Simulation of water hammer in liquid nitrogen supplying system based on AMESim

A dynamic model of liquid nitrogen supplying system （LNSS） for a large cryogenic wind tunnel （CWT） was built based on the advanced modeling environment for simulation of engineering systems （AMESim） platform.The accuracy of the model was verified by the experimental data with the mean deviation less than 6.8%.Accordingly，numerical simulation on water hammer was carried out under two working conditions of instantaneously complete close-down and orderly close-down of the nozzles at the end of the LNSS.Numerical results illustrated that the dynamic model can characterize the features of water hammer in the complex LNSS.The peak pressure at water hammer reached 2.98 MPa under the condition of instantaneous close-down of all the nozzles.By contrast, the peak pressure reached maximum with the value of 2.3 MPa at the last close-down when the nozzles were shut down orderly following four steps.Moreover，fast fourier transform （FFT） analysis illustrated that different frequencies existed in the pressure fluctuations during water hammering.However, the frequencies showed inconspicuous distinct under these two working conditions.The simulation results provide a support for the design check and safe operation of the large CWT.