Numerical Simulation Study On Hydraulic Characteristics Of Aerated Water Flow In Steep Troughs

In this paper,numerical simulation is used to simulate the aerated flow in a steep channel.The hydraulic characteristics of the aerated flow and their influence on each other are discussed.The results are compared with the data obtained from model tests.The conclusions are as follows:The change of flow rate has great influence on the water surface and cavity length,the influence on the side wall is greater than that on the central axis,and the influence on the impact area and reflection area is greater than that on the stable area.The change of vent area will not affect the water surface line along the way,but it has some influence on the length of the cavity,but no flow has a great influence on the length of the cavity.Measured by the sensitivity coefficient,the sensitivity of the length of the cavity at the central axis to the flow is 0.5571,and to the vent area is 0.1726;the sensitivity of the side wall to the flow is 0.6353,and to the vent area is 0.2295.The velocity changes greatly in the impact zone,the direction of velocity is complex,and the flow pattern is chaotic.There is no obvious correlation between flow rate and flow rate in the impact zone.In the back of the reflection zone and the stable zone,the flow rate increases with the increase of flow rate.The influence of flow rate on velocity is more obvious in side wall.In the same process,the velocity of the side wall is obviously smaller than that of the central axis.The time average pressure is the maximum value of negative pressure at the end of the cavity.The highest point of time average pressure is located in the middle of the impact zone.Due to the formation of water wings in the reflection zone,the time average pressure becomes smaller,and the time average pressure rises up to some extent.When the flow velocity increases in the stable zone,the time average pressure begins to decline slowly along the path.The influence of flow rate change on time average pressure decreases from impact zone to stable zone.The probability density curve in the impact zone is more sharp with the increase of the vent area,and the skewness is more obvious.The kurtosis coefficient C_E is up to 3.41,and the skewness coefficient C_S is up to 0.49.Compared with the standard normal distribution,the probability density curve shows the characteristics of peak tip and tail thickness.However,there is still a certain degree of peak distribution.With the decrease of vent area,the phenomenon of peak decreases.The peak coefficient C_E is between 3.05 and3.28.The probability density function of the fluctuating pressure in the stable region is basically consistent with the standard normal distribution.The dominant frequency of the impact zone is concentrated in the range of 0～9Hz,and with the increase of the vent area,the dominant frequency is gradually increased,and the energy carried by each frequency is also increased.The dominant frequency in the reflection area is relatively small,concentrated between 0～6 Hz.The dominant frequency is low and the energy carried by it is relatively large,while the energy carried by other frequency segments is relatively small.The dominant frequency at the side wall is larger than that at the central axis,but the energy is smaller.With the increase of vent area,the energy carried by each frequency is increased,but the proportion of the energy of each frequency to the total pulsating energy is basically unchanged,which has no effect on the distribution range of dominant frequency.The VOF model can not capture the micro bubbles in the water flow very well.The VOF model is mainly suitable for capturing the bubbles with relatively large diameter.According to the model test data,there is no obvious relationship between the change of flow rate and the aeration concentration.With the increase of vent area,the aeration concentration along the way also increases.This paper puts forward a conjecture about the mechanism of air entrainment and erosion reduction.There is a very thin air cushion layer in the middle of the bottom plate of the steep trough.The possibility of its existence and the process of preventing cavitation damage are analyzed.