| The new research scheme for the adjustable contra-rotating fan with external single-motor can effectively improve the problems of poor adjustable performance,low operating efficiency and high motor failure rate of the conventional mining contra-rotating fan.For this new program of fan,this paper focused on its noise and vibration characteristics.It was of utmost importance to develop a new type of fan,improve ventilation efficiency,ensure reliable operation,reduce vibration and noise,and improve ventilation system in mine.Firstly,CFD software FLUENT was used to simulate the three-dimensional flow field of the fan under different conditions and different blade numbers matches to study the internal flow field,pressure field and vorticity distribution.The results showed that the total pressure and turbulence intensity were small,the vorticity variation on blades was small,the disturbance loss in the gas transmission process was less,and the fan performance was better when the inlet wind speed was v=15m/s.When the number of the first stage blades was 14 and the number of the second stage blades was 10,the efficiency of the fan was more efficient.In addition,the flow field in the blade tip region,hub attachment layer,and hub region was greatly affected by the different blade numbers,which can cause large vortex noise and affect the aerodynamic performance of the fan.Then,based on the numerical simulation of the whole flow field of the fan,the broadband noise module was used to study the fan sound power under different conditions and different blade numbers in FLUENT software.With the increase of wind speed at fan inlet,the highest sound power level of the fan showed a trend of decreasing first and then increasing.When the number of blades in one stage was certain,the sound power of the fan increased with the number of blades in the other stage.Then the large eddy simulation was combined with the FW-H acoustic model,and the aerodynamic noise of the fan was numerically simulated by using the FFT technique to analyze the noise generation and spectrum distribution characteristics.The results showed that the aerodynamic noise of the fan was mainly medium and low frequency noise and the sound pressure level was the lowest under the design condition.The main site of the noise generation was the two-stage impeller region.Under low flow conditions,the sound pressure level was higher when the inlet wind speed was12m/s,and the vortex noise was the main noise type.In the case of large flow conditions,the spectrum diagram showed some significant peaks,and the rotation noise accounted for a large proportion.In addition,in the medium-high frequency and high frequency bands,the highest sound power of the first stage blades number Z1=15 was stronger than Z1=13 and Z1=14.With the decrease of the second stage blades number,the increase of blade clearance lead to large changes in the tail blade vortex shedding and blade gap vortex.The loss of gas flow in the flow channel increased and the vortex noise increased,resulting in the overall sound pressure level of Z2=9 was maintained at a high level.Finally,the adjustable two-stage impeller and the whole fan machine were tested in modal experiments by using the hammer test and sweep sine test in LMS Test.Lab.The natural frequencies of the two-stage impeller and the fan did not overlap,avoiding the possibility of resonance superposition.There designs were more reasonable.Subsequently,the vibration characteristics of the contra-rotating fan with external single-motor were experimentally analyzed under different operating speed conditions.Combined with the characteristic frequencies of the fault signal,frequency domain and time domain analysis were used to determine the fan operating status.The rotor imbalance and abnormal vibration caused by long axis led to the most important vibration failure factor when the impeller speed was v=2000r/min.The abnormal vibration transmitted by the gearbox and the unbalance of the first stage impeller caused the vibration intensity at the fan outlet to be higher than inlet.In addition,this paper analyzed the corresponding relationship between the frequency spectrum of the medium and high frequency bands and the blades passing frequencies in the aerodynamic noise spectrum when the fan was abnormally vibrated,and further studied the cause and frequencies distribution of mechanical noise excited by the abnormal vibration of the fan.The unbalanced failure of the first stage impeller,the design of its blades parameters and the abnormal vibration transmitted by the gearbox will have a major impact on the overall vibration and noise of the fan. |
PDF Full Text Request