| Centrifugal fan is one of the commonly used equipment to maintain the normal operation of the ship.At present,the research on the fan is mainly based on the performance,air noise and fuselage vibration.For the military ship,the structural vibration(mainly refers to the machine feet vibration acceleration)is also quite important research content.With the development of dynamic balancing technology and the maturation of sound isolation measures,it has become an important way to reduce vibration and noise by studying the influence of fan operating conditions and structural parameters on vibration and noise.The pressure fluctuations generated by the interaction of gas flow and volute is the main fan excitation source.Therefore,it is of great significance to study the effect of volute tongue parameters and the number of blades on the pressure pulsation characteristics in the fan,especially the blade frequency vibration.This paper studies the effect of the centrifugal fan vibration on the changes of operating conditions and scroll tongue parameters by building a centrifugal fan vibration decoupling test bed whose volute,impeller and motor are separate.Couple the two parameters that effect the vibration to one structure,and analysis the superposition effect from single parameter to double.Study the pressure pulsation characteristics of blade frequency in the fan and the calculation method of fan vibration induced by it using simulation method to provide the experimental and theoretical basis for the low noise design of the centrifugal fan.The details are as follows:The performance characteristics of the fan are obtained by steady calculation and performance test.Synthesize all the analysis and find that the centrifugal fan has a best operating condition which is near the rated flow.The fan pressure pulse,vibration and noise in blade frequency will increase when deviating from it,especially in small flow conditions.The pressure fluctuation amplitude of the blade frequency on the volute tongue and impeller inlet wheel side are the largest,where is the main role of aerodynamic actuation.Verify the speed-vibration and flow-vibration experience formulas.13 is the best blade number by synthesizing the properties and pressure fluctuation trends.Construct a three-dimensional model of the test bed and calculate the modal of each part.And then calculate the vibration response by modal superposition method with ANSYS transient dynamics.Verify the feasibility of the calculation method by comparing the calculated values of blade frequency acceleration with the experimental results and prove that it can be used for acceleration estimates.The influence of the installation distance of volute tongues,volute tongue tilted form,volute tongue tilt angle and the parameter fusion of distance and angle on the vibration of centrifugal fan is studied.The results show that the tilting mode which keeps the radius of the scroll tongue constant is more conducive to reducing the vibration.When the installation pitch and the tilt angle increasing independently,the blade frequency of the volute module decreases first and then increases.And the amplitude change of the volute region is the most significant.Increasing the installation distance is better than tilting the scroll tongue in terms of reducing vibration.However,tilting the scroll tongue in small installation distance can achieve the damping effect in large ones.There is an optimum tilt angle for a particular installation pitch.The change of the tilt angle of tongue under the large installation distance is more sensitive to the fan vibration of the fan.In volute region,the amplitude of the blade frequency is reduced by 12.8dB when using the optimal volute designed based on these two parameters. |
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