Journal of Hydraulics

Journal of Hydraulics

Experimental and numerical study of flow over a triangular broad crested (crump or hump) weir with variable ramp slopes under different head ratios

Document Type : Research Article

Author
fereshtehalsadat Mousavi Pour
civil engineering department, Islamic Azad university of Qom, Qom, Iran
10.30482/jhyd.2024.407121.1712
Abstract
To determine the free surface flow characteristics over a triangular broad crested (crump or hump) weir with different slopes in upstream and downstream, a series of experiments were conducted in hydraulics laboratory using a 5 m long flume. The experiments were simulated by a numerical model, Flow 3D, in order to study the hydrodynamic field over the weir and compare experimental and computational results .The computational results, included testing different turbulence models: two equation k–ε, renormalized group (RNG) and the large eddy simulation (LES) besides nested mesh with high concentration in the weir location, showed a close agreement with experimental data. Flow characteristics such as free surface elevation (water surface profile), Froude number and specially the location of critical flow occurrence and discharge coefficient were studied in different head ratios and ramp slopes. Finally, according to the results it was understood that when steeper ramp slope facies upstream, the critical flow occurs exactly at the crest of the weir, while milder ramp facing upstream makes the critical flow appearance move forward and pass the crest. The critical state location showed no sensetivity to different head ratios. Moreover, discharge coefficients were calculated and it is concluded that Cd equaled 0.95 and 1.30 respectively for steep slope and mild slope facing upstream. It is worth mentioning that among different turbulence models offered by Flow 3D, k–ε model shows the best agreement with experimental data obtained from the laboratory. Hydraulic structures such as weirs are used for flow measurement, water level and sediment control in water channels. There are a wide variety of weir designations which have been developed for various applications (Akbari et al., 2019). Furthermore, they used as hydraulic jump control structure and compactness of stilling basins(Achour et al., 2022). In general, Weirs are categorized into sharp-crested and broad-crested groups.There are some proven advantages for each one. But broad-crested weirs are superior compared to other flow measuring structures, for instance: they show more stability rather than sharp-crested weirs, they are usually used as dams, especially in gabion weirs, etc., with sides ramps especially upstream face of the weir, they can easily pass sediments and floating objects (Malekzadeh et al., 2022).
Keywords
critical flow location
fraud number
weirs
grade change
critical depth meters

Subjects

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  • Receive Date 16 August 2024
  • Revise Date 14 December 2024
  • Accept Date 16 December 2024