RU131416U1 - COOLED GAS TURBINE SHOVEL - Google Patents

Abstract

1. The cooled blade, mainly of high-temperature gas turbines, containing a channel of the inlet edge and a partition, also forming a channel adjacent to the channel of the inlet edge, characterized in that the inner wall of the inlet edge, as well as the wall of the channel of the inlet edge and the channel formed by the partition, are made curved so that they form channels of the diffuser-confuser type. 2. The cooled blade according to claim 1, characterized in that the channel of the input edge and the channel formed by the partition are mutually arranged so that the places of narrowing the area of the passage section of the channel of the input edge are adjacent to the places of expansion of the area of the passage section of the channel formed by the partition, and, conversely, expanding the area of the passage section of the channel of the input edge is adjacent to the places of narrowing the area of the passage section of the channel formed by the partition. 3. The cooled blade according to claim 1, characterized in that in the places of narrowing and expansion of the channel of the input edge in the wall of the channel of the input edge, holes are made for leakage of cooling air to the inner wall of the input edge. The cooled blade according to claim 1, characterized in that the geometric characteristics of the channels lie in the following ranges: the angles of opening of the diffusers 4 ÷ 12 °; the length of the diffuser part (1 ÷ 3) d, where d is the diameter of the channel; the ratio of the lengths of the diffuser and confuser parts 1 : 1 ÷ 3: 1; diameters of leakage holes on the input edge 0.3 ÷ 0.8 mm.

Description

The utility model relates to the field of transport engineering, turbine engineering and may find application in cooled blades of high-temperature gas turbines. The specific parameters of the aircraft turbine engine turbines and stationary units are boosted mainly by increasing the temperature and gas pressure at the inlet of the turbine stage, which creates certain problems in terms of the turbine blade working capacity. This trend is still ahead of the creation of new heat-resistant materials, which causes increased demands on the cooling system (CO) of turbine blades and, as a consequence, further complicates CO.

In modern cooled blades of high-temperature gas turbines, СО is widely used, where air is taken as a working medium, taken from the compressor and entering the system of channels of various configurations located in the blades. The most widely used are the so-called “convective-film” SOs, which combine the organization of a protective sheet with air flowing out of the perforation holes and convective cooling with air in the corresponding channels inside the feather blade. It is desirable that the proportion of convective cooling be as large as possible, since film cooling is irrational both from the point of view of air flow and from the point of view of stress concentration at the perforation holes.

The most heat-loaded element of the blade pen is the input edge, where the heat transfer coefficient from gas is 2–3 times greater than on the other parts of the profile, and therefore, the designers are focused on organizing its cooling. However, due to design features, it is extremely difficult to arrange conventional intensifiers (ribs, grooves, holes, etc.) in the channel of the input edge, which necessitates film cooling with all its drawbacks.

In addition, the use of intensifiers of similar types to solve this problem, as experience shows, is effective in the field of relatively small values Re = (3 ÷ 20) · 10 ³ .

The main objective of the proposed technical solution is to increase the cooling efficiency of the input edge, which will favorably affect the heat-stressed state of the entire pen, will reduce the cooling air consumption and increase the blade life.

The closest technical solutions to the claimed are cooled blades with the so-called "return-loop" WITH, described in RF patents No. 2283432 and No. 2285805 US patent US 2007/0172355. But the channel of the input edge of these blades has a smooth surface and, accordingly, low intensification of cooling.

The technical result in the inventive cooled blade, mainly of high-temperature gas turbines, is achieved by the fact that the walls of the channel of the input edge and the partition forming the adjacent channel are made of a special curved shape, which forms the so-called "diffuser-confuser" channels.

It is known that the intensification of heat transfer can be achieved by organizing the flow of the coolant under the action of an alternating pressure gradient. Such a flow is realized in wavy channels, which are a sequence of alternating confusor and diffuser sections. Intensive vortexes generated in diffuser sections are carried away by the flow and are useful in confuser sections. In the confused areas, the effect of increasing the velocities of the near-wall fluid layers is also used. This was shown by experiments, the results of which are presented in the following sources [1]:

1. "The study of heat transfer and gas-dynamic resistance in a turbulent gas flow in the field of a longitudinal alternating pressure gradient." - "IFZh", vol. ХVI, 1969, No. 4. Author: A.A. Gukhman, V.A. Kirpikov, V.V. Gutarev, I.M. Tsirelman;

2. Migai V.K., Bystrov P.T. Intensification of heat transfer in corrugated pipes. "Heat Power Engineering", 1976, No. 11, p. 74 ... 76.

The following are quotes from the above sources:

“When the gas flows through the channels with sharp edges ... there is an approximate proportionality between the number Nu and Re ^0.8 . In this case, the heat transfer intensity is much higher (~ 2.1-1.4 times) than when flowing along a straight channel with a constant cross-sectional length (Nu = 0.018 Re ^0.8 ). For all types of flow, a slightly higher heat transfer rate takes place in the diffuser-confuser channel 5: 1. The highest heat transfer rate corresponds to a continuous flow.

The experimental data on heat transfer can be approximated by the dependence of the form Nu = A ₁ Re ^0.8 ... "

Below are tables with the geometric characteristics of the channels studied in [1].

The length of the diffuser part was 40 mm, respectively, the ratio of the length of the diffuser part to the channel width was:

- for the channel width a = 47.7 mm - L / a = 0.84;

- for the channel width a = 33.3 mm - L / a = -1.20;

- for the channel width a = 16.8 mm - L / a = 2.38;

Table 1. The value of the coefficient A1 Channel width a, mm 47.7 33.3 16.8 Diffuser-confuser 5: 1 2: 1 1: 1 5: 1 2: 1 1: 1 5: 1 2: 1 1: 1 A ₁ 0.038 0.038 0.038 0.038 0.034 0.031 0.031 0.030 0.026

And further, [1]: “When gas flows through channels with rounded edges, the experimental data ... can be represented as the dependence Nu = Are ⁿ ...”. The values of the quantities A and n are presented in table 2.

Table 2. The value of the coefficient a and n Channel width a, mm 47.7 33.3 Diffuser-confuser 5: 1 2: 1 1: 1 1: 2 1: 3 5: 1 2: 1 BUT 0.049 0.026 0.049 0.072 0.094 0.039 0.039 n 0.76 0.83 0.76 0.715 0.68 0.79 0.79 Channel width a, mm 33.3 16.8 Diffuser-confuser 1: 1 1: 2 1: 3 5: 1 2: 1 1: 1 1: 2 1: 3 BUT 0.041 0.069 0.067 0.016 0.027 0.040 0.069 0.041 n 0.77 0.705 0.705 0.87 0.81 0.76 0.72 0.735

Also in [1], the ratios of heat fluxes in diffuser-confuser channels to heat fluxes in a channel with a constant cross-sectional length are given — coefficient K _Q :

Table 3. The value of the coefficient K _Q Channel width and, mm 47.7 33.3 Diffuser-confuser 5: 1 2: 1 1: 1 1: 2 1: 3 5: 1 2: 1 Re = 10 · 10 ³ 1.52 1.62 1.60 1.60 1.62 1.55 1.58 Re = 80 · 10 ³ 1.25 1.60 1.52 1.36 1.22 1.29 1.55 Channel width a, mm 33.3 16.8 Diffuser-confuser 1: 1 1: 2 1: 3 5: 1 2: 1 1: 1 1: 2 1: 3 Re = 10-10 ³ 1.49 1.50 1.49 1.48 1.46 1.44 1.33 1.20 Re = 80-10 ³ 1.44 1.34 1.21 1.30 1.46 1.34 1.21 1.12

As can be seen from the above experimental data, diffuser-confuser channels, in comparison with smooth channels, have higher cooling efficiency in the entire range of experiments, which is reflected in the final part [1]:

“Comparison of experimental data on heat transfer and resistance for diffuser-confuser channels with those calculated for a channel with a constant cross-sectional length, carried out in accordance with ..., indicates the high efficiency of the studied channels.

For the diffuser-confuser channels, the power consumption necessary for moving the coolant (for a fixed heat flux and surface) and the surface (for a fixed heat flux and power consumption) turn out to be significantly less than for channels with a constant cross-sectional length, and the heat flux ( at a fixed power consumption and surface), on the contrary, more. ... comparison results for diffuser-confuser channels with rounded edges, which turned out to be much more effective than channels with sharp edges.

Thus, it can be stated that the studied channels, the diffuser-confuser are very effective and can be successfully used in the design of heat exchangers. "

The study of heat transfer in diffuser-confuser channels was continued in [2]. The geometric characteristics of the studied pipes are shown in figure 6 and are given in the following table 4.

Table 4. Option Number Geometric characteristics of the studied pipes L _d , mm L _to , mm d _e mm h mm h / d _e , mm β _d , deg β _to , hail one 8 16 17.7 2 0.113 fourteen 7.1 2 16 8 17.7 2 0.113 7.1 fourteen 3 8 16 15.8 one 0.0633 7.1 3.6 four 16 8 15.8 one 0.0633 3.6 7.1 5 8 16 19.2 0.5 0.026 3.6 1.8 6 16 8 19.2 0.5 0.026 1.8 3.6

Experimental data on heat transfer are shown in figure 7. It can be seen that the heat transfer intensity increases with an increase in the opening angle of the diffuser and confuser. The results of experimental studies are expressed in the conclusion [2]:

“Calculations show that with equal losses in hydraulic resistance, the heat removal in the case under consideration is increased by 70% compared to a smooth pipe. Due to the high efficiency of this type of pipe can be widely used in a wide class of heat exchangers ... "

Based on the above excerpts from documents reflecting the experimental results, we can assume that in the channel of the input edge, made according to the "diffuser-confuser" scheme, there will be a significant increase in heat transfer (about 1.7) than in a smooth channel .

In this case, based on structural and technological considerations, the following geometric characteristics of the diffuser-confuser channels can be adopted: the ratio of the lengths of the diffuser-confuser is from 1: 1 to 3: 1, the opening angles of the diffuser β _d are from 4 ° to 12 °; the length of the diffuser part (1.0 ÷ 3.0) · d, where d is the diameter of the channel.

The indicated figures are taken from the following considerations. The experiments carried out with diffuser-confuser channels showed their effectiveness in terms of increasing heat transfer in the entire studied range, therefore, the restrictions can be accepted only for the concrete design of the blade in the process of finishing it. The opening angles of the diffuser and the length of the diffuser part can also be specified based on technological considerations and the dimensions of the blade. The length of the diffuser part can be estimated from the results of experiments in [1] - based on the value of L / a, where a is taken as the diameter of the channel.

Also, to increase the coefficient of heat transfer to the cooler, holes are made on the inner wall of the channel of the inlet edge through which the cooler flows onto the inner surface of the inlet edge. This effect is called “frontal leakage” and differs in that it significantly increases the heat transfer coefficient, which is proportional, ceteris paribus, to the velocity of the leaking jet. The speed of the jet, in turn, is determined by the pressure drop across the hole.

This pressure drop can be increased if both the wall of the inlet edge and the wall of the adjacent channel are curved, as shown in figure 1. The cooler, passing alternately sections with a variable cross-sectional area, will move with a correspondingly variable speed. In accordance with the Bernoulli equation, where the flow rate is higher, the pressure will be less, and vice versa, where the flow rate is lower, the pressure will be higher. Since the alternation of the passage areas of the cross sections is opposite in adjacent channels, an increase in area (and pressure drop) is observed in one channel in one channel and a decrease in area (and pressure increase) in the other channel, respectively. That is, there is an increase in the pressure drop, and, accordingly, an increase in the speed of the oncoming jet and an increase in the intensification of heat transfer.

The geometry of the wall of the input edge and the geometry of the partition (the ratio of the lengths of the diffuser-confuser and the opening angles of the diffuser and confuser) correspond to the geometry of the channel of the input edge. The holes in the partition, based on the experience of designing and manufacturing the working blades of modern aircraft engines, in the chord range from 30 mm to 70 mm, should be made with a diameter of 0.30 ÷ 0.8 mm, respectively.

The figure 1 shows a cooled blade (cross section along the midline), in which both the channel of the inlet edge 1 with the curved inner wall 3 and the adjacent channel 2, formed by the curved partition 5, have a diffuser-confuser shape. 6 - direct septum. The arrows indicate the movement of cooling air.

Figure 2 shows, on an enlarged scale, the place C of figure 1. Here: 3 - curved inner wall of the channel of the input edge; 4-input edge of the scapula; 5 - curved septum forming a diffuser-confusor channel; 6 - the next, already direct partition; 7 - hole in the narrowing of the passage area of the channel of the input edge (but the expansion of the passage area of the adjacent channel); 8 - hole in the area of expansion of the passage area of the channel of the input edge (with opposite characteristics of the hole 7).

The figure 3 shows a section along bb of figure 1 along the axis of the channel of the input edge. The arrows indicate the movement of cooling air.

The figure 4 shows a section along the middle section of the pen blade. The arrow shows the leakage onto the inlet edge through the openings 7 from places with a larger passage area and, accordingly, with a pressure drop directed towards the inlet edge.

In figure 5, the location of the input edge is shown on an enlarged scale. The arrows show the movement of cooling air, which, flowing into the channel of the inlet edge 1 through openings 7 of the narrowing of the passage area of the channel of the inlet edge, flowing around the wall of the inlet edge, is partially evacuated through openings 8 in the places of the expansion of the passage area of the channel of the inlet edge (see Fig. 2), and partially through the hole in the end of the scapula.

Figure 6 schematically shows a diffuser-confuser channel with the accepted designations of geometric characteristics.

The figure 7 presents the results of experiments performed according to [2]. The heat transfer efficiency in corrugated pipes with different geometry of diffuser-confuser channels is compared. The numbers indicate the numbers of options in accordance with Table 4 and Figure 6. On the abscissa axis are the Reynolds numbers (Re · 10 ^-3 ), and on the ordinate axis are the Nusselt numbers (Nu).

The cooling mechanism of the input edge in accordance with the proposed solution can be represented as follows.

The gas flow through the diffuser (that is, in the field of a positive pressure gradient is accompanied by a significant increase in the coefficient of turbulent exchange of momentum. Moreover, in accordance with the concept of identity of the carriers of the momentum and heat, one should expect a noticeable intensification of heat transfer.

At the same time, the gas flow through the confuser (i.e., in the field of a longitudinal negative pressure gradient) is associated with a decrease in heat transfer intensity, which is explained by the cessation of turbulence generation and the degeneration of residual turbulence under the influence of negative pressure gradients. Thus, in the channel, which is a sequential alternation of diffusers with small expansion angles and confusers, the turbulence energy accumulated by the flow in the diffuser is usefully used in the confuser. Of course, the length of the diffuser parts of the channel, even at small expansion angles, should be limited to prevent flow separation, an effect leading to large energy losses. The final geometry of the CO is determined during the refinement of the structure, and some sizes may differ from the above.

Thus, the use of the inventive cooled blade of a gas turbine allows, due to better cooling of the inlet edge of the blade with the same cooling air flow rates compared to existing analogues, increase the gas temperature at the turbine inlet and increase the specific engine parameters, or at the same gas temperature, extend the life of the blade , and, consequently, the engine.

Claims (4)

1. The cooled blade, mainly of high-temperature gas turbines, containing a channel of the inlet edge and a partition, also forming a channel adjacent to the channel of the inlet edge, characterized in that the inner wall of the inlet edge, as well as the wall of the inlet edge channel and the channel formed by the partition, are made curved so that form channels diffuser-confuser type. 2. The cooled blade according to claim 1, characterized in that the channel of the inlet edge and the channel formed by the partition are mutually arranged so that the places of narrowing the area of the passage section of the channel of the input edge are adjacent to the places of expansion of the area of the passage section of the channel formed by the partition, and vice versa , places to expand the area of the passage section of the channel of the input edge are adjacent to the places of narrowing the area of the passage section of the channel formed by the partition. 3. The cooled blade according to claim 1, characterized in that in the places of narrowing and expansion of the channel of the input edge in the channel wall of the input edge, holes are made for leakage of cooling air to the inner wall of the input edge. 4. The cooled blade according to claim 1, characterized in that the geometric characteristics of the channels are in the following ranges: opening angles of diffusers 4 ÷ 12 °; the length of the diffuser part (1 ÷ 3) d, where d is the diameter of the channel; the ratio of the lengths of the diffuser and confuser parts 1: 1 ÷ 3: 1; the diameters of the leakage holes on the input edge of 0.3 ÷ 0.8 mm

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