Accurate positioning method for flow expansion hole of semi-open type centrifugal compressor housing

Abstract

The invention discloses a precise positioning method for a flow expansion hole of a semi-open type centrifugal compressor housing, which comprises the following steps: S1, establishing a compressor model of which the flow needs to be expanded, carrying out flow field simulation analysis, and determining a surge point; s2, determining the opening position of a flow expansion hole of the gas compressor housing so as to obtain a gas compressor model with the flow expansion hole; s3, performing flow field analysis on the compressor model with the flow expansion hole to obtain a curve graph of the inlet flow and the flow value at the flow expansion hole, and obtaining the inlet flow value when the flow value at the flow expansion hole is 0 according to the curve graph; s4, judging whether the position of the flow expansion hole is the optimal position or not, and if yes, completing accurate positioning of the flow expansion hole; otherwise, executing the step S5; and S5, adjusting the position of the flow expansion hole, and repeating the steps S3 to S4. The position of the flow expansion hole can be accurately determined, so that the formed flow expansion hole can play a role in increasing the flow range, and meanwhile it is guaranteed that the aerodynamic efficiency is not affected.

Description

Technical Field

[0001] The invention relates to the technical field of flow control of centrifugal compressors, and in particular to a method for accurately positioning a flow expansion hole of a semi-open centrifugal compressor casing. Background Art

[0002] Semi-open centrifugal compressors are widely used in blowers, air compressors, turbochargers and other fields due to their high efficiency. However, under low flow conditions, these devices may experience surge, that is, reverse backflow of local fluid inside the impeller, resulting in increased vibration or even damage to the equipment. In practice, due to changes in operating conditions (such as ambient temperature, altitude) and the influence of system resistance, centrifugal compressors often need to operate at flow rates lower than the design point. Therefore, it is crucial to expand the application range of small flow rates.

[0003] At present, the most common solution is to determine the opening position of the flow expansion hole of the compressor casing according to the throat position of the blade to expand the operable small flow range. However, it is found in practice that this method is not always effective. For example, sometimes the opening position according to this method cannot significantly increase the flow range and achieve the desired effect. Sometimes, although the flow can be increased, the aerodynamic efficiency will be sacrificed. Summary of the invention

[0004] The invention provides a method for accurately positioning a flow expansion hole of a semi-open centrifugal compressor casing, so as to overcome the technical problem that the prior art cannot effectively determine the optimal opening position of the flow expansion hole.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] A method for accurately positioning a flow expansion hole of a semi-open centrifugal compressor casing, the specific steps comprising:

[0007] S1: Establishing a compressor model that needs to expand flow, and performing flow field simulation analysis on it, including: setting the speed of the compressor model that needs to expand flow, obtaining the curve of inlet flow and outlet pressure at the speed, and determining the surge point of the compressor model that needs to expand flow based on the curve of inlet flow and outlet pressure;

[0008] S2: determining the opening position of the flow expansion hole of the compressor casing based on the throat position of the compressor blade, thereby obtaining a compressor model with the flow expansion hole;

[0009] S3: performing flow field analysis on the compressor model with the flow expansion hole, including: setting the inlet flow of the compressor model with the flow expansion hole based on the inlet flow corresponding to the surge point, and synchronously acquiring the flow value at the flow expansion hole, obtaining a curve graph of the inlet flow and the flow value at the flow expansion hole, and obtaining the inlet flow value when the flow value at the flow expansion hole is 0 according to the curve graph;

[0010] S4: based on the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of the inlet flow and the outlet pressure, determine whether the position of the flow expansion hole is the optimal position; if so, complete the precise positioning of the flow expansion hole of the compressor cover, and execute S6; otherwise, execute step S5;

[0011] S5: adjust the position of the flow expansion hole and repeat S3-S4;

[0012] S6: Optimize the size and inclination angle of the flow expansion hole at the best position.

[0013] Furthermore, based on the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of the inlet flow and the outlet pressure, it is judged whether the position of the flow expansion hole is the optimal position. The judgment rule involved is: if the absolute value of the slope of the curve corresponding to the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of the inlet flow and the outlet pressure is greater than 0.5, it means that the position of the flow expansion hole is the optimal position.

[0014] Further, in S5, adjusting the position of the flow expansion hole includes: adjusting the opening position of the flow expansion hole toward the impeller outlet.

[0015] Further, in S2, determining the opening position of the flow expansion hole of the compressor casing based on the throat position of the compressor blade includes:

[0016] S21: selecting two blades for determining the opening position of the flow expansion hole according to the blade type of the compressor, that is, if the compressor uses long and short blades, the opening position of the flow expansion hole is determined according to two adjacent long blades; if the compressor uses blades of the same length, the opening position of the flow expansion hole is determined according to two adjacent blades;

[0017] S22: Select a starting point from the outer edge of the inlet tip of the pressure surface of any selected blade, and then draw a line to the outer edge of the tip of the suction surface of another blade. The position of the shortest distance of the line is the throat of the blade, and the position corresponding to the compressor cover and the throat is the opening position of the flow expansion hole.

[0018] Furthermore, in S1, the speed of the compressor is set to the speed corresponding to the rated point operating condition or the speed corresponding to the small flow range to be expanded.

[0019] Beneficial effect: The present invention obtains the curve of inlet flow and outlet pressure and the surge point of the compressor based on the compressor model that needs to expand the flow, and opens a hole in the compressor cover. By reading the flow value at the flow expansion hole, the inlet flow value when the flow value at the flow expansion hole is 0 is obtained, and then based on the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of inlet flow and outlet pressure, it is judged whether the position of the flow expansion hole is the optimal position. If so, the flow expansion hole of the compressor cover is precisely positioned. Otherwise, the position of the flow expansion hole is adjusted until the optimal position is obtained, thereby expanding the small flow range in which the compressor can operate. The present invention solves the problem that determining the opening position of the flow expansion hole of the compressor cover according to the throat position of the blade cannot guarantee an effective increase in the flow range, and ensures that the position of the flow expansion hole is accurately determined, so that the opened flow expansion hole can both increase the flow range and ensure that the aerodynamic efficiency is not affected. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0021] Figure 1 It is a flow chart of a method for accurately positioning a flow expansion hole of a semi-open centrifugal compressor casing in the present invention;

[0022] Figure 2 is a curve diagram of the inlet flow rate and the outlet pressure at 25000 r / min in Example 1 of the present invention;

[0023] Figure 3 It is a curve diagram of the inlet flow rate and the flow value at the flow expansion hole at 25000r / min in Example 1 of the present invention;

[0024] Figure 4 A comparison diagram of the compressor flow range before and after the flow expansion hole is set in Example 1 of the present invention;

[0025] Figure 5 The graph of the inlet flow rate and the outlet pressure at 24000r / min in the second embodiment of the present invention;

[0026] Figure 6It is a curve diagram of the inlet flow rate and the flow value at the flow expansion hole at 24000r / min in Example 2 of the present invention;

[0027] Figure 7 This is a comparison diagram of the compressor flow range before and after the flow expansion hole is set in Example 2 of the present invention;

[0028] Figure 8 This is a comparison diagram of the dimensionless multivariable efficiency before and after the flow expansion hole is set in Example 2 of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] This embodiment provides a method for accurately positioning the flow expansion hole of a semi-open centrifugal compressor casing, such as Figure 1 As shown, the specific steps include:

[0031] S1: Establish a compressor model that needs to expand flow, and perform flow field simulation analysis on it, including: setting the speed of the compressor model that needs to expand flow, obtaining the curve of inlet flow and outlet pressure at the speed, and determining the surge point (surge point) of the compressor model that needs to expand flow based on the curve of inlet flow and outlet pressure, that is, the point where the inlet flow decreases and the pressure begins to decrease;

[0032] In a specific embodiment, in S1, when setting the speed of the compressor model that needs to expand the flow rate, it is generally set to the speed corresponding to the rated point condition or the speed corresponding to the small flow rate range to be expanded, and the flow rate is gradually increased from a small flow rate, so as to obtain a curve of the inlet flow rate and the outlet pressure at the set speed. For example, in this embodiment, the rated speed of 24000r / min can be used, and the speed can also be set to 20000r / min corresponding to the small flow rate. The speed corresponding to the small flow rate range to be expanded can be obtained through simulation, which is a conventional technology and is not described in detail here.

[0033] S2: determining the opening position of the flow expansion hole of the compressor casing based on the throat position of the compressor blade, thereby obtaining a compressor model with the flow expansion hole;

[0034] In a specific embodiment, in S2, determining the opening position of the flow expansion hole of the compressor casing based on the throat position of the compressor blade includes:

[0035] S21: selecting two blades for determining the opening position of the flow expansion hole according to the blade type of the compressor, that is, if the compressor uses long and short blades, the opening position of the flow expansion hole is determined according to two adjacent long blades; if the compressor uses blades of the same length, the opening position of the flow expansion hole is determined according to two adjacent blades;

[0036] S22: Select a starting point from the outer edge of the inlet tip of the pressure surface of any selected blade, and then draw a line to the outer edge of the tip of the suction surface of another blade. The position of the shortest distance of the line is the throat of the blade, and the position corresponding to the compressor cover and the throat is the opening position of the flow expansion hole.

[0037] S3: performing flow field analysis on the compressor model with the flow expansion hole, including: setting the inlet flow of the compressor model with the flow expansion hole based on the inlet flow size corresponding to the surge point, i.e., the surge point flow size, and synchronously acquiring the flow value at the flow expansion hole, obtaining a curve graph of the inlet flow and the flow value at the flow expansion hole, and obtaining the inlet flow value when the flow value at the flow expansion hole is 0 according to the curve graph;

[0038] Specifically, in this embodiment, when setting the inlet flow of the compressor model with a flow expansion hole, it can be set starting from the surge flow and then gradually increasing the flow. At the same time, the flow value at the flow expansion hole is calculated, and a curve graph of the inlet flow and the flow value at the flow expansion hole is plotted. Finally, a curve graph is obtained that shows that the flow at the flow expansion hole changes from outflow to inflow (the flow value changes from positive to negative), and then the inlet flow value when the flow value at the flow expansion hole is 0 is obtained.

[0039] S4: based on the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of the inlet flow and the outlet pressure, determine whether the position of the flow expansion hole is the optimal position; if so, complete the precise positioning of the flow expansion hole of the compressor cover, and execute S6; otherwise, execute step S5;

[0040] In a specific embodiment, the inlet flow value when the flow value at the flow expansion hole is 0 is marked on the curve of the inlet flow and the outlet pressure, and the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of the inlet flow and the outlet pressure is observed to determine whether the position of the flow expansion hole is the optimal position. The judgment rule involved is: if the absolute value of the slope of the curve corresponding to the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of the inlet flow and the outlet pressure is greater than 0.5, it means that the position of the flow expansion hole is the optimal position.

[0041] S5: adjust the position of the flow expansion hole and repeat S3-S4;

[0042] In a specific embodiment, in S5, if the absolute value of the curve slope corresponding to the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of the inlet flow and outlet pressure is less than or equal to 0.5, it is necessary to adjust the position of the flow expansion hole, including: adjusting the opening position of the flow expansion hole toward the impeller outlet.

[0043] S6: Optimize the size and inclination angle of the flow expansion hole at the best position.

[0044] Specifically, the process of optimizing the size and inclination angle of the flow expansion hole is a routine operation performed by those skilled in the art. In this embodiment, the position determination of the flow expansion hole is mainly explained. Therefore, the optimization of the size and inclination angle of the flow expansion hole is not described in detail.

[0045] Embodiment 1:

[0046] A newly designed blower 1 uses a semi-open 9-long 9-short centrifugal compressor impeller. The design parameters of the rated point are: inlet flow 54m 3 / min, outlet pressure 60KPa.

[0047] The flow field analysis software CFX is used to perform flow field simulation analysis on the compressor model (without openings in the casing) that needs to expand the flow rate. The working speed under this design condition is 25000rpm. The calculation starts from the large flow rate, and then gradually reduces the flow rate until the calculated compressor outlet pressure drops or the pressure fluctuates significantly or does not converge. The following is obtained: Figure 2 The curve shown in the figure shows that the maximum inlet flow rate of the blower at this speed is 75m 3 / min, the surge point flow rate is 40m 3 / min. The opening position of the flow expansion hole of the compressor casing is determined based on the throat position of the compressor blade, so as to obtain a compressor model with a flow expansion hole; then the flow field is analyzed, and the interface at the flow expansion hole is defined as infer1 during calculation. From the surge point flow rate of 40m 3 / min, gradually increase the flow rate, obtain the flow rate at infer1 under different flow rates, and draw the curve of infer1 flow rate and inlet flow rate, such as Figure 3 As shown, when infer1 is 0, the corresponding inlet flow value is 53m 3 / min, mapping the point to Figure 2 On the curve in , the absolute value of the slope of the curve corresponding to the point position is greater than 0.5. Therefore, it is shown that the position of the flow expansion hole is the best position. At the same time, the smaller flow and the larger flow are calculated according to this position, such as Figure 4 As shown in the figure, it can be seen that the surge point of the compressor model with flow expansion holes is increased from the original 40m3 / min expanded to 25m 3 / min, and the entire flow range has been extended.

[0048] Embodiment 2:

[0049] A newly designed blower 2 uses a semi-open 9-long 9-short centrifugal compressor impeller. The design parameters at the rated point are: inlet flow rate 76m 3 / min, outlet pressure 90kPa.

[0050] The flow field analysis software CFX was used to simulate the flow field of the compressor model (without openings in the casing) that needed to expand the flow rate. The working speed under this design condition was 24000rpm, and the following results were obtained: Figure 5 The curve shown in the figure shows that the maximum flow rate of the blower at this speed is 106.4m 3 / min, the surge point flow is 60m 3 / min. The opening position of the flow expansion hole of the compressor casing is determined based on the throat position of the compressor blade, so as to obtain a compressor model with a flow expansion hole; then the flow field is analyzed, and the interface at the opening is defined as infer1 during calculation. The flow rate at the surge point is 60m 3 / min, gradually increase the flow rate, obtain the flow rate at the interface infer1 at the opening under different flow rates, and draw the curve of infer1 flow rate and inlet flow rate, as shown in the figure. Figure 6 As shown, when infer1 is 0, the corresponding inlet flow value is 65.5m 3 / min, mapping the point to Figure 5 On the curve in , this point is located where the curve is flat (the absolute value of the slope is less than 0.5). Therefore, this point does not meet the requirements, and the position of the flow expansion hole needs to be adjusted, and then the above steps are repeated until the point is located at a position with a larger absolute value of the slope, or a position away from the flat area. In this embodiment, the position of the flow expansion hole is finally moved 8mm closer to the impeller outlet. The performance is recalculated according to the adjusted position of the flow expansion hole, and the following is obtained: Figure 7 The inlet flow and pressure curves shown in the figure show that if the traditional method is used, the gas point will be increased from the original 60m 3 / min becomes 57m 3 / min, the effect is not obvious. However, after adjusting the position of the flow expansion hole to 8mm by this method, the surge point flow rate becomes 45m 3 / min, which significantly expands the use range of small flow rates, and at the same time, the available range of large flow rates is also significantly increased. Figure 8It is a comparison chart of dimensionless polyvariable efficiency. It can be seen that after the method is used to open the hole, the aerodynamic efficiency has no obvious change, where the dimensionless polyvariable efficiency is defined as the ratio of the polyvariable efficiency at each point to the highest polyvariable efficiency. The method provided in this embodiment can not only effectively expand the flow application range of the centrifugal compressor, but also ensure a high aerodynamic efficiency. This is of great significance for improving the reliability and performance of the compressor under various complex working conditions.

[0051] Finally, it should be noted that the above 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 with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for accurately positioning a flow expansion hole of a semi-open centrifugal compressor casing, characterized in that: The specific steps include: S1: Establishing a compressor model that needs to expand flow, and performing flow field simulation analysis on it, including: setting the speed of the compressor model that needs to expand flow, obtaining the curve of inlet flow and outlet pressure at the speed, and determining the surge point of the compressor model that needs to expand flow based on the curve of inlet flow and outlet pressure; S2: determining the opening position of the flow expansion hole of the compressor casing based on the throat position of the compressor blade, thereby obtaining a compressor model with the flow expansion hole; S3: performing flow field analysis on the compressor model with the flow expansion hole, including: setting the inlet flow of the compressor model with the flow expansion hole based on the inlet flow corresponding to the surge point, and synchronously acquiring the flow value at the flow expansion hole, obtaining a curve graph of the inlet flow and the flow value at the flow expansion hole, and obtaining the inlet flow value when the flow value at the flow expansion hole is 0 according to the curve graph; S4: based on the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of the inlet flow and the outlet pressure, determine whether the position of the flow expansion hole is the optimal position; if so, complete the precise positioning of the flow expansion hole of the compressor cover, and execute S6; otherwise, execute step S5; S5: adjust the position of the flow expansion hole and repeat S3-S4; S6: Optimize the size and inclination angle of the flow expansion hole at the best position.

2. The method for accurately positioning the flow expansion hole of a semi-open centrifugal compressor casing according to claim 1, characterized in that: Based on the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of the inlet flow and the outlet pressure, it is judged whether the position of the flow expansion hole is the optimal position. The judgment rule involved is: if the absolute value of the slope of the curve corresponding to the position of the inlet flow value when the flow value at the flow expansion hole is 0 on the curve of the inlet flow and the outlet pressure is greater than 0.5, it means that the position of the flow expansion hole is the optimal position.

3. The method for accurately positioning the flow expansion hole of a semi-open centrifugal compressor casing according to claim 2, characterized in that: In S5, adjusting the position of the flow expansion hole includes: adjusting the opening position of the flow expansion hole toward the impeller outlet.

4. The method for accurately positioning the flow expansion hole of a semi-open centrifugal compressor casing according to claim 3 is characterized in that: In S2, the opening position of the flow expansion hole of the compressor casing is determined based on the throat position of the compressor blade, including: S21: selecting two blades for determining the opening position of the flow expansion hole according to the blade type of the compressor, that is, if the compressor uses long and short blades, the opening position of the flow expansion hole is determined according to two adjacent long blades; if the compressor uses blades of the same length, the opening position of the flow expansion hole is determined according to two adjacent blades; S22: Select a starting point from the outer edge of the inlet tip of the pressure surface of any selected blade, and then draw a line to the outer edge of the tip of the suction surface of another blade. The position of the shortest distance of the line is the throat of the blade, and the position corresponding to the compressor cover and the throat is the opening position of the flow expansion hole.

5. The method for accurately positioning the flow expansion hole of a semi-open centrifugal compressor casing according to claim 1, characterized in that: In S1, the speed of the compressor is set to the speed corresponding to the rated point operating condition or the speed corresponding to the small flow range to be expanded.

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