Abstract: In the study of hydraulic characteristics of the inlet and outlet, especially in physical model tests, the trash rack structure is generally not simulated because of the difficulty in modelling its closely spaced thin fence bars. To investigate the influence of a barrier structure on the hydraulic characteristics of an inlet and outlet under two-way flow conditions, we build a large-scale inlet and outlet test facility, conduct an experiment on a model inlet and outlet that is equipped with a trash rack structure, and compare it with the no trash rack case. The results show adding this structure results in a uniform distribution of time-average flow velocity behind it. In the outlet mode, the coefficient of flow uniformity is reduced by 7.1% from the no rack to the trash rack case; in the inlet mode, it is nearly the same in both cases. The rack disturbs the flow and intensifies velocity pulsation and turbulence intensity. Under its disturbance, the average turbulence intensity is increased by 49.0% and 38.5% in the outlet mode and inlet mode respectively, but flow distribution across different channels has little change in either flow mode. The trash rack structure produces head loss: the loss coefficient in the trash rack case is increased by 6.3% and 7.2% in the outlet mode and inlet mode respectively. The hydraulic indexes of the inlet and outlet in the two cases are not very different except for a large difference in turbulence level. This demonstrates the fact that the results obtained from a model inlet and outlet of no trash rack modeling can basically reflect its hydraulic characteristics.

Key words: inlet and outlet, trash rack, velocity distribution, flow distribution, head loss coefficient