Numerical estimation of discharge coefficient for non-circular bottom intake racks

Abstract

Abstract Current research presents a comprehensive numerical study on the performance of riverbed intake systems equipped with non-circular cross section racks. Three types of bottom racks, such as rhombus bars, rounded-edge rectangle bars, and circular bars, were numerically modeled using Flow3D software with different geometric and hydraulic parameter, all in super critical approaching flow in clear water condition. Subsequently, changes in diverted discharge ratio (DDR) of bottom racks and factors affecting its intensity and manner of changes, were studied using model results. The study reveals that the RNG k-ε turbulence model accurately represents the flow field around the bottom racks. The results indicated that the DDR changes are directly related to rack length changes but is inversely related to the rack slope and upstream flow discharge. Also, rhombus bars outperform circular and rounded bars, with 23.34% and 35.92% higher flow diversion, respectively, attributed to the formation of more negative pressures between bars. The main focus of the present study was on accurate and complete estimation of the diverted discharge coefficient (C d) for racks with different bar shapes—especially non-circular bars using the results of the constructed numerical model. Proposed relations for the diverted discharge coefficient (DDC), especially for non-circular bars, were rigorously validated and showed high accuracy in predicting DDC under diverse hydraulic and geometric conditions.

Keywords

• Bottom rack intake
• Diverted discharge coefficient
• Flow3D
• Numerical modeling
• Spatial varied flow