Abstract: Vertical two-dimensional sloped-bank diffusive tank and vibrating-grid turbulence generating system were set up for studies on the diffusion of instantaneous line-source discharging. The pollutant was discharged from the vertex of the domain with bank slope in eight cases of  θ=360°/β (mapping coefficient of angular filed, β=4, 5,  ,11). The turbulence strength was controlled by three levels of grid vibration frequency n=20, 40, 60 r/min. The two-dimensional concentration field distribution was measured by image collection and digital image processing technology. The results showed that both the transverse and vertical diffusion coefficients were increasing with the growth of grid vibration frequency. The average transverse diffusion coefficients were 18.38  cm²/s, 30.88 cm²/s, 43.94 cm²/s, and the average vertical diffusion coefficients were 1.89 cm²/s, 2.47 cm²/s, and 3.24 cm²/s   respectively when the frequency was  n=20, 40, 60 r/min. The vertical diffusion coefficient was about 7.4% - 10.3% of the transverse diffusion coefficient under grid vibration. Both the two coefficients showed undulating changes with different slope angles. The experiment proves that the concentration of pollutant discharging from the vertex of angular field with sloped bank follows the pattern of periodic variation which depends on the odd/even parity of β and the multiple of β=4. 

Key words: environmental hydraulics, sloped bank, angular field, vibrating-grid turbulence, digital image processing, distribution of concentration, experimental research