Analysis Of Unsteady Flow And Its Excitation Signals In A Centrifugal Pump

The pressure pulsation induced by unsteady flow is one of the main factor causing vibration in a centrifugal pump.Due to the diversity and complexity of internal flow structures,there are lots of hydraulic excitation signals that are difficult to research directly.Actually,pressure pulsation and vibration whose signals can be extracted accurately by both numerical simulation and test methods are the specific performance of hydraulic excitation.Therefore,it is important for revealing the nature and mechanism of fluid induced vibration in a centrifugal pump by to explore the appropriate and effective signal processing methods.Moreover,it will provide new methods for the study of mechanism of fluid induced vibration,and also provide reference for the hydraulic design of the low vibration and noise pump.In this paper,both CFD and test method are applied to investigate the unsteady flow field & its excitation signals in a centrifugal pump.Meanwhile,different signal processing methods are applied to study the excitation signals from various perspectives.The main work and obtained results are listed in the following:1.Summarize the methods for processing signals in a centrifugal pump,in order to reveal more information of internal flow and to establish the relationship between different excitation signals,time-frequency characteristics analysis 、 correlation analysis and coherence analysis are introduced in addition to the traditional methods of time domain and frequency domain analysis.2.Flow field instability in a centrifugal pump are studied by numericalsimulation method with RNG k-ε turbulence model.Pressure and velocity distribution are obtained at different flow rates,meanwhile,transient static pressure values and velocity values on the volute casing are calculated.The research results reveal the essential feature of unsteady flow field in the centrifugal pump.3.The test loop of model pump and LMS test system are set up,pressurepulsation signals on the volute casing are measured with micro pressure transducers placedalong the circumferential direction;vibration at different directions are measured with acceleration sensors placed at the external wall of volute,base,bearing and so on.4.Based on FFT,the influence of sample frequency,locations,flow rates and speed on pressure pulsation spectra are studied.Based on STFT,the time-frequency characteristics of pressure pulsation is studied,the result highlights the unsteady flow especially at low flow rates.Correlation between pressure pulsation near volute tongue and other monitoring points are analyzed by cross-correlation function,the result prove the propagation path of pressure pulsation in the volute.Meanwhile,coherence are analyzed by coherence function,finding the high degree of coherence at blade pass frequency and its harmonic frequencies.5.Based on FFT,the influence of locations,directions,flow rates on vibration spectra are studied.RMS(Root mean square)of vibration energy between 0-1000 Hz at different directions are caculated under various flow rates,as well as the total vibration energy E.Coherence function is applied to establish the relationship between pressure pulsation signals and vibration acceleration signals,the results highlight the great influence of rotor-stator interaction on vibration at fBPF and its harmonic frequencies in the pump.