Heat-exchange system for a turbine engine

Abstract

Disclosed is a heat-exchange system (10) for a turbine engine, in particular for an aircraft, comprising a compression zone and an item of equipment to be cooled, the heat-exchange system comprising a collection zone (31) for collecting a secondary flow (Fs) of ambient air, a heat exchanger (3) comprising exchange piping (32) for exchange of heat with a flow circulating in the heat-exchange system and within which a hot flow (F1) that is to be cooled, bled from the outlet of the compression zone, is intended to circulate, and a secondary-flow ejector (2) comprising an inlet (21), wherein, in the direction of a flow circulating in the heat-exchange system, the heat exchanger is arranged upstream of the inlet of the ejector and downstream of the collection zone, such that, during operation, an exchange of heat is established between the secondary flow and the exchange piping.

Description

DESCRIPTION TITLE: HEAT EXCHANGE SYSTEM FOR TURBOMACHINE TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to the field of turbomachinery, particularly for aircraft. Specifically, the invention relates to a heat exchange system for a turbomachine. The invention also relates to a turbomachine comprising such a heat exchange system. STATE OF PRIOR ART

[0002] A turbomachine typically comprises, in one flow direction from upstream to downstream, an inlet section, a compressor section, a combustion section, a turbine section, and an exhaust section. During operation, air enters through the inlet section, which may include a fan to accelerate the incoming air, and flows to the compressor section where one or more compressors progressively compress the air until it reaches the combustion section, where combustion gases are generated. The combustion gases then flow from the combustion section along a defined hot gas stream in the turbine section and exit the turbine section through the exhaust section. Such a turbomachine produces mechanical power capable of propelling a motor vehicle, such as an aircraft.

[0003] In some turbomachines, it is necessary to include a cooling system for certain components, such as the high-pressure turbine, which is part of the turbine section and located directly downstream of the combustion chamber forming the turbomachine's combustion section. Subjected to the high temperatures of the combustion gases from the combustion section, these high temperatures can compromise the integrity of the high-pressure turbine, leading to degraded performance and consequently, a loss of optimal efficiency.

[0004] To enable cooling of the high-pressure turbine, one solution is to use air drawn from the compressor section. Cooling the upstream areas of the high-pressure turbine requires high-pressure cooling air, and this air is drawn from the outlet of the compressor section; however, this air is hotter than if it had been drawn from an area further upstream of the compressor section. To optimize cooling performance, this drawn air can be cooled using a heat exchanger before being used in the high-pressure turbine. Currently, the heat exchanger systems used include an ejector with a heat exchanger at its outlet.The ejector collects a secondary stream of ambient air, accelerates it, and mixes it with a primary stream drawn from the turbomachine's compression section. This cooled mixed stream is then sent through a heat exchanger containing a heat exchange tube through which a hot stream, drawn from the turbomachine's compression section outlet, circulates. Once cooled within the heat exchanger, this hot stream is injected into a high-pressure turbine cooling circuit. At the outlet of this cooling circuit, the hot stream mixes with the combustion gases exiting the high-pressure turbine.

[0005] Indeed, one of the ejector's roles is to draw in ambient air (secondary flow) using compressed air taken downstream of a compressor stage (primary flow). The primary and secondary flows then mix downstream of an ejector outlet. This mixed flow is then routed to the heat exchanger and circulates through it as a cold flow. The hot flow to be cooled comes from another intake taken even further downstream of the compressor stages (at a higher pressure and temperature than the primary flow described above). This hot flow is cooled as it circulates through the heat exchanger.

[0006] One drawback of such a prior art heat exchange system is its poor heat exchange performance. Downstream of the ejector, the mixed flow velocity is high. This high cold flow velocity results in poor flow distribution at the heat exchanger inlet. This degrades the system's performance in two ways: poor cold fluid distribution reduces heat exchange efficiency due to inefficient use of the exchange surface, and a diffuser component located between the ejector and the heat exchanger produces high pressure drops due to diffusion and forced changes in direction of the high-velocity incoming flow. DESCRIPTION OF THE INVENTION

[0007] One aim of the invention is to provide a heat exchange system for turbomachinery which does not have the disadvantages of the prior art.

[0008] To this end, the invention provides a heat exchange system for a turbomachine, particularly for aircraft, comprising a compression zone and a component to be cooled, the heat exchange system comprising a collection zone for a secondary flow of cold air taken from outside or upstream of the turbomachine, a heat exchanger comprising an exchange circuit with a flow circulating in the heat exchange system and within which a hot flow to be cooled is intended to circulate, taken from the compression zone, and an ejector comprising an inlet for the secondary flow, in which, in the direction of a flow circulating in the heat exchange system, the heat exchanger is positioned upstream of the inlet of the ejector and downstream of the collection zone, so that, during operation, a heat exchange is established between the secondary flow and the exchange tube.

[0009] Advantageously, but optionally, the heat exchange system according to the invention has at least one of the following technical characteristics: - the secondary flow inlet of the ejector has a connecting component with a convergent shape in the direction of a flow circulating in the heat exchange system; - the ejector includes an outlet diffuser comprising a channel diverging in the direction of a flow circulating in the heat exchange system; - the ejector includes a supply pipe for a primary flow taken from the compression zone and a conduit which is convergent-divergent and fluidically connected to the supply pipe; - the conduit is convergent in shape in the direction of a primary flow circulating in the supply pipe; - through which the supply pipe passes through the heat exchanger; - the exchange tubing is spiraled between an inlet port (32) and an outlet port (33); - the exchange tubing is provided around the supply tubing; and, - the collection zone is a pavilion open upstream of a flow circulating in the heat exchange system.

[0010] The invention also provides for a turbomachine, particularly for aircraft, comprising at least one heat exchange system having at least one of the preceding technical characteristics.

[0011] Advantageously, but optionally, the heat exchange system according to the invention has at least one of the following technical characteristics: - the turbomachine comprises a compression zone, a combustion chamber downstream of the compression zone and a component comprising a cooling circuit, the ejector being fluidly connected to the compression zone and the heat exchanger being fluidly connected at the inlet downstream of the compression zone and upstream of the combustion chamber, and at the outlet to the circuit of cooling. BRIEF DESCRIPTION OF FIGURES

[0012] Other features and advantages of the invention will become apparent from the following description of an embodiment of the invention. See the attached drawings. [Fig.1] is a schematic axial cross-sectional view of a first embodiment of a heat exchange system according to the invention; [Fig.2] is a schematic view of a turbomachine comprising the heat exchange system according to the invention of figure 1; [Fig.3] is a three-dimensional view of a second embodiment of a heat exchange system according to the invention; [Fig.4] is a three-dimensional cross-sectional view of the heat exchange system in Figure 3; [Fig.5] is a partial three-dimensional schematic view of the heat exchange system in Figure 1 where cold flow lines are shown within the heat exchanger; [Fig. 6] is a graph illustrating a comparison of pressure losses between a prior art heat exchange system and a heat exchange system according to the invention; and, [Fig.7] is two images to compare a distribution of heat transfer at the level of the heat exchange circuit between a prior art heat exchange system and a heat exchange system according to the invention.

[0013] For clarity, identical or similar elements are identified by the same reference symbols throughout the figures. DETAILED DESCRIPTION OF AN IMPLEMENTATION METHOD

[0014] With reference to figure 1, we will describe a first embodiment of a heat exchange system 10 according to the invention.

[0015] The heat exchange system 10 according to the invention comprises, in a direction of flow within the heat exchange system 10 according to the invention, a heat exchanger 3, a connecting component 21, an ejector 2 and an outlet diffuser 22. The connecting component 21 allows the heat exchanger 3 to be fluidly connected with the ejector 2. In one embodiment, the connecting component 21 has a convergent shape, its cross-section decreasing in the direction of a flow circulating within the heat exchange system 10 according to the invention.

[0016] The heat exchanger 3 includes a collection zone 120 for a secondary flow Fs and, downstream, a heat exchange volume 35. An outlet of the heat exchange volume 35 is fluidically connected to the connecting component 21. Within the heat exchange volume 35, the heat exchanger 3 includes a hot flow circuit 32. The hot flow circuit 32 has an inlet port 31 for a hot flow to be cooled F1 and an outlet port 33 for a cooled hot flow F2. The hot flow circuit 32, shown here, includes a tube. Other embodiments of the hot flow circuit 32 are possible. For example, the hot flow circuit is a plate heat exchanger.

[0017] The collection zone 120 can be in the form of a pavilion open upstream to optimally collect the secondary flow Fs, as illustrated in Figure 5. This upstream open pavilion shape aims to supply the heat exchanger 3 as uniformly as possible. In this Figure 5, flow lines of the secondary flow Fs collected by the collection zone 120 are shown, then circulating around the heat exchanger tube 32 within the heat exchanger volume 35 of the heat exchanger 3. The flow lines of the secondary flow Fs flow uniformly over the entire heat exchanger tube 32, thus ensuring optimal heat exchange between the cold fluid formed by the secondary flow Fs and the hot flow to be cooled F1 circulating within the heat exchanger tube 32.

[0018] The ejector 2 has a known structure and is here of the jet-trigger type. The ejector 2 includes an acceleration duct 25 fluidically connected at its inlet to the connecting component 21 so as to receive an outgoing flow from the heat exchanger 3. Within the acceleration duct 25, the ejector 2 includes a Venturi nozzle, here formed by a convergent-divergent duct 24 fed by a supply pipe 23. The supply pipe 23 allows a primary flow Fp to circulate. The primary flow Fp, through the convergent-divergent duct 24, will drive and accelerate the outgoing flow from the heat exchanger 3 by the Venturi effect. To this end, the convergent-divergent duct 24 has a first decreasing section, in the direction of a primary flow Fp circulating in the supply pipe 23, followed by a second increasing section.This shape accelerates the primary flow, creating a low-pressure area at the outlet of the convergent-divergent duct 24. This low pressure draws in the heated cold flow exiting the heat exchanger 3. The heated cold flow from the heat exchanger 3 then mixes with the primary flow in the acceleration duct 25, forming a mixing zone. The resulting flow in this acceleration duct 25 has high velocities and low pressure. Alternatively, the Venturi nozzle is a convergent duct; the abrupt change in cross-section at the outlet of the convergent duct, which transitions to a cross-section of the acceleration duct 25, creates the aforementioned low pressure.

[0019] At the outlet of ejector 2, a mixed flow (a mixture of the primary flow Fp and the flow exiting the heat exchanger 3) is ejected through the outlet diffuser 22. The outlet diffuser 22 is, in this case, a diverging nozzle, its cross-section increasing in the direction of the flow circulating in the heat exchange system 10 according to the invention. The outlet diffuser 22 slows down the resulting flow from the acceleration duct 25.

[0020] With reference to Figure 2, we will describe a turbomachine 1 according to the invention comprising a heat exchange system 10 according to the invention.

[0021] The turbomachine 1 comprises, in a manner known per se, in the direction of gas flow, an inlet 40 generally including a compression zone comprising, as illustrated here, a first decompressor stage 11, referred to as the low-pressure stage, followed by a second compressor stage 12, referred to as the high-pressure stage. At the outlet of the compression zone, the turbomachine 1 according to the invention includes a combustion chamber 15 supplied with fuel C. The combustion gases from the combustion chamber are at a high temperature and enter, as illustrated here, a first turbine 13, referred to as the high-pressure turbine, then a second turbine 14, referred to as the low-pressure or free turbine, depending on the architecture of the turbomachine 1. Finally, the turbomachine 1 according to the invention includes a combustion gas exhaust zone 41. Mechanical power 42 is recovered at the outlet of the second turbine 14.The heat exchange system 10 according to the invention is positioned here at an external periphery of the compression zone, the combustion chamber and the first 13 and second 14 turbines, in order to reduce the fluidic connection devices between these elements of the turbomachine 1 according to the invention and the heat exchange system 10 according to the invention.

[0022] The primary flow supply pipe 23 Fp is fluidically connected between the first 11 and second 12 compressor stages in the compression zone. This allows compressed air to be drawn downstream of the first compressor stage 11, forming the primary flow Fp.

[0023] The inlet port 31 of a hot stream to be cooled F1 is fluidically connected upstream of the combustion chamber 15 and downstream of the compression zone, in particular of the second compressor stage 12. The outlet port 33 of a cooled hot stream F2 is, in turn, connected here to a cooling circuit of the first turbine 13. Alternatively, the outlet port 33 is also connected to a cooling circuit of the second turbine 14. It should be noted that any other component of the turbomachine 1 according to the invention can be cooled in this way by being connected, for this purpose, to the outlet port 33.

[0024] Now we will briefly describe a second embodiment of a heat exchange system 100 according to the invention, with reference to Figures 3 and 4.

[0025] The heat exchange system 100 according to the invention differs from the heat exchange system 10 according to the invention previously described by the fact that the supply pipe 23 of a primary flow Fp passes through the heat exchanger 35 before feeding the Venturi nozzle 24 positioned within the acceleration duct 25 of the ejector 2. Here, the supply pipe 23 is coaxial with the heat exchanger 3. It enters the exchange volume 35 through the collection zone 120, then passes through the linking component 21 downstream of which the Venturi nozzle 24 is positioned.

[0026] Within the exchange volume 35, the exchange tubing 32 is arranged in a spiral, the turns of the exchange tubing 32 surrounding the supply tubing 23, between the inlet ports 32 and outlet ports 33.

[0027] It follows from the above that the implementation of a heat exchange system 10, 100 according to the invention within a turbomachine 1 presents many advantages.

[0028] One initial advantage is a lower cold stream temperature. With a prior art heat exchange system, the cold flow supplied to the heat exchanger is a mixture of compressed air (primary flow) and ambient air (secondary flow). Since the temperature of the compressed air is necessarily higher than that of the ambient air (a thermodynamic process), the temperature of the mixture between the primary flow (compressed air) and the secondary flow (ambient air) is also higher than that of the ambient air. Consequently, the cold fluid used in the heat exchanger will have a lower heat exchange capacity with the hot flow to be cooled than ambient air would. Indeed, the heat transfer between a hot source and a cold source is determined, to a first approximation, by their temperature difference. The temperature of the mixture can be estimated by averaging the enthalpies of the primary and secondary flows.With a heat exchange system 10,100 according to the invention, the cold fluid supplied to the heat exchanger consists exclusively of ambient air. The temperature difference with the hot source is therefore greater. This results in an increase in the heat exchangeable power, and thus greater cooling of the hot flow.

[0029] A second advantage is improved distribution of the cold fluid at the heat exchanger inlet. The Mach number at the ejector outlet is estimated to be between approximately 0.4 and 0.8, depending on the heat exchange system's dimensions, under typical operating conditions. Therefore, a diffuser must be inserted between the ejector outlet and the heat exchanger. Furthermore, a typical prior art heat exchange system design involves a sharp turn of approximately 90 degrees between the ejector diffuser outlet and the cold fluid inlet to the heat exchanger. These two factors result in a heterogeneous distribution of the cold fluid at the heat exchanger inlet. A direct correlation has been observed between the cold fluid distribution and heat exchange. Areas with high cold fluid flow exhibit high heat transfer coefficients.Conversely, areas with insufficient cold fluid exhibit low heat transfer coefficients. This heterogeneity in heat exchange within the heat exchanger necessarily results in a low-efficiency heat exchange system, as heat transfer is ensured by only a limited portion of the heat exchange tube surfaces. With the heat exchange system 10,100 according to the invention, the distribution of the cold fluid on the heat exchange tube is optimal. Indeed, the cold fluid is positioned immediately downstream of a collection zone, here a pavilion allowing for ambient air intake (secondary flow), which enables a low Mach and homogeneous supply. Under these conditions, the heat exchange tube 32 is supplied with cold fluid uniformly, as illustrated in Figure 5.Figure 6 compares the pressure losses obtained with a prior art heat exchanger (curve C1) and those obtained with a 10,100 heat exchanger according to the invention (curve C2). Figure 7 compares the heat transfer distribution obtained with a prior art heat exchanger (a) and that obtained with a 10,100 heat exchanger according to the invention (b)). The heat transfer is better distributed with the 10,100 heat exchanger according to the invention, leading to improved efficiency of the heat exchanger.

[0030] A third advantage is a reduction in pressure losses in the cold stream. The lower Mach number, the absence of a diffuser, and the 90-degree bend upstream of the heat exchanger inlet also contribute to reducing pressure losses in the cold stream of the heat exchange system. Aerodynamic calculations have shown that this reduction can reach a factor of 10, as illustrated in Figure 6. This is a significant advantage for the 10,100 heat exchange system according to the invention. Indeed, the reduction in pressure losses allows for a decrease in the need for primary flow extraction to drive the secondary flow through the ejector (less work expended to compress the fluid to a lower pressure).

[0031] A fourth advantage is an extended thermomechanical fatigue life of the heat exchange system. Prior art heat exchange systems result in heterogeneous heat transfer within the heat exchanger. This leads to significantly higher temperature gradients in the structural parts of the heat exchange system (e.g., the heat exchange tube) than those obtained with a heat exchange system according to the invention. The latter reduces the thermal gradients within the heat exchanger and therefore the resulting thermomechanical stresses.

[0032] A fifth advantage is improved compactness of the architecture. The heat exchange system 10, 100 according to the invention draws in and reintroduces the various flows (primary, hot to be cooled, and hot cooled) in an order naturally adapted to the sequence of components constituting the turbomachine 1. This is illustrated in Figure 2. The draw-in and reintroduce circuits do not intersect and therefore have a minimal impact on mass and size. In contrast, the prior art heat exchange system requires longer circuits with crossings, and thus has a more detrimental impact on mass and size.

[0033] A sixth advantage is an improvement in the reliability of the turbomachine 1 when equipped with a heat exchange system 10,100 according to the invention. Due to the compactness of the heat exchange system 10,100 according to the invention and its axial location on the turbomachine 1, it is possible to eliminate the long hot-flow supply lines of the prior art heat exchange system. These long lines are subject to high vibration levels and are therefore prone to failures such as rupture. The consequence of a hot-flow pipe rupture in the heat exchange system is the loss of cooling to hot parts of the turbomachine 1. The use of the heat exchange system 10,100 according to the invention thus eliminates this failure scenario by using short supply lines.

[0034] Naturally, the invention described above is by way of example. It is understood that a person skilled in the art is capable of carrying out different embodiments of the invention without departing from its scope.

[0035] It is emphasized that all features, as they are apparent to a person skilled in the art from the present description, drawings and attached claims, even if in practice they have only been described in relation to other specific features, both individually and in any combinations, may be combined with other features or groups of features disclosed herein, provided that this has not been expressly excluded or that technical circumstances render such combinations impossible or meaningless.

Claims

DEMANDS 1. Heat exchange system (10, 100) of a component (13, 14) to be cooled of an aircraft turbomachine (1) comprising a compression zone (11, 12), the heat exchange system comprising a collection zone (120) for a secondary flow (Fs) of cold air taken from outside or upstream of the turbomachine, a heat exchanger (3) comprising a heat exchange circuit (32) with a flow circulating in the heat exchange system and within which a hot flow (F1) to be cooled taken from the compression zone is intended to circulate, and an ejector (2) comprising an inlet (21) for the secondary flow, wherein, in the direction of a flow circulating in the heat exchange system, the heat exchanger is positioned upstream of the ejector inlet and downstream of the collection zone, so that, during operation, heat exchange is established between the secondary flow and the exchange tubing.

2. Heat exchange system according to claim 1, wherein the secondary flow inlet of the ejector comprises a linking component (21) of convergent shape in the direction of a flow circulating in the heat exchange system.

3. Heat exchange system according to any one of claims 1 to 2, wherein the ejector comprises an outlet diffuser (22) including a channel diverging in the direction of a flow circulating in the heat exchange system.

4. Heat exchange system according to any one of claims 1 to 3, wherein the ejector comprises a supply tube (23) of a primary flow (Fp) taken from the compression zone and a conduit (24) which is convergent-divergent and fluidically connected to the supply tube.

5. Heat exchange system according to claim 4, wherein the conduit (24) is convergent in the direction of a primary flow circulating in the supply pipe.

6. Heat exchange system according to any one of claims 4 to 5, wherein the supply pipe passes through the heat exchanger.

7. Heat exchange system according to any one of claims 1 to 6, wherein the exchange circuit is spiraled between an inlet port (31) and an outlet port (33).

8. Heat exchange system according to claims 6 and 7, in which the exchange circuit is provided around the supply pipe.

9. Heat exchange system according to any one of claims 1 to 8, wherein the collection zone is a pavilion open upstream of a flow circulating in the heat exchange system.

10. Turbomachine (1), in particular for aircraft, comprising at least one heat exchange system according to any one of claims 1 to 9.

11. Turbomachine according to claim 10, wherein the turbomachine comprises a compression zone (11,12), a combustion chamber (15) downstream of the compression zone and a component (13,14) comprising a cooling circuit, the ejector being fluidly connected to the compression zone and the heat exchanger being fluidly connected at the inlet downstream of the compression zone and upstream of the combustion chamber, and at the outlet to the cooling circuit.

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