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Hydraulic jumps occur in natural systems like streams and rivers as well as manufactured systems. Samples of the latter occurance are jumps in water distribution and irrigation networks formed downstream of hydraulic structures such as spillways, sluice gates, and drops. These structures are usually designed for a specific tailwater depth. Stilling basins with baffle blocks are frequently used as energy dissipators downstream of hydraulic structures. Baffle blocks are often used to stabilize the jump, decrease its length and increase the energy dissipation. If the flow rates become more than the design discharge, the tail water depth will be greater than the one required for a free jump. These situations are common in low head hydraulic structures including low diversion dam spillways and gates. Under such conditions the hydraulic jump will be submerged.  The performance of the blocks in submerged jump (SJ) condition differs from the free jump (FJ) case. According to some factors such as Froude number, block shape and location and submergence factor, flow regimes on baffle blocks in condition of submerged hydraulic jumps which occurs in stilling basins, are classified into two regimes, the deflected surface jet (DSJ) and reattaching wall jet (RWJ). In this article a numerical study was conducted to investigate flow pattern, vortexes and the magnitude of vorticity in submerged hydraulic jumps with baffle blocks downstream of a sluice gate. The results were compared to ones in same conditions without blocks. 3D RANS simulations have been applied by Fluent software. RSM turbulence model were used which illustrated much precise results in verification. Three numerical models have been created; Submerged wall jet without blocks, submerged hydraulic jumps with baffle blocks in the condition of deflected surface jet flow regime and submerged hydraulic jumps with baffle blocks in the condition of reattaching wall jet flow regime. Flow pattern has been exhibited for each model and results were compared with each other. Vortexes formed in such situations classified into three groups according to axis which they whirl around. It was observed that deflected surface jet regime has more vortexes in comparison to the two other conditions. In addition, by measuring the average magnitude of vorticity in cross-sections it has been concluded that z-vortexes –vortexes which rotate around z axis– much more powerful than x- and y-vortexes as they determine the kind of flow regime. Furthermore, this magnitude is about two times larger in deflected surface regime than two other situations. This fact leads to more turbulence in the flow that makes deflected  surface jet  regime the desirable condition in which baffle blocks perform more efficiently as energy dissipators in comparison to two other investigated models. In order that, from energy vantage point, conditions should be provided in a way to form submerged hydraulic jump as deflected surface jet regime.

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One of the most frequently encountered cases of rapid varied flow is the hydraulic jump. Stilling basins are used to dissipate the excess kinetic energy of flow to ensure the safety of overflow spillway, chutes, sluices, pipe outlets etc. in this study the topic of block in stilling basins is investigation in a general approach and it’s effect on energy dissipation and downstream scouring are analyzed. In the present research, the energy dissipation and scouring phenomenon were studied in different hydraulic and geometric conditions. Moreover, the present paper was focused on the effect of presence of blocks as an effective parameter on energy dissipation on stilling basin performance. To analyze and assessment of formed hydraulic jump in the stilling basins, the experimental data of many recent researches were achieved and compared. It was concluded that presence of blocks has significant effect on energy dissipation from 1% to 34%. It is also shown that with increasing the Fr Number, the secondary depth increases and the using a rough bed causes reducing the secondary depth between 18% to 37% in comparison with smooth one. Moreover, installing a rough bed also reduced the length of hydraulic jump between 27% to 67%. Using block in the stilling basins, reduces the scouring depth from USBR standard recommendation. Finally, it was concluded that using blocks increased the efficiency of the stilling basin performance.