The impeller machinery is a kind of rotating machinery that uses blades to convert mechanical energy and fluid energy. It is widely used in fields such as energy power and aviation, which are closely related to national economy and national defense. The research work on the internal flow of impeller machinery has been carried out for many years under the condition that the time and space structure have been simplified. Although the steady flow theory for a single flow component has been summarized, it has become increasingly Meet the needs of the impeller machinery towards high load, high efficiency, low noise. Therefore, studying the unsteady characteristics inside the impeller machinery, mastering the unsteady flow field structure and energy loss mechanism, and proposing the unsteady flow theory which is more in line with the actual internal flow characteristics of the turbomachinery has become the development trend of the international impeller machinery research field. In recent years, the research on leakage loss caused by unsteady gap leakage flow has received great attention from scholars at home and abroad. A dynamic pressure sensor is embedded in the casing of a single-stage axial compressor test bench. The high-speed dynamic pressure measurement system is used to measure the pressure pulsation of the end wall surface at the rotor tip clearance to obtain the dynamic performance of the tip clearance flow. Since the pressure waveform directly obtained by the experimental method is a set of data related to the amount of time, the real-time domain waveform, if the waveform is directly subjected to time domain analysis, usually cannot reveal the frequency domain structure of the signal and the magnitude of each frequency component. . The frequency domain analysis method widely used in dynamic testing, that is, the frequency is used as an independent variable to reveal the correspondence between the amplitude, phase and frequency of each frequency component of the signal, and the amplitude and phase of the signal are described by the frequency domain. The signal components of various frequencies in the signal can be revealed very clearly. By changing the rotor speed or the outlet back pressure, the relationship between the unsteady flow spectrum characteristics of the tip clearance and the operating parameters of the compressor is discussed, and it is related to the aerodynamic performance and airflow stability of the compressor. 1 Experimental equipment and data processing 1. The experimental bench experiment was carried out on a small axial compressor test bench, as shown. The rotor and the stator are composed of 6 and 13 blades respectively, the rotor hub ratio is 0.37, and the rotor tip clearance is 3. 55mm. The compressor rotor is driven by an AC variable frequency motor, and the rotor speed can be 0~ 3000r/min stepless speed regulation. There is a back pressure regulating butterfly valve at the outlet end of the compressor. By adjusting the angle of the butterfly valve by turning the hand wheel, the cross-sectional area of ​​the compressor outlet is changed, thereby controlling the outlet flow rate, and the purpose of changing the back pressure of the compressor outlet is achieved. 1. 2 acquisition system The entire measurement system consists of dynamic pressure sensor, signal conditioner, signal collector, signal trigger and microcomputer. The XCQ208025D gauge pressure dynamic pressure sensor from Kulite of the United States was selected. The response frequency of the sensor is 300 kHz, and the pulsation frequency of the unsteady flow of the tip clearance is only 300 Hz at the maximum speed of 3000 r/min. Therefore, the sensor can capture harmonics of 10th order or higher. The characteristics can fully meet the requirements of the experiment. The sensor is only 2mm in diameter and is easy to install on the casing near the leading, middle and trailing edges of the rotor blade in an axial arrangement to measure the unsteady flow field dynamic pressure at the tip, middle and trailing edge of the rotor blade. distributed. The sensor converts the pressure signal of the tip gap flow field into a voltage signal of only a few millivolts to several tens of millivolts, and is amplified by the 8300XWB signal conditioner of the US PRESTON company, and then sent to the signal acquisition system. The signal acquisition system uses JV53500A signal acquisition system. The sampling port sampling frequency is up to 100kHz and the precision is 16 bits. The triggering mode of the acquisition system supports external triggering, and the phase-trigger sampling is implemented by the external triggering mode to ensure that the system always collects in the same circumferential position. In the experiment, the E6B22CWZ1X axis encoder from Omron Corporation of Japan was used as a trigger source. Since there is no static part at the front end of the compressor rotor, the shaft encoder is not directly mounted on the rotor shaft, but the compressor rotor is directly mounted on the output shaft of the motor rotor. Therefore, the shaft encoder is directly connected to the tail of the motor rotor and placed. In the motor tail fairing, the shaft encoder is fixed by the motor housing. Not only is it easy to install, but it also avoids the introduction of the shaft encoder to the flow field. In order to reduce the interference of the inverter and the motor to the measurement system, the motor grounding and sensor signal line twisted-sleeve shielding net are adopted in the experiment. The sensor adopts positive and negative power supply and low-pass filter of the conditioner to improve the measurement accuracy. Compressor outlet back pressure is obtained directly from the static pressure measurement system. 1. 3 Experimental scheme and data processing Before the test, the entire measurement system is calibrated, and the collector automatically converts the collected sensor voltage signal into a pressure signal in the flow field. In the test, the sampling frequency was set to 100 kHz and the sampling length was 100 k. The experiment collected the outlet back pressure regulating butterfly valve fully open (α = 0°), and the rotor speed ω was 1500r/min, 2000r/min, 2500r/min, 3000r/min. The dynamic pressure field waveform of the tip clearance and the dynamic pressure field waveform of the tip clearance when the rotor rotation speed is 2500r/min and the back pressure adjustment butterfly valve opening degree is 0°, 20°, 25°, 30°, 35° Machine outlet back pressure. Since the unsteady pulsating pressure field of the tip clearance is mainly studied, the collected dynamic pressure time domain waveform data is calculated by the following formula, and the waveform data about the pulsating pressure P~ is obtained, where P is the pressure average. P~= P - P , P = 1 n 6 n- 1 i =0 pi(1) Finally, the corresponding dynamic pressure spectrum is obtained by calculating the fast Fourier transform FFT. 2 Results analysis 2.1 Analysis of pressure pulsation waveform in the middle of rotor tip clearance When the rotor speed is 2500r/min, the pressure pulsation time domain and amplitude-frequency diagram of the middle of the rotor tip clearance. It can be seen from the time domain diagram that the pressure waveform has a certain periodicity, because the pressure sensor sweeps through each blade channel, the pressure will be from the minimum value of one blade back of the rotor to the next. The maximum value is obtained when the basin is used. When the pressure sensor scans through a moving blade, its pressure pulsation waveform changes from a maximum value to a minimum value, but the change is complicated. From the time domain diagram, only a small amount of information can be obtained from the time domain map. As can be seen from the amplitude-frequency diagram, peaks appear at frequencies of 250 Hz, 500 Hz, 750 Hz, etc., and the peaks are sequentially decreased. Among them, 250 Hz is called the dominant frequency. These peaks are obtained by the pressure sensor scanning the rotor blades during the measurement, because the pressure sensor changes from the minimum value to the maximum value when scanning from the back of one blade to the back of the next blade. A small value is achieved, completing a cycle. The frequency f of the main frequency has a relationship with the number of rotor blades n of the compressor and the rotor speed ω, that is, f = ωn 60 (2). Therefore, under the operating conditions shown in the figure, the pressure sensor scans the rotor blade frequency f = 2500 × 6 / 60 = 250 Hz, this frequency agrees with the frequency shown in the amplitude-frequency diagram. 2. The influence of rotor speed variation on the pressure pulsation spectrum characteristics in the middle of the tip clearance is given. The outlet back pressure adjustment butterfly valve opening degree α is 20°, and the rotor speed ω is 1500r/min, 2000r/min, 2500r/min, 3000r. / min, the amplitude of the pressure pulsation in the middle of the rotor tip clearance is compared. It can be seen that as the rotor speed increases, the frequencies of the primary frequency, the second-order frequency, and the third-order frequency gradually increase; the peaks of the primary frequency, the second-order frequency, and the third-order frequency increase with the increase of the rotor speed. The circumferential unevenness of the pressure field in the middle end of the tip is increased, and the pressure field is periodically periodic along the circumference. 2. The influence of the outlet back pressure change on the pressure pulsation spectrum characteristics in the middle of the tip clearance is given as the rotor speed ω is 2500r/min, and the outlet back pressure adjustment butterfly valve opening degree α is 0°, 20°, 25°, 30°, At 35°, the pressure amplitude amplitude of the rotor tip clearance is compared. The compressor outlet back pressure p measured by the static pressure measuring system in each state has been indicated in the figure. As the angle α of the outlet back pressure valve increases, the cross section of the compressor outlet decreases, resulting in an increase in the outlet back pressure. The peaks at the main frequency, second-order frequency, and third-order frequency are also decreased, which is reflected in the change of the compressor outlet back pressure. It has an influence on the pressure field distribution at the upstream rotor, which leads to a decrease in the circumferential unevenness of the flow field at the central end of the tip. 2. 4 tip clearance flow field pressure pulsation spectrum characteristics at the leading edge, the middle and trailing edge of the blade gives a rotor speed ω of 2500r / min, the outlet back pressure adjustment butterfly valve opening degree α is 20 °, the rotor tip Contrast map of the amplitude and pressure of the flow field at the leading edge, middle and trailing edge. As can be seen from the figure, the frequency (250 Hz) and its multiplication. The main frequency, the double frequency and the like have larger peaks at the leading edge, the middle of the leaf and the trailing edge, and the largest in the leaf, the leading edge is the second, and the trailing edge is the smallest. This shows that the pressure fluctuation field of the gap pressure field is larger in the middle of the interlobes, and the pressure field in the circumferential direction is better. At the leading edge, there are double frequency and triple frequency multiplication in the spectrum, but The double-frequency equal-octave peak in the spectrum at the trailing edge is small because the airflow is between the stator and the rotor at the trailing edge, where there is a wake flow, mutual interference between the stationary and moving blades, etc. The influence of the secondary flow causes the airflow with a large pulsation in the middle of the tip to flow there, and the pulsation amount gradually decreases, and the periodicity is very poor. 3 Conclusions Using the method of spectrum analysis to study the unsteady pressure field in the middle of the rotor tip, the following conclusions are obtained: (1) There is a frequency closely related to the rotational speed, ie the dominant frequency, in the pressure pulsation spectrum diagram in the middle of the tip clearance. It is only related to the rotor speed and the number of rotor blades, regardless of the compressor outlet back pressure. As the speed increases, the frequency of the main frequency increases accordingly; in the spectrum diagram, there are double frequency and triple frequency equal frequency multiplications related to the main frequency; (2) the main frequency and the peak value of the multiplier along with the rotor speed Increase and increase, and decrease with the increase of outlet back pressure; this shows that as the rotation speed increases and the back pressure decreases, the circumferential non-uniformity of the unsteady pressure field at the middle end of the rotor tip increases; 3) The main frequency has the largest peak value in the leaf, which shows that the pressure field at this point has high circumferential unevenness and the circumferential periodicity is obvious; at the trailing edge, the main frequency peak is small, and the double frequency and other peaks are close to zero. The performance of the flow field is strongly disturbed by factors such as secondary flow, and the periodicity of the flow field is poor. Lily Bulb,Fresh Lily Bulb,Lily Bulb Fresh,Premium Lily Bulb GanSu Port Logistics Co.,Ltd , https://www.gskouan.com