عنوان مقاله [English]
Contractions are widely used in channels with supercritical flow, such as water conveyance systems from dams to tunnel spillways, chutes and flood delivery conduits.Technically, production and development of the mentioned waves are undesirable due to water depth increase because of several times increasing of inflow water depth, its spread at a wide range in downstream of channel and water surface roughness. Any weak design of channels under supercritical condition can cause to scour bed and wall the channel, damage to equipment in the flow direction, raising maintenance costs and reduce water conveyance efficiency. In the present research, the formation of shock waves in contractions of open-channel with trapezoidal sections was investigated using experimental and numerical models. The length of transition walls (0.5 and 1m) and angle of side walls (35º, 45º, 60º and 70º) were intended as geometric variables. In different point of shock waves the values of height and instantaneously velocity were measured in the contractions for Froude number and convergence ratio 7.26 and 0.5 respectively. In this research Flow-3D software and in order to simulate turbulent flow, the k-ε RNGmodel was used. Experimental results showed that increasing the angle of side walls and reducing the length of transition walls caused increment of the shock waves height and velocity. The average relative errors of calculation of shock waves height for different angles: 35º-70º and length of transition walls: 0.5m and 1m were respectively in the range of 4.29-5.06 and 2.28-3.14 percent. Also, the average relative errors of calculation of shock waves velocity for mentioned models were respectively in the range of 3-4.90 and 5.68-7.63 percent.