Instrumented flow passage of a turbine engine

Abstract

An annular air flow passage, particularly for a turbine engine, comprising two radially internal and external annular walls. A measuring element is elongated in a direction between the internal and external annular walls, and a first of the internal or external ends of the element is fixed rigidly to a first of the internal or external walls. The element includes at least one tubular cavity extending along the element and supplied with pressurized fluid.

Claims

1. An apparatus, comprising: an annular air flow passage including a radially internal annular wall and a radially external annular wall; a source of pressurized fluid; an elongated measuring element extending in a direction between the radially internal annular wall and the radially external annular wall, with an end of the measuring element fixed rigidly to the radially internal annular wall or the radially external annular wall, said measuring element comprises at least one tubular cavity extending along the measuring element and configured to receive pressurized fluid from the pressurized fluid source, the at least one tubular cavity being in a closed circuit with the source of the pressurized fluid.

2. The apparatus according to claim 1, wherein the measuring element has, in a plane perpendicular to its direction of elongation, a U shape formed of two branches and wherein, among said at least one tubular cavity, at least one cavity is arranged in each of the branches.

3. The apparatus according to claim 1, wherein the measuring element comprises a tubular body delimiting said at least one tubular cavity and includes nozzles, wherein the at least one tubular cavity extends along said direction of elongation and houses a plurality of cables connected to the nozzles for measuring the characteristics of the air flow in the flow passage, oriented in an upstream direction.

4. The apparatus according to claim 3, further comprising a ring, surrounding the tubular body, through which the at least one tubular cavity is supplied with pressurized fluid.

5. The apparatus according to claim 1, wherein the elongated measuring element extends in the annular flow passage in a primarily radial direction, wherein the end of the measuring element is fixed rigidly to the radially external annular wall, wherein the end of the measuring element is fixed to the radially external annular wall corresponds to a first end of the measuring element, and wherein a second end of the measuring element opposite said first end is free.

6. The apparatus according to claim 1, wherein the pressurized fluid is pressurized air.

7. A turbine engine comprising the apparatus according to claim 1 and an annular row of blades configured to be driven in rotation by a rotor, wherein said elongated measuring element is arranged in said flow passage downstream from said annular row of blades.

8. The apparatus according to claim 4, wherein the ring further includes annular seals.

9. Method for varying the stiffness of an elongated measuring element, in an annular flow passage having a radially internal annular wall and a radially external annular wall, the elongated measuring element extending in a direction between the radially internal annular wall and the radially external annular wall, with an end of the measuring element is fixed rigidly to the radially internal annular wall or the radially external annular wall, said measuring element comprising at least one tubular cavity extending along the measuring element and configured to receive pressurized fluid from a pressurized fluid source, the at least one tubular cavity being in a closed circuit with the source of the pressurized fluid; the method comprising: a) identifying the pressure in said at least one tubular cavity of the elongated measuring element; b) measuring the vibration frequency f.sub.1 of the elongated measuring element; c) determining the natural frequency f.sub.r1 of the elongated measuring element based on the pressure identified in the at least one tubular cavity and obtaining the absolute value |f.sub.1f.sub.r1|; d) comparing the absolute value |f.sub.1f.sub.r1| with a threshold and establishing a risk of resonance in response to determining that the absolute value is less than or equal to the threshold; and e) in response to establishing the risk of resonance, varying the pressure in the at least one tubular cavity of the elongated measuring element until the risk is no longer present.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood, and other details, characteristics and advantages of the invention will appear upon reading the following description given by way of a non restrictive example while referring to the appended drawings wherein:

(2) FIG. 1 already described is a cross-sectional axial diagrammatic half-view of an aircraft turbofan of a known type;

(3) FIG. 2 already described is a perspective diagrammatic view of an element for measuring characteristics of a flow according to the known technology;

(4) FIG. 3 is a diagrammatic view of a measuring element according to the invention;

(5) FIG. 4 is a perspective diagrammatic view of connection of the means of pressurized air supply to an element according to a first practical embodiment of the invention;

(6) FIG. 5 is a perspective sectional diagrammatic view of the element in FIG. 4;

(7) FIG. 6 is a perspective diagrammatic view of a second practical embodiment of an element according to the invention;

(8) FIG. 7 is a perspective cross-sectional view of the element in FIG. 6;

(9) FIG. 8 is a diagrammatic view along a longitudinal cross-section of the element in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) FIG. 3 represents a portion of a turbine engine annular flow passage such as an annular secondary air flow passage, comprising a measurement device 56 for measuring characteristics of the air flow featuring a measuring element 58 extending in the air flow between internal 60 and external 62 revolution walls delimiting the air flow.

(11) The measuring element 58 comprises a first radially external end 64 and a second end 66, radially internal. The radially external end is connected to a cylindrical portion 68 interdependent with a disc-shaped base 70 perforated by four holes 72 (FIGS. 3 and 6). The measuring element 58 is inserted radially from outside the radially external wall 62 into an opening in the latter such that the cylindrical portion 68 and the disc 70 engage in recesses of matching shape formed in the thickness of the external wall 62. Fixing screws are subsequently inserted into the holes 72 in the base 70 and into the holes opposite in the external wall 62. The first end 64 of the element 58 is thus fixed rigidly in all directions to the radially external wall 62 (FIG. 3).

(12) According to the invention, the element 52 comprises at least one tubular cavity 63 extending along the measuring element 52 and in fluid communication with means of supply with pressurized fluid 74 allowing injection of a pressurized fluid into the cavity 63. The means of supply with pressurized fluid are controlled during operation by means of control 76 connected on entry to means of measurement 78 of the vibration frequency of the element, such as a dynamic strain gauge.

(13) In a first practical embodiment of the invention, the element 80 has, in a plane perpendicular to its direction of elongation, a U shape formed of two branches 82a, 82b connected to each other by a junction section 83 of the branches 82a, 82b. A housing 86 is thus defined between the two branches 82a, 82b of the element 80 and the junction section 83. The junction section 83 has the nozzles 54 passing through it, which emerge in the housing 86 on one side and protrude outwards on the other side and are designed to measure the characteristics of an air flow. It will be noted that the U shape gives the element 80 and aerodynamic profile so as to limit the impact of the measuring element 80 on circulation of the air flow.

(14) A first branch 82a comprises two tubular cavities 84a and a second branch 82b comprises two tubular cavities 84b. The two cavities 84a of the first branch 82a are connected to their radially internal ends. Likewise, the two cavities 84b of the second branch 82b are connected to their radially internal ends. The tubular cavities 84a, 84b are connected to the means of supply with pressurized air 74 with which they form a closed circuit. The tubular cavities 84a, 84b of the element form sealed cavities which are only in fluid communication with the means of supply with pressurized air.

(15) Although the element comprises four tubular cavities 84a, 84b in the embodiment in FIGS. 4 and 5, it is understood that it could only comprises a single cavity in each branch 82a, 82b.

(16) In this embodiment, the cables connected to the measuring nozzles extend in the direction of elongation of the element and are arranged in the housing 86 formed between the two branches 82a, 82b of the element 80. The radially internal end of the housing 86 could be closed by a wall.

(17) According to the invention, varying the fluid pressure inside the cavities 84a, 84b of the branches 82a, 82b of the element 80 makes it possible to vary the stiffness of the element 80, which allows modification of the natural frequency of the element 80.

(18) Indeed, it is clear that the fixing method of the measuring element 80, with the first external end 64 fixed rigidly in all directions and the second end 66 devoid of any fixing in the three axial, radial and circumferential directions, resembles a single-embedded beam model and that varying the stiffness by modifying the pressure allows modification of the natural frequency of the element 80 (refer to equation 1 above).

(19) FIGS. 7 to 9 represent a second embodiment of the invention in which the element 88 comprises a cylindrical-section tubular body 90, the inside of which comprises a tubular cavity 91 in which cables 92 are engages for connection to nozzles for measuring the characteristics of a flow. These nozzles may for example be formed at the radially internal end of the element and be spaced apart from one another in the circumferential direction.

(20) As illustrated in FIG. 7, a ring 96 is hermetically engaged, by means of annular seals 98, around a section 94 of the radially external part of the tubular body 90, wherein this section is arranged on the outside of the radially external wall 62. The ring 96 comprises a through orifice 100 aligned at its radially internal end with an orifice of the section 94 of the tubular body 90, the radially external end of which receives hermetically the downstream end of a duct 102 of the means of supply with pressurized fluid 74 (FIGS. 8 and 9). With such an assembly, the fluid circulating under pressure feeds the tubular cavity 94 for passage of the connection cables 92 to the measuring nozzles.

(21) In the embodiments, the fluid is preferably air rather than a liquid, which offers the advantage of having a very low density that therefore has little influence on the mass of the element.

(22) Application of pressure variation in the cavity or cavities of the element 80, 88 is performed by the means of control 76, which allow comparison of the vibration frequency f.sub.1 with the resonance frequency of the element fr.sub.1. In this respect, the means of control 76, connected to the means of measurement of the vibration frequency of the element, allow analysis and adaptation of the pressure in the cavity or cavities 84a, 84b, 91 as a function of the absolute value of the difference between a vibration frequency f.sub.1 of said element 80, 88 and the resonance frequency fr.sub.1 in order to check that the behaviour of the element 80, 88 is consistent with that which is expected.

(23) Consequently, the method for varying the stiffness of the element comprises the steps involving: a) identifying the pressure in said at least one tubular cavity of the measuring element 80, 88; b) measuring the vibration frequency f.sub.1 of said element 80, 88; c) determining the natural frequency fr.sub.1 of the measuring element based on the pressure identified in the cavity 84a, 84b, 91 and obtaining the absolute value |f.sub.1fr.sub.1|; d) comparing the absolute value |f.sub.1fr.sub.1| with a threshold and establishing a risk of resonance if this absolute value is less than or equal to the threshold in this case; and e) if a risk of resonance has been established at the preceding step, varying the pressure in said at least one tubular cavity 84a, 84b, 91 of the measuring element 80,88 until the risk is no longer established.

(24) Identification of the pressure in the tubular cavity may for example be performed in two different ways. The first may involve a direct measurement of the pressure in the cavity using a pressure sensor arranged in the cavity 84a, 84b, 91. The second may involve an indirect measurement estimated based on the pressure of the fluid sent into the closed circuit, which is determined based on the means of supplying with pressurized fluid. Naturally, the means of control must receive the pressure data in the cavity in order to be able to control the means of supply with pressurized fluid.

(25) During operation, the element 80,88 will vibrate at a frequency f.sub.1 following mainly the frequential excitation f derived from rotation of the blades, without however excluding other sources of vibrations. When the frequencies f.sub.1 and fr.sub.1 are not sufficiently wide apart, two cases may arise: f.sub.1>fr.sub.1 corresponding to a situation in which the vibration frequency f.sub.1 of the element 80,88 is greater than the natural frequency fr.sub.1. f.sub.1<fr.sub.1 corresponding to a situation in which the vibration frequency f.sub.1 of the element 80,88 is greater than the natural frequency fr.sub.1.

(26) In practice, the difference |f.sub.1fr.sub.1| should be at least equal to 10% of the value of fr.sub.1 and in absolute terms should not be less than 5% of fr.sub.1. The method of varying the stiffness of the element 80,88 makes it possible to safeguard the vibratory dynamics of the element by rendering the pressure in the element 80,88 dependent on the difference |f.sub.1fr.sub.1| and by maintaining the frequency f.sub.1 at a maximum of 95% of fr.sub.1 or a minimum of 105% of fr.sub.1, hence excluding the interval [0.95 fr.sub.1; 1.05 fr.sub.1] and preferably the interval [0.9 fr.sub.1; 1.1 fr.sub.1].

(27) Consequently, fr.sub.1 needs to be moved apart from f.sub.1 avoiding equality between these two values. This is achieved through a reduction in fr.sub.1 when f.sub.1 is higher and an increase in fr.sub.1 when f.sub.1 is lower.

(28) Concretely, the reduction in fr.sub.1 is obtained by reducing the pressure in the cavity or cavities 84a, 84b, 91 of the element 80, 88 and the increase in fr.sub.1 is obtained by increasing the pressure in the cavity or cavities 84a, 84b, 91 of the element 80, 88.

(29) The upwards or downwards variation in the natural frequency may be made possible by initial pressurizing of the cavities 84a, 84b, 91 of the element 80, 88 at a pressure greater than atmospheric pressure. The reduction in the pressure applied in relation to the initial pressure allows a reduction in the stiffness and therefore a decrease in the natural frequency of the element 80, 88. The reduction in the pressure applied in relation to the initial pressure applied allows an increase in the stiffness and therefore an increase in the natural frequency of the element 80, 88.

(30) Such a method makes it possible to control the natural frequencies fr.sub.1 of the element taking account of the excitation frequency f.sub.1 induced by operation of the turbine engine.