**Part 4**

**Multiphase Phenomena: Air-Water Flows and Sediments** 

234 Hydrodynamics – Natural Water Bodies

Zou, Desen, 1990, The hydrodynamic and PLT in the mouth region of Yangtze River and its

summary).

training, Journal of Sediment Research, 3, 27-34 (in Chinese with English

**12** 

*Brazil* 

**Stepped Spillways:** 

*University of São Paulo* 

**Theoretical, Experimental** 

André Luiz Andrade Simões, Harry Edmar Schulz, Raquel Jahara Lobosco and Rodrigo de Melo Porto

Flows on stepped spillways have been widely studied in various research institutions motivated by the attractive low costs related to the dam construction using roller-compacted concrete and the high energy dissipations that are produced by such structures. This is a very rich field of study for researchers of Fluid Mechanics and Hydraulics, because of the complex flow characteristics, including turbulence, gas exchange derived from the twophase flow (air/water), cavitation, among other aspects. The most common type of flow in spillways is known as skimming flow and consists of: (1) main flow (with preferential direction imposed by the slope of the channel), (2) secondary flows of large eddies formed between steps and (3) biphasic flow, due to the mixture of air and water. The details of the three mentioned standards may vary depending on the size of the steps, the geometric conditions of entry into the canal, the channel length in the steps region and the flow rates. The second type of flow that was highlighted in the literature is called nappe flow. It occurs for specific conditions such as lower flows (relative to skimming flow) and long steps in relation to their height. In the region between these two "extreme" flows, a "transition flow" between nappe and skimming flows is also defined. Depending on the details that are relevant for each study, each of the three abovementioned types of flow may be still subdivided in more sub-types, which are mentioned but not detailed in the present chapter.

Figure 1 is a sketch of the general appearance of the three mentioned flow regimes.

Fig. 1. Flow patterns on stepped chutes: (a) Nappe-flow, (b) transition flow and (c)

**1. Introduction** 

skimming flow.

**and Numerical Studies** 
