Abstract
Spillways are the most important structures of large dams that are responsible for releasing the excessive flood discharge from the reservoir. Although many studies have been performed to determine the flow characteristics over these structures, however, the available information on the shockwaves’ characteristics for spillways’ design is limited. The supercritical flow below the chute piers generates an aerated flow known as shockwaves. Due to the flow interaction with the chute piers, three kinds of standing waves just downstream of the pier, in the middle of the chute, and on the sidewalls are generated. This phenomenon affects the flow domain and its hydraulic characteristics along the chute spillway. The height of the waves increases downstream, where they hit the chute walls and reflect again into the flow to interact together again. The process repeated and intensified downstream in a lozenge shape. The height of these waves can be more than twice the depth flow and thus run over the sidewalls. This is important for the design of chute walls in chute spillways with control gates. In this study, the experimental formation of the shockwaves and their behavior along the chute and their reduction measures are presented. Experiments were conducted on a scaled physical model (1/50) of Kheirabad Dam, Water Research Institute, Iran. It was realized that apart from the geometry of piers and chute spillway, Froude number of flow and gate opening are the main effective parameters on the hydraulic performance of shockwaves’ formation and their development on gated spillways.
Highlights
Spillways are one of the most significant structures of high or small dams that are responsible for discharging the excessive flood flow of the reservoir. eir flow hydraulic characteristics have drawn the attention of many researchers. ese characteristics are high velocity, pressure loss, cavitation probability, and aeration
Investigations on the formation of the shockwaves flow in a horizontal rectangular channel by Reinaur and Hager [19] showed that, for the state of constant flow depth h0 and constant pier width bp, the height of waves 1 and 2 and their width increase with increasing of the Froude number. ey showed that wave 1 height was only a function of the ratio of the flow depth to the pier width Ho/bp. e wave 1 height and wavelength increase by the Froude number increment
The longitudinal and transverse profiles of the waves for the operation of two middle gates, 4 mid gates, and 6 gates were investigated. e longitudinal sections are in the direction of the flow. e transverse sections are at the location of the maximum wave height
Summary
Spillways are one of the most significant structures of high or small dams that are responsible for discharging the excessive flood flow of the reservoir. eir flow hydraulic characteristics have drawn the attention of many researchers. ese characteristics are high velocity, pressure loss, cavitation probability, and aeration. Despite many studies on the hydraulic characteristics of flow in chute spillway, there is insufficient knowledge of the formation of shockwaves. Investigations on the formation of the shockwaves flow in a horizontal rectangular channel by Reinaur and Hager [19] showed that, for the state of constant flow depth h0 and constant pier width bp, the height of waves 1 and 2 and their width increase with increasing of the Froude number. Investigations on this type of flow were presented as the standing wave analysis in a chute spillway [25, 26]. Reinauer and Hager [19, 22] found that shockwaves characteristics only depended on the ratio of approach flow depth to pier width in a series of experiments conducted in a horizontal channel and sloping chutes. The wave 2 impact on the wall of the chutes produced a new wave which is called wave 3 in this study (Figure 1, section 3). e chutes design and structures exposed to these flows should include the quantitative and qualitative identification of the abovementioned waves and their detrimental effects on the performance of the spillway structure and in particular its walls [36]. erefore, identifying their formation location, the characteristics of these waves, evaluating their pressure field and its variations, were considered as significant design hydraulic parameters. is information will considerably assist the designers of these structures
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