A controllable external excitation generating device based on aerodynamic disturbance

Abstract

The application provides a controllable external excitation generation device based on aerodynamic disturbance, and relates to the field of combustion stability test of an aero combustion chamber. The device generates vortex shedding through a spoiler target, and controls excitation frequency and excitation strength by adjusting the blockage ratio of the spoiler target and the flow velocity. At present, the excitation mode of the inlet velocity disturbance of the combustion chamber generally adopts a loudspeaker for excitation. However, under the high-temperature and high-pressure operating conditions of an aero-engine, the excitation capacity of the loudspeaker is greatly limited, and it is difficult to meet the test requirements in engineering. The controllable external excitation generation device based on aerodynamic disturbance has good applicability under high-temperature and high-pressure conditions, and has a relatively simple structure. In the use process, there is almost no loss, and no external energy needs to be added. The use stability is strong, the scientific research period can be reduced, and the scientific research fund can be saved to a certain extent.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aero-engine combustion chamber unstable combustion measurement, and particularly relates to a controllable external excitation generation device based on aerodynamic disturbance. BACKGROUND

[0002] Unstable combustion phenomenon is an important difficulty encountered in the design of low-pollution civil engine combustion chamber and advanced military engine afterburner and ramjet combustion chamber. When unstable combustion occurs in the combustion system, the unsteady heat release of the flame in the system and the sound wave are coupled with each other, and the weak pressure disturbance caused by the unsteady process such as fuel-air ratio fluctuation and turbulent flow field fluctuation can all lead to continuous increase of pressure oscillation amplitude, until reaching a limit cycle state. At this time, the combustion chamber deviates from the design working condition, resulting in a decrease in efficiency. In an extreme case, severe pressure fluctuation can also damage the combustion chamber structure, leading to backfire, flameout, explosion and other accidents of the combustion chamber, and bringing serious challenges to the efficiency and safety of the equipment.

[0003] In order to avoid the occurrence of unstable combustion phenomenon, it is particularly important to test the combustion stability of the combustion chamber under typical working conditions in the design stage. In the combustion stability test of an aero-engine combustion chamber, it is often necessary to study the combustion response of the flame under different disturbance conditions, in order to optimize the structure of the combustion chamber and improve the combustion stability, which requires a controllable disturbance excitation scheme. At present, for laboratory-level combustion chambers, the mainstream excitation scheme mainly adopts a loudspeaker to add excitation. The loudspeaker mainly generates excitation by driving the vibration of a paper cone through an electromagnet, and different intensity and frequency air flow disturbances can be output by controlling the power and frequency of the loudspeaker. However, for actual aero-engine combustion chambers of engineering level, the typical design working condition is high temperature and high pressure, and under the action of high pressure gas in the combustion chamber, the vibration of the paper cone is greatly inhibited, resulting in limited actual excitation range of the loudspeaker, which greatly limits the test range of controllable disturbance, so that this acoustic excitation scheme cannot meet the test needs in engineering practice. SUMMARY

[0004] In order to solve the above problems, to expand the application method of controllable external excitation source in the combustion stability test of the combustion chamber, and to provide basis and means for optimizing the thermal-acoustic stability performance of the aero-engine, the present application provides a controllable external excitation generation device based on aerodynamic disturbance, which can be applied to the test of real aero-engine combustion chambers under high temperature and high pressure operating conditions.

[0005] The controllable external excitation generation device based on aerodynamic disturbance of the present application comprises an excitation main body and a spoiler target arranged on the excitation main body; the excitation main body comprises an air inlet pipeline, a spoiler target mounting plate and a plurality of spoiler target mounting holes; the spoiler target mounting holes are arranged along the center line in the flow direction;

[0006] The turbulence target installation plate is arranged on the side of the air inlet pipe, and a turbulence target installation hole is arranged on the corresponding position of the turbulence target installation plate and the air inlet pipe. The turbulence target is arranged on the air inlet pipe through the turbulence target installation hole and the turbulence target installation plate. The turbulence target disturbs the gas in the air inlet pipe to generate airflow with obvious main frequency and certain amplitude. The closer the turbulence target is to the outlet of the air inlet pipe, the greater the disturbance amplitude.

[0007] When the turbulence target installation hole is not provided with the turbulence target, a plug is arranged in the turbulence target installation hole.

[0008] When the airflow for excitation just enters the excitation generating device, the airflow can be approximately regarded as a steady flow. After the airflow passes through the target surface of the turbulence target, two rows of line vortices with opposite rotation directions and regular arrangement are periodically shed on both sides of the target surface. In the range of Re = 200-15000, the vortex shedding frequency is proportional to the flow velocity, so the excitation frequency can be controlled by adjusting the flow velocity. During the movement of the vortex, the energy is gradually dissipated. Therefore, the closer the turbulence target is to the upstream, the smaller the excitation amplitude provided by the outlet of the excitation device. During use, the position of the turbulence target can be adjusted to control the excitation amplitude.

[0009] Further, the turbulence target comprises a plug, a connecting segment and a replaceable target surface.

[0010] The plug is connected to the target surface through the connecting segment, and the target surface and the connecting segment are connected through bolts.

[0011] When the turbulence target is arranged in the air pipe through the installation hole and the turbulence target installation plate, the target surface is located in the air inlet pipe, and the plug is located in the turbulence target installation hole.

[0012] During use, the target surface of different sizes can be replaced according to the needs. At the same time, the angle between the target surface and the airflow can be changed by rotating the turbulence target, so as to adjust the blockage ratio of the turbulence target, and realize the continuous change of the excitation strength.

[0013] Further, the dynamic pressure is introduced from the system through the pressure lead pipe, and the sound pressure signal is obtained through the microphone. Finally, the excitation characteristics are calculated by using the double microphone method.

[0014] Further, the position of the turbulence target is adjustable. The closer the turbulence target is to the outlet of the air inlet pipe, the greater the disturbance amplitude.

[0015] Further, after the dynamic pressure is introduced from the system through the pressure lead pipe, the sound pressure signal is obtained through the microphone. Finally, the excitation characteristics are calculated by using the double microphone method.

[0016] The sound pressure near the double microphone measuring point position is represented as the superposition of the uplink and downlink sound waves:

[0017]

[0018] where k = ω / c0 is the wave number, is the pressure fluctuation amplitude, are the up and down wave amplitudes respectively. The expression of velocity fluctuation is obtained according to the momentum equation:

[0019]

[0020] ρ0, x0 are the incoming flow density and sound speed respectively. The pressure fluctuation is expressed in the form of complex number as:

[0021]

[0022] Substitute (3) into (1), the equation group is obtained:

[0023]

[0024] a A , b A , a B , b B The FFT of dynamic pressure signal is obtained, divide both sides of (4) by e iωt , and write in the form of matrix:

[0025]

[0026] Multiply both sides by the inverse matrix to obtain the wave amplitude of up and down waves, and obtain the expression of pressure fluctuation and velocity fluctuation of double microphone measuring point position from the following equation:

[0027]

[0028]

[0029] The spectral distribution of velocity fluctuation can be obtained by the above formula, and then the excitation amplitude and frequency are obtained.

[0030] Advantages:

[0031] (1) The controllable external excitation generating device based on aerodynamic disturbance disclosed in the application can not only be used as an excitation source for combustion stability experiment of a laboratory level combustion chamber under normal temperature and pressure, but also is especially suitable for combustion stability test experiment of an engineering level aero-engine combustion chamber under high temperature and high pressure, and meets the requirements of the excitation source in the test process.

[0032] (2) Traditional acoustic excitation methods involve the conversion of electrical energy into mechanical energy during use, and there is energy loss during the conversion process. However, the controllable external excitation generating device based on aerodynamic disturbance disclosed in this invention does not require additional energy input during use, nor does it require consideration of complex circuit control systems, thus reducing experimental costs and saving experimental expenses to a certain extent.

[0033] (3) The controllable external excitation generating device based on aerodynamic disturbance disclosed in this invention is relatively simple in design and low in cost. Compared with traditional loudspeaker excitation schemes, this invention does not have a fragile paper cone structure or easily aged circuit lines, and there is almost no wear and tear problem during use, so theoretically the service life is longer. Attached Figure Description

[0034] Figure 1 This is a front cross-sectional view of the main structure of the excitation device of the present invention.

[0035] Figure 2 This is a left view of the main structure of the excitation device.

[0036] Figure 3 This is a three-dimensional front view of the turbulence target structure.

[0037] Figure 4 This is a schematic diagram of the excitation device assembly.

[0038] Among them, 1—pressure tapping pipe, 2—excitation body, 3—turbulence target, 4—flange connection hole, 5—flange, 6—turbulence target mounting plate, 7—turbulence target mounting hole, 8—inlet pipe, 301—plug, 302—bolt, 303—target surface, 304—connection section. Detailed Implementation

[0039] The invention will be further illustrated below with reference to the accompanying drawings.

[0040] The core idea of ​​this invention lies in achieving controllable external excitation based on aerodynamic disturbance. One such controllable external excitation generation device based on aerodynamic disturbance is... Figure 1 The figure shown is a front cross-sectional view of the excitation main structure of the present invention, including an excitation main body 2 and a turbulence target 3 for being mounted on the excitation main body 2; the excitation main body 2 includes an air intake pipe 8, a turbulence target mounting plate 6, and a plurality of turbulence target mounting holes 7; the turbulence target mounting holes 7 are arranged along the flow direction centerline;

[0041] The turbulence target mounting plate 6 is set on the side of the intake pipe 8. The turbulence target mounting plate 6 and the intake pipe 8 are respectively opened with turbulence target mounting holes 7. The turbulence target 3 is set on the intake pipe 8 through the turbulence target mounting holes 7 and the turbulence target mounting plate 6. It is used to adjust the disturbance amplitude at the combustion chamber inlet. The closer the turbulence target 3 is to the outlet of the intake pipe 8, the greater the disturbance amplitude it generates.

[0042] When the spoiler target 3 is not arranged in the spoiler target mounting hole 7, the plug 301 is arranged in the spoiler target mounting hole 7.

[0043] The airflow passing through the inlet pipe 8 is affected by the spoiler target, and the airflow with disturbance has a main frequency and a certain amplitude, and the airflow with disturbance is merged into the main flow through the outlet, and the excitation is added to the combustion chamber.

[0044] The spoiler target 3 comprises a plug 301, a connecting section 304 and a replaceable target surface 303; the plug 301 is connected to the target surface 303 through the connecting section 304, and the connecting section 304 is connected to the target surface 303 through a bolt 302; when the spoiler target 3 is arranged in the air pipe through the mounting hole and the spoiler target mounting plate 6, the target surface 303 is located in the inlet pipe 8, and the plug 301 is located in the spoiler target mounting hole 7.

[0045] The device further comprises a pressure guide pipe 1; the pressure guide pipe 1 is vertically arranged on the side of the inlet pipe 8, close to the outlet of the inlet pipe 8, and communicates with the inlet pipe 8. The pressure guide pipe 1 is mainly used for guiding the pressure in the system out, so as to facilitate the measurement of the excitation characteristics through the double microphone method.

[0046] The excitation device body of the present application is made of 304 stainless steel, and if the incoming flow temperature is high, copper and alloy materials can be considered, and the flow passage area can be designed according to the experimental conditions. In the present example, the inlet pipe 8 has a square cross section of 50mm*50mm, the total length of the flow passage is 270mm, and the wall thickness is 2mm.

[0047] The outlet end of the inlet pipe 8 is connected to the position needing to add excitation upstream of the combustion chamber through a flange. The flange plate 5 is provided with a flange connecting hole 4.

[0048] The inlet end of the excitation device is connected to the upstream air source through a flange. If the upstream air source is a centrifugal fan or other air source with periodic disturbance, a flow regulating device such as a honeycomb flow regulating grid can be added upstream to stabilize the air source and reduce the experimental uncertainty.

[0049] In the present example, the flange plate 5 is 5mm thick, connected by 4 bolts, and the nuts are provided with gaskets. Considering that the blocking ratio of the spoiler target 3 needs to be adjusted by rotation in actual use, the bottom plate is locally thickened at the spoiler target 3 mounting position to meet the process requirements of the threaded holes. The spoiler target mounting hole 7 is in the form of a threaded hole for mounting the spoiler target 3, and multiple spoiler target mounting holes 7 can be arranged in the axial direction to meet the different excitation strength requirements. In the present example, M20*1.5 fine thread is used, and 4 spoiler target mounting holes 7 are arranged, and the center distance between adjacent mounting holes is 30mm.

[0050] Figure 2For the left view of the main structure of the device, the inlet end and the outlet end of the device are connected to the air source and the combustion chamber inlet pipeline respectively through flanges 5.

[0051] Figure 3 For the three-dimensional front view of the spoiler target structure, the connecting section 304 is welded by a cuboid stainless steel block and a standard plug 301. The weld should be as small as possible to avoid affecting the airflow and increasing the experimental uncertainty. The target surface 303 is designed to be replaceable, and the spoiler target blockage ratio can be adjusted by changing the size of the target surface 303. The material of the target surface 303 can be copper or various alloys. In this example, due to the low flow velocity and temperature in the test conditions, 304 stainless steel is used for cost considerations.

[0052] Figure 4 For the assembly diagram of the excitation device, this example only shows one mode, which installs the spoiler target 3 at the second mounting point, and the remaining mounting points are installed with plugs 301. In actual use, the spoiler target 3 can be installed at any position of the four mounting points according to actual needs, and the blockage ratio to the flow can be changed by rotating.

Claims

1. A controllable external excitation generation device based on aerodynamic disturbance, comprising an excitation body and a spoiler target arranged on the excitation body. The excitation body comprises an air inlet pipe, a spoiler target mounting plate, and a plurality of spoiler target mounting holes; the spoiler target mounting holes are arranged along the center line of the air inlet pipe in the flow direction. The spoiler target mounting plate is arranged on the side of the air inlet pipe, and the spoiler target mounting plate and the air inlet pipe are provided with spoiler target mounting holes at corresponding positions; the spoiler target is arranged on the air inlet pipe through the spoiler target mounting holes and the spoiler target mounting plate. The spoiler target is used to adjust the disturbance amplitude at the inlet of the combustion chamber. When no spoiler target is arranged in the spoiler target mounting hole, a plug is arranged in the spoiler target mounting hole. The spoiler target comprises a plug, a connecting section, and a replaceable target surface. The plug is connected to the target surface through the connecting section. When the spoiler target is arranged in the air pipe through the mounting hole and the spoiler target mounting plate, the target surface is located in the air inlet pipe, and the plug is located in the spoiler target mounting hole. The blockage ratio of the spoiler target is adjusted by changing the angle between the target surface and the incoming flow. The position of the spoiler target is adjustable; the closer the spoiler target is to the outlet of the air inlet pipe, the greater the excited disturbance amplitude. The excitation frequency is controlled by adjusting the incoming flow velocity; increasing the incoming flow velocity will increase the excitation frequency, and decreasing the incoming flow velocity will decrease the excitation frequency.

2. A controllable external excitation generating device based on aerodynamic disturbance according to claim 1, characterized in that, It also comprises a pressure lead pipe and a double microphone for measuring the excitation disturbance amplitude and frequency. The pressure lead pipe is arranged vertically on the side of the air inlet pipe, close to the outlet of the air inlet pipe, and communicates with the air inlet pipe.

3. A controllable external excitation generating device based on aerodynamic perturbation according to claim 1, characterized in that: The dynamic pressure is led out of the system through the pressure lead pipe and measured by the microphone; the sound pressure signal obtained by the microphone can be represented as the superposition of uplink and downlink sound waves: where k = ω / c0is the wave number, is the pressure fluctuation amplitude, are the upgoing and downgoing acoustic wave amplitudes, respectively; the expression for the velocity fluctuation is obtained from the momentum equation as where is the amplitude of the velocity fluctuation, and p0, c0are the air density and sound speed, respectively. The pressure fluctuation is represented in complex form as Substitute equation (3) into equation (1) to obtain the equation group: a A , b A , a B , b B The FFT of the dynamic pressure signal can be taken, and (4) can be written as a matrix by dividing both sides by e iωt ​ Multiply both sides by the inverse matrix to obtain the wave amplitude of the uplink and downlink sound waves, and then obtain the expressions of the pressure pulsation and velocity pulsation of the double microphone measurement point position in the frequency domain from the following equation: The spectral distribution of the velocity pulsation can be obtained by the above equation, and then the excitation amplitude and frequency are obtained.

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