Patent Publication Number: US-2011048116-A1

Title: Apparatus for experimental investigation of axial seal systems of gas turbines

Description:
The present invention relates to an apparatus for experimental investigation of axial seal systems of gas turbines. 
     BACKGROUND OF THE INVENTION 
     As known, the study of the features of systems of axial seals normally used between rotor and stator in gas turbines is carried out on test benches, by using appropriate apparatuses based on specific models which reproduce the features of the seal systems under investigation. The currently available investigation apparatuses essentially are of two main types. 
     There are rotating apparatuses, in which the seal is mounted on a circular crown as on real machines, and static apparatuses, in which the dummy rotor and stator portions of the axial seal systems are stationary. Both suffer however from drawbacks which seriously limit their use possibility. 
     Firstly, the versatility of known investigation apparatuses is generally poor, with regards to variety of both the seal systems which may be tested and the measurements which may be carried out. The models used in stationary apparatuses, and to a greater extent in rotating apparatuses, are indeed generally suitable for testing only one type of seal system. They are however very complex and form the main core of the whole apparatus. Therefore, testing different axial seal system geometries is very costly. 
     Static apparatuses allow to carry out discreet temperature measurements by means of variously located sensors and to determine estimates of the thermal exchange coefficient along the seal system on the basis of these measurements. The estimate is however rather rough and may be improved only at the cost of a considerable increase of complexity, because many sensors should be added, and housings and connections should be provided for each of them. Rotating apparatuses have even greater limitations, related to the presence of moving parts and leakages which may damage the correctness of measurements. Estimating the heat exchange coefficient may not even be feasible. 
     Furthermore, the known solutions typically employ a compressor upstream of the seal system, which feeds an air flow. However, the compressor causes a non-controllable heating of the air (indeed, the entity of the heating depends on the pressure needed to feed the seal system, and thus on its features, which are not known being the object of investigation). The known apparatuses include a heat exchanger (intercooler), which reduces the intake air temperature. The heat exchanger (of the air-air or air-water type) however implies a high additional cost, in addition to management problems related to dimensions and noise. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide an apparatus for experimental investigation of axial seal systems of gas turbines which is versatile, in particular from the point of view of the measurements to be carried out. 
     According to the present invention, an apparatus for experimental investigation of axial seal systems of gas turbines is provided as defined in the attached claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described with reference to the accompanying drawings, which illustrate a non-limitative embodiment thereof, in which: 
         FIG. 1  is a simplified block chart of an apparatus for experimental investigation of axial seal systems of gas turbines according to one embodiment of the present invention; 
         FIG. 2  is an exploded perspective view of a test structure incorporated in the apparatus in  FIG. 1 ; 
         FIG. 3  is a side view of the test structure in  FIG. 2 ; 
         FIG. 4  is a side view of the test structure in  FIG. 2 , taken along a longitudinal plane; 
         FIG. 5  is a top plan view of a first element of the test structure in  FIG. 2 ; 
         FIG. 6  is a side view of the first element in  FIG. 5 , taken along the plotting plane VI-VI in  FIG. 5 ; 
         FIG. 7  shows an enlarged detail of the view in  FIG. 6 ; 
         FIG. 8  is a bottom plan view of a second element of the test structure in  FIG. 2 ; 
         FIG. 9  is a side view of the second element in  FIG. 8 , taken along the plotting plane IX-IX in  FIG. 8 ; 
         FIG. 10  shows an enlarged detail of the view in  FIG. 9 ; 
         FIG. 11  is a top plan view of the first element of the test structure in  FIG. 2 , in a different operating configuration; and 
         FIG. 12  is a top plan view of the second element of the test structure in  FIG. 2 , in a different operating configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , an apparatus for experimental investigation of axial seal systems of gas turbines is indicated as a whole by numeral  1 , and comprises a test structure  2 , an air feeding system  3 , a processing unit  5 , a plurality of sensors  7 , an image acquisition unit  8  and a storage unit  9 . 
     The test structure  2  is made of a transparent material, e.g. polymethylmethacrylate, and has a test chamber  10 , which defines an enlarged scale model of an axial seal system of a gas turbine during a step of investigating. The test structure  2  is further provided with a stabilization chamber  13  having the purpose of adjusting the air flow through the test chamber  10  and an outlet chamber  14 , arranged upstream and downstream of the same, respectively. 
     The air feeding system  3  comprises a heater  16  and an adjustable throttle valve  17 , at the inlet of the stabilization chamber  13 , and a flow meter  18  and a sucking pump  19 , downstream of the outlet chamber  14 . 
     The heater  15  may be used to heat the air at the inlet of the test structure  2  in a controlled manner, in order to measure the convective heat exchange coefficient. The throttle valve  17  is instead usable to adjust the air pressure at the inlet of the test structure  2 . 
     The sucking pump  19  is fluidically coupled to the inside of the test chamber  10  and causes a vacuum at the outlet of the test structure  2 , so as to bring back an air flow which crosses heater  15 , throttle valve  17 , stabilization chamber  13 , leaks through the test chamber and reaches the outlet chamber  14  and the flow meter  18 . 
     Sensors  7  comprise a plurality of temperature and pressure sensors (not shown here in detail) distributed about the test chamber  10  and thermally and fluidically coupled to the inside of the latter, respectively, to detect the temperature and pressure of the flowing air in respective locations. 
     The image acquisition unit  8  is controlled by the processing unit  5  to acquire images, in use, of the test chamber  10  which, as the rest of the test structure  2 , is made of transparent material. The acquired images are stored in the storage unit  9 . 
     The processing unit  5  also receives and processes temperature and pressure signals S i , . . . , S N  from the sensors  7 , as well as a flow signal S F , indicating the leakage through the test chamber  10 , supplied by the flow meter  18 . Furthermore, the processing unit  5  controls the operation of heater  16 , throttle valve  17  and sucking pump  19 . 
     The test structure  2  will be described in greater detail, with reference to  FIGS. 2-10 . 
     The test structure  2  comprises a plurality of modular elements, essentially made of the same transparent material, mutually sealingly coupled and sandwiched by means of locking elements. In one embodiment, the modular elements are made of polymethylmethacrylate (PMMA). Alternatively, other transparent materials may be used, such as for example special glasses, in particular low dispersion glasses and low distortion glasses. 
     In particular, the test structure  2  extends along a longitudinal axis A and, as shown in  FIGS. 2-4 , comprises: 
     an inlet module  20 , a grid housing  21  and a connection module  22 , which define the stabilization chamber  13  therein; 
     a structural module  25 , a rotor module  26 , a stator module  27  and a spacer element  28 , which define the test chamber  10 ; and 
     an outlet module  30 , which defines the outlet chamber  14 , downstream of the test chamber  10 , and has an outlet aperture  30   a.    
     The test structure  2  further comprises a bridge-like joining element  31  ( FIGS. 2 and 4 ), placed between the connection module  22  and the structural module  25 , as will be explained in further detail below. 
     The inlet module  20  is provided with an inlet aperture  32 , obtained about the axis A (see  FIG. 4 , in particular). The grid housing  21  is placed downstream of the inlet module, supporting grids  33  adapted to uniform the air flow and make the speed and pressure profiles homogeneous at the inlet of the test chamber  10 . 
     The connection module  22  ( FIGS. 2 and 4 ) has a hollow coupling portion  34 , which extends about the axis A and engages a corresponding seat  35 , obtained in a wall of the structural module  25  and communicating with the inside thereof through an aperture  36 . The coupling portion  34  and the aperture  36  define a fluid passageway, which couples the stabilization chamber  13  to the test chamber  10 . The bridge-like element  31  is placed in the fluid passageway and limits the transversal section thereof. In particular, the thickness of the bridge-like element  31  is chosen to prevent turbulences when entering the test chamber  10  due to sudden section variations. 
     Inlet module  20 , grid housing  21  and connection module  22  are sandwiched by means of locking means including tie rods  37  inserted in respective seats  38  ( FIG. 3 ). Seal rings  39  ( FIG. 2 ) are accommodated in respective seats  40  of the inlet module  20  and of the grid housing  21 , and cooperate with sealing surfaces, defined by faces  21   a ,  22   a  of the grid housing  21  and of the connection module  22 , respectively, adjacent to the seal rings  39  themselves. Thereby, leakages through the walls of the stabilization chamber  13  are prevented. 
     As previously mentioned, the test chamber  10  is defined by structural module  25 , rotor module  26 , stator module  27  and spacer element  28 . In detail, the structural module  25  is frame-shaped ( FIG. 2 ) and has longer walls which extend parallel and on opposite sides to the axis A, laterally delimiting the test chamber  10 . As mentioned, aperture  36  is obtained in one of the walls of the structural module  25 , in particular one of the shorter walls adjacent to the stabilization chamber  13  ( FIGS. 2 and 4 ), and communicates with the seat  35 , which accommodates the coupling portion  34  of the connection module  22 . A further aperture  41  is made in the opposite shorter wall of the structural module  25 . Aperture  36  and aperture  41  are aligned along axis A. 
     The rotor module  26  and the stator module  27  are removably carried on opposite faces  25   a ,  25   b  of the structural frame-like element  25  and close it so as to form a hollow body defining the test chamber  10  therein. 
     In detail, the rotor module  26  closes the structural element  25  on one side and defines a base of the test chamber  10 . With further reference to  FIGS. 5-7 , the rotor module  26  comprises a plate  43 , frame-shaped in the example shown, from which a base  44  extends. Plate  43  rests against the face  25   a  of the structural element  25  ( FIGS. 2 and 4 ), so that the base  44  is arranged within the structural element  25  itself. 
     Base  44  carries, in turn ( FIGS. 4-6 ), a series of ribs  45  transverse to axis A, projecting in the direction opposite to the plate  43  towards the inside of the structural element  25 . Furthermore, the ribs  45  are arranged in an axially asymmetric manner with respect to the base  44 , which further has a dimension smaller than an inner dimension of the structural element  25 , in the direction of axis A. Thereby, the rotor module  26  may be arranged in a plurality of positions along axis A and, furthermore, in positions rotated by 180°. Therefore, the axial position of the ribs  45  may also be varied. 
     The rotor module  26  is provided with a plurality of housings  47  adapted to receive respective sensors  7 , which in the embodiment shown herein include thermocouples and pressure switches (also see the enlarged detail in  FIG. 7 ). In particular, the housings  47  are obtained close to respective ribs  45 . 
     Moreover, the ribs  45  comprise metal inserts  48  ( FIGS. 5 and 7 ) arranged close to the housings  47  and facing the inside of the test chamber  10 . From the sensors  7 , the thermocouples are thermally coupled to respective metal inserts  48 , and through the latter, to the air present in the test chamber  10 . The pressure switches are placed in respective housings  47  communicating with the inside of the test chamber  10 , so as to ensure fluid coupling. 
     In one embodiment (not shown), housings  47  and metal inserts  48  are selectively made close to some of the ribs  45 . 
     The stator module  27  closes the structural element on one side opposite to the rotor module  26  and defines an opposite base of the test chamber  10 . The spacer element  28 , also frame-shaped, is interposed between a face  25   b  of the structural element  25  (opposite to the face  25   a ) and the stator module  27 . 
     Also with reference to  FIGS. 8-10 , the stator module  27  comprises a frame-shaped plate  50 , from which a base  51  extends. The plate  50  is coupled with one face  25   b  of the structural element  25 , opposite to the face  25   a , so that the base  51  is arranged inside the structural element  25  itself, facing the base  44  of the rotor module  26  ( FIGS. 2 and 4 ). The base  51  carries a series of ribs  52  transverse to axis A, projecting in a direction opposite to the plate  50  towards the inside of the structural element  25  ( FIGS. 8 and 9 ). 
     In test chamber  10 , the rotor module  26  and the stator module  27  define the axial seal system along axis A which, as previously mentioned, is an enlarged scale model of a corresponding axial seal system for a gas turbine (see  FIG. 4  in particular). For convenience, such a module will be simply referred to as labyrinth seal system  53 . In the described embodiment, the axial seal system  53  is of the labyrinth type. In particular, the rotor portion of the axial seal system  53  is defined by base  44  and ribs  45  of the rotor module  26 , while the corresponding stator portion is defined by base  51  and ribs  52  of the stator module  27 . Ribs  45  and ribs  52  are intercalated along axis A ( FIG. 4 ), with reciprocal distances depending on the pitch and on the axial position of the rotor module  26  which, as previously explained, is adjustable. It is worth noting that the pitch of the ribs  45  in the direction of axis A normally does not coincide with the pitch of the ribs  52 . The radial clearance between ribs  45  and ribs  52 , i.e. the reciprocal distance in the direction perpendicular to axis A, is defined by the thickness of the spacer element  28 , which is specifically made and interchangeable. According to the type of axial seal system  53 , ribs  45  and ribs  52  may be engaged or not. In alternative embodiments, the spacer module  28  may be omitted, may be interposed between the structural element  25  and the rotor module  26 , or several spacer modules may exist. 
     The stator module  27  is further provided with a plurality of housings  57  adapted to receive respective sensors  7  (also see the enlarged detail in  FIG. 10 ). In particular, the housings  57  are obtained close to respective ribs  52 , which comprise metal inserts  58  facing the inside of the test chamber  10 . The sensors  7  are thermally coupled to respective metal inserts  58  and, through the latter, to the air present in the test chamber  10 . 
     In one embodiment (not shown), housings  57  and metal inserts  58  are selectively made close to some of the ribs  52 . 
     Structural element  25 , rotor module  26 , stator module  27  and spacer element  28  are reversibly sandwiched by means of locking means, which include tie rods  60  into respective seats  61  ( FIG. 3 ). The rotor module  26  comprises, along the plate  43  in a direction parallel to axis A, a higher number of seats  61  close to one another, which allow the adjustment of the axial position of the rotor module  26  itself and the related locking ( FIG. 2 ). 
     Seal rings  62  are housed in respective seats  63  of structural element  25 , rotor module  26 , and spacer element  28 , and cooperate with sealing surfaces, defined by faces  25   a ,  27   a ,  28   a  of structural element  25 , stator module  27  and spacer element  28 , respectively, adjacent to the seal rings  62  themselves. 
     The sandwiching of structural element  25 , rotor module  26 , stator module  27  and spacer element  28  may be easily released by removing the tie rods  60 . During the test campaign, this allows to remove the rotor module  26  and the stator module  27  in order to apply thermochromatic layers  64 ,  65  to their surfaces  66 ,  67  facing the inside of the test chamber  10 , as shown in  FIGS. 11 and 12 . The thermochromatic layers  64 ,  65  containing thermochromatic liquid crystals, for example, locally take a color depending on the temperature and thus allow heat exchange maps to be defined through their surface. In the described embodiment, in particular, the thermochromatic layers  64 ,  65  are applied to portions of the surfaces  66 ,  67  of rotor module  26  and of stator module  27  and extend both on the respective bases  44 ,  50  and on the ribs  45 ,  52 . 
     Once the thermochromatic layers  64 ,  65  have been applied, the rotor module  26  and the stator module  27  are repositioned to close the structural element  25  and are sandwiched again to estimate the heat exchange coefficient of the axial seal system  53  under investigation. 
     Apparatus  1  may be used for carrying out many tests and for estimating or measuring various parameters. 
     A first type of test has been just mentioned above and exploits the thermochromatic layers  64 ,  65 . In practice, the sucking pump  19  brings back a fluid flow (air) through the test chamber  10 , where the rotor module  26  and the stator module  27  form the axial seal system  53 , subject to leakage. The fluid flow passing modifies the pressure distribution inside the test chamber  10  and, if heated by the heater  16 , causes temperature variations, in particular on the surfaces  66 ,  67  of rotor module  26  and stator module  27 . The thermochromatic layers  64 ,  65  locally modify their color according to temperature variations, which may be so detected by the imagine acquisition unit  8  because the test chamber  10  is optically accessible. The acquired images, which thus represent temperature maps, are then processed by the processing unit  5 , also off line, to obtain local values of the heat exchange coefficient. 
     Again by virtue of the optical accessibility of the test chamber  10 , apparatus  1  allows to investigate the motion field along the axial seal system  53  by means of PIV (Particle Image Velocimetry) techniques, in order to determine fluid-dynamic parameters indicating its efficiency. In this case, a tracer is added to the fluid flow at the inlet of the test chamber  10 , so that the vortexes which are formed along the axial seal system  53  may be displayed by means of a light source  68 , e.g. a laser source, and may be filmed by the image acquisition unit  8 . In one embodiment, the tracer is atomized oil. 
     Moreover, pressure and temperature measures are obviously available, detected by means of the sensors  7  (thermocouples and pressure switches) placed in the test structure  2 , as well as flow measures supplied by the flow meter  18 . 
     The described apparatus offers various advantages. 
     A first advantage is that the test structure, in particular the rotor module and the stator module, is made of transparent material, and thus offers optical access to the test chamber. The apparatus thus allows to easily carry out a wide range of measurements, which would not be otherwise available. In particular, by acquiring images from the outside of the test structure and then processing them, the fluid motion field in the test chamber may be studied and the local heat exchange coefficient on the walls of the axial seal object of investigation may be accurately estimated. 
     Another advantageous aspect is the modularity of the test structure, which allows to replace one or more elements of the test structure without modifying the remaining parts. Thereby, for example, a series of rotor modules and stator modules may be provided, which correspond to different axial seal types and may be validly used both during the step of designing, for testing the efficiency of the alternative solutions, and during the step of checking existing systems. In practice, modifying the scale module of the axial seal requires replacing only two modules, made by using rather cost-effective materials and methods. Furthermore, the use of various spacer elements and the possibility of varying the relative position of the rotor module and of the stator module allow to test different configurations of the same seal, thus ensuring the absence of leakage in all cases. 
     The apparatus is thus versatile from the point of view of the variety of structures which may be investigated both according to the type, and to variations of axial set-up and of radial clearance of the ribs in the same axial seal. 
     Using a sucking pump arranged downstream of the test chamber is also advantageous. Thereby, indeed the air at the inlet of the test chamber is avoided from being heated by compression in a poorly predictable manner. The need for a heat exchanger upstream of the test chamber is therefore overcome, with a consequent benefit in terms of costs and dimensions. 
     It is finally apparent that changes and variations may be made to the apparatus described, without departing from the scope of the present invention, as defined in the appended claims. 
     In particular, the rotor module and the stator module may be made so as to define axial seal models of different type. For example, the number, pitch, shape and arrangement of the ribs may be varied. Furthermore, the ribs may be made on only one side of the seal, either the rotor side or the stator side, while the other side may be defined by a flat surface.