A controllable external excitation generating device suitable for high-pressure inflow conditions

Abstract

The present invention provides a controllable external excitation generating device suitable for high-pressure inflow conditions, and relates to the field of combustion stability testing of aircraft engine combustion chambers. The device generates aerodynamic excitation through an aluminum turntable driven by a motor. The turntable is provided with circumferentially distributed circular holes. When the motor is working, it will drive the turntable to rotate. By adjusting the motor speed, excitations of different frequencies can be obtained. The excitation intensity is controlled by adjusting the opening of the two butterfly valves upstream of the device. The greater the amount of gas passing through the excitation turntable branch, the greater the excitation intensity generated downstream of the device, thereby achieving controllable excitation amplitude and frequency. The controllable external excitation generating device suitable for high-pressure inflow conditions of the present invention is particularly suitable for full-operating-condition combustion stability testing of real gas engines. It has a relatively simple structure, high overall structural strength, is not easily damaged by high-temperature and high-pressure inflow, and has good operating stability.

Description

Technical Field

[0001] The present invention relates to the field of unstable combustion measurement in aviation combustion chambers, and in particular to a controllable external excitation generating device suitable for high-pressure incoming flow conditions. Background Art

[0002] Unstable combustion is a major difficulty encountered in the design of low-pollution engine combustion chambers and advanced military engine afterburner and ramjet combustion chambers. During operation, the combustion chamber often produces oscillating combustion under specific working conditions. Large pressure fluctuations can lead to extremely unstable combustion conditions, severe mechanical oscillations and noise, causing the combustion chamber to flame out, and potentially damaging engine components, reducing component service life, and increasing pollutant emissions. Currently, many foreign engine companies with strong R&D capabilities, such as GE, PW, Siemens, Rolls-Royce, etc., have conducted research on the design, testing, and diagnosis of solutions to combustion instability problems, and can propose corresponding solutions from the design and testing stages.

[0003] In combustion stability testing, a commonly used test scheme is to introduce acoustic excitation through a loudspeaker to test the combustion stability of the combustion chamber under different excitation intensities and frequencies, thereby providing data support for optimizing the combustion chamber structure and improving combustion stability. The method of introducing external excitation through a loudspeaker is effective for laboratory-level combustion chambers, but for real combustion engines operating under high-temperature and high-pressure conditions, the excitation capacity of the loudspeaker is greatly reduced. This is because the loudspeaker mainly uses an electromagnet to drive the paper cone to vibrate and produce sound. When there is high-pressure gas in the combustion chamber, the vibration displacement of the paper cone is limited, and the excitation intensity is difficult to meet the experimental requirements. In extreme cases, the high-temperature and high-pressure gas may directly destroy the paper cone structure and cause serious damage to the loudspeaker. Therefore, the traditional method of introducing controllable acoustic excitation through a loudspeaker can no longer meet the testing requirements under high-pressure conditions in real combustion chambers, and a new controllable external excitation generation scheme is urgently needed. Summary of the Invention

[0004] In order to solve the above problems, expand the application scheme of controllable external excitation in the combustion stability test of the real aircraft engine combustion chamber, and provide a basis and means for optimizing the thermoacoustic stability of the combustion system, the present invention provides a controllable external excitation generating device suitable for high-pressure incoming flow conditions, which is particularly suitable for the combustion stability test of the real aircraft engine operating under high-pressure incoming flow conditions.

[0005] The present invention provides a controllable external excitation generating device suitable for high-pressure inflow conditions, characterized in that it includes an excitation pipeline, a branch pipeline, and a downstream dual-microphone speed measuring device; the excitation pipeline is provided with an excitation pipeline butterfly valve and an excitation turntable for gas volume control; the dual-microphone speed measuring device includes two dual-microphone speed measuring pressure pipes perpendicular to the excitation pipeline; the branch pipeline is provided with a branch pipeline butterfly valve for gas volume control; the excitation pipeline butterfly valve is located upstream of the excitation pipeline, and the branch pipeline butterfly valve is located upstream of the branch pipeline;

[0006] The excitation turntable includes an excitation turntable stator and an excitation turntable rotor arranged opposite to each other; the excitation turntable rotor is driven to rotate by a drive motor, and the excitation frequency of the excitation turntable is controlled by adjusting the motor speed; the drive motor is fixed in the excitation pipeline through a motor mounting plate; the drive motor and the motor mounting plate are connected by bolts;

[0007] The drive motor shaft and the excitation turntable rotor are connected by a key to transmit torque, and the excitation turntable stator is mounted on the motor shaft through bearings to ensure good concentricity between the stator and rotor. The excitation turntable stator has a stator airflow channel, and the excitation turntable rotor has multiple rotor airflow channels.

[0008] Furthermore, the outer ring surface of the excitation turntable rotor is equipped with a labyrinthine closed structure. Each time the airflow passes through a tooth, the pressure decreases. As the specific volume of the flowing gas increases, the speed through the gap increases, resulting in a greater pressure drop as the gas passes through each tooth downstream. This process repeats tooth by tooth until all the seals are passed. The pressure decreases, the specific volume increases, and the airflow speed increases, until the pressure approaches the back pressure, while the temperature remains constant, achieving the desired sealing effect.

[0009] Furthermore, the number N of rotor airflow channels is determined according to the required excitation frequency range. When the motor speed is n rpm, the excitation frequency f of the excitation turntable satisfies f=n*N / 60. The excitation frequency is controlled by adjusting the drive motor speed. The higher the drive motor speed, the higher the excitation frequency. Combined with the frequency conversion controller, continuous change of the excitation frequency can be achieved.

[0010] Furthermore, the excitation intensity is controlled by the pneumatic butterfly valves upstream of the excitation pipeline and the branch pipeline. The larger the opening of the butterfly valve upstream of the excitation pipeline, the greater the excitation air flow, and the greater the excitation intensity in the downstream mainstream. The excitation pipeline air flow is The gas flow rate of the branch pipeline is When the excitation intensity Amp satisfies

[0011] Furthermore, a microphone measurement pressure-leading tube is provided downstream of the excitation pipeline for measuring the excitation amplitude and frequency in combination with a dual-microphone method;

[0012] Furthermore, the dynamic pressure signal drawn out from the pressure-inducing tube is measured by a microphone. The sound pressure signal obtained by the microphone can be expressed as the superposition of the uplink and downlink sound waves:

[0013]

[0014] Where k = ω / c0 is the wave number, is the pressure pulsation amplitude, are the amplitudes of the up and down sound waves respectively; the expression of velocity pulsation obtained according to the momentum equation is:

[0015]

[0016] in, is the velocity pulsation amplitude, ρ0 and c0 are the airflow density and sound speed respectively; the pressure pulsation is expressed in complex form as:

[0017]

[0018] Substituting (3) into (1), we obtain the following equations:

[0019]

[0020] a A 、b A 、a B 、b B The dynamic pressure signal can be obtained by performing FFT on it, dividing both sides of equation (4) by e jωt , written in matrix form:

[0021]

[0022] Multiplying both sides by the inverse matrix simultaneously can obtain the amplitude of the uplink and downlink sound waves, and then obtain the expressions of the pressure pulsation and velocity pulsation in the frequency domain at the dual-microphone measurement point position from the following equations:

[0023]

[0024]

[0025] The above formula can be used to obtain the frequency spectrum distribution of the velocity pulsation, and then the excitation amplitude and frequency. The beneficial effects of the present invention are:

[0026] (1) The present invention discloses a controllable external excitation generating device suitable for high-pressure inflow conditions, which is not only suitable for combustion stability testing of a mechanism combustion chamber under normal temperature and pressure, but is also particularly suitable for combustion stability testing of a real aircraft engine combustion chamber under high-temperature and high-pressure inflow conditions. It can even test the operating stability of the combustion chamber under extreme working conditions, thus meeting the requirement of a continuously adjustable excitation source during the test.

[0027] (2) The present invention discloses a controllable external excitation generating device suitable for high-pressure inflow conditions, which avoids the fragile paper cone structure of traditional speakers and replaces it with a metal excitation turntable. The overall strength of the system is high and will not be damaged by harsh inflow conditions;

[0028] (3) The present invention discloses a controllable external excitation generating device suitable for high-pressure inflow conditions, with a pressure-inducing pipe for dual-microphone velocity measurement arranged downstream, which can be combined with an acquisition card and acquisition software to monitor the excitation addition in real time;

[0029] (4) The present invention discloses a controllable external excitation generating device suitable for high-pressure inflow conditions. The overall design is standard parts, with low processing difficulty and low cost. There is almost no loss problem during use, and the service life is long and the operation stability is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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 only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 It is the overall isometric drawing of the device of the present invention.

[0032] Figure 2 This is a schematic diagram of the excitation turntable assembly.

[0033] Figure 3 This is the isometric view of the excitation turntable stator.

[0034] Figure 4 This is the front and side view of the motor mounting plate.

[0035] Figure 5 It is the isometric view of the excitation turntable rotor.

[0036] Among them, 1-intake connecting flange, 2-excitation pipeline butterfly valve, 3-excitation turntable, 4-exhaust connecting flange, 5-dual-microphone speed measurement pressure pipe, 6-branch pipeline butterfly valve, 7-excitation pipeline, 8-branch pipeline, 301-excitation turntable stator, 302-motor mounting plate, 303-drive motor, 304-excitation turntable rotor, 301a-bolt mounting hole, 301b-bearing mounting hole, 301c-stator airflow channel, 302a-flange, 302b-cross-shaped mounting plate, 302c-threaded hole, 304a-maze closure structure, 304b-keyway, 304c-rotor airflow channel. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only 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 making creative efforts are within the scope of protection of the present invention.

[0038] The core idea of ​​the present invention is to realize controllable external excitation based on aerodynamic disturbance. The present invention is a controllable external excitation generating device suitable for high pressure inflow conditions, such as Figure 1 The figure shows the overall isometric view of the device of the present invention, which includes pneumatic butterfly valves 2 and 6 for distributing the air volume of the excitation pipeline 7 and the branch pipeline 8, an excitation turntable 3, a pressure pipe 5 for dual-microphone speed measurement, and flanges for connecting the air inlet and outlet pipes; the excitation turntable 3 includes a turntable stator 301, a motor mounting plate 302, an excitation motor 303, and a turntable rotor 304;

[0039] During operation, the device distributes the airflow through the excitation pipe 7 and the branch pipe 8 by adjusting the opening of pneumatic butterfly valves 2 and 6, thereby adjusting the excitation intensity. The greater the opening of butterfly valve 2 in the excitation pipe, the greater the amount of excitation airflow, and the greater the excitation intensity of the mainstream air after it merges into the main flow. The excitation frequency can be adjusted by the motor speed. During operation, the excitation addition status can be monitored in real time in conjunction with a downstream dual-microphone speed measurement device to obtain the combustion chamber inlet airflow disturbance required for the experiment.

[0040] The core component of the device of the present invention is the excitation turntable 3, which mainly includes an excitation turntable stator 301, a motor mounting plate 302, an excitation motor 303 and a turntable rotor 304; the excitation turntable stator 301 is fixed to the motor shaft through a bearing, and the outer ring of the motor mounting plate 302 is a flange 302a. In this case, a DN50 standard flange is used, and a "cross"-shaped mounting plate 302b is welded inside, and is connected to the motor through a threaded hole 302c.

[0041] The outer side of the excitation turntable stator 301 has eight mounting holes 301a, which are used for bolt connection flange positioning. The central opening 301b of the turntable stator 301 is used to fix the bearing and connect the motor shaft through the bearing. The turntable stator 301 also has a circular through hole as an airflow channel.

[0042] A sealing groove 304a is opened on the side of the excitation turntable rotor 304 for labyrinth sealing to ensure good airtightness during the operation of the device; a circular hole is opened in the center of the turntable rotor 304, and a key slot 304b is opened to connect to the motor shaft and transmit torque; the turntable has 304c circular holes for air flow channels evenly distributed around the circumference, and the number of circular holes can be designed according to the required excitation frequency range. In this example, 6 circular holes are designed as air flow channels.

[0043] The intake duct is connected to the excitation device through the intake connecting flange 1. After being excited by the device, the outlet airflow disturbance will have a significant main frequency and amplitude. The disturbed airflow will be connected to the exhaust duct through the outlet connecting flange 4 to add excitation to the combustion chamber.

[0044] The device also includes a pressure-inducing pipe 5 for dual-microphone velocity measurement; this pipe is welded vertically to the outside of the pipeline, near the outlet flange 4. This pipe is primarily used to draw pressure from the system, facilitating measurement of its excitation characteristics using the dual-microphone method, and, in conjunction with an acquisition card and software, to monitor outlet velocity pulsation characteristics in real time.

[0045] The main body of the excitation device of the present invention is made of 304 stainless steel. If the incoming flow temperature is high, materials such as copper and alloys can be considered. The pipe diameter can be designed according to the specific experimental conditions. In this example, the pipes used are all DN50 standard round pipes, the flanges use DN50 convex flanges, and are connected with 8 bolts, and gaskets need to be installed on the nut side; in addition, in order to reduce the dead weight of the excitation turntable and thus reduce the motor load, in this example, the excitation turntable rotor is made of aluminum.

[0046] Figure 2 This is a schematic diagram of the excitation turntable assembly. The excitation turntable 3 can be used as an integral component and directly incorporated into the pipeline to be excited by relying on the bolt holes on the outer ring of the stator 301 and the motor mounting plate 302. When excitation is not needed, the entire turntable can be removed without affecting the normal use of the pipeline.

[0047] Figure 3 This is a front view of the stator of the excitation turntable. The stator is provided with bolt holes 301a, bearing mounting holes 301b and air flow channel holes 301c. The size of the bolt holes is consistent with that of the flange.

[0048] Figure 4 This is a front and side view of the motor mounting plate. It is welded from a standard 302a flange to a cross-shaped mounting plate. To avoid affecting flow field uniformity, the weld seam should be kept as small as possible. A small hole is required in the cross-shaped plate to connect the motor to the mounting base.

[0049] Figure 5This is a positive isometric view of the excitation turntable rotor. In this case, in order to reduce the rotor's own weight, the rotor is processed entirely from aluminum, and a labyrinth closed structure 304a is used around it to ensure good airtightness around the rotor under high pressure. A keyway 304b is opened in the center of the rotor for connection to the motor shaft. In this case, a 4mm high flat key is used for connection.

Claims

1. A controllable external excitation generating device suitable for high-pressure inflow conditions, characterized in that: It includes an excitation pipeline, a branch pipeline and a downstream dual-microphone speed measuring device; the excitation pipeline is provided with an excitation pipeline butterfly valve and an excitation turntable for gas volume control; the dual-microphone speed measuring device includes two dual-microphone speed measuring pressure pipes perpendicular to the excitation pipeline; the branch pipeline is provided with a branch pipeline butterfly valve for gas volume control; The excitation pipeline butterfly valve is located upstream of the excitation pipeline, and the branch pipeline butterfly valve is located upstream of the branch pipeline; The excitation turntable includes an excitation turntable stator and an excitation turntable rotor arranged opposite to each other; the excitation turntable rotor is driven to rotate by a drive motor, and the excitation frequency of the excitation turntable is controlled by adjusting the motor speed; the drive motor is fixed in the excitation pipeline through a motor mounting plate; the drive motor and the motor mounting plate are connected by bolts; The drive motor shaft and the excitation turntable rotor are connected by a key to transmit torque, and the excitation turntable stator is mounted on the motor shaft through bearings to ensure good concentricity between the stator and rotor. The excitation turntable stator has a stator airflow channel, and the excitation turntable rotor has multiple rotor airflow channels. The number of rotor airflow channels N Determined according to the required excitation frequency range, the motor speed is n rpm, the excitation frequency of the excitation disk f satisfy f = n * N / 60 ; The excitation pipeline gas flow rate is , the branch pipeline gas flow is When the incentive intensity satisfy .

2. A controllable external excitation generating device suitable for high-pressure inflow conditions according to claim 1, characterized in that: The outer ring surface of the excitation turntable rotor is provided with a labyrinth closed structure.

3. The controllable external excitation generating device suitable for high-pressure inflow conditions according to claim 1, characterized in that: The dual-microphone speed measurement pressure tube is set downstream of the excitation pipeline and is used to measure the excitation amplitude and frequency in combination with the dual-microphone method.

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