CN102032218B - A method for processing a cavity-backed perforated plate casing - Google Patents

Abstract

A method for processing a back cavity perforated plate casing, firstly designing a casing processing that only includes an annular back cavity and a perforated plate with round holes or inclined slots, and then setting the back cavity perforated plate type casing processing in the axial flow compressed air The front end of the machine rotor inlet and covers the casing corresponding to the leading edge part of the rotor blade. The cavity-back perforated plate casing processing method forms adaptive flow in the back cavity and generates unsteady shedding vortices at the perforated plate. The wave-vortex interaction can effectively absorb and dissipate the energy of low-frequency disturbance waves in the compressor flow field and Suppressing the non-linear amplification of the precursor wave of the stall, so that the occurrence of the precursor stall in the compressor can be delayed, and the stable working range of the compressor system can be increased; in addition, the present invention does not directly affect the structure of the mainstream flow field of the compressor, so it will not cause damage to the compressor system. The pressure ratio drop and efficiency loss, and the structure is simple and compact, which can meet the engineering restrictions on the casing size.

Description

A method for processing a cavity-backed perforated plate casing

technical field

The invention relates to a processing method for a cavity-backed perforated plate type case, which is used for widening the stable operation range of an axial flow compressor, especially for modern high-load transphonic axial flow compressors; the invention belongs to the technical field of turbomachines.

Background technique:

As one of the three key components of the air-breathing propulsion system, the axial-flow compressor has been widely used in compression systems of aero-engines, air-breathing cruise missiles, and chemical and energy industries. However, in the design work of modern high-load transonic axial flow compressors, the stability problem represented by rotating stall is particularly prominent, which seriously affects the stable working range of axial flow compressors. As the workload continues to increase, it is more likely to cause insufficient stability of the compressor within the working range. Therefore, the stability design task of the high-load transonic axial flow compressor becomes more and more difficult. It can be said that the proper control of the rotating stall not only directly affects the pressure ratio, efficiency and other working performance of the axial flow compressor, but also is closely related to various problems and failures that occur during the development and use of the air-breathing propulsion system.

In order to solve the above-mentioned problem of unstable working conditions during the operation of the compressor, researchers have tried many methods to expand the stable working range of the compressor. However, at present, passive control measures such as mid-level air release and casing treatment are used in engineering practice, but the traditional casing treatment technology will not only affect the pressure ratio, efficiency and other working characteristics of the system, but also there is no unified design guidelines.

Through a large number of experimental studies, it is found that the casing treatment with a larger perforation rate can indeed improve the margin of the low-speed and transonic compressors, and the effects of different structures are significantly different. However, casing treatment affects not only the tip flow and stall margin, but also affects the pressure rise performance and efficiency of the compressor, and the key to the application of casing treatment is how to deal with the relationship between margin and efficiency. relationship between. When researchers apply casing processing technology, they generally pay for the loss of efficiency, and the greater the stability expansion margin, the greater the loss suffered. What the designer has to do is to minimize the efficiency loss as much as possible according to the existing knowledge.

This is because the traditional casing treatment design is based on the expansion mechanism of the casing treatment to control flow separation. It is believed that the flow at the tip and root of the axial flow compressor is the most complex and harsh, and the stall is usually at the tip or Occurs at the blade root. For a transonic compressor with a high load and high pressure ratio, the flow in the tip wall area is more complicated, the mixing of the tip leakage vortex and the boundary layer of the end wall, the interference of the shock wave and the boundary layer, etc. etc. will cause the flow loss and airflow blockage at the tip. Therefore, if the flow at the tip or the root can be effectively improved, the accumulated boundary layer can be effectively eliminated, the flow loss can be reduced, and the load on the tip can be reduced. Naturally, the stall can be delayed. occur.

The existing casing treatment design based on experience and "trial and error" methods may achieve occasional success by changing the flow field structure in the compressor tip area, but it is difficult to meet the needs of extended stability design. One model of compressor employs a successful casing treatment or patent, while another compressor either expands the most effective area of stabilization away from the design point, or has no effect at all.

Contents of the invention

The technical problem of the present invention is to overcome the deficiencies of the prior art and provide a method for processing the cavity-backed perforated plate casing, which can broaden the stable working range of the axial flow compressor while maintaining the original pressure ratio and working efficiency of the compressor Basically unchanged.

Technical solution of the present invention: a method for processing a cavity-backed perforated plate type casing. As shown in FIG. A perforated plate 2 with a round hole or a chute, the annular back cavity 1 is located on the outside of the perforated plate 2 and is connected by a stop bolt structure to form an airtight air chamber, and then the back cavity perforated plate type processing casing is set at the inlet of the axial compressor rotor The front end covers the front end of the rotor blade 3 corresponding to the casing. The cavity-backed perforated plate processing casing forms an adaptive flow in the annular back cavity 1 and generates an unsteady shedding vortex at the perforated plate 2. The wave-vortex interaction Effectively absorb and dissipate the energy of low-frequency disturbance waves in the compressor flow field and suppress the nonlinear amplification of stall precursor waves, thereby delaying the occurrence of precursor stall in the compressor and increasing the stable operating range of the compressor system.

The principle of the invention: whether the treatment of the casing with air chambers changes the blocking characteristics in the blade passages that lead to the stall or acts on the precursor wave in the initial stage of the stall, and at the beginning of the stall, it is not at all There is no blockage. Although the development of an uncontrolled precursor wave will lead to blockage or even a stall, it is completely different to conduct research from the perspective of a controlled stall. If it is considered that the casing treatment is due to the suppression of the precursor wave of the stall and thus realizes the extended stability, the unsteady method should be used to study the mechanism of its suppression of the disturbance wave; if viewed from the traditional point of view, it should be explained from the steady point of view The results of the momentum and mass exchange caused by the return flow of the air chamber of the casing are used to explain the mechanism of stability expansion. All efforts to be made are to design the return channel in the air chamber so that the casing can achieve the maximum stability expansion effect and reduce the stability of the machine. Flow losses inside the casket keep the efficiency of the compressor high.

In the experimental research on the return channels in various casing air chambers, it was found that in the case of a fixed cavity depth, no matter whether the streamlined blades or purely rectangular partitions are arranged in the air chamber return channels, the casing cannot be significantly changed. The stability expansion effect of the treatment does not increase the working efficiency of the compressor due to the use of streamlined guide vanes or decrease the efficiency of the compressor due to the use of non-streamlined guide vanes. Obviously, it is doubtful to use the traditional flow blockage to explain the expansion mechanism of the casing treatment. In addition, experiments have confirmed that the flow through the casing is a small amount relative to the main flow, and the effect on efficiency is not direct. Therefore, the current understanding of the expansion mechanism of the casing treatment is phenomenological and empirical. To obtain a better design method, a deeper understanding of the mechanism of the expansion stability of the casing treatment must be obtained.

The traditional casing treatment is expected to work by changing the blockage of the flow, especially the blockage of the blade tip area. Different from the starting point of these studies, the present invention will design a new type of casing treatment to affect the evolution of the stall precursor wave instead of changing the compressed air The average flow field in any region of the machine. As shown in Fig. 1, the present invention has designed a casing processing without complicated geometry such as guide vanes and diverter rings, and the casing only includes an annular back chamber 1 and a perforated plate with round holes or inclined grooves 2. It can adjust the wall impedance boundary condition of the compressor system by adjusting the perforation rate of the perforated plate and the volume of the back cavity. First of all, it is necessary to clarify several important parameters about the casing processing structure: a-the axial length of the perforated plate, b-the axial coincidence between the perforated plate and the rotor, c-the radial cavity depth of the back cavity, d-the axial length of the back cavity Cavity depth, e-perforated plate thickness, f-perforated plate aperture. Thus, the casing treatment installed in the blade tip area will inevitably produce the same return flow channel as the existing grooved casing treatment (as shown in Figure 2). Obviously, this backflow will naturally exist no matter what the working conditions of the compressor are. For this kind of casing with an air chamber, the tip airflow will flow into the air chamber from the trailing edge of the perforated plate hole, and then flow out from the leading edge of the perforated plate hole. The shedding vortex street or The vortex ring interacts with various pressure disturbances in the flow field, that is, wave-vortex interaction (also known as vortex-acoustic interaction). Thus, this recirculation process in casing processing can provide an unsteady boundary to influence the generation and development of low-frequency perturbations associated with stall precursor waves.

Therefore, this casing treatment actually changes the boundary conditions of the system and provides an unsteady "soft" boundary, that is, the energy of the stall precursor wave incident on the casing wall is dissipated due to the wave-vortex interaction mechanism , thereby suppressing the instability caused by its nonlinear amplification. The present invention studies the flow stability of the axial flow compressor from the perspective of the unsteady suppression of the stall precursor wave by the casing with a cavity back, which will lead to a more effective design and stabilize the high-load transonic axial flow compressor. At the same time, there will be no obvious loss of efficiency.

The advantage of the present invention compared with prior art is:

(1) The present invention utilizes a perforated plate processing casing with a back chamber installed at the front edge of the inlet of the axial flow compressor, and the pressure difference caused by the work of the rotor will form an adaptive flow, which will generate abnormal flow at the edge of the aperture. Steady shedding vortex, based on the wave-vortex interaction mechanism, can effectively absorb and dissipate the energy of low-frequency disturbance waves in the compressor flow field, and delay the occurrence of precursor stall in the compressor by suppressing the nonlinear amplification of stall precursor waves , Increase the stable working range of the compressor system. In addition, due to the delicate setting of the processor, it does not directly interfere with the main flow field structure of the compressor, so it will not cause the pressure ratio drop and efficiency loss of the compressor system, avoid the trouble caused by redesign and matching of engine components, and the structure is simple and compact , which can meet the engineering restriction on the size of the casing, and has a good prospect of engineering practical application.

(2) The present invention has been verified experimentally on the experimental benches of Beijing University of Aeronautics and Astronautics and the Institute of Engineering Thermophysics of the Chinese Academy of Sciences, and has achieved a good expansion and stability effect, and there are no disadvantages such as changes in pressure ratio characteristics and efficiency losses. Condition.

Description of drawings

Fig. 1 is the structural representation of the back chamber perforated plate type processing casing of the present invention;

Fig. 2 is a functional schematic diagram of the cavity-backed perforated plate type processing casing of the present invention;

Fig. 3 is the energy power spectral density analysis diagram of the dynamic pressure disturbance signal of the compressor flow field under the condition of a smooth wall;

Fig. 4 is an analysis diagram of the energy power spectrum density of the dynamic pressure disturbance signal of the flow field of the compressor under the treatment condition of the cavity-backed perforated plate casing of the present invention.

Detailed ways

The cavity-backed perforated plate casing treatment method is to process the cavity-backed perforated plate casing at the leading edge of the compressor rotor to change the boundary conditions of the entire power system to affect its system evolution behavior and achieve the purpose of broadening the stable working range of the compressor. The specific action mechanism is due to the power boosting effect of the rotor, as shown in Figure 2, the self-adaptive flow phenomenon 5 that will naturally form in the back cavity 1 of the perforated plate casing processing back cavity. The inflowing and outflowing airflow will form an unsteady shedding vortex at the edge of the perforated plate 2. When the pressure disturbance wave in the flow field is incident on the unsteady impedance boundary, the wave-vortex interaction mechanism will effectively absorb and dissipate the vortex. Dissipate the energy of the pressure disturbance wave, thereby suppressing the nonlinear amplification of the stall precursor wave, and achieving the purpose of expanding stability.

As shown in Figures 1 and 2, the cavity-backed perforated plate processing casing is composed of an annular back cavity 1 and a perforated plate 2 with holes, which can be round holes or inclined grooves. Among them, the perforation rate of the perforated plate 2 is 4%-30% of the area of the annular area, and the trailing edge of the perforated plate 2 is located at the 1/3-2/3 axial chord length position above the compressor rotor to form the main flow of the compressor. The flow field enters the airflow of the casing processing back cavity 1; the front edge of the perforated plate 2 is located at the front edge of the rotor 3 at the position of 1/3-1 times the axial chord length at the front end of the rotor 3 inlet, so as to form the flow entering from the casing processing back cavity 1 For the air flow in the mainstream flow field of the compressor, the radial depth of the back cavity 1 is 5mm-200mm to form a flow channel 5 flowing from the trailing edge of the perforated plate 2 to the leading edge, and the axial length of the annular back cavity 1 is 2/3- 2 times the axial chord length, in order to ensure the establishment of an adaptive flow channel and reduce the flow loss as the principle, the purpose is to suppress and absorb the energy of the low-frequency disturbance wave 6, thereby broadening the stable working range of the axial flow compressor, but it is limited by practical applications , should be considered on a case-by-case basis.

The axial coincidence degree of the perforated plate 2 and the rotor 3 is a very important parameter affecting the expansion effect of the cavity-backed perforated plate casing. Selecting an appropriate axial coincidence degree will result in a greater stall margin improvement and maintain the compressor On the contrary, the expansion stability effect is not obvious or the working efficiency of the compressor is reduced. The perforation rate of the perforated plate 2 and the geometric size of the back cavity 1 are also important structural parameters, both of which will have a significant impact on the expansion stability effect and the operating characteristics of the compressor. It is necessary to adjust the structural parameters of the casing according to the wall impedance model or experimental test methods , combined with the actual use to obtain a larger wall impedance, thereby suppressing the amplification of low-frequency disturbances in the flow field of the compressor, and achieving the purpose of broadening the stable working range of the axial flow compressor.

The position of the trailing edge of the perforated plate 2 in the axial flow compressor should be downstream of the leading edge of the rotor blade 3. Due to the work added by the rotor, the pressure in the mainstream flow field is higher than the pressure in the casing processing back chamber 1. Under the action of the pressure difference inside and outside the casing processing back chamber 1, an inflow airflow flowing into the casing processing back chamber from the main flow field of the compressor will be formed at the trailing edge of the perforated plate 2. When the unsteady pressure disturbance wave is incident on the unsteady impedance interface, the energy of the pressure disturbance wave will be converted into the vortex energy of the unsteady shedding vortex at the edge of the hole on the outer wall of the perforated plate 2 due to the interaction of wave vortex, thus consuming Dissipate and absorb the energy of the pressure disturbance wave.

The above-mentioned mechanism also exists at the front edge of the perforated plate 2, because the pressure in the back chamber 1 will be higher than the pressure of the main flow field at the front edge of the rotor 3 at this time, thus forming a flow from the casing back chamber 1 to the main flow of the compressor The outflow of the flow field. When various unsteady pressure disturbance waves in the mainstream flow field are incident, wave-vortex interaction will occur at the edge of the inner wall surface of the perforated plate 2, which can also dissipate the energy of the pressure disturbance wave and suppress its nonlinear amplification. So as to achieve the purpose of expansion.

In the energy power spectral density analysis of the dynamic pressure disturbance signal in the flow field, it can be seen that at the same flow start point and the same interception velocity, the amplitude of the low-frequency disturbance is in the order of more than 1E-6 under the condition of light wall It will enter a stall (after 180 rpm as shown in Figure 3), and under this flow state, the existence of casing processing will not only absorb the disturbed energy to keep it at a low level (as shown in 180 rpm in Figure 4), When the flow rate decreases further (that is, the time axis moves to the right), the amplitude of the low-frequency disturbance can gradually increase, even exceeding the magnitude of 1E-6, reaching the level of 1.5E-6 without stalling, until the flow rate increases with further Cut off and reduce to a lower state (as shown in Figure 4 after 680 revolutions) before entering a stall. This fully demonstrates that the casing treatment can effectively suppress the development of the stall precursor wave, thereby delaying the compressor system from entering the stall state and expanding its stable working range.

As the flow rate decreases, the energy of the disturbance wave increases gradually, which means that the energy of the low-frequency disturbance wave is closely related to the stability of the compressor. In the case of large flow rate and the presence of casing processing, the amplitude of low-frequency disturbance energy is lower than that of light wall. As the flow rate decreases, the amplitude of the disturbance excitation increases gradually, and the interaction between the pressure disturbance wave and the shedding vortex also gradually strengthens. In the case of light walls, when the system cannot overcome the increasing disturbance, the system will suddenly become unstable, and the compressor will enter a stall state. In the presence of casing processing, the boundary impedance characteristics of the system are changed, which enhances the ability to absorb low-frequency disturbance wave energy, and can suppress the further amplification of low-frequency disturbance waves, keeping its energy at a low level. Therefore, although the peak energy of the low-frequency disturbance in the case of casing processing will increase after the light-walled casing stalls, the unsteady impedance boundary provided by the casing processing can still overcome this energy-increasing disturbance excitation until it decreases to Stall occurs at lower flow rates.

Therefore, the cavity-backed perforated plate casing treatment can not only control the disturbance energy at a lower level, but also enable the system to withstand a higher level of disturbance than the bare wall case without instability. This fully demonstrates that the casing treatment affects the evolution behavior of the system by changing the boundary conditions of the wall.

In addition, the new casing treatment of the cavity-backed perforated plate, regardless of the type of the stall precursor wave, can effectively suppress the stall precursor wave through the interaction of the wave and vortex, change the evolution process of the system, and finally realize the stable operation of the compressor Widening of scope.

Parts not described in detail in the present invention belong to the well-known technology in the art.

Claims (1)

1. A back cavity perforated plate type casing processing method is characterized in that: first prepare a back cavity perforated plate type processing casing, and the back cavity perforated plate type processing casing includes an annular back cavity and a circular hole or a chute Perforated plate, the annular back cavity is located outside the perforated plate and connected by seam bolt structure to form a closed air chamber, and then the back cavity perforated plate processing casing is set at the front end of the axial flow compressor rotor inlet and covers the front edge of the rotor blade corresponding At the casing, the cavity-backed perforated plate processing casing forms an adaptive flow in the annular back cavity and generates unsteady shedding vortices at the perforated plate. The wave-vortex interaction effectively absorbs and dissipates low-frequency disturbances in the compressor flow field The energy of the wave and suppress the nonlinear amplification of the stall precursor wave, so that the occurrence of the precursor stall in the compressor can be delayed, and the stable working range of the compressor system can be increased; The trailing edge of the perforated plate is located at 1/3 to 2/3 of the axial chord length above the compressor rotor; The front edge of the perforated plate is located at 1/3 to 1 times the axial chord length of the front end of the rotor inlet; The perforation rate of the perforated plate is 4% to 30%; The radial depth of the annular back cavity is 5 mm to 200 mm; The axial length of the annular back cavity is 2/3 to 2 times the axial chord length.

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