Fluid circuit in a turbine engine

Abstract

A device for controlling feed of fluid to equipment, such as a heat exchanger, the device including: a fluid slide valve mounted in a fluid circuit including a slide movable between two positions, a first position in which it allows the fluid to flow through the equipment, and a second position in which it prevents the fluid from flowing through the equipment; a laminar flow constriction arranged in the fluid circuit upstream from the slide valve; and a drive mechanism moving the slide of the slide valve between its two positions by head loss of the fluid in the laminar flow constriction.

Claims

1. A device for controlling a feed of fluid to a heat exchanger, the device comprising: a fluid slide valve mounted in a fluid circuit and including a slide movable between first and second positions, the first position in which the slide allows a fluid to flow through the heat exchanger, and the second position in which the slide prevents the fluid from flowing through the heat exchanger; a laminar flow constriction arranged in the fluid circuit upstream from the slide valve; and a drive means for moving the slide of the slide valve between the first and second positions by head loss of the fluid in the laminar flow constriction, wherein the drive means comprises first and second chambers separated by the slide, the first chamber being in fluid flow communication with an inlet to the laminar constriction, and the second chamber being in fluid flow communication with an outlet from the fluid flow constriction, wherein the drive means further comprises return means configured to bring the slide into the first position when a pressure difference between the inlet and the outlet of the laminar constriction is less than a predetermined threshold, wherein the slide valve includes at least one fluid outlet connected to a parallel pipe in parallel with the heat exchanger, the slide of the slide valve allowing fluid to flow to the parallel pipe when the slide is in the second position, and preventing fluid from flowing in the parallel pipe when the slide is in the first position, and wherein the parallel pipe is incorporated in a support of the heat exchanger and extends at least in part in immediate proximity of the heat exchanger to transmit heat between the parallel pipe and the heat exchanger through the support.

2. A device according to claim 1, wherein the return means of the slide comprises a compression spring arranged in the chamber that is connected to the outlet of the laminar constriction, between a face of the slide and an end wall of the chamber.

3. A device according to claim 1, further comprising a pressure release valve mounted in a channel connecting an upstream end of the slide valve to a downstream end of the heat exchanger, the release valve being configured to allow fluid to flow in the channel when a head loss in the heat exchanger is greater than a predetermined threshold.

4. A device according to claim 1, wherein the laminar constriction includes a tube.

5. A device according to claim 4, wherein an inside surface of the tube possesses a surface roughness defined by a coefficient R.sub.a of about 15 ?m, with an accuracy of ?5%.

6. A device according to claim 1, wherein the laminar constriction includes a tube in which a length of the tube is greater than a diameter of the tube.

7. A device according to claim 6, wherein the tube has a length of about 30 cm with an accuracy of ?1.5%, and a diameter of about 8.15 mm, with an accuracy of ?1.5%.

8. A turbine engine, or an airplane turboprop or turbojet, comprising at least one device according to claim 1.

9. A turbine engine according to claim 8, wherein the fluid is oil and the heat exchanger is an oil/air heat exchanger connected upstream from an oil/fuel heat exchanger.

10. A device for controlling a feed of fluid to a heat exchanger, the device comprising: a fluid slide valve mounted in a fluid circuit and including a slide movable between first and second positions, the first position in which the slide allows a fluid to flow through the heat exchanger, and the second position in which the slide prevents the fluid from flowing through the heat exchanger; a laminar flow constriction arranged in the fluid circuit upstream from the slide valve; and a drive means for moving the slide of the slide valve between the first and second positions by head loss of the fluid in the laminar flow constriction, wherein the laminar constriction includes a tube, and wherein an inside surface of the tube possesses a surface roughness defined by a coefficient R.sub.a of about 15 ?m, with an accuracy of ?5%.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Other details, characteristics, and advantages of the invention appear on reading the following description made by way of nonlimiting example and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagrammatic perspective view of a turbine engine of known type;

(3) FIG. 2 is a fragmentary diagrammatic representation of an oil circuit of the prior art; and

(4) FIG. 3 is a diagrammatic representation of a device of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) In well-known manner to the person skilled in the art, a turbine engine 10 comprises a combustion chamber 12, with the combustion gas from the chamber 12 driving a high-pressure turbine 14 and a low-pressure turbine 16. The high-pressure turbine 14 is coupled by a shaft to a high-pressure compressor arranged upstream from the combustion chamber 12 and feeding the combustion chamber with air under pressure. The low-pressure turbine 16 is coupled by another shaft to a fan wheel 18 arranged at the upstream end of the turbine engine 10.

(6) An accessory gearbox (AGB) 20 is connected by a mechanical power takeoff 22 to the high-pressure turbine shaft and has a set of gearwheels for driving various pieces of equipment in the turbine engine, such as pumps and generators, in particular electricity generators.

(7) FIG. 2 shows an oil circuit of the FIG. 1 turbine engine.

(8) From upstream to downstream in the oil flow direction, the oil circuit 24 comprises various assemblies 26 making use of lubricating and/or cooling oil: recovery pumps 28 serving to recirculate the oil from the equipment to a tank 30; feed pumps 32; and a filter 33.

(9) In addition to the oil used for lubricating and cooling the turbine engine, in particular bearings of turbine and compressor shafts, the overall flow of oil may include oil that is used for lubricating the AGB 20 and for lubricating and cooling one or more electricity generators.

(10) The oil circuit has three heat exchangers connected in series between the filter 33 and the assembly 26, namely: a main oil/fuel heat exchanger 34, a secondary oil/fuel heat exchanger 36, and an oil/air heat exchanger 38.

(11) Thus, in operation, at the outlet from the feed pumps 32, the oil passes through the oil/air heat exchanger 38, the secondary oil/fuel heat exchanger 36, and then the main oil/fuel heat exchanger 34. A pipe 40 is installed in the oil circuit as a parallel connection around the oil/air heat exchanger 38; it has an inlet as a branch connection between the outlet of the filter 33 and the inlet of the oil/air heat exchanger 38, and an outlet as a branch connection between the outlet of the oil/air heat exchanger 38 and the inlet of the secondary oil/fuel heat exchanger 36. A hydraulic valve 42 is connected in the parallel pipe and causes the flow of oil to pass through the oil/air heat exchanger 38 or to pass through the parallel pipe 40 and the oil/air heat exchanger 38. The oil leaving the main oil/fuel heat exchanger 34 then flows towards the oil tank 30.

(12) The oil/air heat exchanger 38 may be of the surface cooling type, i.e. of the type having oil ducts swept by a stream of cold air coming from a stream of air bypassing the turbojet, which may also be referred to as the secondary air stream. By way of example, such a heat exchanger may be housed on a wall of the passage for the bypass stream, immediately downstream from the fan 18 (FIG. 1).

(13) The oil/air heat exchanger 38 may also be of the air/oil plate type, having passing therethrough a stream of air taken from the bypass air stream and reinjected into the bypass stream at the outlet from the heat exchanger.

(14) As mentioned above, during cold operating conditions, the valve opens to allow oil to pass through the parallel pipe 40. Nevertheless, the oil/air heat exchanger 38 continues to be fed with oil, thereby contributing to further cool the oil. Furthermore, that type of valve may operate in unstable manner, as mentioned above.

(15) The invention provides a solution to those problems and also to the other problems mentioned above, by incorporating a laminar constriction 44 upstream from a member 46 for distributing fluid to the oil/air heat exchanger 48, and by causing the supply of oil to the oil/air heat exchanger to be opened or closed by means of the head loss in the laminar constriction, with this head loss depending on the flow rate and on the temperature of the oil.

(16) FIG. 3 shows a device for controlling the supply of fluid to the oil/air heat exchanger in accordance with the invention.

(17) The device comprises a slide valve 46 having a hollow body 50, such as a cylinder, slidably receiving a slider 52 hermetically separating a first chamber 54 from a second chamber 56. The inlet to the laminar constriction 44 is in fluid flow communication with the first chamber 54, and its outlet is in fluid flow communication with the second chamber 56, which second chamber is at the opposite end of the slide 52 relative to the first chamber 54.

(18) The slide 52 has two recesses or slots 58 and 59 that are axially spaced apart from each other along the travel axis of the slide 52. A first recess 58 of the slide 52 is for connecting together a first inlet pipe 60 and a first outlet pipe 62. The second recess 59 is for connecting together a second inlet pipe 64 and a second outlet pipe 66.

(19) The oil/air heat exchanger 48 is connected in the first outlet pipe 62 from the slide valve 46. The second outlet pipe 66 forms a parallel pipe around the oil/air heat exchanger 48, opening out downstream from the oil/air heat exchanger 48.

(20) The width of each recess 56, 59 is determined so as to allow oil to flow between the associated inlet and outlet pipes 60, 64 and 62, 66. Also, the spacing between the recesses 58 and 59 of the slide is determined in such a manner that, in a first position (FIG. 3), the first inlet pipe communicates via the first recess 58 with the first outlet pipe 62, and fluid flow communication between the second inlet pipe 64 and the second outlet pipe or parallel pipe 66 is blocked by a wall of the slide 52, and in such a manner that, in a second position, the second inlet pipe 64 communicates via the second recess 59 with the second outlet pipe or parallel pipe 66, and fluid flow communication between the first inlet pipe 60 and the first outlet pipe 62 is blocked by a wall of the slide 52.

(21) A compression spring 68 is mounted in the second chamber 56 connected to the outlet of the laminar constriction 44 between a face of the slide 52 and an end wall of the second chamber 56 in such a manner as to exert a force urging the slide 52 in the direction that increases the volume of the second chamber 56.

(22) The compression of the spring 68 is determined so as to allow the slide to move in its first position when the pressure difference between the inlet and the outlet of the laminar constriction is less than a predetermined threshold. When the pressure difference between the inlet and the outlet of the laminar constriction 44 is greater than the threshold, then the sum of the forces exerted by the spring on the slide and by the oil in the second chamber 56 becomes less than the force exerted by the oil in the first chamber 54, thereby moving the slide 52 into its second position.

(23) It can thus be understood that the pressure difference at which it is desired for the slide to switch from its first position to its second position is determined by calibrating the force of the spring and also by the surface areas 55 and 57 of the slide 52 against which the oil pressure acts.

(24) The device also has a pressure release valve 70 mounted in a channel 72 connecting the upstream end of the slide valve 46 to the downstream end of the oil/fuel heat exchanger 48. The release valve 70 is configured to allow fluid to flow in the channel 72 when the pressure upstream from the valve 70 is greater than a predetermined threshold. This threshold may be reached in the event of the slide 52 becoming blocked, e.g. by seizing, or in the event of a viscous plug of cold oil forming in the oil/air heat exchanger 48.

(25) The entire device of the invention can be incorporated in a casing 74. To do this, the parallel pipe 66 and the oil/air heat exchanger 48 are incorporated in the casing 74.

(26) The parallel pipe 66 of the oil/air heat exchanger includes at least a portion 76 that extends in the immediate proximity of the oil/air heat exchanger 48 in order to enable heat to be exchanged by thermal conduction through the material of the casing.

(27) When the slide 52 is in its second position preventing oil from flowing towards the oil/air heat exchanger 48, the oil present in the oil/air heat exchanger continues to be cooled by the air and can form a plug of oil that blocks the flow of oil in the oil/air heat exchanger 48 when the slide 52 is switched into its first position. The pipe 76 formed in the immediate proximity of the oil/air heat exchanger 48 serves to heat the stagnant oil in the oil/air heat exchanger 48.

(28) By way of example, the device of the invention is incorporated in the oil circuit of FIG. 2 between the outlet from the filter 33 and the inlet to the secondary oil/fuel heat exchanger 36, and it replaces the oil/air heat exchanger 38, the parallel pipe 40, and the valve 42 as described with reference to FIG. 2.

(29) The use of a laminar constriction 44 upstream from the slide valve enables the head loss in the constriction 44 to depend both on the flow rate of oil in the constriction and on the temperature of the oil.

(30) The flow rate is given by the following relationship:

(31) $Q=\mathrm{ks}?\sqrt{\frac{?P}{?}}$
where: Q represents the flow rate through the laminar constriction 44 in liters per hour (L/h); ks represents the head loss coefficient of the constriction 44 and depends on the surface state and on the shape (length, diameter) of the laminar constriction 44. This coefficient is determined empirically; ?P represents the head loss between the inlet and the outlet of the laminar constriction 44 in bars; and ? represents the density of the oil in kilograms per liter (kg/L).

(32) The density ? depends on the temperature of the oil and it increases when the temperature decreases.

(33) It can be understood that in order to reach a given head loss in the laminar constriction, it suffices to have a laminar constriction with a coefficient ks that is appropriate, and to do this, it suffices to make a laminar constriction having appropriate geometrical characteristics (length, diameter) and an appropriate surface state.

(34) In a particular embodiment of the invention, the laminar constriction 44 is formed by a tube having a rough inside surface so as to generate head loss by friction in the laminar constriction 44. A tube with this design makes it possible in particular to enhance the friction of the peripheral layers of the fluid against the inside wall of the tube, thereby increasing the head loss through the laminar constriction, in particular when the fluid presents high viscosity.

(35) In practice, the tube may have a length of about 30 cm and a diameter of about 2 cm.

(36) While the turbine engine is operating cold, and since the density of oil is greater when cold than when hot, there is an increase in the pressure difference across the ends of the laminar constriction 44, thereby causing the slide 52 to move into its second position, in which it prevents oil from flowing to the oil/air heat exchanger 48. This avoids cooling the oil that is used for heating fuel via the main and secondary oil/fuel heat exchangers 34 and 36.

(37) When the temperature of the oil increases, the pressure difference in the laminar constriction 44 decreases, thereby acting, at a threshold pressure difference value, to cause the slide 52 to move into its first position in which it allows oil to flow through the oil/air heat exchanger 48.

(38) During a take off stage, the flow of oil through the constriction 44 increases strongly, thereby leading to a new increase in the head loss through the laminar constriction 44, and causing the slide 52 to move into its second position. The device of the invention is calibrated in such a manner that for a take off in cold weather the slide 52 is in its second position, and for a take off in hot weather the slide 52 is in its first position.

(39) While cruising, when the outside temperature is cold, the slide is maintained in its second position because of the low temperature of the oil.

(40) The laminar constriction 44 introduces additional head loss in the oil circuit that it is desirable to minimize. To do this, it is preferable to have large surface areas against which pressure is applied at each end of the slide 52 so that the pressure difference across the terminals of the laminar constriction 44 gives rise to a clear difference in the force applied to the slide 52. Nevertheless, the overall size of the slide valve 46 must not be excessive in order to avoid significantly increasing the weight of the device 74.

(41) The slide valve described with reference to FIG. 3 has two positions for the slide 52 and four fluid flow ports. The slide valve could also have two positions for the slide 52 and three fluid flow ports, comprising one oil inlet and two oil outlets, the oil inlet feeding one or the other of the oil outlets selectively depending on the position of the slide. Such a three-port slide valve presents a transition zone for switching the flow of oil into the parallel pipe 66 or to the oil/air heat exchanger 48, and it presents dynamic behavior that is not as good as a four-port slide valve having two inlets and two outlets dedicated to the flow of fluid to the oil/air heat exchanger 48 and in the parallel pipe 66.

(42) In a variant of the invention, the spring could be arranged in the first chamber 54 and configured so as to work in traction, thereby enabling the slide to be moved in identical manner to that described above.

(43) In another variant of the invention, the first and second chambers 54 and 56 of the slide valve 46 could be in fluid flow communication with a component that is already present in the oil circuit upstream from the device 74 and acting as a laminar constriction.

(44) The device of the invention could be used in the same manner with a heat exchanger making use of a pair of fluids other than oil and air. It is thus possible to use the device of the invention with an oil/fuel heat exchanger or with an air/fuel heat exchanger. When used with an oil/fuel heat exchanger, the fluid could be fuel that is diverted into a parallel pipe by the head loss of fuel in a laminar constriction in a manner similar to that described above.