| The stilling basin with sudden expansion and drop sill is an environmentally friendly energy dissipator with high water head,large unit width and good application prospects.As energy dissipation structure for flood discharge of high dam,the stability of the stilling basin with sudden expansion and drop sill is of great significance to energy dissipation and scouring prevention as well as the safety of the whole hydraulic structure.The stilling basin with sudden expansion and drop sill has sudden expansion laterally at the entrance and drop sill vertically,which makes the fluid structure and pressure distribution in stilling basin more complicated and may destroy the stilling basin to some extent.Understanding the turbulent characteristics of water flow in stilling basin with sudden expansion and drop sill is very important to ensure the safety of flood discharge,energy dissipation and scour prevention structure of stilling basin.Based on the methods of model test,numerical simulation and theoretical analysis,the turbulence characteristics of stilling basin with sudden expansion and drop sill were researched,including the flow pattern of stilling basin,distribution of the bottom plate of fluctuating pressure on stilling basin and its related characteristics,bottom velocity distribution and turbulent characteristics of stilling basin.The results obtained can provide reference for reasonable protection and safety design of stilling basin.The main research results and conclusions were as follows:(1)Based on the model test and numerical simulation,the flow patterns in the sudden expansion sill stilling basin and the non-sudden expansion sill stilling basin were analyzed,and the shapes of aeration area and clear water area are obtained.With the increase of sudden expansion ratio,the aeration area decreases and the clear water area increases,and two vertical axis vortices with opposite symmetrical directions were formed on both sides of the sudden expansion.The larger the sudden expansion,the greater the influence range.The high velocity area of the stilling basin with sudden expansion and drop sill is within 0.34 l from the drop sill in the longitudinal direction and within 0.34 B symmetrical to the central line in the transverse direction.This area was the key protection area of the stilling basin bottom plate.(2)Based on the model test,the intensity characteristics of fluctuating pressure on the bottom plate of the stilling basin without sudden expansion and it with sudden expansion were studied.It was concluded that the longitudinal distribution law of pulse pressure coefficient of the stilling basin with sudden expansion sill and the stilling basin without sudden expansion sill was basically the same,both show a trend of attenuation along the way,the peak appears at the head of the stilling basin,and the attenuation of the stilling basin with sudden expansion sill was more rapid along the way;The pulse pressure coefficient of stilling basin without sudden expansion has a relatively uniform transverse distribution and decreases slightly from the middle line to both sides;The fluctuating pressure coefficient of sudden expansion bucket stilling basin diffuses laterally obviously,which increases first and then decreases from the middle line to both sides.The position with large fluctuating pressure coefficient of sudden expansion drop sill stilling basin moves outward than that without sudden expansion drop sill stilling basin,and changes from line 1/2 of stilling basin to line1/4,that was,between the extension line of discharge chute and the 1/2 center line.In terms of fluctuating pressure,the area between the extension line of the discharge chute at the front end of the stilling basin and the central line was the key protection area of the bottom plate of the stilling basin with sudden expansion and drop sill.(3)By analyzing the longitudinal space and time integral scale of fluctuating pressure of the bottom plate of the stilling basin,it was found that in the impact zone,the scale of vortex in the stilling basin with sudden expansion and drop sill was smaller than that in the stilling basin without sudden expansion,and the eddy retention was poor.In addition,the flow turbulence between the extension line of t discharge chute and 1/4 line in the stilling basin with sudden expansion and drop sill was the most severe,the scale of eddy was the smallest,the eddy retention was the worst,the second line in 1/2 and the side wall line was the smallest.(4)Based on the model test and numerical simulation,the distribution characteristics of the flow velocity near the bottom of the stilling basin with sudden expansion and drop sill were analyzed and compared.It was concluded that the sudden expansion can disperse the high flow velocity area and effectively reduce the flow velocity near the bottom.The decrease was the largest when the sudden expansion ratio was 1.3;The maximum temporary bottom velocity of the stilling basin with sudden expansion and drop sill was between the extension line of the chute and the 1/2 middle line.From the perspective of temporary bottom velocity,the area between the extension line of the chute of the stilling basin and the middle line was the key protection area of the bottom plate of the stilling basin with sudden expansion and drop sill.(5)Based on numerical simulation,the turbulent characteristics of stilling basin without sudden expansion and it with sudden expansion were analyzed,including the distribution characteristics of turbulent energy,turbulent intensity and turbulent dissipation rate.It was concluded that 1/4h ? 3/4h was the turbulent core area,and the turbulent energy,turbulent intensity and turbulent dissipation rate were relatively large at 1/2h;The turbulent energy,turbulent intensity and turbulent dissipation rate of the stilling basin without sudden expansion sill were large near the 1/2 middle line.The turbulent area of the stilling basin with sudden expansion sill was dispersed,and the turbulence is large between the extension line of the discharge chute and the 1/2 middle line. |
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