The effect of roughness in pressure fluctuations in the stilling basin with sudden expansion

Subject Areas : Farm water management with the aim of improving irrigation management indicators

Mahnaz Karimi ¹ , Seyed Habib Musavi Jahromi ² , Mahmood Shafai-Bajestan ³

1 - Ph.D Student, Faculty of Water Science Engineering, Shahid Chamran University, Iran
2 - Professor, Faculty of Water Science Engineering, Shahid Chamran University, Iran
3 - Professor, Faculty of Water Science Engineering, Shahid Chamran University, Iran

Received: 2013-10-10 Accepted : 2015-02-02 Published : 2014-12-21

Keywords: fluctuating pressure, hydraulic jump, rough bed, stilling basin, sudden expansion,

Abstract :

Stilling basins with sudden expansions are one of the energy dissipater structures. This structure has many applications downstream of hydraulic structures, such as spillways, sluice gates and chutes. In the jump, the pressure fluctuations resulting from intense macro-scale turbulence must be carefully considered during the design of the structure. Roughness can also cause changes in the behavior of stream line and vortices. So far its effects on the hydrodynamic characteristics of the jump have not been studied. In this study many tests are conducted in a relatively large flume size of 0.8 meter wide and 12 meter length. Channel expansions ratio (B1/B2) was 0.33 and data are presented for Froude numbers from 4-9.2. Measurements were conducted in the bed of flume by means of pressure transducers systems. The final results of this study show that roughness decreases Intensity of fluctuating pressure in sudden expansion stilling basin. Test results were compared with those of smooth sudden expansion jump and classical jump which indicates that the peak values of RMS dimensionless pressure fluctuations (Cp'), are 53% lower than smooth sudden expansion jump and are reduced 70% compared with classical jump. Intensity of fluctuating pressure at the position of about (0.15-0.3) Lj, can reach the maximal value. Peak values of RMS dimensionless pressure fluctuations C'p max up to 0.023 and maximum positive (negative) deviation Cp-and Cp-values up to 0.08 were obtained. In addition to dimensionless coefficients of pressure fluctuations, the longitudinal distribution of pressures and determined pressure fluctuations and extreme values occurring during flow are obtained.