A two-stage diffuser

Abstract

The present invention provides a two-stage diffuser, which includes a diffuser body, a first-stage diffuser vane, and a second-stage diffuser vane. The diffuser body is annular. The first-stage diffuser vane and the second-stage diffuser vane are sequentially arranged radially on the diffuser body. The first-stage diffuser vane is of a straight-arm type, evenly distributed on the diffuser body, and deflected in the clockwise direction. The second-stage diffuser vane is of an airfoil type, evenly distributed on the diffuser body, and deflected in the counterclockwise direction. The two-stage diffuser of the present invention designs a vane diffuser on the vane diffuser to form a two-stage diffuser. By adopting the combination of straight-wall vanes and airfoil vanes, it can achieve the effect of reducing the flow velocity of the air flow after passing through the diffuser from the impeller outlet and improving the flow in the small flow rate region.

Description

Technical Field

[0001] The present invention relates to a diffuser structure, and particularly to a two-stage diffuser. Background Art

[0002] In practice, in order to improve the efficiency of a compressor unit, it is necessary to increase the output gas pressure. A diffuser is to convert the dynamic pressure of the air flow into static pressure, reduce the speed, and increase the static pressure. Therefore, its role is particularly important. The diffusers of centrifugal compressors are generally divided into two categories: vaneless diffusers and vaned diffusers. A vaneless diffuser consists of an annular channel formed by two flat walls; a vaned diffuser is formed by evenly distributing blades along the circumference in the annular channel of the vaneless diffuser. By the shape of the blades, the flow direction of the air flow is restricted, thereby shortening the overall structural size of the diffuser channel. The vaned diffuser includes: vane diffuser and straight-wall diffuser. Its working principle is to convert the velocity energy into pressure energy by using different flow cross-sectional areas.

[0003] In practice, a vaneless diffuser is simple in design, easy to manufacture, low in cost, has a flat performance curve, and a wide operating range; however, it has large flow losses and low efficiency. For a conventional compressor, the form of a vane diffuser is generally selected. According to the theoretical calculation and test of the diffuser, the vane diffuser has the advantages of large pressure ratio and small size, and the loss under the design condition is smaller than that of the vaneless diffuser. Its flow path is short and the flow loss is small, so the efficiency is relatively high. However, at the same time, when the flow rate of the compressor under off-design conditions decreases, the air flow impact loss is large, and serious flow separation often occurs first in the vane diffuser, thereby causing the compressor to surge, and the stable operating range is narrow. Summary of the Invention

[0004] Aiming at the defects or deficiencies existing in the above-mentioned prior art, the purpose of the present invention is to provide a two-stage diffuser to solve the problems of large air flow impact loss and easy occurrence of serious flow separation in the current vane diffuser, resulting in unstable working conditions.

[0005] For this purpose, the present invention adopts the following technical solutions:

[0006] A two-stage vane diffuser includes a diffuser body, a first-stage diffuser vane, and a second-stage diffuser vane. The diffuser body is circular, and the first-stage diffuser vane and the second-stage diffuser vane are sequentially arranged radially on the diffuser body;

[0007] The first-stage diffuser vane is straight-arm shaped, evenly distributed on the diffuser body, and deflected in the clockwise direction, and the number is between 16 and 23;

[0008] The second-stage diffuser vane is airfoil shaped, evenly distributed on the diffuser body, and deflected in the clockwise direction, and the number is between 16 and 23;

[0009] The first-stage blades of the diffuser are arranged staggeredly with the second-stage blades of the diffuser, and the staggering distance is 1 / 3 - 1 / 2 of the outlet width value of the first-stage blades of the diffuser;

[0010] The relationship between the inlet airflow angle α3 of the first-stage blades of the diffuser and the outlet airflow angle α2 of the impeller is

[0011] tanα3 = b2 / b3 tanα2, where b2 is the outlet width of the impeller and b3 is the inlet width of the first-stage blades of the diffuser.

[0012] Preferably, the difference between the outlet geometric angle of the second-stage blades of the diffuser and the inlet geometric angle of the first-stage blades of the diffuser is 12° - 15°.

[0013] Preferably, the ratio of the outlet diameter D4 of the second-stage blades of the diffuser to the outlet diameter D2 of the impeller is between 1.35 - 1.45.

[0014] Preferably, the inlet width b3 of the first-stage blades of the diffuser is greater than the outlet width b2 of the impeller.

[0015] More preferably, the inlet width b3 of the first-stage blades of the diffuser is greater than the outlet width b2 of the impeller by 1 - 2 mm.

[0016] Most preferably, the inlet width b3 of the first-stage blades of the diffuser is greater than the outlet width b2 of the impeller by 1.08 - 1.15 mm.

[0017] In addition, the number of the first-stage blades of the diffuser or the number of the second-stage blades of the diffuser is less than the number of the moving blades of the impeller and is not an integer multiple of the number of the moving blades.

[0018] The present invention has the following beneficial effects:

[0019] The two-stage diffuser of the present invention is designed according to the requirements of the centrifugal compressor to increase the outlet static pressure and improve the flow in the small flow rate region. A vane diffuser is designed on the blade diffuser to form a two-stage diffuser. The combination of straight-wall blades and airfoil blades is adopted. The airflow first passes through the straight-wall blades of the diffuser from the impeller outlet and then passes through the airfoil blades, realizing the functions of reducing the flow velocity, increasing the static pressure, improving the flow in the small flow rate region, expanding the range of the high-efficiency region, and increasing the adjustment range of the diffuser after the airflow passes through the diffuser from the impeller outlet. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of the staggering distance between the first-stage blades of the diffuser and the second-stage blades of the diffuser.

[0021] Figure 2 It is a schematic flow chart of the system of the present invention.

[0022] In the figure, 1 is the diffuser body, 2 is the first-stage diffuser vane, and 3 is the second-stage diffuser vane.

[0023] The geometric parameters and their physical meanings of the impeller and vane diffuser include: the impeller outlet width b2, the impeller outlet diameter D2, the impeller outlet gas flow angle α2, the first-stage diffuser vane inlet width b3, the second-stage diffuser vane outlet width b4, the diffuser inlet and outlet diameters D3, D4, the diffuser inlet gas flow angle α3, the vane outlet geometric angle α4, the number of vanes Z and the profile, and the first-stage diffuser vane outlet width b5. Specific implementation mode

[0024] The straight-arm type or airfoil type described in the present invention is a conventional profile selection for diffuser vane design. Among them, the straight-arm type is also called the straight-line type, and the vane is a straight plate with equal thickness, and the design is relatively simple. If the diffuser vane is of the airfoil type, the center line of the airfoil vane is bent into the required shape, and the C-4 airfoil is often used.

[0025] The geometric angles of the inlet and outlet of the vane described in the present invention are the angles between the tangent direction of the vane camber line and the opposite direction of the rotational circumferential velocity direction.

[0026] The following other parameters of the diffuser described in the present invention are all the conventional understandings in the art.

[0027] Example 1:

[0028] As Figure 1-2 shown, the present invention provides a two-stage vane diffuser, including a diffuser body 1, a first-stage diffuser vane 2, and a second-stage diffuser vane 3. The diffuser body is in a circular ring shape, and the first-stage diffuser vane 2 and the second-stage diffuser vane 3 are sequentially arranged radially on the diffuser body; the first-stage diffuser vane 2 is of the straight-arm type, evenly distributed on the diffuser body 1, and deflected in the clockwise direction. The second-stage diffuser vane 3 is of the airfoil type, evenly distributed on the diffuser body 1, and deflected in the clockwise direction, which can significantly reduce the degree of air flow separation at the inlet and outlet of the diffuser, and at the same time can convert the dynamic pressure into static pressure energy to a large extent.

[0029] When designing the diffuser vane according to the flow field parameters, a combination of a straight-wall vane and an airfoil vane is adopted to form a two-stage diffuser. The air flow first passes through the straight-wall vane of the diffuser from the impeller outlet, and then passes through the airfoil vane, as Figure 1 . Further, the vanes all adopt binary vanes, and the vane design is carried out according to the average value of the flow field parameters.

[0030] Furthermore, the first-stage vanes of the diffuser are straight-walled, and its passage is basically straight. The air flow velocity and pressure distribution are relatively uniform, and the flow loss is small. They are evenly distributed on the circumference after a section of clearance at the impeller outlet. The second-stage vanes of the diffuser are airfoil-shaped, with small flow loss and good off-design performance. They are evenly distributed on the circumference at the outlet of the first-stage vanes. As Figure 1 , the first-stage vanes of the diffuser and the second-stage vanes of the diffuser are staggeredly arranged, and the stagger distance L is equal to 1 / 3 - 1 / 2 pitch (the pitch is: the outlet width of the first-stage vanes of the diffuser).

[0031] Furthermore, the inlet width b3 of the first-stage vanes of the diffuser is greater than the outlet width b2 of the impeller, and there is a section of clearance between them. This clearance is actually equivalent to a very short vaneless diffuser, which can make the gas flowing out of the impeller become uniform and the speed decrease before entering the diffuser, improve the inlet state of the diffuser, and at the same time reduce the noise generated by the air flow pulsation.

[0032] Furthermore, as described above, b3 = b2 + (1 - 2) mm, control the inlet Mach number of the diffuser to be less than 0.8, and generally the length of the vaneless section in the vane diffuser is D3 / D2 = 1.08 - 1.15.

[0033] Furthermore, for the intermediate stage: D4 / D2 = 1.45 - 1.55; for the last stage of the volute: D4 / D2 = 1.35 - 1.45; for the stage of the radial straight vane impeller: D4 / D2 = 1.55 - 1.65.

[0034] Furthermore, the difference between the outlet geometric angle and the inlet geometric angle of the vane diffuser is 12° - 15°, which evenly controls the air flow.

[0035] Furthermore, the inlet air flow angle α3 of the diffuser can be calculated by the formula:

[0036] tanα3 = b2 / b3 tanα2,

[0037] which can reduce the flow loss in the second vane.

[0038] Furthermore, the number of vanes Z of the diffuser is generally 16 - 23, and it should be less than the number of moving vanes of the impeller. To avoid resonance, the number of vanes of the diffuser and the impeller should not be equal or in integer multiples.

[0039] Effect verification:

[0040] The test parameters of the centrifugal compressor: the impeller speed is 60000 r / min, the highest efficiency point of the centrifugal compressor is the design point, and the efficiency near the design point working condition is about 3.5% higher than the highest efficiency of the traditional vane diffuser.

[0041] As described above, the present invention can be preferably implemented. The above embodiments are only one kind of embodiments of the present invention, and are not used to limit the implementation scope of the present invention, that is, all equal changes and modifications made with the present invention are covered by the scope required to be protected by the claims of the present invention.

Claims

1. A two-stage diffuser, comprising a diffuser body, the first-stage diffuser vanes and the second-stage diffuser vanes. The diffuser body is in an annular shape, and the first-stage diffuser vanes and the second-stage diffuser vanes are sequentially arranged radially on the diffuser body; Characterized in that: The first-stage diffuser vanes are in a straight-arm type, evenly distributed on the diffuser body, and deflected in the clockwise direction, and the number is between 16 and 23; The second-stage diffuser vanes are in an airfoil type, evenly distributed on the diffuser body, and deflected in the clockwise direction, and the number is between 16 and 23; The first-stage diffuser vanes and the second-stage diffuser vanes are staggeredly arranged, and the staggering distance is 1 / 3 - 1 / 2 of the outlet width value of the first-stage diffuser vanes; The relationship between the inlet flow angle α3 of the first-stage diffuser vanes and the outlet flow angle α2 of the impeller is tanα3 = b2 / b3 tanα2, where b2 is the outlet width of the impeller and b3 is the inlet width of the first-stage diffuser vanes; The difference between the outlet geometric angle of the second-stage diffuser vanes and the inlet geometric angle of the first-stage diffuser vanes is 12° - 15°; The ratio of the outlet diameter D4 of the second-stage diffuser vanes to the outlet diameter D2 of the impeller is between 1.35 and 1.45; The inlet width b3 of the first-stage diffuser vanes is greater than the outlet width b2 of the impeller; The number of the first-stage diffuser vanes or the number of the second-stage diffuser vanes is less than the number of the moving blades of the impeller, and is not an integral multiple of the number of the moving blades; The inlet Mach number of the first-stage diffuser vanes is less than 0.

8.

2. The two-stage diffuser according to claim 1, wherein, The inlet width b3 of the first-stage diffuser vanes is 1 - 2 mm greater than the outlet width b2 of the impeller.

3. The two-stage diffuser according to claim 2, wherein The inlet width b3 of the first-stage diffuser vanes is 1.08 - 1.15 mm greater than the outlet width b2 of the impeller.

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