fan section. Airfoil arrays in the compressor section rotate to compress the air, which is then mixed with fuel and combusted in the combustor section. The products of combustion are expanded to rotatably drive airfoil arrays in the turbine section. Rotating the airfoil arrays in the turbine section drives rotation of the fan and compressor sections. The hot gas is then exhausted through the exhaust section. 
     Some turbomachines include perforated, cylindrical liners. An augmentor liner within the exhaust section is one type of perforated, cylindrical liner. The augmentor liner establishes a passage between an inner cylinder and an outer cylinder. Cooling air, obtained from the compressor or fan, flows through the passage and through perforations within the inner cylinder. The air moving through the passage and through the cylinders facilitates removing thermal energy from this area of the gas turbine engine. 
     During assembly of the augmentor liner, the surfaces of the inner cylinder that will be exposed to the hot air are typically coated with a thermal barrier coating. The inner cylinder is then laser drilled to create perforations. If the thermal barrier coating extends into the perforations, the thermal barrier coating can block air movement through the perforations. 
     SUMMARY 
     An example method of coating a surface includes rotating a sprayer about an axis and directing spray away from the axis using the sprayer. The method coats a surface with the spray. The method moves a fluid through apertures established in the surface to limit movement of spray into apertures. The apertures are configured to direct the fluid toward the axis. 
     Another example method of coating an inner surface of an annular component includes inserting a sprayer within a bore established by an annular component and coating an inwardly directed surface of the annular component using a spray from the sprayer. The method moves a fluid through perforations established in the inwardly directed surface during the spraying. 
     An example component having a thermal barrier coating includes an annular component including an inwardly facing surface establishes perforations. A coating is secured to at least a portion of the inwardly facing surface. The inwardly facing surface is configured to direct a fluid through perforations to limit movement of the coating into perforations when spraying the coating against the inwardly facing surface. 
     These and other features of the disclosed examples can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows an example gas turbine engine. 
         FIG. 2  shows a perspective view of a radially inner cylinder of an augmentor liner in the  FIG. 1  engine. 
         FIG. 3  shows a schematic end view of the augmentor liner of the  FIG. 1  engine. 
         FIG. 4  shows a close-up view of a portion of the  FIG. 3  augmentor liner. 
         FIG. 5  shows a top view of another example perforation that can be established within the  FIG. 3  augmentor liner. 
         FIG. 6  shows a top view of yet another example perforation that can be established within the  FIG. 3  augmentor liner. 
         FIG. 7  shows a section view at line  7 - 7  in  FIG. 6 . 
         FIG. 8  shows an example of negative flow through perforations in the  FIG. 3  augmentor liner. 
         FIG. 9  shows a close-up view of a portion of the  FIG. 3  augmentor liner receiving an angled nozzle. 
         FIG. 10  shows a top view of an example perforation surrounded by a coating applied with the  FIG. 9  nozzle. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an example gas turbine engine  10  includes (in serial flow communication) a fan section  12 , a compressor section  14 , a combustor section  16 , a turbine section  18 , and an exhaust section  20 . The gas turbine engine  10  is circumferentially disposed about an engine axis X. The gas turbine engine  10  is an example type of turbomachine. 
     During operation, air is pulled into the gas turbine engine  10  by the fan section  12 . Some of the air is pressurized by the compressor section  14 , mixed with fuel, and burned in the combustor section  16 . The turbine section  18  extracts energy from the hot combustion gases flowing from the combustor section  16 . 
     Some of the air pulled into the gas turbine engine  10  by the fan travels along a bypass path  22  rather than entering the compressor section  14 . Air flowing along the bypass path  22  follows a path generally parallel to the axis X of the gas turbine engine  10 . 
     In the two-spool engine design shown, a portion of the turbine section  18  utilizes the extracted energy from the hot combustion gases to power a portion of the compressor section  14  through a high speed shaft. Another portion of the turbine section  18  utilizes the extracted energy from the hot combustion gases to power another portion of the compressor section  14  and the fan section  12  through a low speed shaft. The examples described in this disclosure are not limited to the two spool architecture described, however, and may be used in other architectures, such as the single spool axial design, a three spool axial design, and still other architectures. That is, there are various types of gas turbine engines, and other turbomachines, that can benefit from the examples disclosed herein. 
     Referring now to  FIGS. 2-4  with continued reference to  FIG. 1 , the example exhaust section  20  includes an augmentor liner  23  having a radially inner cylinder  24  and a radially outer cylinder  26 . The radially inner cylinder  24  and the radially outer cylinder  26  are made of an austenitic nickel-chromium-based superalloys or Inconel™ in this example. 
     A passage  28  is established between the radially inner cylinder  24  and the radially outer cylinder  26 . At least some of the air flowing through the bypass path  22  flows through the passage  28 . 
     The inner cylinder  24  establishes a plurality of perforations  30  or apertures. The example perforations  30  are laser drilled. In another example, the perforations  30  are formed with rotating drill bits. Only a few perforations  30  are shown for clarity. The inner cylinder  24  typically includes an order of magnitude of 100,000 individual perforations  30 . 
     Air moving through the passage  28  flows through the perforations  30  toward the axis X of the engine. The air facilitates removing thermal energy from this area of the augmentor liner  23  when the augmentor liner  23  is installed within the engine  10 . 
     The inner cylinder  24  and the outer cylinder  26  are annular or ring shaped. The passage  28  established between the inner cylinder  24  and the outer cylinder  26  is also annular. The perforations  30  may be formed prior to, or after, shaping the inner cylinder  24  into a cylinder. 
     The inner cylinder  24  establishes a bore  38  and includes a surface  32 . The surface  32  is concave and faces inwardly toward an axis X 1 . Notably, the axis X 1  of the augmentor liner  23  is coaxial with the axis X of the engine  10  when the augmentor liner  23  is installed within the engine  10 . 
     As can be appreciated, the surface  32  is exposed to more thermal energy than other areas of the augmentor liner  23 . The surface  32  is coated with a thermal barrier coating  34  to protect the surface  32 , and other portions of the augmentor liner  23 , from thermal energy. 
     In this example, a sprayer  36  is used to apply the thermal barrier coating  34  to the surface  32 . The coating  34  is a ceramic based coating that is plasma sprayed against the surface  32 . The coating  34  is about 0.005 inches (0.127 millimeters) after curing, for example. Other examples include much thicker coatings. 
     The sprayer  36  is inserted within the bore  38  when spraying the coating  34 . The sprayer  36  is rotated about the axis X 1  while spraying the thermal barrier coating from a nozzle  44 . The spray from the sprayer  36  is directed away from the axis X 1  toward the surface  32 . The spray includes the coating  34 , which adheres to the surface  32  to coat the surface  32 . 
     As the sprayer  36  applies the thermal barrier coating, a flow of air  40  (or another type of fluid) is directed through the perforations  30  established in the inner cylinder  24 . The perforations  30  are shaped to promote directed flow coating buildup in one example. For example, a perforation  30   a  ( FIG. 5 ) has an hour-glass shape. Another perforation  30   b  ( FIGS. 6-7 ) is a heart shaped. Interaction between the thermal barrier coating  34  and the perforation  30   a  and  30   b  as the thermal barrier coating  34  is applied cause the contours of the thermal barrier coating  34  around perforations  30   a  and  30   b  to vary. A person having skill in this art and the benefit of this disclosure would be able to vary the shape of the perforations  30   a  and  30   b  to achieve the desired contours. 
     The flow of air  40  blocks the thermal barrier coating  34  from entering the perforations  30  as the coating  34  is sprayed and cured. The air  40  is pressurized to 12 psi (0.827 bar) for example. The air  40  is directed through the perforations  30  after applying the thermal barrier coating  34  and before the thermal barrier coating  34  has cured. 
     In some examples, the air  40  is heated to help prevent adherence. The air  40  could also be cooled. The air  40  also may be cycled with positive and negative flow to create optimal shape of the coating surrounding the perforations  30 . An example of negative flow is shown by the flow of air  40   a  ( FIG. 8 ). The negative flow of air  40   a  may be utilized to form the thermal barrier coating  34  around the aperture  30  into a desired shape. 
     In some examples, air is directed radially outboard, rather than radially inboard, through the perforations  30 . The negative flow of air  40   a  is one example of radially outboard directed air. In some of these examples, the air  40   a  is pressurized on the nozzle side of the inner cylinder  24  to pull and form the thermal barrier coating  34  around the perforations  30 . In such examples, the air  40  may result from a periodic controlled internal explosions, such as a shock pulses, that clear the thermal barrier coating  34  from the perforations  30 . 
     In some examples, the thermal barrier coating  34  may have partially cured and covered the perforation  30 , and the shock pulse breaks apart the portion covering the perforation  30 . The air  40  or  40   a  is pulsed in some examples to fracture thin coating buildup over perforations  30 . 
     The air  40  may include elements that chemically combine locally with the thermal barrier coating  34 . The chemical combination helps prevent the thermal barrier coating  34  from adhering near the perforations  40 . 
     Referring again to  FIGS. 2-3 , in this example, the perforations  30  are radially aligned such that the perforations  30  direct the air radially toward the engine axis X. Other examples may utilize perforations configured to direct the air in other directions relative to the axis X. 
     In this example, the sprayer  36  applies the spray to the inner surface  32  prior to installing the augmentor liner  23  within the engine  10 . Accordingly, an air supply  42  is used to supply air that is moved through the passage  28  during the spraying. The air supply  42  communicates air through the passage  28 , which is the same path that air will travel from the bypass path  22  through the perforations  30  when the augmentor liner  23  is installed within the engine  10 . 
     An example method of thermally protecting the augmentor liner  23  includes spraying the coating  34  against the surface  32  while rotating the sprayer about the axis X and while communicating the flow of air  40  through the perforations  30 . 
     In one example, the augmentor liner  23  has been used within the engine  10  and already includes a used coating (not shown). In such an example, the used coating may be removed, by a chemical process for example, prior to applying the coating  34 . The example method thus facilitates recoating used augmentor liners and other components. 
     Although described as coating the augmentor liner  23 , the method could be applied to many other components, such as turbine blades, burner cans, and exhaust cases, for example. 
     Referring to  FIGS. 9 and 10 , in some examples, the nozzle  44  is angled axially during the spraying, which results in shaped application of coating around perforations  30  (teardrops or chevrons as shown in  FIG. 10 , etc.) Further, in some examples, the nozzle  44  is angled off-centerline during the spraying, resulting in the profile or the coating having a circumferential feature, which creates a swirl or opposes a swirl in the engine  10 . 
     Features of the disclosed examples include applying a sprayed coating to a component by rotating a sprayer relative to the concave surface while moving air through perforations in the concave surface to prevent the spray from blocking the perforations. Another feature of the disclosed example is providing the ability to recoat a used component with a thermal barrier coating. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.