Patent Publication Number: US-10309419-B2

Title: Turbomachine centre blade comprising a curved portion

Description:
TECHNICAL FIELD 
     The invention relates to a turbomachine blade which is implemented in such a way as to limit the coincidences of vibrational frequencies of the blade in relation to the frequencies of solicitation of the blade during the operation of the turbomachine, which would risk resulting in a deterioration of the blade or even breakage of it. 
     PRIOR ART 
     During the operation of a turbomachine, the flow of gas along stator blades causes the blades to vibrate. 
     Each blade has one or several natural frequencies for which the amplitude of the vibration can become excessive and cause the deterioration or breakage of the blade. 
     U.S. Pat. No. 3,745,629 describes a turbomachine blade which is curved according to a profile which is similar to the profile of a blade in vibration in one of its natural frequencies. 
     This curvature makes it possible to limit the vibrations of the blade in a range of frequencies that correspond to the operating conditions of the turbomachine, and as such limit the risks of breakage of the blade. 
     However, such a curvature also reduces the effectiveness and the aerodynamic performance of the blade. 
     The invention has for purpose to propose a turbomachine blade which is carried out in such a way that the natural frequency or frequencies are different from the frequencies of solicitation of the blade during the operation of the turbomachine. 
     DESCRIPTION OF THE INVENTION 
     The invention proposes a turbomachine compressor blade of radial main orientation with respect to the main axis of the turbomachine, with the blade comprising a radially internal root portion, a radially external tip portion and a radially intermediate portion, 
     characterised in that the blade comprises a curved portion in tangentially direction and at least one straight portion on the root portion and/or on the tip portion. 
     Such a tangentially curved portion modifies the vibrational response of the blade to the vibrational solicitations, and removes the frequencies at risk outside of the operating range of the blade. 
     More preferably, the radial length L 1  of the curved portion is between 30% and 60% of the radial length L of the blade. 
     More preferably, the tangential amplitude A of the curved portion is between 1% and 5% of the radial length L of the blade. 
     More preferably, said straight portion is inclined by an angle less than or equal to 30° with respect to the main radial direction of the blade. 
     More preferably, the curved portion is positioned radially on the root portion. 
     More preferably, the curved portion is positioned radially on the tip portion. 
     More preferably, the curved portion is positioned radially on the median portion. 
     More preferably, the curved portion is tangentially curved in the direction of the intrados of the blade. 
     The invention also proposes a turbomachine compressor stator comprising radial blades distributed around the main axis of the turbomachine, characterised in that each blade is carried out such as defined hereinabove. 
     The invention also proposes a turbomachine comprising a stator that comprises blades such as defined hereinabove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention shall appear when reading the following detailed description for the understanding of which reference will be made to the annexed figures along which: 
         FIG. 1  is a diagrammatical drawing in perspective of a blade comprising a curved portion according to the invention; 
         FIG. 2  shows the tangential stacking law of the centre of gravity of the sections of a blade according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS 
     In the following description, identical, similar or analogous elements shall be designated by the same reference numbers. 
     For the description of the invention, in a non-limiting manner the radial, tangential and axial orientations shall be adopted according to the marking R, T, A shown in  FIG. 1 , wherein the radial orientation is the main orientation of the blade and the tangential orientation is the orientation perpendicular to a main axial plane of the blade. 
       FIG. 1  shows a blade  10  that is part of a stator (not shown) of the compressor of a turbomachine. 
     The compressor comprises a plurality of blades  10  which are evenly distributed around the main axis of the turbomachine, in order to form an annular set, called a rectifier grid, through which a flow of gas, here air, passes. 
     The blade  10  extends globally radially according to the orientation R with respect to the main axis of the turbomachine. 
     The blade  10  comprises a radially internal portion  12 , called the root of the blade, on which the blade  10  is fixed to an inner ferrule of the compressor (not shown). 
     The blade  10  comprises a radially external portion  14  called the tip of the blade, on which the blade  10  is fixed to an outer ferrule of the compressor (not shown). 
     The blade  10  comprises an intermediate portion  16  that connects the root  12  to the tip  14  of the blade  10 . 
     The inner ferrule and the outer ferrule of the compressor delimit an annular duct called a stream, wherein the flow of air flows and interacts with the blade  10 . 
     The blade  10  further comprises a leading edge  18 , which is located axially upstream according to the direction of the gas flow with respect to the blade  10 , and a trailing edge  20  that is located axially downstream according to the direction of the gas with respect to the blade  10 . 
     The blade  10  is furthermore cambered and comprises a face  22  called intrados, that is located on the side opposite the camber and a face  24  called extrados that is located on the side of the camber. 
       FIG. 2  shows a curve  26  showing the tangential stacking law of the centre of gravity of the sections of the blade  10 . 
     This tangential stacking law corresponds to the position of the centre of gravity of each section of the blade according to a plane perpendicular to the main radial direction of the blade, with respect to the main radial axis of the blade  10 . 
     This curve  26  comprises a root portion  28  corresponding to the root  12  of the blade  10 , a tip portion  30  corresponding to the tip  14  of the blade  10  and an intermediate portion  32  corresponding to the intermediate portion of the blade  10 . 
     According to the invention, the blade  10  is carried out in such a way that it comprises a portion  34  that is curved tangentially and at least one straight portion. 
     As such, as can be seen in more detail in  FIG. 2 , the curve  26  comprises a tangentially curved portion  36  corresponding to the curved portion  34 . The curve  26  further comprises at least one curved portion corresponding to the straight portion of the blade  10 . 
     According to the invention, the straight portion of the blade  10  is located on the root  12  and/or on the tip  14  of the blade  10 , according to the position of the curved portion  34 . 
     As such, the straight portion of the curve  26  is located on the root portion  28  and/or on the tip portion  30 , according to the radial position of the curved portion  36 . 
     According to a first aspect of the invention, the curved portion  34  is located radially on the root  12  of the blade  10 . The straight portion is then located on the tip  14  of the blade  10 . Consequently, the curved portion  36  is located radially on the root portion  28  and tip portion  30  of the curve  26  is straight. 
     According to a second aspect of the invention, the curved portion  34  is located radially on the tip  14  of the blade  10 . The straight portion is then located on the root  12  of the blade  10 . The curved portion  36  of the curve  26  is consequently located radially on the tip portion  30  and the root portion  28  of the curve  26  is straight. 
     According to a third aspect of the invention, the curved portion  34  is located radially on the intermediate portion  16  of the blade  10 . The root  12  and the tip  14  of the blade  10  each form a straight portion of the blade  10 . 
     Consequently, the curved portion  36  is located radially on the intermediate portion  32  and the root portion  28  and the tip portion  30  of the curve  26  are both straight. 
     Furthermore, according to a preferred embodiment, the blade  10  is curved in such a way that the curved portion  34  is tangentially curved in the direction of the intrados  22 , as shown in  FIG. 1 . 
     According to an alternative embodiment not shown, the curved portion  34  is curved in the direction of the extrados  24 . 
     The dimensions of the curved portion  36  are defined with respect to the radial length “L” of the blade  10 . 
     As such, the radial dimension “L 1 ” of the curved portion  36  is between 30% and 60% of the radial dimension “L” of the blade  10 . 
     As such, the tangential dimension “A” of the curved portion  36  is between 1% and 5% of the radial dimension “L” of the blade  10 . 
     As was mentioned hereinabove, according to the radial position of the curved portion, the root portion  28  and/or the tip portion  30  is straight. 
     In this case, each root portion  28  and/or tip portion  30  that is straight, is inclined with respect to the main radial direction of the blade by an angle of which the value is less than or equal to 30°.