Experimental Study On Flow-noise Of Centrifugal Pump In Variable Working Condition

As the centrifugal pumps are developing in the direction of large flow,high power and high load,the noise problem of centrifugal pumps have become more serious gradually.Actually,the centrifugal pumps always change the working conditions during operating,and the generated noise during operation also changes inevitably with the working conditions.To establish theoretical basis for the flow noise control technology of centrifugal pumps,and provide guidance for optimal design of low noise centrifugal pumps,it is necessary to study the flow noise of centrifugal pumps under various working conditions,reveal the changing law between flow noise and flow rate,rotational speed,and obtain the noise amplitude under different frequencies.In this paper,IS-80-50-250,a single-stage,single-suction centrifugal pump,is chosen as the model pump,and the experimental platform for noise measurement of centrifugal pumps is established.In this experimental platform,the radiation noise receivers in circumferential direction and internal flow noise receivers in outlet pipe are arranged for noise measurement,and then the changing law,as well as frequency characteristics of noise under different rotational speed,flow rate conditions are studied,meanwhile,the distribution law of radiation noise of the model pump on the volute tongue is also discussed.Firstly,the changing rule of centrifugal pump noise under rated operational condition is studied,the radiation noise of the centrifugal pump is characterized by broad band,and the peak value appears in the shaft frequency,the frequency and their frequency multiplication,the maximum value is reached between 1000～2000Hz and the sound pressure level(SPL)in the high frequency region is gradually reduced.The frequency characteristics of internal flow noise in the outlet pipe is consistent with the radiation noise,but the noise amplitude is less than the radiation noise apparently,which is about 1/3-1/2 times of that of radiation noise.Compare the noise amplitude of radiation noise in the outlet direction and the internal flow noise in outlet pipe measured by hydrophone,it is found that the radiation noise amplitude is 86.7dB,and the flow noise is 43.9dB at 1000Hz,furthermore,the distribution of radiation noise on the volute tongue has the characteristics of dipole,and the SPL in the direction facing the tongue is higher than the direction against the tongue,specifically,the amplitude of the measuring point in the direction facing the tongue is 4.8%higher than that of the direction against the tongue.Under various rotational speed conditions,which include keeping rated flow unchanged and valve open unchanged.In the two kinds of conditions,the distribution characteristic of the total sound pressure level(TSPL),SPL of every receiver,internal flow noise in outlet pipe and radiation noise on tongue section show similar pattern,and this pattern is more obvious in the valve open conditions than that of rated flow conditions.The TSPL,SPL and the internal flow noise in outlet pipe increases with the increment of rotational speed,and the TSPL is about 2 times of the internal flow noise in outlet pipe,and the distribution of the radiation noise on the section of tongue has the characteristics of dipole,and the SPL in the direction facing the tongue is higher than that of against the tongue.On the frequency characteristics,the radiation noise reaches the maximum at the shaft frequency,blade-passing frequency and their frequency multiplication under the two kinds of conditions,and the SPL at 1000Hz and 2000Hz are much higher than that at other frequencies.Additionally,the internal flow noise in outlet pipe has the similar frequency characteristics,which reaches the maximum at 500Hz,and then reduces gradually.Under various flow rate conditions,the TSPL,SPL and internal flow noise in outlet pipe show a gradual increasing trend with the increment of flow rate,and the distribution of radiation noise on the section of tongue also shows the similar characteristics with the various rotational speed conditions.On the frequency characteristics,the radiation noise and internal flow noise reach the maximum at the shaft frequency,blade-passing frequency and their frequency multiplication,and the noise of blade-passing frequency,as well as the frequency multiplication are much higher than that of shaft frequency and it’s frequency multiplication,which indicates that the pressure pulsation caused by the dynamic interference of the impeller and the tongue is the main source of the noise of the centrifugal pump.Through the study of the frequency range between 1000Hz and 4000Hz under three kinds of working conditions,which is sensitive to ears,it is found that the SPL in this range is closer to the TSPL,and the acoustic energy in this range is about 90%of the total acoustic energy under the various rotational speed conditions that keeps rated flow unchanged,while this ratio reduces to 50%-60%under the two other working conditions.The conclusions of this paper can provide guidance for optimizing the operating conditions to achieve the noise reduction of the centrifugal pumps and the different frequency noise control technology.