IMPROVED COUNTER-ROTATING TURBOFAN

Description

The turbofan, often referred to by the English term 'turbofan', is a propulsion system based on a gas turbine, often referred to by the English term 'gas turbine', which drives a ducted fan that accelerates a flow of air that provides the propulsive action together with the combusted gases. A turbofan typically comprises a fan section, or propeller, consisting of one or more impellers with corresponding straightening blades, and a gas generator, which includes a compressor section, a combustor section, and a turbine section. Using a multi-stage fan allows for optimizing the aerodynamic efficiency of the stages or achieving thrust conditions sufficient for supersonic flight without the use of a postburner, a process known as supercruise. Figure 1 shows a typical cross-section of a high-bypass counter-rotating turbofan. Air enters the turbofan at section A and splits into two flows B and C. Flow B, also called the cold flow, is compressed by two axial impellers 1 and 8, and then expanded by an array of outlet guide vanes 15, sometimes called outlet guide vanes (GV), increasing the outlet velocity of the air at section d to generate thrust. Flow C, also called the hot flow, is first compressed by the fan impellers and conveyed into a compressor 21, followed by a combustion chamber 26 where the air is mixed with the fuel and ignited to generate a high-energy burnt gas flow.The gas flow expands through the high-pressure axial turbine section 27 which drives the high-pressure compressor and a low-pressure axial turbine section 12 which drives the fan impellers via a gearbox. The flow downstream of the low-pressure turbine expands into nozzle 29 with exhaust temperatures in the range of 50°C - 60°C. Other turbofans are generally characterized by a parameter called the by-pass ratio, often referred to as the English term by-pass. Tucix - counter-rotating bladed fan Ciavant-ors ; S. Sail .otti i ratio, or the ratio between the cold flow and the flow processed by the gas generator. In modern turbofans there is a tendency to adopt high bylution ratios, for example greater than 6, to obtain low specific fuel consumption. A high-bypass turbofan is characterized by a fan 1 that is much larger than the compressor 4 of the gas generator, since the volumetric flow rate of a turbomachine is proportional to the square of the diameter of the rotating parts. This also requires a different rotation speed between the fan and the gas generator, since the rotation speed of a turbomachine tends to be inversely proportional to its diameter. The turbofan configuration shown in Fig. 1, also known as a "twin-shaft" configuration, allows the fan to operate at a lower speed than the compressor, with the two axial turbine sections mounted on separate shafts. Typically for a large fan operating at 4000 rotations per minute (indicated by J / acronym) driven by the low pressure turbine keyed to the same shaft, the corresponding gas generator operates at rotational speeds above 12000 RPM or with a ratio of approximately 4. In general the size of the low pressure turbine is much larger than the high pressure turbine even though it processes the same flow rate of combustion gases. An excessive difference in speed, and therefore in diameter, between the low-pressure turbine and the high-pressure turbine has negative effects on the weight of the engine, its fluid dynamics and in general on propulsive efficiency. To overcome this problem, for example when the dilution ratio is greater than 10, a gear reducer is introduced between the gas generator and the fan as shown in Rolls-Royce patents EP 3 730 768 A1 and US2O21OO17S11A1. This solution has obvious disadvantages in terms of weight, cost, and reliability, which does not limit its use to medium-large sized engines. DNA alternative solution, which does not currently find practical application in the public domain, is shown in the patent US2014 / 054733 of United Technologies Corporation (Prati and Whitney} relating to a TccOoventijia a palettat iia controrocarm;; ah.<pÀorava s lisvéntniv: G.Merlotti ì turboventola controxotante a ciclo rigenerativo. in questo brevetto la turbina assiale di bassa pressione atìona direttamente la ventola con la palettatura della turbina calettata su un anello sostenuto meccanìoaifiente dalle pale della ventola. Questa soluzione ha lo svantaggio di. aumentare notevolmente la sezione frontale del motore, che non é limitata dal diametro della ventola ma si estende per contenere anche le turbine assiali e i relativi condotti disposti radialmente esterni alla ventola, inoltre la soluzione ha evidenti limiti per quanto attiene il progetto meccanico e fluidodi.namico della palettatura del propulsore. le pale della ventola infatti sono soggette alla forza centrifuga dei componenti ad esse collegate, in questo caso le pale turbina e del relativo supporto.This force is combined with the centrifugal force generated by the mass of the fan blade, limiting its peripheral speed with negative effects on the performance of the impellers. It should also be noted that the blades of these turbines must comply not only with the same rotation speed as the impeller, a constraint which is also present in gearbox-less turbines, but also with a geometric constraint on the minimum diameter of the blades, which generally negatively influences the appearance of the turbine blade profiles and therefore the fluid dynamics, for example. Given the limitations described above, the need for systems and methods to develop high-bypass ratio turbofans with a simple architecture and high efficiency is highlighted. It is known that a simple mechanical architecture, i.e., with a minimal number of components, can lead to savings in weight, cost, and greater reliability. Summary of the invention The subject of the present invention is a centring turbofan with an architecture that allows for the efficient realization of a high bylution ratio, for example greater than 12, without the use of a fan and with the turbine stages having diameters generally smaller than those of the fan impellers, thus avoiding the aforementioned limitations of the prior art. The invention also aims to increase the thermodynamic efficiency of the turbofan by means of an inter-refrigerated regenerative cycle and direct regulation systems mounted therein without compromising either the cross-section turtoventela ό costraroustg yesimproved < Xcszustar?:: frontal nor the aspects of simplicity and lightness that an aircraft engine must have. The present invention provides a gas generator with the turbine exhaust conveyed perpendicularly to the axis of rotation and fluidly connected to a counter-rotating multi-stage centrifugal radial turbine which directly drives, via a shaft, the two impellers of the fan with an interposed array of poles which, appropriately directed via an actuation system, vary the power of the engine and the consumption, as a function of the thrust requirements and the external temperature, or of the peripheral Mach number of the blades.The use of a series of variable pitch stator blades downstream of the first impeller allows for a recovery of static pressure, a variation in the distribution of power between the two impellers of the fan, both of which benefit greater efficiency, and an improvement in the pumping margin, or the ability to reach high altitudes, without resorting to complicated and cumbersome systems for varying the angle of the stator blades, the design of which is strongly influenced by the high centrifugal stresses induced by their rotation, or to XGV (inlet guide vanes) which introduce significant fluid dynamic losses. The use of a radial turbine, rather than the axial type commonly used in the prior art, allows us to overcome the problem of a sudden increase in the height of the gas channel present when turbines have two sets of axial blades that process the same flow but with very different rotational speeds. From simple geometric considerations it can be demonstrated that, with the same average peripheral speed of the blades, the radial turbine has a smaller radial footprint of the gas flow, or rather the flow that allows the flow entering and exiting the blades, than the channel associated with an axial turbine with the same volumetric flow rate.The use of the radial turbine with a rotating shaft makes it possible to efficiently couple a fast gas generator, for example with a speed of 100,000 rotations per minute, with a slow fan, for example 14,000 rotations per minute, or with a reduction ratio of approximately ; without interposing a complex system of gears and without adding the extra weight of the blade, fans which can thus reach optimal mechanical speeds, for example 400 m / s, without introducing excessive stresses in the blades and their supports. Bladed wind turbine c&ntrwrot&nte rflaltcrata (Inver: tors: ·::·;. Mar lot-.ij The counter-rotating centrifugal radial turbine consists of two sets of suitably shaped blades rotating in opposite directions with respect to a crown axis. The blades are supported by mechanically connected rings falling at the end of the profile and cp.i««5t:.xa which are in turn joined by a disk keyed to the same shaft that supports the fan impeller. In the counter-rotating turbine, the enthalpy drop occurs without the use of sets of stationary blades, therefore, for the same enthalpy drop and rotation speed, smaller radial dimensions are achieved compared to a unidirectional centrifugal radial turbine which requires stator stages. Advantageously, the use of a counter-rotating fan, characterized by an almost axial flow at the exit of the second impeller, allows for the assembly of stator blades with regenerative exchangers characterized by faces parallel to the axis of rotation, i.e. prismatic, which are simpler to construct than an exchanger shaped according to a curved profile necessary to straighten a strongly tangential flow such as that coming from non-counter-rotating impellers. The regenerators allow for the transfer of a portion of the heat from the combusted gases to the flow of compressed air coming from the last impeller of the gas generator compressor before it enters the combustion chamber. Advantageously, the last impeller of the compressor is mounted antipodal to the turbine exhaust in order to obtain countercurrent exchange and maximize the length of the regenerator exchangers, which are arranged circumferentially around the gas generator and limited in length by the distance between the impeller and the turbine exhaust. Advantageously, the annular fan channel has a radial footprint large enough to accommodate exchangers without any interpenetration. These exchangers, fed by low-volume dynamic air intakes, allow inter-cooled compression of the compressor without obstructing the cold flow channel. Thanks to the present invention, it is possible to obtain an improvement of 15-30% in specific consumption with an increase in weight 1 imitated compared to a solution according to the known art. Features and embodiments are described below and further detailed in the accompanying claims which form part of 'itrànvactesla a pai®stataira coj'.t.ror^tsnte Kiglierata iìsverstoré; ÌL Ksri&rri; of this specification. The above brief description identifies features of the various embodiments of the present invention so that the following detailed description may be better understood. The various embodiments of the invention are not limited in their application to the construction details and arrangements of components described in the following description and illustrated in the drawings. The invention may be embodied in other embodiments and may be practiced and implemented in various ways. Brief description of the Figures Further features and advantages of the invention will become more evident in light of the detailed description of preferred, but not exclusive, embodiments of an improved recuperative cycle turbofan - illustrated by way of example, and not by way of limitation, with the aid of the attached drawings in which: Fig. 1 illustrates a cross-sectional view of a two-stage, counter-rotating, high-bypass ratio turbofan according to the prior art, e.g., General Electric U.S. Patent 603,844. Fig. 2 illustrates a simplified meridian section of a counter-rotating bladed turbofan according to one embodiment of the subject matter described herein. The same drawing shows the geometric details of some components of the assembly, also derived from different views and section planes. Fig. 3 shows a section perpendicular to that shown in Fig. 2 with the detail of the transition zone between the turbine exhaust and the heat exchangers-generators. Fig. 4 illustrates the typical configuration of a centrifugal radial turbine stage. The same numbers and reference letters in the figures identify the same elements or components. Description. in di iors&& di resiizzezinne px®^®xxt;^ of the invention TuacnovsnAola a paletv-awsra eontrorocante »igi«orata {Inventors : S.nariottii passages for the auxiliary systems of the engine, some fluids (for example: oil and fuel} and electrical cables, The impeller 1 is connected with a removable mechanical coupling to the shaft 2 which is rotoidally mounted and coaxial to the shaft 6 on two rolling bearings, for example roller bearings 4. The shaft is on a turret and keyed with removable mechanical assembly. The impeller 8 is rotoidally supported by two rolling bearings 3, for example 3-point ball bearings at the front which act as a thrust bearing and cylindrical roller bearings on the turbine side, or oblique rollers, as in the figure, to be able to support radial and axial loads coming from the two shafts 2 and 6. Both shafts are connected axially with shims and a thrust bearing 5 which supports the mutual axial forces of the two shafts. These are mechanically connected to two discs 10 and which support the turbine stages 12 and 13, three stages per disc cantilevered from the bearings and designed in a similar configuration to that shown in Fig. 4, with the blade support rings connected to the turbine disc, Fig. 11, via a flange, The bearings 3, 4, 5 of the shafts 2 and 4 are isolated from the external environment with one or more chambers, not entirely shown in the figure, filled with air bled from the gas generator according to a known technique and conveyed through special channels passing through the blades 7. The bearings and the shafts are supported on a frame integrated with the support of the mobile arrays where the same blades 7 connect the conical supports 3 to the flange 36 where the attachment points, not shown, of the engine to the aircraft structure are made according to a known technique. The compressed air flow from the impeller 1 passes through the blade array 7 where the static pressure increases and is directed appropriately, for example with a total pressure of 1.2 Bar, lifts the impeller 8 which further increases the total pressure, for example 1.4 Bar. The air flow leaves the impeller 8 in an almost axial direction, i.e. with a reduced tangential component, and enters an annular section 38 delimited by the blades 15 and the walls 30 and 31 where it is heated by the heat released by the surfaces of the blades 15 up to the trailing edge of the blades 28 and accelerated up to the exit of the duct 29 at a speed of approximately 250 m / s. The walls of the blades 15 in short contact with the fan flow in the passage section 38 are made of material having good conductivity. Counter-rotating fan turbocharger (inventor: G.Mriotti) made of thermal material, for example aluminum, so as to cool and temporarily energize, or annihilate the temperature, the compressed air in the fan, increasing its thrust capacity compared to a fully expanded air in the nozzle 29. The nozzle 29 may optionally incorporate a cone 41 or a movable pin to vary the flow section, according to a known technique, only if the engine is used in supersonic applications with two fan stages having a high pressure ratio, for example greater than 1.8. The blades 15, numbered between 8 and 15, are profiled to receive the compressed air from the impeller S with a tangential component of the minimum velocity. This allows for the blade walls to have a predominantly rectilinear development and considerable length, for example comparable to that of a gas generator, i.e. corresponding to the center distance between the radial turbine and the last impeller of the compressor. The length of the blades allows for the housing, within them, of exchangers-regenerators 17 of considerable length, and therefore surface area, with low pressure drops. Furthermore, the heat exchange surface of the blades 15 is maximized, with obvious thermodynamic and structural benefits. The blades 15 house, near the leading edges, pipes or cables for the engine's auxiliary services. The exchangers 17, being mounted in straight prismatic blades, can be made simply and economically using 3D printing techniques or, preferably, using relief-machined plates arranged next to each other and brazed to form panels where the fluids alternate with countercurrent flow or with diffusion bonding techniques. The blades 1.5, and possibly the exchangers 17, help to strengthen the engine structure. The assembly formed by the blades 15, the walls 30 - 31 and everything connected to them is mechanically and fluidically connected to the ring 36, which supports the blades 7, by means of a crown of screws. Inside the delimited duct 38, a part of the compressed air from the fan is tapped, for example 10% by mass at 1.4 Bar, and conveyed through suitable openings 18, for example submerged NACA dynamic intakes, to a plenum 19 which feeds the impellers of the centrifugal compressor 21 through an array of mobile vanes ''IGV'' made, actuated and controlled according to a known technique. The delivery of the second stage of the compressor is mechanically connected and TsjrbovUritolfi -a pAUUituiu.vs: coutirorotSHt-Q ilKvcnuori-: G.^ricvrid.? fluidly to a heat exchanger 23 which cools the compressed air from the first two stages of the gas generator compressor. Colder air is drawn from the flow coming from the fan through special openings 24, for example submerged air intakes, which similarly re-introduce it into section 38 once it has heated up in the exchanger. The flow of cooling air is guaranteed by the dynamic pressure difference in the air intakes 24 or by special ducts, not visible in the figure, connected to areas with lower pressure than that present in section 38. The exchanger 22 is made in a single piece using 3D printing or using brazed sectors in aluminium and titanium to form an annular structure contained within the surface 30 which internally delimits the channel of the flow coming from the fan.The air cooled in the exchanger 22 feeds the third stage of the gas generator compressor comprising an impeller 23 mounted cantilevered externally to the cushions 20 of the rotor 39 and with the suction oriented opposite to the direction of thrust of the engine. The cooling between the second and third stages of the compressor reduces the head, and therefore the power, necessary to reach the final delivery pressure of the compressor, for example between 8 and 15 Bar, improving consumption. The impellers are mechanically connected to the shaft by means of geometric couplings, for example a BIRTH joint with a central tie rod.The cushions 28 are mounted inside the crankcases which are connected via channels 16, not completely visible in the drawing, to the part of the engine external to the wall 31 where the auxiliary piping systems are located, partially shown in the figure, for lubrication and compressed air to pressurize the engine cavities. Some of the channels 16 pass through suitable cavities inside the blades 15 so as not to obstruct the flow of the fan in section 38 and through the profiles of the stator compartments 40 of the gas generator turbine which include the first nozzle of the radial turbine. The compressor impeller diffuser 23 is mechanically and fluidly connected via a transition element, conceptually similar to that shown in Fig.3, which connects a cylindrically developed surface with a plurality of openings fluidly connected to the blades 15 containing the regenerator exchangers 17. The compressed air of the compressor conveyed inside the profile of the straightening blades 15 passes through the regenerator 17 in counter-flow with the high temperature combustion gas and, once heated, feeds the combustion chamber. Turboveiìtola * paiettat'-ssa costrorocants improved (Inventor: combustion 26 passing through supply channels 25. The combustion chamber 26 is of the radial development type with a fuel distributor, for example kerosene and hydrogen, of the rotating ring type keyed to the shaft according to a known technique not shown in the figure. The air-fuel mixture is ignited at start-up by means of an ignition device, not shown, which passes through the blades 15 near their leading edge and therefore without interfering with the flow of air from the fan until it reaches the area outside the wall 31 where the turbofan accessories not shown in the figure are positioned. The combustion chamber 26, according to a known technique, has holes and openings that allow the air to be appropriately distributed for the combustion process. The burnt gases from the combustion chamber 26 are expanded in the high-pressure turbine 27, first in a nozzle and then in the moving blades according to a known technique. The two high-pressure axial turbine stages have their respective disks mechanically connected, for example by HIRTH couplings, to the shaft 39 so as to drive the compressor which operates at the same rotational speed as the turbine, for example 100,000 rotations per minute. The flow of hot gases downstream of the axial turbine is directed perpendicular to the axis of rotation to further expand in the high-pressure turbine consisting of counter-rotating radial centrifugal turbine stages 12 and 13. The first nozzle of the low-pressure radial turbine is supported by the diaphragm 40 which also houses the drainage and vent channels of the stator cushion 16 of the high-pressure turbine and the first nozzle of the radial turbine. The exhaust gases are expanded in the counter-rotating centrifugal radial turbine, i.e. with stages that rotate in opposite directions with the rotation speed of the turbine that drives the second stage generally different from the rotation speed of the turbine that drives the first stage to limit the onset of sonic phenomena on the fan and to allow for variations in engine load. The two counter-rotating stages can have mirror-like blade profiles or, in general, with leading and trailing edges, even different from each other, positioned mirror-like according to a known technique.Downstream of the turbine stages there is a transition element 14 which distributes the flow from an annular surface to openings positioned in correspondence with the blades 15, the structure of this component is also visible in big.3. The flow of. .improvement of the center-rotated bladed impeller inventor: G. Marrotti hot gases burned at 500-600°C pass through, releasing heat both in the regenerator exchangers 17 inside the blades 15 and on the surface of the blades 10. The heat released to the flow of compressed air coming from the impeller 23 reduces the consumption of fuel to be injected into the combustion chamber. The blades 15 themselves, heated by the hot gases circulating inside them, form heat exchangers which, by releasing heat to the cold flow coming from the impeller, increase its temperature, or enthalpy content, and therefore its capacity to produce useful thrust. To maximize the flow of heat exchanged, the surfaces of the blades 15 are equipped with fins and turbulators to maximize the convective coefficient of heat exchange.For example, the heat of the exhaust gases can be dropped directly from the regenerators 17 in quantities of 10-33% to the compressed air flow and 2-3% from the blade surfaces 15 to the cold flow of the fan, allowing for energy recovery with obvious advantages in terms of thermodynamic efficiency. The flow of the burnt gases, having traveled through the vanes 15, is discharged upstream of the nozzle 23, or in some embodiments downstream, from the exhaust section 28 of the blades 15. The exhaust section is designed to have the same speed in section 38 or in section 29, in order to minimize mixing losses with obvious advantages in terms of efficiency. A system is installed in the exhaust area of ​​the engine.Auxiliary Gear Box, an electric generator 32 driven by a planetary gearbox 42 that is driven by a joint, not shown in the figure, mechanically connected to the impeller 23 of the gas generator. The planetary gearbox allows for coupling a fast gas generator, for example 1000-30 RPM, to a 20330 RPM electric generator, or to use an electric generator with a relatively high power, approximately 15% of the power of the gas generator, useful for applications such as unmanned aircraft where the on-board electronic devices have a relatively high electrical consumption. The advantages of the present invention are based on a turbofan architecture which allows the exhaust gas from the gas generator to be used to heat both the fan air flow before it is expelled. p^- .let x I-τχ'^Ine^χ'^ the compressor air flow before entering the combustion chamber. To the obvious advantages due to the recovery of energy from the exhaust gases is added an engine architecture which uses a radial turbine Counter-rotating vane turbine (Inventors: G. Mariotti) allows a simple and compact design of a high bypass ratio turbofan with the possibility of optimizing fan performance using variable geometry stator vanes and a regenerative gas generator with intercooling, thus improving both propulsive efficiency and thermodynamic efficiency of the engine. The simple architecture is characterized by a limited number of components, which is particularly advantageous for low-power engines that are poorly suited to complex configurations such as those used on modern high-power, high-bypass turbofan engines.

Claims

1. Turbofan with propeller comprising: — a first impeller 1 coupled to a rotor driven by a multistage centrifugal radial turbine 11; — a second impeller 8 rigidly connected to a shaft 6, coaxial with shaft 2, driven by a multistage centrifugal radial turbine 11 which rotates in the opposite direction to the turbine 10; 2. Turbofan according to claim 1 with an array of stator pairs interposed between the two impellers and both fluidly connected.

3. Turbofan according to claim 2 wherein the stator blades 7, with a structural function, are of the variable geometry type with an actuation and control system which varies the angular position of the trailing edge of the blade by means of an actuator 34 as a function of the operating parameters of the engine and the aircraft.

4. Turbofan according to claim 1 or 3 wherein: the turbines 10 and 11 are fluidically connected, but not mechanically, to a reverse flow gas generator, i.e. with the direction of the exhaust of the turbine 27 opposite to the direction of the engine thrust, which houses a plurality of centrifugal compression stages, the last impeller of which, mounted cantilevered with respect to the bearings of the rotor 39, is antipodal with respect to the exhaust of the turbine 13 and with the inlet of the impeller 23 positioned in the direction of motion. - the delivery of the last impeller of the compressor 23 is connected fluidically to a plurality. of heat exchangers x?, housed inside blades 10, which extend for a length not less than 70% of the distance between the last impeller of the compressor and the exhaust of the turbine 13 which is also fluidly connected to the exchangers 17.the blades 15, lapped by the flow of the propeller, are fluidly connected to the delivery of the last impeller of the compressor 23 and to the turbine exhaust 13, and have on the internal and external surface of the profile means suitable for maximising the heat exchange such as fins and turbulators.

5. Turbofan according to claim 4 wherein: The counter-rotating bladed turbofan (Loventerei (y.Marrontr) of the heat exchangers 22, with a bulk included within a delimited area of ​​the lower surface 33 of the fan channel 38 and fluidly connected thereto via low profile dynamic intakes, are also fluidly connected to the delivery of the last impeller 21 mounted between the cushions and to the suction of the first cantilever impeller of the compressor.