Skip to main content Accessibility help
×
Home

Flow Field in a Skimming Flow Over a Vertical Drop Without End-Sill

  • Chang Lin (a1), S.-C. Hsieh (a1), W.-J. Lin (a2), S.-H. Chou (a1) and R. V. Raikar (a3)...

Abstract

The flow structure in the shear layer and in the recirculation zone of a skimming flow downstream of a vertical drop without end-sill measured using high speed particle image velocimetry (HSPIV) and flow visualization method is presented. The interface between the sliding jet and the recirculation zone (zone below sliding jet) was enhanced through non-ventilation condition between the drop structure and the jet. The flow field measured through HSPIV was used to represent the characteristics of mean streamwise velocity in the shear layer and mean horizontal velocity in the recirculation zone. With the growth of shear layer as the jet slides down over the recirculation zone, the momentum exchange from the sliding jet into the recirculation zone via the shear layer increases along with energy loss. Hence, it was observed that the amount of energy dissipated in the skimming flow at the drop structure without ventilation is greater than that with ventilation by an average value of 50% for Yc / H ≥ 0.2 (where Yc = critical depth and H = drop height). However, the flow structure in the recirculation zone is found to be analogous to that of turbulent plane wall jet. The nonlinear regression analysis is used to fit the regressed velocity profiles to the measured HSPIV mean velocity distributions. Further, the appropriate characteristic velocity and length scales are selected to attain the unique similarity profiles both in the shear layer and in the recirculation zone of the skimming flow. The selection of the characteristic scales is also discussed. The similarity profiles are well comparable with those of napped flow without end-sill and with ventilation as well as of skimming flow with end-sill and without ventilation. It is interesting to observe that, the proposed similarity profiles for the shear layer also map the data of backward-facing step flow and cavity shear flow. In addition, the turbulence characteristics in the shear layer, including turbulence intensities, turbulent kinetic energy, viscous and Reynolds shear stresses, and turbulence energy-budget balance, are illustrated in detail. From the variation of turbulence production it is observed that near the drop structure the energy exchange is from the chaotic recirculation zone to the sliding-jet flow, while in the later part it is reversed. Furthermore, the analysis of turbulence energy-budget balance indicates very significant role of turbulence production, pressure diffusion and turbulence diffusion as compared with turbulence advection that has very minor role in turbulence energy-budget balance for the central part of the shear layer.

Copyright

Corresponding author

* Corresponding author (clin@mail.nchu.edu.tw)

References

Hide All
1.Rouse, H., “Discharge Characteristics of the Free Overfall,” Civil Engineering, 6, p. 257 (1936).
2.White, M. P., “Discussion on Energy Loss at the Base of a Free Overfall,” Transactions, ASCE, 108, pp. 13611364 (1943).
3.Moore, W. L., “Energy Loss at the Base of Free Overfall,” Transactions America Society Civil Engineering, 108, pp. 13431360 (1943).
4.Rand, W., “Flow Geometry at Straight Drop Spillways,” Proceedings America Society Civil Engineering, 81, pp. 113 (1955).
5.Rajaratnam, N. and Chamani, M. R., “Energy Loss at Drops,” Journal of Hydraulic Research IAHR, 33, pp. 373384 (1995).
6.Chamani, M. R. and Beirami, M. K., “Flow Characteristics at Drops,” Journal of Hydraulic Engineering, ASCE, 128, pp. 788791 (2002).
7.Tokyay, N. and Yildiz, D., “Characteristics of Free Overfall for Supercritical Flows,” Canadian Journal of Civil Engineering, 34, pp. 162169 (2007).
8.Lin, C., Hwung, W. Y., Hsieh, S. C. and Chang, K. A., “Experimental Study on Mean Velocity Characteristics of Flow over Vertical Drop,” Journal of Hydraulic Research IAHR, 45, pp. 3342 (2007).
9.Chanson, H., “Discussion on Energy Loss at Drop,” Journal of Hydraulic Research IAHR, 34, pp. 273278 (1996).
10.Huang, H. S., “Hydraulic Characteristics of Free Overfall-Impacted Channel Flow over Sloping Bed,” Ph.D. Thesis, Dept. of Civil Engineering, National Chung-Hsing University, Taiwan (2010).
11.Chen, J. Y., Yao, C. Y., Liao, Y. Y. and Huang, H. S., “Impact Force on Downstream Bed of Weir by Free Overfall Flow,” Journal of the Chinese Institute of Engineers, 31, pp. 10471055 (2008).
12.Chen, J. Y., Huang, H. S., Hong, Y. M. and Liu, S. I., “The Impact Characteristics Analysis of Free Overfall Flow on a Downstream Channel Bed,” Journal of the Chinese Institute of Engineers, 34, pp. 403413 (2011).
13.Etheridge, D. W. and Kemp, P. H., “Measurements of Turbulent Flow Downstream of a Rear-Facing Step,” Journal of Fluid Mechanics, 86, pp. 545566 (1978).
14.Armaly, B. F., Durst, F., Pereira, J. C. F. and Schonung, B., “Experimental and Theoretical Investigation of Backward-Facing Step Flow,” Journal of Fluid Mechanics, 127, pp. 473496 (1983).
15.Troutt, T. R., Scheelke, B. and Norman, T. R., “Organized Structures in a Reattaching Separated Flow Field,” Journal of Fluid Mechanics, 143, pp. 413427 (1984).
16.Grant, I., Owens, E. and Yan, Y. Y., “Particle Image Velocimetry Measurements of the Separated Flow Behind a Rearward Facing Step,” Experiments in Fluids, 12, pp. 238244 (1992).
17.Pereira, J. C. F. and Sousa, J. M. M., “Experimental and Numerical Investigation of Flow Oscillations in a Rectangular Cavity,” Journal of Fluids Engineering, ASME Transaction, 117, pp. 6874 (1995).
18.Kuo, C. H., Huang, S. H. and Chang, C. W., “Self-Sustained Oscillation Induced by Horizontal Cover Plate Above the Cavity,” Journal of Fluids and Structural, 14, pp. 2548 (2000).
19.Kuo, C. H. and Jeng, W. I., “Lock-On Characteristics of a Cavity Shear Layer,” Journal of Fluids and Structural, 18, pp. 715728 (2003).
20.Lin, C., Hwung, W. Y., Hsieh, S. C. and Chang, K. A., “Reply to the Discussion: Experimental Study on Mean Velocity Characteristics of Flow over Vertical Drop,” Journal of Hydraulic Research IAHR, 46, pp. 425428 (2008a).
21.Kiyani, G. A. and Rajaratnam, N., “Discussion: Experimental Study on Mean Velocity Characteristics of Flow over Vertical Drop,” Journal of Hydraulic Research IAHR, 46(3), pp. 424425 (2008).
22.Lin, C., Hsieh, S. C., Kuo, K. J. and Chang, K. A., “Periodic Oscillation Caused by a Uniform Flow over a Vertical Drop Energy Dissipator,” Journal of Hydraulic Engineering, ASCE, 134, pp. 948960 (2008b).
23.Lin, W. J., “Flow Characteristics in Skimming Flow over a Vertical Drop Pool,” Ph.D. Thesis, Department of Civil Engineering, National Chung Hsing University, Taiwan (2009).
24.Jaung, R. H., “Study on the Characteristics of Periodic Oscillation Downstream of Plunging Pool,” Master Thesis, Department of Civil Engineering, National Chung Hsing University, Taiwan (2000).
25.Chou, S. H., “Study on the Characteristics of Skimming Flow,” Master Thesis, Department of Civil Engineering, National Chung Hsing University, Taiwan (2008).
26.Hinze, J. O., Turblence, McGRAW-HILL, New York (1959).

Keywords

Related content

Powered by UNSILO

Flow Field in a Skimming Flow Over a Vertical Drop Without End-Sill

  • Chang Lin (a1), S.-C. Hsieh (a1), W.-J. Lin (a2), S.-H. Chou (a1) and R. V. Raikar (a3)...

Metrics

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed.