| Flow-pressure-regulating plunger valve is widely used in engineering for its large regulating range,small driving force and easy replacement of the valve spool.Cavitation is difficult to avoid when the valve is operating under the conditions of highpressure drop and large flow rate,which may cause problems such as vibration,noise and decrease of adjustment accuracy.In this research,theoretical analysis,numerical simulation and experiment of multi-physical quantity measurement are adopted to investigate the characteristics of cavitation flow and noise of flow-pressure-regulating plunger valve.Based on some related national standards and the operation specification of ISA,visual experimental apparatus of the test valve is built to measure the underwater noise,air noise and vibration of valve body and pipe which are induced by cavitation flows in different cavitation coefficients.As well,the experimental images of cavitation structure in the changing process are obtained by a high-speed camera.Two kinds of diameters of throttle orifice are compared,includingφ10 andφ5,and the effects of cavitation coefficient,back pressure and valve opening degree on cavitation noise and cavitation structure are analyzed.The main achievements of this investigation are as follow:(1)Mechanism studies of cavitation phenomenon and noise are conducted by bubble dynamics theory,acoustic wave equation and acoustic analogy equation.Cavitation noise belongs to the noise type of monopole source which has the highest efficiency of acoustic radiation when the flow velocity is less than the sound velocity.The cavitation similarity criterion of regulating valve is summarized,considering the influence of “Pressure scale effect” and “Size scale effect” on cavitation similarity.In addition,the theoretical estimation method of the flow noise induced by the regulating valve is also summarized,and the error range of this method is verified to be within 5d B(A)compared with the experimental results of noise.And this method will be more accurate in the prediction of flow noise as the cavitation strength being stronger.(2)The incipient cavitation coefficients of each valve opening degree of the test valve are obtained by the peak frequency method.When the backpressure is fixed,the incipient cavitation coefficient will increase parabolically with the increase of valve opening degree,and the expression of incipient cavitation coefficient changing with valve opening degree is obtained by the polynomial fitting.In addition,the incipient cavitation coefficient in the situation of big throttle orifice is slightly larger than that of small throttle orifice.It indicates that reducing the orifice diameter and increasing the number of orifices is beneficial to the anti-cavitation performance of flow-pressureregulating plunger valve while the flow area remains unchanged.(3)The total sound pressure level of cavitation noise at each opening degree of the test valve has a similar changing process as the cavitation coefficient decreases: in the stage of non-cavitation turbulent flow,the noise increases slowly and the overall amplitude is small;during incipient cavitation and weak cavitation,the noise increases rapidly and reaches the local peak;with the cavitation coefficient decreasing further,the noise tends to decrease first and then continues to rise at last.In addition,the cavitation noise has a wide peak continuous spectrum,which is consistent with the characteristics of the monopole sound source.In the same condition of inlet and outlet pressure,compared with the situation of small throttle orifice,the center frequency of wide peak noise spectrum is higher and the total pressure level of noise is larger in the situation of big throttle orifice.(4)The influence of backpressure and valve opening degree on cavitation noise is investigated by experimental data.In the same cavitation coefficient condition,the cavitation noise of the test valve increases with the increase of backpressure,and it increases first and then decreases with the increase of valve opening degree.(5)The flow field simulation results of the incipient cavitation distribution are basically consistent with the experimental results of high-speed photography.In the test valve,the incipient cavity is mainly distributed in the upstream sidewall and the adjacent area of outlet side of the throttle orifice.In the stage of incipient cavitation,the cavitation pattern belongs to the type of shear vortex cavitation which is attached to the wall,but it changes to spiral cavitation during development and collapse of the cavitation structure.In the cavitating flow field inside the valve,the large-scale spiral cavitation structure and the small-scale free bubbles coexist,which induced the characteristics of the wide peak continuous spectrum of cavitation noise of the flowpressure-regulating plunger valve.The results of this investigation are beneficial to engineering application for acoustic analysis and judgment of cavitation strength as well as the study on cavitation noise suppression of flow-pressure-regulating plunger valve. |
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