Analysis and recommendations Aeroacoustics in Centrifugal Fan Research Methods
Release date：2015/8/10
Analysis and recommendations Aeroacoustics in Centrifugal Fan Huang research methods, Yu Hong Qi Datong countenance main fluid Machinery Research Institute, Xi'an Jiaotong University study based on the current method of centrifugal fan aerodynamic noise is analyzed, summed up the simulation and calculation method is not perfect ʱ??
Centrifugal fan volute is proposed to simplify the ideas into a housing having a hard boundary ideal model to study based on fan aerodynamic noise.
1 Introduction noise centrifugal fan with aerodynamic noise, mainly in nature can be divided into discrete noise and broadband noise. Its aerodynamic noise produced mainly by gas and the interaction of the volute and impeller blades and are spread through the air passage in and out. Volute dimensional unsteady flow field and the special shape of the housing makes it difficult to carry out their research. In recent years, domestic and foreign experts as 18,131HoJeon 5 for centrifugal fans made a lot of noise in sound research filling sound source mechanism are spread simulation testing technology have achieved a lot of breakthroughs, but there is still a lot to improve and perfect place progress ʱ?? Fully recent article 6 1 theory calculations and experimental research methods obituaries extensive literature inside and outside, and also proposed new proposals. 2 theoretical calculation method 2.1 point source model for the fan, the point source model is a kind of very useful technology. This approximation criterion is the wavelength of the highest frequency to be studied should be much larger than the physical dimensions of the sound source 1. To meet the requirements of this criterion, to transmit high frequency noise of the blades, in the application of point source model, can each a related area or volume deemed relevant will be the sum of the fan blades with a solitary point source along the blade length distribution of exhibition to simulate the sound source isolated small size. Currently being examined in a free-field rotation point source of acoustic characteristics through the wave equation is derived out of the sound field formulation moving point source generated, the formula is adapted to the blade of each micro-element it ran all the micro-elements on the blade integrating it blade movement can be calculated sound field but drawn blade infinitesimal point source size is difficult, and generally speaking the fan blades are not straight blade, even a great distortion in space, with a point source model to simulate prone to large errors ʱ?? Further, the study based on the free field for, and centrifugal fan must consider the impact of the volute.
2.2 volute tongue of the wedge simulation theory against the edge of the turbulent boundary layer equations stationary plate acoustic emission had come, but the need for progress in improving the turbomachinery noise. Lu Guilin considered the blades rotate AE's influence, combined with relevant experimental data. The introduction of blade child relationship where a combination of parameters, deduced a centrifugal fan impeller blade 2 blade trailing edge of the turbulent boundary layer acoustic emission calculation formula. These are assumed noise without scroll the calculating formula. In order to simulate the presence of the volute case. 1.. Place a sharp split in the vicinity of a simulated volute tongue to generate discrete noise it as a sound source.
1. By this model to calculate the flow field and then calculate the effect of the blade on the force infinitesimal unsteady Bernoulli equation to calculate the sound field formula Finally, any motion derived community 80 point source sound pressure elsewhere herein Numerical Simulation of Wen Su Ping 曹淑珍 using the model of the fan noise can get a lot of valuable numerical results, which change some parameters such as the gap between the number of leaves, the rotational speed of the impeller and the impeller and the wedge between the new entrants like cup boil juice count. Leaves can be analyzed and compared by factors frequency noise centrifugal fan noise instructive, especially for analysis of discrete causes of noise and noise reduction method has a more important role. But it can only simulate the fan base frequency noise, and still do not consider the existence of a complete volute.
Qualitative analysis of 2.3 based on simulated Broadband Noise Broadband noise is also called vortex noise, it depends on the corresponding flow properties corresponding sound field solution, so many of them are still experimental vortex noise research or theory. From the specific boundary conditions 0 equation and centrifugal fans of departure can be drawn on the basis of the basic equations and magnitude analysis, we made some simplified, and the entire flow field is divided into the main area and the boundary area to be discussed separately. Finally, tests were carried out, it is proved right foot into the qualitative analysis of the construction, two do not, do not use the area, or fool a natural plant utilization Fu leaves. Dimensional analysis and transform the city's law school like the following relationship is derived spectral density of the acoustic pressure in the experimental study of the formula for the relationship can benefit ⑴ come to analyze the relationship between sound and spectral density with the parameters. As can be seen, take advantage of the model solution, we need to use the test to determine the relationship between the sound pressure and body among the parameters. So small 1 can better solve centrifugal fan directly from the theoretical noise ask.
2.4 boundary element method to calculate the boundary element method of calculation examples more, but are similar, the focus here give Liji Fang numerical example to illustrate, he uses! Also integral equations obtained spiral surface velocity distribution and sound pressure volute surface integral relationship between the Green's function can get the whole spiral sound power radiated outward acceleration sensors can spiral surface vibration velocity distribution, then by formula calculated volute surface sound pressure, or it can import and export pressures for blessing acoustic power emitted by the fan inlet or outlet of the sound, and then obtain the total synthesis of sound power. As can be seen, the calculation method may calculate the noise caused by vibration blessing shoot volute can also calculate out the noise transmitted through the import and export pipelines.
However, when measuring the sound pressure import and export, due to airflow, the measurement subject to greater interference, and therefore the sound pressure measured variable is the true value; In addition, since the vibration of each point volute uneven surfaces, not just vertically in the face of vibration, even over time. Need to measure vibration velocity measurements of a large number of points, workload, and the reliability is not it should be the method has limitations 2.5 volute acoustic-electric analogy model It has long been proposed acoustic-electric analogy method and calculated the heart of the fan 3 The corpse resonance frequency, and with the Board modal analysis method analyzes several higher frequency than the Helmholtz resonance peaks having a closed trial painted with volute pressure points according to standardized. Song Huang Qibai after another on the basis of the fundamental resonance volute proposed noise rise caused by the mathematical model, and finally deduced at the resonant frequency of the far-field noise level at a point of total growth and out of the pit of noise from air intake to increase; With this type can be a bit far-field noise level total value prediction and optimization. These domestic trials have confirmed the volute base frequency resonance noise conditions in a small stream 2 to sex.
2.6 Acoustic affinity laws recommended by the International Organization for Standardization standard series to determine the noise power, the same applies to the fan. Experiment with different types and sizes of turbine requires a lot of test equipment and time, and expensive. Thus the law of similarity used in fans aerodynamic noise, can greatly reduce costs. 1 in accordance with test data so that one kind of fan size, similar to the size of the different dimensional sound and power of the fan series 1; seven 101 pairs of fan noise made by dimensional analysis, and the resulting relationship between the dimensionless parameter random noise The spectral noise may have different definitions, 63 rectangular wedge school intends to pay the volute tongue seven volute centrifugal wheel called acoustic radiation research traitor. Further results, loyalty to the test there is some 4 machine. Guests source of its similarity relations for this. Exchange; dimensionless similar fan noise Zhu! Spectrum, can any one of the above two formulas, but with the series and fans of different sizes, constants, functions 3 and 6 or where the corpse, 6 should be divided, corresponding to equal.
Acoustic similar law application also needs to know in advance of a dimensionless similar test data in order to carry out the fan calculation of acoustic radiation is not simply to carry out acoustic design theory directly addresses the centrifugal fan noise Q 3 Test Methods 3.1 import and export pipeline test due to the lack of accurate theoretical data, so a lot of trial and qualitative analysis based on the theory test, generally have taken the inlet or outlet pipe with muffler noise measurements in import and export, then the test results into the small spectral analysis to determine the noise source and transmission. During the test, usually considered separately first axial divergence angle and radial clearance of imported expansion lengths volute tongue and the impeller and volute volute tongue clearance angle of inclination radius volute tongue and the impeller vane type number and other parameters, namely the analysis of these parameters on centrifugal Fan noise impact, but such conduct workload analysis and testing too, but ignored the interaction between the various parameters.
3.2 centrifugal fan casing acoustically optimized enclosure type line for centrifugal fan aerodynamic noise is extremely important in terms of how to get an excellent chassis-type line is that many people are concerned about asking the most current study, only By modifying the volute casing tongue area to reduce the fundamental strength. Motion for 1 and other changes throughout the volute tongue to find the optimal shape design on noise generation.
As a kind of test instrument, play six meters with the flora and fauna it home 10 10 variables in a variety of angles to the wall volute tongue position from the rotor shaft is to describe the volute tongue. By random changes in variable households 1 households produce 10 offspring volume group 9, 9 offspring optimum amount profile. While this test is only taken into account the impact of the volute own parameters, while ignoring the structural parameters of the impeller.
Optimization Test Method 3.3 high core fan structure of a large number of trials are conducted under the premise to ensure that other parameters constant, changing only some parameters of the test results to optimize the structure of its parameters, thus ignoring the correlation between the various parameters, so use Test methods for orthogonal regression design optimization method, the optimal regression design method is very necessary. These documents have been calculated by different instances regression function SPL fans and series parameters, and uses an optimized method were calculated. The basic idea is in the choice of structural parameters of centrifugal fan, taking into account the various TV + off between the number of men in the occasion should benefit optimization husband back, method, non-linear regression test series data obtained objective function value of the noise, get After nonlinear equations to optimize the design. For example, the SPL 1 8 3 times regression design parameters obtained their relationship and then taken one by one to the gradual normalization analysis into a variable factor into the screening. Each introduction of new variables to the front of variable significance tests, reserves the right to 5 where significant effects of variables which, excluding the five had no significant effect of variables, which can obtain an optimal regression equation which contains all of a significant impact variables. This optimization means with fewer test can arrive at a more satisfactory results, but it can not get the noise contribution of each source to the recipient.
3.4 Coherent analysis techniques in order to compensate said defect analysis techniques such as Fen-Basha view machine made with phase 1 pour undertaken to identify the source of the beep. Through; circumstances encountered perceived noise system from multiple noise sources, through coherent analysis, on a similar pay within a family pay each recipient a source of influence, which has been seeking a technology should roar Yu Min in the literature has been used inside and outside Analysis & Technical Analysis phase centrifugal fan indole sound source characteristics and produce machine now, the base wood processing is based on the noise transfer system as independent of each other between a multi-input output system backup system input source, 3 ʱ??
Noise simulation and calculation of centrifugal fan volute concern consider is the need to resolve the question. Therefore, the recommendations can be simplified into a centrifugal fan volute ideal case with a hard boundary model, 4 and temporarily ignore the effects of import and export soft border, the Green's function in vivo derived hatched, then the Green's function of this promotion to consider the case of import and export soft border, and then use the Solution of the function of internal centrifugal fan pneumatic sound field generated by the rotation of the impeller can be obtained when the theoretical solution of the equation. After calculating dimensional unsteady flow field inside the centrifugal fan, the use of the models and theories can find the solution of equations and flow field corresponding pneumatic sound field, so that you can make up for lack of other butterfly numerical simulation methods, I am going theoretical and computational work in this area, but also aerodynamic noise centrifugal blower colleagues calculated as a reference. Currently, the Green's function has been to ignore the import and export 3.5 computer instruction test the boundaries of the volute soft body test equipment due to heavy workload, handle data cumbersome, so the use of acquisition and processing computer monitoring tests and test data is essential You can now be digitized by computer analysis of static and dynamic tests. Virtual Instruments and Katerini instrument called a small people called 0 1 technology developed rapidly, virtual instrument is known as noise and vibration control technology revolution dynamics. Large-capacity data acquisition and signal processing software system 05 large Shi Pu software virtual instrument library has the international advanced level, its powerful, versatile, can carry 1 to vibration. Shock. Noise. Signals, information processing. Computer-aided measurement type. School modal analysis, structural dynamics modification. Fault diagnosis and, based detect ambient vibration and noise tests, and many other analytical work. But so far, the virtual instrument applications fan industry, little, if widely used, would make the centrifugal fan test measured style. Data collection and analysis into the outer new phase, 4 to discuss a centrifugal fan for aerodynamic noise, the numerical simulation and calculation methods are not yet mature, and can not be obtained for aerodynamic noise centrifugal fan theoretical formulas, and some even with sound pressure and linkages between the various parameters, but also need the help of tests to determine the specific relationship, apparently limited to these methods have been calculated fan, but not in the new aerodynamic design of the fan acoustic design simultaneously. Therefore, according to the Green's function is obtained, the domain solution but because of ignoring the impact of the import and export soft spiral border, this formula there is a large gap between the actual situation Volute sound field, it is also necessary to have in-depth research to domain solver get inside when Importers soft border volute and when Green's function.
2 With the rapid development of computers, noise test test technology development has been relatively rapid, the more advanced testing methods already used in fans, but still not enough; in other industries, the use of virtual instrumentation and simulation have significantly reduced the manpower and resources, makes a lot of test difficult becomes easy to carry out, the recommendations should be applied to these advanced testing methods as soon as aerodynamic noise fan industry and continue to develop to expand its range of applications
