Patent Grant
8408864
The invention relates to the general field of ventilating a turbine section of a turbomachine. The invention relates more particularly to a device for regulating the flow rate of air for feeding to a turbine ventilation cavity in a turbine section of an aviation turbomachine.
In the present description, the term “ventilating” is used in respect of a turbine section to cover both a function of cooling the various vanes and/or blades of the turbine section, and a purging function to prevent hot air in the primary flow passage through the turbine from being reintroduced elsewhere.
When an aviation turbomachine is operating at high speed (typically at full throttle), the temperatures of the gases flowing in the primary flow passage of the turbomachine reach values that cannot be withstood without damage by the parts situated outside said passage, in particular parts situated around the turbine section(s) of the turbomachine (low pressure turbine and/or high pressure turbine). It is thus essential to prevent the gas stream that is flowing in the primary flow passage from penetrating outside that passage when the turbomachine is operating at high speeds.
For this purpose, it is known to feed compressed air to a cavity (referred to herein as the turbine ventilation cavity) that is formed around the outer casing of the turbine and that communicates with the flow passage for the gas stream through the turbine section(s), the compressed air being fed via a circuit comprising a series of orifices and bushings. Since the air in the turbine ventilation cavity is taken from a compressor state of the turbomachine, the turbine ventilation cavity is at a pressure that is higher than that existing in the flow passage for the gas stream through the turbine. As a result, the compressed air penetrating into the flow passage via the air insertion orifices serves to keep the gas stream that is flowing through the turbine sections confined inside the flow passage. The turbine is then said to be properly purged. The compressed air present in the turbine ventilation cavity is also used for cooling certain parts of the turbine, such as for example the first nozzle of the low pressure turbine (for a turbomachine of two-spool architecture).
The air in the turbine ventilation cavity is generally conveyed by tubular ducts connecting the turbine ventilation cavity to a take-off cavity that communicates with the flow passage for the stream of air passing through the compressor of the turbomachine. Diaphragms may be located inside these ducts in order to calibrate the flow rate of the air that is taken off. A check valve may also be located inside each duct at its end leading into the turbine ventilation cavity. In the event of the duct accidentally breaking and the pressure inside it dropping, the check valve prevents the gas stream flowing in the primary passage of the turbine from escaping therefrom. Reference can be made to document EP 1 312 763 that describes an embodiment of a check valve.
Nevertheless, taking compressed air to deliver it to the turbine ventilation cavity via ducts provided with flow rate calibration diaphragms as described above, does not enable the flow rate of the air that is taken off to be regulated as a function of the operating speed of the turbomachine. Since the diaphragms disposed in the ducts are of constant flow section, the air take-off flow rate is substantially constant for the various operating speeds when expressed as a percentage of the flow rate of air flowing in the primary passage of the compressor. It is thus common practice for the diaphragms to be dimensioned so as to enable air to be taken off at a flow rate that is sufficient to ventilate turbines (i.e. purge them and cool parts thereof) when the turbine is operating at high speed (such as full throttle). In flight at a lower speed of operation, where temperature levels in the turbomachine are not so high (such as when cruising), a smaller air flow rate would be sufficient for ventilating the turbines, so as a result too much air is taken off during such speeds of operation. Unfortunately, the air that is taken from the compressor and reintroduced further downstream into the turbine at a location where the pressure level is lower does less work in the turbine than it would have done if it had not been taken off. This has the consequence of penalizing fuel consumption. In order to optimize fuel consumption, it is therefore desirable to minimize air take-off from the compressor at each of the operating points of the turbomachine.
A main object of the present invention is to mitigate such drawbacks by proposing to regulate the flow rate of air for feeding to the turbine ventilation cavity as a function of the operating point of the turbomachine.
This object is achieved by a device for regulating the flow rate of air feeding a turbine ventilation cavity of a turbomachine turbine section, the device comprising:
at least one tubular duct opening out at one end into a take-off cavity communicating with a flow passage for a stream of air in a compression section of the turbomachine and leading at an opposite end into a turbine ventilation cavity that communicates with a flow passage for a gas stream in a turbine section of the turbomachine, the pressure inside the take-off cavity being higher than the pressure inside the turbine ventilation cavity;
a flow rate regulation valve disposed in the tubular duct, suitable for moving under the effect of the pressure difference between the take-off cavity and the turbine ventilation cavity between a maximum closure position for the duct in which some minimum air flow rate passes through the valve and a minimum closure position for the duct in which a maximum air flow rate passes through the valve; and
mechanical return means for holding the valve in its maximum closure position for the duct so long as the pressure difference between the take-off cavity and the turbine ventilation cavity remains below a predetermined threshold pressure.
The mechanical return means of the device of the invention and the predetermined threshold pressure are advantageously dimensioned so as to obtain:
When the threshold pressure is predetermined to be set at cruising speed, the valve remains in its maximum closure position for the duct up to cruising speed, and at higher speeds the closure of the duct becomes smaller with minimum closure being obtained for the duct at full throttle. Closure between cruising and full-throttle speeds can thus take place progressively or else almost instantaneously between the maximum and minimum closure positions.
Thus, while flying at cruising speed, a minimum flow rate of air passes through the valve and feeds the turbine ventilation cavity, this minimum flow rate being calibrated to provide sufficient purging and where appropriate sufficient cooling of the turbine vanes when the turbomachine is operating at such speeds. Likewise, while flying at full throttle, a maximum flow rate of air passes through the valve and feeds the turbine ventilation cavity, this maximum flow rate being calibrated to ensure effective purging and cooling of the turbine vanes at such operating speeds of the turbine. Nevertheless, the threshold pressure may be set for a speed of operation other than cruising speed. In particular, it may be zero, which means that the amount of closure for the duct begins to be reduced as soon as the turbomachine starts.
As a result, the device of the invention serves to regulate the flow rate of air for providing ventilation of a turbine section as a function of the operating point of the turbomachine. This results in optimized take-off of air from the compressor. For a given thrust level, fuel consumption can be reduced compared with a prior art take-off device. More precisely, for a two-spool bypass turbomachine, the savings in terms of specific consumption are estimated at around 0.3%.
The device of the invention also presents the advantage of being of simple and reliable design, of not requiring any particular power supply circuit, and above all of presenting very low weight.
In an advantageous disposition, the device further includes means for completely closing the duct when the pressure inside the duct becomes significantly lower than the pressure inside turbine ventilation cavity. Such means make it possible, in the event of the duct being accidentally broken, to prevent the gas stream flowing in the primary flow section of the turbine escaping therefrom.
The flow rate regulation valve may present the form of a disk centered on the longitudinal axis of the duct, the valve being made up of two half-disks with their diameters pivotally mounted on a rigid shaft that is secured to the duct and that extends transversely across the duct, the half-disks being suitable for deploying into a plane extending substantially transversely across the duct when the valve is in its maximum closure position for the duct and of retracting into a substantially longitudinal plane of the duct when the valve is in its minimum closure position for the duct.
In an embodiment, each half-disk is connected to one end of a return spring having its opposite end secured to the duct, the springs being tensioned so as to keep the half-disks deployed so long as the pressure difference between the take-off cavity and the turbine ventilation cavity remains below a predetermined threshold pressure.
In another embodiment, the half-disks are made of an elastic material and they are suitable for deforming elastically under the effect of a pressure difference between the take-off cavity and the turbine ventilation cavity, and for returning to their initial state when the pressure difference returns to zero.
The device may further include a ring mounted at the end of the duct that leads into the turbine ventilation cavity, the ring including at least one abutment that comes to bear axially against at least one of the two half-disks when the flow regulation valve is in its maximum closure position for the duct, said abutment being suitable for deforming under the effect of pressure inside the turbine ventilation cavity being higher than the pressure inside the duct, so that the flow rate regulation valve comes into axial abutment against the ring so as to close the duct completely.
Preferably, the duct does not have a diaphragm for calibrating the rate of flow inside the duct. The device of the invention serves to take the place of a flow rate calibration diaphragm as known in the prior art.
Also preferably, the duct does not have a check valve. The device of the invention can also take the place of a check valve as known in the prior art.
The invention also provides a turbomachine including a device as defined above.
Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawings that show embodiments having no limiting character. In the figures:
Naturally, the invention applies more generally to any air take-off device made by means of tubes and presenting pressure differences between the air take-off zone and the air re-insertion zone.
The device of the invention comprises a plurality of tubular ducts 12 (only one is shown in
The take-off cavity 14 is an annular cavity formed around the outer shroud 18 of the high stream compressor 20 of the turbomachine. An inner shroud 22 disposed concentrically inside the outer shroud co-operates therewith to define a flow passage 24 for a stream of air passing through the high pressure compressor. The take-off cavity 14 communicates with this flow passage 24 via a plurality of air take-off orifices 26 (or via a slot) formed through the outer shroud 18 of the compressor.
By way of example, the air taken off by the orifices 26 comes from the fourth stage of the high pressure compressor. The pressure P1 that exists inside the take-off cavity 14 is a function of the operating speed of the turbomachine: it may thus lie in the range 4 bars at cruising speed and 12 bars at full throttle.
The turbine ventilation cavity 16 is likewise an annular cavity that is formed around an outer casing 28 of the high pressure turbine 30 of the turbomachine. The high pressure turbine is made up in particular of a plurality of moving blades 32 disposed upstream from a plurality of stationary vanes 34 forming a nozzle. The moving blades and the stationary vanes are disposed in a flow passage 36 for a stream of gas passing through the turbine.
The air inside the turbine ventilation cavity 16 is at a pressure P2 lower than the pressure P1 inside the take-off cavity 14. By way of example, the pressure P2 may vary over the range 2 bars at cruising speed to 6 bars at full throttle.
Given this pressure differential, air present inside the turbine ventilation cavity 16 passes through each stationary vane 34 of the high pressure turbine by passing through bushings 38 mounted therein. This air fraction contributes to cooling the stationary vanes 34 prior to being injected into the passage 36 (arrows 40). Some of the remaining air that is exhausted from the stationary vanes via their roots penetrates into the passage 36 via clearance 41 that exists between the bottom platforms of the fixed vanes and the moving blades (arrow 42) in order to “purge” the high pressure turbine.
Furthermore, a flow rate regulation valve 100 is located inside at least one of the tubular ducts 12. Under the effect of the pressure difference between the take-off cavity 14 and the turbine ventilation cavity 16, the valve is suitable for moving between a maximum closure position for the duct in which a minimum rate of air flow passes the valve (
In the embodiment shown in
Depending on the pressure difference between the take-off cavity and the turbine ventilation cavity, the half-disks 102 are suitable for deploying in a plane extending substantially transversely relative to the duct 12 when the valve is in its maximum closure position for the duct (
When the half-disks 102 are deployed (
Having a non-zero, residual flow section even when the flow rate regulation valve is in its maximum closure position presents at least two advantages. In the event of one or more of the valves jamming and remaining blocked in the maximum closure position, the residual flow section still allows some minimum flow rate of air to pass and thus provide some minimum level of ventilation (purging and cooling) for turbines at full throttle. Furthermore, in the event of the pressure difference between the take-off cavity and the turbine ventilation cavity reaching the threshold from which the valve begins to tilt, only above cruising speed (speed for which the closure thus remains at its maximum), the residual flow section allows some minimum flow rate of air to pass at cruising speed so as to ventilate the turbine.
Mechanical return means are also provided to hold the valve 100 in its maximum closure position for the duct so long as the pressure difference between the take-off cavity and the turbine ventilation cavity remains below a predetermined pressure threshold PS.
Thus, in the embodiment of
The pressure chosen for the threshold pressure PS is associated with the pressures that exist inside the take-off and turbine ventilation cavities at various operating points of the turbomachine, and in particular at cruising speed and at full throttle.
Changeover from the maximum closure position to the minimum closure position may occur almost instantaneously when the pressure difference between the take-off cavity and the turbine ventilation cavity reaches the threshold pressure PS. Alternatively, this changeover from one extreme position to the other may take place progressively when the pressure difference between the take-off cavity and the turbine ventilation cavity reaches and then exceeds the threshold pressure PS.
For almost instantaneous changeover from the maximum closure position to the minimum closure position, the threshold pressure PS is selected to lie in the range 2 bars to 6 bars (using the above-mentioned numerical examples for the pressures P1 and P2).
By selecting a value that is less than or equal to 2 bars for PS (difference P1−P2 equal to 2 bars for cruising speed), the valve will be in its minimum closure position for the duct once cruising speed is reached, which is not the intended object since there would then be a constant flow section from cruising speed up to full throttle. In contrast, by selecting a value lying in the range 2 bars to 6 bars for PS, the valve will be in its maximum closure position for the duct at cruising speed and in its minimum closure position for the duct at full throttle (difference P1−P2 equal to 6 bars for full throttle). The maximum closure position for the duct at cruising speed makes it possible to reduce the air flow rate and optimize fuel consumption.
When changeover from the maximum closure position to the minimum closure position is progressive, the threshold pressure PS may be selected to lie in the range 0 bars and a value that is less than 6 bars (using the same above-mentioned numerical examples for the pressures P1 and P2). Under such circumstances, the valve may return to its minimum closure position for the duct at full throttle (where the difference P1−P2 is equal to 6 bars).
As a result, at cruising speed, the valve may still be in the maximum closure position for the duct (if the threshold pressure PS lies in the range 2 bars to 6 bars) or it may be in a position intermediate between the maximum closure position and the minimum closure position (if the threshold pressure PS lies in the range 0 to 2 bars).
In both variant embodiments (changeover from one extreme position to the other being almost instantaneous or else being progressive), the diameter D1 of the valve that calibrates the minimum air flow rate feeding the turbine ventilation cavity is selected as a function of the threshold pressure PS so as to convey air at a flow rate sufficient for purging the turbines, and if necessary for cooling them, at all operating points, even in the event of a breakdown (e.g. in the event of a valve breaking down and remaining jammed in its maximum closure position for the duct or in the event of an engine breakdown that affects the turbine ventilation flow rate levels).
Furthermore, the mechanical return means enabling the valve to be held in its maximum closure position for the duct may be of some other kind. For example, in a variant embodiment (not shown in the figures), the half-disks could be made of an elastic material capable of deforming under pressure and returning to its initial shape when the pressure difference between the take-off cavity and the turbine ventilation cavity returns to zero (the half-disks thus being subjected to elastic deformation). In another variant embodiment (not shown), the half-disks could be held in the deployed position by means of hinges made of an elastic material or else by using elastic damper type elements (instead of the springs of the embodiment shown).
Furthermore, with the air flow regulation device of the invention, the ducts advantageously do not have a flow rate calibration diaphragm of the kind known in the prior art.
With reference to
In this variant, the valve 100 also acts as a check valve. The valve is located at the downstream end of the duct leading into the turbine ventilation cavity and it is provided with means for closing the duct 12 completely when the pressure P3 inside the duct becomes sufficiently small relative to the pressure P2 inside the turbine ventilation cavity.
More precisely, a ring 108 is mounted at the downstream end of the duct that leads into the turbine ventilation cavity. This ring includes two axial abutments 110, each abutment coming to bear axially against one of the two half-disks 102 when the flow rate regulation valve is in its maximum closure position for the duct (
Furthermore, the abutments 110 act as fuses: when the pressure P2 inside the turbine ventilation cavity becomes greater than the pressure P3 inside the duct 12 by a sufficient amount, the half-disks 102 of the valve deform the abutments, which buckle under this mechanical force so that the half-disks come into axial abutment against the ring, thereby completely closing the duct 12 (
In the event of the duct 12 being accidentally broken (represented by a hole 112 in
The use of a valve as described with reference to this embodiment makes it possible to avoid having recourse to a check valve of the kind known in the prior art.
It should be observed that the number, the shape, the stiffness, and the locations of the axial abutments of the device in this embodiment may vary depending on application conditions.
More generally, the shape of the valve of the air flow regulation device of the invention may differ from that described with reference to the embodiments of
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| 08 57642 | Nov 2008 | FR | national |
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