Design method for centrifugal compressor of asymmetric vaned diffuser coupling volute tongue

Abstract

The invention discloses a design method of a centrifugal compressor with an asymmetric bladed diffuser coupled with a volute tongue, which adopts the asymmetric bladed diffuser and increases the distance from the outlet of the diffuser to the volute tongue on the asymmetric bladed diffuser to improve the structure of the existing centrifugal compressor. The non-uniformity, caused by a volute tongue structure, of an internal flow field of the centrifugal compressor is effectively reduced, internal flow separation of the vaned diffuser is restrained, the efficiency and the pressure ratio of the compressor are improved, meanwhile, the stable working range of the centrifugal compressor is widened, and the pneumatic stability of the centrifugal compressor is improved.

Description

Technical Field

[0001] The invention relates to the technical field of rotary machinery, and in particular to a design method for a centrifugal compressor with an asymmetric vaned diffuser coupled with a volute tongue. Background Art

[0002] The vaned diffuser is an effective measure to improve the efficiency of the centrifugal compressor under the requirement of high pressure ratio. The two sides of the flow channel are fixed with a back plate and a casing, and in the middle are blades with a specific airfoil. The traditional vaned diffuser is axisymmetric, and the blade installation angle is equal at different circumferential positions. Under the assumption of uniform circumferential flow, the optimal performance of the design point is guaranteed, and the kinetic energy of the impeller outlet airflow can be effectively converted into static pressure. Usually, the flow of air in the diffuser and volute is uniformly decelerated and pressurized. Once a sudden pressure change occurs, it means that certain geometric structures have interfered with the flow, which in turn leads to flow separation or mixing loss, and ultimately affects the efficiency and stability of the compressor. When the flow rate is further reduced, the flow instability is further aggravated, resulting in larger-scale flow separation or even gas reflux, inducing surge in the compressor. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a design method for a centrifugal compressor with an asymmetric vaned diffuser coupled with a volute, thereby reducing the non-uniformity of the internal flow field of the centrifugal compressor caused by the volute structure, inhibiting the flow separation inside the vaned diffuser, improving the compressor efficiency and pressure ratio, while broadening the stable operating range of the centrifugal compressor and improving the aerodynamic stability of the centrifugal compressor.

[0004] The object of the present invention is achieved in that:

[0005] A design method for a centrifugal compressor with an asymmetric vaned diffuser coupled with a volute tongue.

[0006] The compressor flow range is defined as:

[0007]

[0008] Where: M c is the dimensionless mass flow rate at the clogging point, M s is the dimensionless mass flow rate near the stall point, M d is the dimensionless mass flow rate at the design point;

[0009] The compressor stall margin is:

[0010]

[0011] The static pressure fluctuation amplitude is:

[0012]

[0013] Among them, A i is the amplitude of the diffuser outlet at the circumferential angle i, P i is the static pressure at the diffuser outlet at the circumference i°, P ave is the average circumferential static pressure at the diffuser outlet;

[0014] Diffuser outlet geometry:

[0015] α2=α des +0.1*(α-α1) (4)

[0016] Among them, α2 is the diffuser outlet geometry angle, α1 is the diffuser inlet geometry angle, and α des is the design value of the symmetrical diffuser outlet geometry angle, α is the diffuser inlet flow angle;

[0017] The centrifugal compressor design method includes the following steps:

[0018] S1. Design of symmetrical diffuser

[0019] The design point of the symmetrical diffuser is calculated to obtain the flow field and circumferential static pressure distribution, and the flow field analysis is performed. The static pressure fluctuation amplitude is calculated according to formula (3) to obtain the main influencing area that causes the diffuser to produce flow separation.

[0020] S2. Design of asymmetric diffuser structure

[0021] The two diffuser blades in the volute tongue influence area are merged into one, and the diffuser blade is set in the middle position of the original two diffuser blades to form an asymmetric diffuser blade. The adjustment method of the asymmetric diffuser blade is:

[0022] The blade inlet installation angle α1 remains unchanged, and the diffuser blade leading edge radius R E , trailing edge radius R A Keep unchanged, adjust the outlet installation angle α2 of the asymmetric diffuser blade, and adjust the asymmetric diffuser blade

[0023] A i -A i-1 ≤0.01

[0024] The calculation is performed according to formula (4), and this cycle is repeated until A i holds true, where subscript i is the i-th iteration and A is the static pressure fluctuation amplitude;

[0025] S3, increase the ratio of the radial distance from the diffuser outlet to the volute tongue to the diffuser outlet radius, that is, L = D / R, where D is the distance from the diffuser outlet to the volute tongue, and R is the diffuser outlet radius;

[0026] According to L i =L i-1 +0.05 gradually increases Li The value is , where the subscript i is the i-th iteration, and the radial dimension of the volute is enlarged while keeping the volute passage area unchanged. The enlarged new volute is combined with the asymmetric diffuser to form an asymmetric diffuser and new volute combination structure, and CFD calculation and analysis are performed until

[0027] A i -A i-1 ≤0.01

[0028] To A i holds, where the subscript i is the i-th iteration.

[0029] Furthermore, in S1, the main influencing area causing flow separation in the diffuser is the area at the volute tongue.

[0030] Furthermore, in S3, L increases to 0.3.

[0031] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0032] The present invention proposes a method of using an asymmetric vaned diffuser and further increasing the distance from the diffuser outlet to the volute tongue on the asymmetric vaned diffuser, thereby improving the structure of an existing centrifugal compressor, so as to effectively reduce the non-uniformity of the internal flow field of the centrifugal compressor caused by the volute tongue structure, inhibit the flow separation inside the vaned diffuser, improve the compressor efficiency and pressure ratio, broaden the stable operating range of the centrifugal compressor, and improve the aerodynamic stability of the centrifugal compressor.

[0033] The isentropic efficiency of the compressor was increased by 1.11%, the pressure ratio was increased by 2.47%, the static pressure distortion amplitude at the diffuser outlet at the compressor volute was reduced from 5.5% to 1.29%, and the stall margin of the high-pressure ratio centrifugal compressor was widened by 2.63%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a cross-sectional view of a centrifugal compressor;

[0035] Figure 2a is a schematic diagram of symmetrical diffuser distribution;

[0036] Figure 2b is the circumferential distribution diagram of static pressure at the symmetrical diffuser outlet;

[0037] Figure 3 Schematic diagram for comparison between symmetric and asymmetric diffusers;

[0038] Figure 4 This is a schematic diagram of the diffuser installation angle;

[0039] Figure 5 Schematic diagram of diffuser outlet radius and distance between diffuser and volute tongue;

[0040] Figure 6a This is a comparison chart before and after optimization (performance curve);

[0041] Figure 6b Comparison before and after optimization (circumferential distribution of static pressure at the diffuser outlet).

[0042] Reference numerals

[0043] In the accompanying drawings, 1 is a rotating shaft, 2 is an impeller, 3 is a diffuser mounting plate, 4 is a blade diffuser, and 5 is a volute flow passage. DETAILED DESCRIPTION

[0044] In order to accurately determine the impact of the diffuser on the compressor operating range, the compressor flow range is defined as:

[0045]

[0046] Where: M c is the dimensionless mass flow rate at the clogging point, M s is the dimensionless mass flow rate near the stall point, M d is the dimensionless mass flow rate at the design point.

[0047] The compressor stall margin is:

[0048]

[0049] The static pressure fluctuation amplitude is:

[0050]

[0051] Among them, A i is the amplitude of the diffuser outlet at the circumferential angle i, P i is the static pressure at the diffuser outlet at the circumference i°, P ave It is the average circumferential static pressure at the diffuser outlet.

[0052] Diffuser outlet geometry:

[0053] α2=α des +0.1*(α-α1) (4)

[0054] Among them, α2 is the diffuser outlet geometry angle, α1 is the diffuser inlet geometry angle, and α des is the design value of the symmetrical diffuser outlet geometry angle, and α is the diffuser inlet flow angle.

[0055] A design method for a centrifugal compressor with an asymmetric vaned diffuser coupled with a volute tongue:

[0056] 1. Design a symmetrical diffuser and use a numerical calculation method that has been verified by experiments to calculate the design point, and obtain the flow field and circumferential static pressure distribution, see Figure 2a , Figure 2b.Depend on Figure 2a , Figure 2b It can be seen that the asymmetry of the volute tongue causes serious circumferential non-uniformity in the flow inside the diffuser near the volute tongue, resulting in flow separation in the diffuser at the volute tongue, and a low-pressure area appears downstream of the volute tongue. The maximum amplitude of static pressure variation in the near-stall condition is 5.5%, and the affected range is 30° to 90° circumferentially; among them, the static pressure fluctuation amplitude is calculated according to Formula 3.

[0057] 2. Based on the flow field analysis in the first step, an asymmetric diffuser structure is designed on the basis of the symmetrical diffuser with blades: one diffuser blade in the main influence area of ​​the volute tongue is reduced and its distribution is adjusted. In this embodiment, the two diffuser blades in the influence area of ​​the volute tongue are merged into one, and the diffuser blade is set in the middle of the original two diffuser blades to form an asymmetric diffuser blade. The structure is shown in FIG. Figure 3 .Will Figure 3 The asymmetric diffuser blade 1 is adjusted: the blade inlet installation angle α1 remains unchanged, and the diffuser blade leading edge radius R E , trailing edge radius R A Keep unchanged, adjust the diffuser blade 1 outlet installation angle α2, and the adjustment method is calculated according to formula (4), and repeat this cycle until holds true, where the subscript i is the i-th iteration and A is the static pressure fluctuation amplitude. The asymmetric diffuser design reduces the static pressure distortion amplitude of the diffuser outlet near the volute tongue from 5.5% to 2.9%;

[0058] Figure 4 The symbols mean: diffuser blade inlet installation angle α1, diffuser blade outlet installation angle α2, diffuser blade leading edge radius R E , trailing edge radius R A .

[0059] 3. In order to further reduce the influence of the asymmetric structure of the volute tongue on the flow in the diffuser, the ratio of the radial distance from the diffuser outlet to the volute tongue to the diffuser outlet radius is increased, that is, L = D / R, where D is the distance from the diffuser outlet to the volute tongue, and R is the diffuser outlet radius. Figure 5 ; L i According to L i =L i-1 +0.05 gradually increases L i value, where the subscript i is the i-th iteration; and the radial size of the volute is enlarged while keeping the volute passage area unchanged, the enlarged new volute is combined with the asymmetric diffuser in the previous step to form an asymmetric diffuser + new volute structure, and CFD calculation and analysis are performed until holds, where the subscript i is the i-th iteration. In this paper, when L increases from 0.15 to 0.3, its efficiency is improved by 1.11%, and the static pressure distortion amplitude of the diffuser outlet near the volute tongue is reduced from 2.9% to 1.29%.

[0060] 4. The final design of the asymmetric diffuser and volute increases the isentropic efficiency of the compressor by 1.11%, the pressure ratio by 2.47%, the static pressure distortion amplitude of the diffuser outlet at the compressor volute tongue is reduced from 5.5% to 1.29%, and the stall margin of the high-pressure ratio centrifugal compressor is widened by 2.63%. See Figure 6.

[0061] The isentropic efficiency of the compressor of the present invention is increased by 1.11%, the pressure ratio is increased by 2.47%, the static pressure distortion amplitude at the diffuser outlet at the compressor volute is reduced from 5.5% to 1.29%, and the stall margin of the high-pressure ratio centrifugal compressor is widened by 2.63%. See Figure 6.

[0062] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A design method for a centrifugal compressor with an asymmetric vaned diffuser coupled with a volute tongue, characterized in that: The compressor flow range is defined as: Where: M c is the dimensionless mass flow rate at the clogging point, M s is the dimensionless mass flow rate near the stall point, M d is the dimensionless mass flow rate at the design point; The compressor stall margin is: The static pressure fluctuation amplitude is: Among them, A i is the amplitude of the diffuser outlet at the circumferential angle i, P i is the static pressure at the diffuser outlet at the circumference i°, P ave is the average circumferential static pressure at the diffuser outlet; Diffuser outlet geometry: α2＝α des +0.1*(α-α1) (4) Among them, α2 is the diffuser outlet geometry angle, α1 is the diffuser inlet geometry angle, and α des is the design value of the symmetrical diffuser outlet geometry angle, α is the diffuser inlet flow angle; The centrifugal compressor design method includes the following steps: S1. Design of symmetrical diffuser The design point of the symmetrical diffuser is calculated to obtain the flow field and circumferential static pressure distribution, and the flow field analysis is performed. The static pressure fluctuation amplitude is calculated according to formula (3) to obtain the main influencing area that causes the diffuser to produce flow separation. S2. Design of asymmetric diffuser structure The two diffuser blades in the volute tongue influence area are merged into one, and the diffuser blade is set in the middle position of the original two diffuser blades to form an asymmetric diffuser blade. The adjustment method of the asymmetric diffuser blade is: The blade inlet installation angle α1 remains unchanged, and the diffuser blade leading edge radius R E , trailing edge radius R A Keep unchanged, adjust the outlet installation angle α2 of the asymmetric diffuser blade, and adjust the asymmetric diffuser blade The calculation is performed according to formula (4), and this cycle is repeated until holds true, where subscript i is the i-th iteration and A is the static pressure fluctuation amplitude; S3, increase the ratio of the radial distance from the diffuser outlet to the volute tongue to the diffuser outlet radius, that is, L = D / R, where D is the distance from the diffuser outlet to the volute tongue, and R is the diffuser outlet radius; According to L i =L i-1 +0.05 gradually increases L i The value is , where the subscript i is the i-th iteration, and the radial dimension of the volute is enlarged while keeping the volute passage area unchanged. The enlarged new volute is combined with the asymmetric diffuser to form an asymmetric diffuser and new volute combination structure, and CFD calculation and analysis are performed until arrive holds, where the subscript i is the i-th iteration.

2. The design method of a centrifugal compressor with an asymmetric vaned diffuser coupled with a volute tongue according to claim 1, characterized in that: In S1, the main influencing area that causes flow separation in the diffuser is the volute tongue area.

3. The design method of a centrifugal compressor with an asymmetric vaned diffuser coupled with a volute tongue according to claim 1, characterized in that: In S3, L increases to 0.3.

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