RU2484264C2 - Continuous transient channel between high-pressure turbine and low-pressure turbine of double-flow aircraft engine - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: continuous annular transient channel between a high-pressure turbine and a low- pressure turbine with expansion degree of more than 1.6 and an equivalent opening angle of a flat diffuser of more than 12° includes external and internal perforated walls. Flow swirl after the high-pressure turbine runner is transformed in the direction of its amplification at walls and attenuation in the centre. The swirl is transformed due to shaping of a stage of the high-pressure turbine and due to a swirling device located after the runner of the high-pressure turbine with the height of 10% of the channel height to 5% of the height on internal and external walls of the channel, or due to a twisting-untwisting device of total height.

EFFECT: invention allows reducing losses in a transient channel between high-pressure and low-pressure turbines.

3 cl, 6 dwg

Description

FIELD OF THE INVENTION

The invention relates to the field of aircraft gas turbine engines, in particular to a node located between a high pressure turbine and a low pressure turbine of the internal circuit of a dual-circuit aircraft engine.

State of the art

Double-circuit aviation gas turbines are designed to drive compressors. The high pressure turbine is designed to drive the high pressure compressor, and the low pressure turbine is designed to drive the low pressure compressor and fan. In fifth-generation aircraft engines, the mass flow rate of the working fluid through the internal circuit is several times smaller than the flow rate through the external circuit. Therefore, the low-pressure turbine in its power and radial dimensions is several times higher than the high-pressure turbine, and its rotation speed is several times lower than the rotational speed of the high-pressure turbine.

This feature of modern aircraft engines is structurally embodied in the need to make the transition channel between the high pressure turbine and the low pressure turbine, which is an annular diffuser.

Severe restrictions on the overall and mass characteristics of the aircraft engine with respect to the transition channel are expressed in the need to run the channel of a relatively short length, with a high degree of diffusivity and a clearly tear-off equivalent opening angle of the flat diffuser. The degree of diffuseriness refers to the ratio of the output cross-sectional area to the input. For modern and promising engines, the degree of diffusivity is close to 2. By the equivalent opening angle of a planar diffuser is meant the opening angle of a planar diffuser having the same length as the annular conical diffuser and the same degree of diffusivity. In modern aviation gas turbine engines, the equivalent opening angle of a planar diffuser exceeds 10 °, while the continuous flow in a plane diffuser is observed only at an opening angle of no more than 6 °.

Therefore, all completed designs of the transition channels are characterized by a high loss coefficient, due to separation of the boundary layer from the diffuser wall. The figure 1 shows the evolution of the main parameters of the transition channel of the company General Electric. In figure 1, the horizontal axis shows the degree of diffusivity of the transition channel, the vertical axis is the equivalent opening angle of the flat diffuser. Figure 1 shows that initially high values of the effective opening angle (≈12 °) evolve to significantly lower values, which is associated only with a high level of losses. According to the results of studies of a ring diffuser with a degree of opening of 1.6 and an effective opening angle of a flat diffuser of 13.5 °, the loss coefficient varied from 15% to 24% depending on the law of distribution of swirl over the channel height [1].

Analogs of the invention

Remote analogues of the invention are diffusers described in US 2007/0089422 A1, DAS 1054791. In these structures, to prevent separation of the flow from the diffuser wall, the boundary layer is sucked from a section located in the middle of the channel with the suction gas being ejected into the nozzle. However, these diffusers are not transition channels between the high pressure turbine and the low pressure turbine.

Brief Description of the Drawings

Non-limiting embodiments of the present invention, its additional features and advantages will be described in more detail below with reference to the accompanying drawings, in which:

figure 1 depicts the evolution of the flow part of the inter-turbine transition channel at the turbofan engine company General Electric,

в виде линейной аппроксимации, где ν=0 - равномерная по высоте закрутка потока; ν=-1 - увеличивающаяся по высоте закрутка потока; ν=1 - уменьшающаяся по высоте закрутка потока; у=-1,36Ф_ст+0,38 - аппроксимационная зависимость, соответствующая коэффициенту достоверности R=0,76,figure 2 depicts the dependence of the kinetic energy loss of the flow in the channel from the integral parameter of the swirl flow $${\overline{F}}_{\mathrm{FROM}T}$$

in the form of a linear approximation, where ν = 0 is the flow swirl uniform in height; ν = -1 - increasing in height swirl flow; ν = 1 - decreasing flow swirl; y = -1.36F _st +0.38 - approximation dependence corresponding to a confidence coefficient R = 0.76,

figure 3 depicts the extrapolation of loss of separation in the annular diffuser from the magnitude of the wall twist,

figure 4 depicts a transition channel diagram,

5 depicts a perforation diagram,

6 depicts a diagram of the device power rack with a feed channel.

Disclosure of invention

The problem to which the present invention is directed, is to create a transition channel with a degree of opening of more than 1.6 and with an equivalent opening angle of a planar diffuser exceeding 12 °, the flow in which would be continuous, and the level of losses is accordingly minimally possible. It is proposed to reduce the loss factor from 20-30% to 5-6%.

The problem is solved:

1. Based on the transformation of the existing swirl behind the high-pressure turbine at the entrance to the annular diffuser in the direction of its amplification on the inner and outer wall of the channel and attenuation in the middle of the channel.

2. Based on the variable perforation length of the inner and outer walls of the annular diffuser, adapted to the local turbulence structure.

3. Based on the suction of the boundary layer from the zone of possible separation of the flow from the walls of the diffuser.

In this connection, a continuous annular transition channel between a high-pressure turbine (HPT) and a low-pressure turbine (LPT) with a degree of expansion of more than 1.6 and an equivalent opening angle of a flat diffuser of more than 12 °, containing an outer wall and an inner wall, is proposed. The outer and inner walls are perforated, and the spin located behind the impeller of the high-pressure turbine (HPD) is transformed in the direction of its strengthening at the walls and weakening in the center. The swirl is converted by profiling the stage of the high pressure turbine (HPT) and by means of a swirling device located behind the impeller of the high pressure turbine (HPT) with a height of 10% of the channel height at 5% of the height on the inner and outer walls of the channel, or by tightening full height unwinder.

The converted twist is limited by the achievement of the integral twist parameter to the level Ф _st = 0.3-0.35. The perforation section, located at a distance of 0.6-0.7 of the length of the transition channel from the inlet section, is connected to the cavity in power racks having slots at 80% of the height of the racks symmetrically to the geometric middle of the channel, and the slots are located near the input edge.

As you know, the gas moves in the diffuser by inertia in the direction of pressure increase, and the separation (delamination) of the flow from the walls is physically caused by the insufficient inertia of the inner wall layers of the boundary layer. Paragraphs 1, 2 are designed to increase the inertia of the motion of the near-wall gas flow by increasing the speed of movement, and accordingly its kinetic energy.

The presence of a swirl in the near-wall gas flow increases the speed of movement, and hence its kinetic energy. As a result, the flow resistance to separation (peeling from the walls) increases, and losses are reduced. The figure 2 shows the results of a pilot study of a ring diffuser with a degree of opening of 1.6 and an equivalent opening angle of a flat diffuser of 13.5 °. The vertical axis shows the loss coefficient, determined in the traditional way: the ratio of the loss of mechanical energy in the diffuser to the kinetic energy of the gas stream at the inlet to the diffuser. The horizontal axis represents the integral spin parameter, defined as follows:

$$F_{\mathrm{from}t}=\frac{F_{\mathrm{at}t}+F_{PeR}}{F.},$$

Where $$F.=\frac{2\pi {\displaystyle \underset{R}{\overset{R+H}{\int }}\rho wu{r}^2\mathrm{<figure-callout\; id="2"\; label="d\; r"\; filenames="00000016.png,00000019.png"\; state="\{\{state\}\}">d\; </figure-callout>}r}}{2\pi {\displaystyle \underset{R}{\overset{R+H}{\int }}\rho w^{2}rdr\left(R+\frac{H}{2}\right)}}$$

is the integral parameter of the swirl at the entrance to the channel, ρ is the density, w is the axial velocity, u is the peripheral speed, r is the current radius, R is the radius with the internal generatrix of the diffuser, N is the height of the channel, and _Fw is the integral parameter of swirl considered in height range from 0% to 5% of the sleeve section, i.e.

$$F_{\mathrm{at}t}=\frac{2\pi {\displaystyle \underset{R}{\overset{R+0.05H}{\int }}\rho wu{r}^2\mathrm{<figure-callout\; id="2"\; label="d\; r"\; filenames="00000016.png,00000019.png"\; state="\{\{state\}\}">d\; </figure-callout>}r}}{2\pi {\displaystyle \underset{R}{\overset{R+H}{\int }}\rho w^{2}rdr\left(R+\frac{H}{2}\right)}};$$

F _per - the same parameter, but in the height range from 95% to 100% of the sleeve section, i.e.

$$F_{PeR}=\frac{2\pi {\displaystyle \underset{R+0.95H}{\overset{R+H}{\int }}\rho wu{r}^2\mathrm{<figure-callout\; id="2"\; label="d\; r"\; filenames="00000016.png,00000019.png"\; state="\{\{state\}\}">d\; </figure-callout>}r}}{2\pi {\displaystyle \underset{R}{\overset{R+H}{\int }}\rho w^{2}rdr\left(R+\frac{H}{2}\right)}}.$$

As can be seen from figure 2, the loss in the transition channel decreases as the proportion of parietal twist increases.

The figure 3 presents a linear extrapolation of the dependence ξ (f _article ) to the level of friction loss in the equivalent channel of constant cross section. In this case, the near-wall swirl (10% of the channel height) should account for approximately 30% of the swirl of the flow.

В последнем выражении µ - динамическая вязкость, τ_ст - напряжение трения на стенке. Как известно, напряжение трения быстро убывает вдоль диффузора, а в точке отрыва оно вообще равно нулю. Поэтому толщина ламинарного подслоя в переходном канале со сплошной стенкой стремительно нарастает по ходу потока. Соответственно увеличивается толщина пристеночного слоя течения с малым уровнем кинетической энергии.As is known, with a turbulent flow regime in the channels, a laminar flow regime takes place right near the wall due to the impossibility of transverse pulsating motion. The thickness of the laminar sublayer is approximately $$\frac{10\mu }{\sqrt{\rho {\tau }_{\mathrm{from}t}}}.$$

In the last expression, µ is the dynamic viscosity, τ _st is the friction stress on the wall. As is known, the friction stress rapidly decreases along the diffuser, and at the separation point it is generally equal to zero. Therefore, the thickness of the laminar sublayer in the transition channel with a continuous wall is rapidly increasing along the flow. Accordingly, the thickness of the wall layer of the flow with a low level of kinetic energy increases.

Perforation of the inner and outer walls of the transition channel makes possible transverse pulsation movement at any distance from the perforated wall. Since the longitudinal pulsation flow is statistically related to the transverse one in a turbulent flow, perforation allows to increase the area of the turbulent flow itself. The higher the degree of perforation of the wall, the thinner the laminar sublayer, the higher the gas velocity in the wall layer, the higher the kinetic energy of the wall flow and its resistance to separation (peeling from the wall).

Description of the design of the transition channel between the high pressure turbine and the low pressure turbine

The transition channel between the high-pressure turbine (high pressure turbine) and the low-pressure turbine (low pressure turbine) of the internal circuit of a dual-circuit turbojet engine (Figure 4) is an annular diffuser having an inner wall 1 and an outer wall 2. The inner and outer walls at the junction with the turbine and high pressure turbines specific mating radii.

Through the transition channel pass power racks 3, which provide lubrication, venting and cooling of the supports of the rotors of the high pressure fuel pump and high pressure pump. Racks 3 have an asymmetric aerodynamic profile in cross section, which ensures the promotion of the flow in the center of the channel and the twisting of the flow at the channel walls to the level Ф _st = 0.3-0.35.

Walls 1 and 2 are perforated (Figure 5). To avoid overflow of the working fluid in the perforations, the parts of the perforation 4 are isolated from each other by transverse walls 5.

From the perforation section 9, located at a distance of 0.6-0.7 from the entrance to the diffuser, suction and removal through the feed channel 6 in the slots 7 of the racks 3 is organized. Removing the suction part of the boundary layer is done through slots located near the edge of the racks profile in the zone minimum local static pressure. In the channel connecting the cavity 9 with the cavity of the uprights 3, measuring washers 8 are installed that control the gas flow.

Behind the impeller of the theater 11 is installed a twisting apparatus 12, which increases the swirl of the flow at the walls. The height of the blades of the apparatus 12 is 10% of the height of the channel at the entrance. If necessary, the twisting apparatus 12 can be converted into a twisting-twisting apparatus located along the entire height of the channel. The central part of the apparatus spins up the flow, and the wall part spins up, so that as a result of the swirling of the flow at the inlet to the diffuser, it is Ф _st = 0.3-0.35.

In the event that an uninterrupted flow in the diffuser is achieved only due to the profiling of the nozzle apparatus 10 and the impeller 11 of the turbine engine and the twisting-unwinding effect of the power struts 3, the twisting device 12 and slots 7 with channel 6 are absent.

The implementation of the invention

The continuous flow regime in the transition channel is achieved by swirling the flow in the near-wall zones of the flow, by unwinding the flow in the center, by perforating the meridional components of the transition channel, by suction of the boundary layer.

The features of the organization of the working process in modern gas turbine engines are such that behind a high-pressure turbine there is a swirling flow of about 30-40 °. A high level of swirling at the inner and outer walls (at a distance of 5% of the height of the channel) should be maintained, and if necessary, strengthened by profiling the step and, if necessary, by installing a twisting blade device at the entrance to the transition channel. The flow swirl at heights from 5% of the sleeve section to 95% of the same section should be reduced both due to the profiling of the stage, and due to the unwinding of the flow by power struts constructively passing through the channel. If necessary, to achieve the necessary promotion of the flow should be the installation of an additional spinning vane apparatus at the entrance to the transition channel. The promotion of the flow in the central part of the channel is designed to reduce the radial gradient of static pressure and to reduce the intensity of secondary flows, thickening the boundary layer and reducing its resistance to separation. The value of the relative parietal twist should be as close as possible to a value of 0.3-0.35.

Since the installation of an additional blade apparatus is associated with the appearance of losses in this apparatus, it should be installed only if the decrease in the loss coefficient in the transition channel significantly exceeds the amount of losses in the additional twisting and untwisting device. Alternatively, it is possible to install an additional twisting apparatus on the sleeve and periphery limited by heights of 5% to 10% N (Figure 4).

, что всего лишь в 2 раза меньше скорости на границе ламинарного подслоя, в то время как как скорость течения собственно в ламинарном подслое (на этом расстоянии) в 4 раза меньше, а удельная кинетическая энергия в 16 раз меньше.Perforation of the meridional components of the transition channel changes the flow regime in the laminar sublayer to turbulent. Extrapolation of the logarithmic velocity profile [2] to the region of the laminar sublayer to a distance from the solid wall equal to 8% of the thickness of the laminar sublayer gives for the velocity value $$\sqrt[6.5]{\frac{{\tau }_{\mathrm{from}t}}{\rho }}$$

, which is only 2 times less than the velocity at the boundary of the laminar sublayer, while the flow velocity in the laminar sublayer itself (at this distance) is 4 times less, and the specific kinetic energy is 16 times less.

The extrapolation of the logarithmic law of velocity distribution, which is characteristic of the purely turbulent flow regime to the region of the laminar sublayer, implies complete freedom for the movement of turbulent vortices. This possibility exists under two conditions: 1) the degree of perforation of a solid surface is close to 100%;

2) turbulent vortices of all sizes in a given section have complete freedom for movement in the transverse direction.

In reality, these conditions are unattainable in full, but you can practically get close to them. As a result, the speed of movement at the perforated surface will be several times higher than the speed of movement at the same distance from the wall at the continuous surface. The density of the perforation elements and its structure should be consistent with the maximum energy spectrum of turbulent pulsations in relation to their linear size for a given section of the transition channel.

The perforation density (the ratio of the perforation area to the total area) should be maintained as high as possible for structural and stiff reasons.

The perforation structure is adapted to the linear size of energy-containing vortices of local turbulence, determined by the height of the transition channel and its average radius in this section. The following model can be adopted as a model of the perforation structure:

d = l _e (R, II);

d _min = (0.2-0.5) l _e (R, II);

d _max = (1.5-2) l _e (R, II);

; $$\overline{d}=(0.6-0.8)$$

;

; $$\overline{d_{\min }}=(0.2-0.3)$$

;

; $$\overline{d_{\max }}=(0.1-0.2)$$

;

Where

- доля основного размера перфорации; S_d - площадь перфорации, выполненная по размеру d=(l_э(R, II); S - общая площадь перфорации; $$\overline{d_{\min }}=\frac{S_{d\min }}{S}$$

- доля минимального размера перфорации; S_dmin - площадь перфорации, выполненная по размеру d_min; $$\overline{d_{\max }}=\frac{S_{d\max }}{S}$$

- доля максимального размера перфорации; S_dmax - площадь перфорации, выполненная по размеру d_max (Фиг.5).d _min - the minimum diameter of the perforation; d = l _e (R, II) - the main diameter of the perforation equal to the linear size of the energy-containing vortices of the turbulent structure; d _max - the maximum diameter of the perforation; $$\overline{d}=\frac{S_d}{S}$$

- the proportion of the main size of the perforation; S _d is the area of perforation made in size d = (l _e (R, II); S is the total area of perforation; $$\overline{d_{\min }}=\frac{S_{d\min }}{S}$$

- the proportion of the minimum size of the perforation; S _dmin is the perforation area, made in size d _min ; $$\overline{d_{\max }}=\frac{S_{d\max }}{S}$$

- the proportion of the maximum perforation size; S _dmax is the perforation area, made in size d _max (Figure 5).

The size of energy-containing vortices l _e (R, II) is determined by calculation, depending on the accepted turbulence model.

, где $$\overline{S}=\frac{S_{пер}}{S}$$

, S_пер - общая площадь перфорированной поверхности, S - суммарная площадь меридиональных обводов) может не хватить для организации безотрывного течения по всей длине переходного канала. В этом случае возможный отрыв на последней трети длины диффузора следует предотвратить путем отсоса пограничного слоя через часть перфорации. Удаление отсасываемого газа следует организовать в центральную часть канала через соответствующие отверстия в силовых стоках, которые расположены вблизи входной кромки профиля стенок, т.е. там, где местное статическое давление минимально. Площадь части перфорации 9, работающей на отсос, и площади проходных сечений в стойках 7 должны быть согласованны между собой.In transition channels with a very large degree of expansion (n> 2) and a very large equivalent opening angle of a flat diffuser (α _equiv > 17 °), the maximum achievable near-wall twist (Ф _ст ≈0.3) and the maximum achievable and properly structured perforation ( $$\overline{S}\approx 0.8$$

where $$\overline{S}=\frac{S_{PeR}}{S}$$

, S _per - the total area of the perforated surface, S - the total area of the meridional contours) may not be enough to organize a continuous flow along the entire length of the transition channel. In this case, a possible separation in the last third of the length of the diffuser should be prevented by suction of the boundary layer through part of the perforation. The removal of the suction gas should be arranged in the central part of the channel through the corresponding openings in the power drains, which are located near the inlet edge of the wall profile, i.e. where local static pressure is minimal. The area of the part of the perforation 9, working on the suction, and the area of the passage sections in the racks 7 should be consistent with each other.

The cavity in the power racks has slots located near the input edge, the vertical length of which can reach 0.8 of the height of the racks. Slots are located symmetrically relative to the middle of the channel. The set of cavities and channels associated with perforation and slots in the power racks, organizes the suction of the boundary layer in the transition channel.

The organization of suction of the boundary layer is advisable only if the loss of mixing when injecting the suction gas at the entrance to the transition channel is less than the reduction in losses in the diffuser due to suction.

List of references

1. Gladkov Yu.I. Study of the variable along the radius of the input swirl of the flow on the efficiency of the inter-turbine transitional channels of the gas turbine engine [Text]: dissertation abstract for the degree of candidate of technical sciences 05.07.05 / Yu.I. Gladkov - P.A.Soloviev Rybinsk State Aviation Technological Academy. - 2009 - 16 p.

2. Schlichting, G. Theory of the boundary layer [Text] / G. Schlichting. - M .: Nauka, 1974.- 724 p.

Claims (3)

1. An uninterrupted annular transition channel between a high-pressure turbine (HPT) and a low-pressure turbine (LPT) with a degree of expansion of more than 1.6 and an equivalent opening angle of a flat diffuser of more than 12 °, comprising an external wall and an internal wall, characterized in that the external and the inner wall is perforated, and the spin located behind the impeller of the high pressure turbine (HPT) is converted in the direction of its strengthening at the walls and weakening in the center due to the profiling of the high pressure turbine stage (HPT) and due to twisting guide device located behind the impeller of high pressure turbine (HPT) 10% of the height of the channel height of 5% of the height on the inner and outer walls of the channel, or by podkruchivayusche-untwisting device total height. 2. The channel according to claim 1, characterized in that the converted twist is limited by the achievement of the integral twist parameter to the level of f _article = 0.3-0.35. 3. The channel according to claim 1, characterized in that the perforation section located at a distance of 0.6-0.7 of the length of the transition channel from the inlet section is connected to the cavity in power racks having slots 80% of the height of the racks symmetrically to the geometric middle of the channel , and the slots are located near the input edge.

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