While the steam power plant runs at low load, the drastic vibration and noise of the steam discharge pipes will be induced by the discharging process of high temperature and high pressure steam. Motived by this, the analytical model of inner flow field of the steam discharge pipes is modeled in this paper. The large eddy simulation method is used to analyze the characteristics of the inner flow field of the steam discharge pipes. The mechanism of transient noise in the process of steam discharging, by the comparison of variation law of the inner flow field with different opening angles of control valve or different time, is obtained. On this basis, the K-FWH method is employed to calculate the transient noise of steam discharging. The results show that the key factors of transient noise generation can be owed to the impact effect of steam jet flow on the surface of valve structure, the shear and friction effect induced by the uneven flow, the energy loss of vortex collapse in the process of valve throttling, and the surface noise sources induced by turbulent flow and so on. The throttle noise induced by control valve is presented as significant broadband characteristics in the frequency domain, and the level of transient noise increases with the decreasing of the opening angle of control valve.

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