AXIAL COMPRESSOR WITH TANDEM BLADES

Abstract

Axial compressor with tandem blades consists of a compressor stage (1) with a double (2), or triple (3) blade arrangement, around an axial (A) rotor disk and corresponding stator (B), to increase the fluid flow deflection angle, with greater camber of the double, or triple profile, greater variation in isentropic total temperature and, consequently, greater rate of compression per stage, which can form multiple stages of the rotor and stator assembly with the same configuration of double or triple blades, providing the assembly with a greater rate of compression.

Description

This is a request for a patent for the invention of an axial compressor with tandem blades, especially an axial compressor comprised, by stage, of a rotor followed by a stator, repeated in series, including a front blade, followed by at least one, or two, posterior blades arranged axially and circumferentially to each other. The posterior blade is positioned to receive the flow from the frontal blade, or the central one in the case of three blades, providing greater deflection of fluid flow, with greater camber of the double, or triple, profile of the rotor and respective stator, maintaining an acceptable overall efficiency and stability margin. Due to the high camber conditions in the rotor, the stator model follows the same order of double, or triple blades in order to avoid fluid flow boundary layer separation on the blade suction surface and reposition it to the next rotor, in similar conditions to that of the previous rotor. The last stator, at the compressor outlet, has the same number of blades as the rest, in order to release the flow without swirl in the axial direction. Blade profile is a result of the type of flow and the compressor design.

The invented axial compressor has an application field in the gas turbine industry, turbo motors, propellants and a compressor assembly for generating gas or compressed air.

Technician in the matter knows that traditionally, conventional axial compressors have a single blade assembly for each rotatory disk and its corresponding stator.

Specifically, as per FIG. 7, the main parameters of the rotor and corresponding stator, of the traditional axial compressor are:

• • Rotor tangential speed (rotation) U=ωr
  • Input axial speed in the rotor (u₁);
  • Input flow angle in the rotor (β₁);
  • Output flow angle (β₂) through rotor blades;
  • Absolute input speed of the rotor (V₁);
  • Absolute output speed of the rotor (V₂);
  • Relative input speed of the rotor (V_1R);
  • Relative output speed of the rotor (V_2R);
  • Input flow angle off the rotor (α₁);
  • Output flow angle off the rotor (α₂).

Angles (β₁ and β₂) in the conventional rotors are limited by virtue of the criteria adopted in flow calculations through the profile of their blades. One of them, called the Haller criterion, the relative output speed (V_2R) cannot exceed the relative input speed (V_1R) in rotor blades of a value of around 0.72, because otherwise the losses would be high. On the other hand, there is the criterion of losses based on the diffusion factor, referred to as the D-Factor, which also limits such speeds. Thus blade profile camber obeys a limit, which impedes greater load on them, because if this criterion is exceeded, the flow loses contact with the blade profile, making the rotor lose its efficiency.

In the current state of the technique, some gas turbine axial compressor stator models have a dual blade configuration; however, in the last stage of compression. In this case, the stator assembly is a static piece and it does not exert work as in the rotor disks.

The dual blade configuration is also seen in some compression rotors, generating greater efficiency, called the booster effect, in the first stage, without a dual blade stator assembly.

In the document, U.S. Pat. No. 4,529,358, the configuration of the dual blades is slightly similar to this patent request; however the concept is diverse. In this example, although the blades position themselves in a similar manner, the posterior blade has part of the leading edge in the interior of the canal formed by the front blades, that is, the posterior blade overlaid the frontal blade, and the concept of operation is based on shock waves.

Another, subsonic model, however, with a dual profile position only in the rotor and overlaid, that is, the second blade begins inside the first, but with a stator assembly of just one profile. In this case, the compressor has its principle applied in flow efficiency only along the rotor disk blades, not considering the gain in fluid deflection angle, as in the request claimed here.

Aware of the state of the technique and of the existing gap nozzle in it was why the inventor, a person active in the segment in question, after studies and research, created the axial compressor with tandem blades, which is the object of this patent request, in which the rotor disk, with a double or triple blade arrangement, permits a greater variation in speeds related to output (V_2R) and input (V_1R), implying a greater camber between the input (β₁) and output (β₂) angles of fluid flow through the rotor channels, that is, a greater deflection of the fluid, resulting in greater efficiency regarding the increase in isentropic total temperature, and consequently, a greater rate of compression. Due to this effect in the rotor disk, the corresponding stator is obliged to have the same configuration of double or triple blades along the crown in order to accommodate the flow at output in a situation that meets the similar conditions of subsequent rotor disk input, or even the compressor output condition in the case of the last stage. Multiple stages of the rotor and stator assembly with the same double or triple blade configuration can be in juxtaposition to provide a greater rate of compression for the whole assembly, thus forming stages of compression.

Below, the invention is explained with reference to the constructive and functional technical details, where, for a better understanding, reference is made to the attached drawings in which they are represented in an illustrative and unlimited manner:

FIG. 1: Lateral and upper cut perspective of the first stage of the axial compressor with tandem blades;

FIG. 2: Detail of the double blade profiles in the rotor and corresponding stator of the axial compressor with tandem blades;

FIG. 3: Detail of the triple blade profiles in the rotor and corresponding stator of the axial compressor with tandem blades;

FIG. 4: Comparative triangle of rotor speeds of the axial compressor with tandem blades with the rotor of the conventional axial compressor;

FIG. 5: Detail of the smaller blade profiles in the last channel formed by the second blade of the axial compressor with tandem blades;

FIG. 6: Schematic diagram of profiles of an axial compressor with tandem blades with two stages of compression;

FIG. 7: Schematic diagram showing the main parameters of the rotor assembly and corresponding stator of the axial compressor with tandem blades;

FIG. 8: Lateral and upper cut perspective of the first stage of the conventional axial compressor;

The axial compressor with tandem blades consists of a compressor (1) with a double (2), or triple (3) blade arrangement, around an axial (A) rotor disk and corresponding stator (B), to increase the fluid flow deflection angle, with greater camber of the double, or triple profile, greater variation in isentropic temperature and, consequently, greater rate of compression per stage, which can form multiple stages of the rotor and stator assembly with the same configuration of double or triple blades, providing the assembly with a greater rate of compression.

More specifically, the compressor (1) claimed is comprised, by stage, of a set of double blades (2) as per the illustration in FIG. 2, or triple blades (3) as illustrated in FIG. 3, tandem in a cluster configuration, one behind the other, involving the rotor disk (A) and its corresponding stator (B), providing greater camber of the double or triple profile, and greater deflection of the fluid flow (Δβ) without separation of fluid flow contact with the suction surface of the profiles, which, if it occurred could generate enormous losses. As illustrated in FIG. 4, observe that in the axial compressor with tandem blades, the radial speed variation component (Δυ_WTB) is greater due to the increase in flow deflection through the profile, providing a higher Δβ value, which, in turn, permits a greater rate of compression. The principle claimed is based on the smaller output angle β₂, which produces a greater fluid flow deflection angle, because Δ_β1,2=β₁−β₂, thus increasing total temperature variation, according to the expression:

$\Delta T_t=\frac{\lambda {\mathrm{Uu}}_1\left(\tan \mathrm{\beta 1}-u_2/u_1\tan \mathrm{\beta 2}\right)}{c_p}$

where:
ΔT_t=total temperature variation in the stage;
λ=correction factor;
U=ωr=tangential do rotor speed;
u₁ and u₂=axial components of the respective rotor input and output speeds;
c_p=specific fluid heat.

Observe in the expression that the lower the value for tan β₂, that this tandem configuration of the compressor tends to approach zero, the greater the ΔT_t, consequently generating a greater rate of compression. The β₂ value is established and limited by the flow diffusion criterion and, rigorously, also obeying the Haller number criterion, in which the ratio of relative output speeds through each blade's channel (V_2R), and the input speed in the same blade's channel (V_1R) is a ratio greater than or equal to 0.72. Thus, with the compressor (1) with the tandem blade configuration, one has greater deflection in fluid flow, with a smaller Haller number through the rotor with the controlled diffusion factor, D-Factor. As a result of great deflection in the rotor (A), its corresponding stator (B) should have the same double (2) or triple (3) blade configuration in order to repeat the same input conditions in the subsequent rotor. Regardless of having double (2) or triple (3) blades, the posterior blade, in the rotor (A) as well as in the stator (B), is positioned where there is a gap nozzle between it and the blade in front, using the X and Y datum points shown in FIG. 2 as reference. The gap nozzle in the position of the posterior blade in the axial direction occurs with X=0, that is, when the front blade ends, the back blade begins in the same rotor disk, or in the stator cascade, but with gap Y in circumferential positioning, or better, the posterior blade is separated from the front blade at datum point Y, which is a function of compressor characteristics and it is calculated to adjust flow through the channel. The Y gap datum point is calculated to avoid minimizing the wake from the first blade, in order to intervene as little as possible in second blade performance. The precise positioning of Y depends fundamentally on flow characteristics, in the sense of minimizing losses. For greater efficiency of the compressor rotor, as illustrated in FIG. 5, an assembly of small blades, called splitter blades (4), one at each rotor output channel, can be used to improve fluid flow at rotor output. With the cluster arrangement of the rotor disk and stator, as illustrated in FIG. 6, one can form compressors with multiples stages, greatly increasing the rate of compression.

Claims

1. Axial compressor with tandem blades, wherein is comprised, by stage, of an assembly of double (2) or triple (3) tandem blades in a cluster configuration involving the rotor disk (A) and its corresponding stator (B), arranged one after the other in the axial and circumferential direction, providing greater camber of the double or triple profile, with greater deflection of fluid flow (Δβ) without fluid flow losing contact with the blade suction surface, greater variation in isentropic total temperature and greater rate of compression.

2. Axial compressor with tandem blades, according to claim 1, wherein the posterior blade, in the rotor (A) and stator (B), is positioned with a gap nozzle in relation to the front blade; the gap nozzle in the posterior blade position in the axial direction occurs with X=0, when the front blade ends, the back blade begins in the same rotor disk, or in the stator cascade, but with a Y gap in the circumferential positioning.

3. Axial compressor with tandem blades, according to claim 2, wherein by the Y datum point as a function of flow through the channel, calculated to avoid minimizing the wake from the first blade, in order to intervene as little as possible in second blade performance.

4. Axial compressor with tandem blades, according to claim 1, wherein the greater efficiency of the compressor rotor is due to his position in an assembly of small blades, cascade of splitter blades, (4) in the rotor output channels.

5. Axial compressor with tandem blades, according to claim 1, wherein there is a cluster arrangement of the rotor disk (A) and of the stator (B) in order to form compressors with multiple stages.