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Experimental results indicate that an additional lateral deflector built on the outlet can increase the cavity length in aerators with a sudden vertical drop and lateral enlargement. Observation shows that the cavity length is affected by both the vertical and lateral dimensions of the deflector. A larger deflector increases the cavity length substantially and connects the bottom cavity with the sidewall ones which results in more sufficient aeration. However, the backward flow on the bottom may reduce the length of bottom cavity and the effectiveness of aeration. Factors affecting the bottom cavity length, including the slope of the outlet, the bucket angle of sill, and the shape of lateral deflector, should be included in the estimation of the bottom cavity length. Based on test results, an equation has been proposed to predict the cavity length. DOI: 10.1061/(ASCE)0733-9429(2003)129:7(536) CE Database subject headings: Aeration; Cavitation control; Cavities.

Experiments show that a rough surface reduces the pressure drop and likelihood of cavitation downstream of the roughness. A rough surface upstream of an irregularity significantly reduces the pressure drop caused by the irregularity. The effect of the rough surface is a function of the roughness d/s and can prevent cavitation damage. If an irregularity is inevitable, increasing the roughness of the upstream surface in front of the irregularity will reduce the possibility of cavitation caused by the irregularity. For the curved open channel used in this study of the flow in a spillway, the critical height of the irregularity was increased six to eight times at the downstream tangential point of the curve, and the negative pressure caused by the irregularity was reduced enough to prevent cavitation.