جستجوی مقالات مرتبط با کلیدواژه « کانال ذوزنقه ای » در نشریات گروه « آب و خاک »

One of the most important issues to be considered in trapezoidal channels is the effect of side slope effects on the shear stress and jump characteristics including energy loss, jump length and conjugate depths ratio which have been studied in this study. For this purpose, at first, model has been calibrated by using an experimental results published for trapezoidal channel of 45 degree side slope, the RGN model was selected from the turbulent models, and then the model for different hydraulic conditions (Froude number between 1.5 to 12) and two slopes of 60 and 75 degrees has been performed and the results have been obtained. Due to the shear stress importance, which is usually not investigated in experimental researches, in this study the distribution of bed shear stress has been calculated in all three channels side slopes, and also the hydraulic jump characteristics. The results of this study on the three side slopes show different behavior of hydraulic jumps and shear stress in trapezoidal channel of 45 degree side slope, in which the asymmetry of jump is very tangible and the shear stress concentration is observed on the left side of the channel wall. Comparison of the shear stress results show a significant reduction in shear stress after jump which the maximum amount of this reduction is related to the trapezoidal channel of 45 degree side slope. It was also found that by increasing the side slope the amounts of shear stress and the sequent depths ratio increase, and the amounts of energy loss and length of jump decrease.

The bed and sidewall average shear stresses in smooth trapezoidal open-channels are determined by solving the continuity and momentum equations. The isovels and orthogonals for a trapezoidal channel section with 1:1 sidewall aspect ratio were obtained by using conformal mapping technique. New equations were drived by determining a portion of bed shear stress from total shear stress. As a first approximation, the boundary shear stress equations were obtained after neglecting the secondary currents and assuming a constant eddy viscosity. In comparison with laboratory measurements, the first assumption overestimated the average bed stress by 20% but it underestimated the average sidewall shear stress by -24%. The second approximation was then presented by introducing two lumped empirical correction factors for the effects of secondary currents, variable eddy viscosity and other unexpected effects. Comparison between laboratory measurements and those from the second approximation, showed an excellent agreement (R2>0.993 and average relative error less than 1.2%) between them with experimental measurements over a wide range of width-depth ratios.