Showing 8 results for Vortex
S. M. A. Zomorodian, M. R. Bagheri Sabzevari,
Volume 9, Issue 4 (1-2006)
Abstract
The vertical pipe intake is an economical structure relative to the other alternatives. VPI usually installed near the water surface and prevents from the coarse sediment entrance to the system. The strong vortex in VPI entrance is a major problem which may reduce the system efficiency. Recognizing the vortex affected parameters, helping engineers to design anti vortex structures. In this study an experimental model is built to study the effect of tangential velocity, flow direction at approach channel outlet on the discharge coefficient of vertical pipe intake. By dimensional analysis it is indicated that the vortex in VPI could be defined by the dimensionless numbers (Reynolds, Weber, Froude, Circulation and Submergence). The relationship between the Froude, Circulation and Submergence numbers are presented. By using this relation one can determine the Submergence number and then calculate the discharge coefficient of vertical pipe intake.
A. Masjedi, M. Gholamzadeh Mahmoodi,
Volume 15, Issue 55 (4-2011)
Abstract
Every year river flooding causes serious damage to the bridges at the time needed most. One of the most effective factors causing bridge failure is scouring around the piers in a river bend. One of the methods to decrease scouring around the bridge piers is fitting them with a coller on the piers. The collars protect the river bed against vortex flow in the vicinity of the pier base. An experiment was conducted to study lab flumes made of Plaxiglass with a 180 degree bend and 2.8 m central radius and a 0.6 m width. In this study, a 6cm diameter pier was placed with a circular collar with four different collar sizes in one position in bend with constant discharge and depth under clear-water conditions. The collar was placed at four different elevations. The soil material had a diameter of d50 = 2mm and geometric standard deviation of σg = 1.3. The results of the model study indicated that the maximum depth scouring was highly dependent on the experimental duration. It was observed that as the size of a collar plate increases, the scour decreases. So, minimum depth of scour is dependent on the 3D coller and -0.1D elevation. Circular collar results in maximum reduction in scour depth (93%) compared with no circular collar.
A. A. Kamanbedast, S. R. Mousavi,
Volume 20, Issue 78 (1-2017)
Abstract
Morning glory spillway is one of the spillways and used when it is not possible to use any other spillways. With the onset of submergence and flow loss, and intensification of circulation and vortexes, spillway performance decreases severely. With decreasing discharge coefficient, the height of water in the reservoir increases and the risk of dam damage, caused by the lack of spillway ability of great flow discharge, increases. Anti-vortex piers are used to solve this problem. The increase of the submergence threshold can provide ability of greater flow discharging, without spillway submergence and its negative consequences. Anti-vortex piers, in addition to correcting circulation and vortexes, may also be effective in increasing the submergence threshold. To investigate this possibility, 110 experiments were performed with the physical model on spillways with square and circular inlet section in different modes and number of anti-vortex piers. Results show that increasing number of Anti-vortex piers increases the submergence threshold and spillway can discharge greater inflow and height of water without being submerged. The effect of the overflow of the circle shape, because currents and vortexes spinning in a circle overflow is higher than square spillway. Also the maximum discharge coefficient was observed when 4 vortex breakers were installed at the angle of 90 degrees.
Mr A. Nouri Imamzadehei, Manouchehr Heidarpour, M. R. Nouri Imamzadehei, B. Ghorbani,
Volume 21, Issue 2 (8-2017)
Abstract
Flood currents are considered threatening factors by creating local scour along bridge piers. One method for decreasing local scour is to strengthen the bed against imposed tensions. Among methods which can directly be appropriate in decreasing and controlling local scour of bridge piers is to employ geotextile around bridge piers. In the present study, the effect of geotextile layer in decreasing local scour of cylindrical single-pier was investigated with the purpose of proposing the best effective method of covering bridge pier. So, layers with circular and oval shapes were put around the pier, in proportion with pier diameter, and the performance of each was compared with the unprotected pier. Test results showed that with installing the oval geotextile layer, final scour depth around the pier reached to 1.25D. Also, comparing geotextile and collar with 2D diameter, the delay of scour process around geotextile was 40 times higher than the collar, but the collar decreased the ultimate scour depth further than geotextile.
R. Amirjani, A. Kamanbedast, M. Heydarnejad, A. Bordbar, A. Masjedi,
Volume 22, Issue 4 (3-2019)
Abstract
In a pressure flushing method, when the water is discharged from the bottom outlet, after a period of flushing, a flushing cone will be formed at the front of the bottom outlet; the dimension of this cone is affected by several parameters such as outlet discharge flow, water depth of reservoir, and the kind of sediments accumulated in the reservoir. In this study, for the effect of cohesive & non-cohesive sediments, a physical model using specific dimensions was employed in order to develop the sediment evacuation method, and them a Semi-Cylinder structure in front of the lower drain was tested. The experiments were carried out using cohesive & non-cohesive sediments under two conditions: with the semi-cylinder and without it, at 90 experiments. The results indicated that the with discharge was increased, on i average, under both conditions and the volume of the score cone was increased. With decreasing the water depth, the flow mood was changed to free flushing, increasing the length and volume of the score cone. Semi-Cylinder form, on average, increased the volume of sedimentation and the length of sedimentation; this increase could be due to the formation of a pair of rotating Vortexes inside the Semi-Cylinder structure on both sides of the central axis of the valve.
M. Majedi Asl, M. Fuladipanah,
Volume 22, Issue 4 (3-2019)
Abstract
A labyrinth weir is a nonlinear weir folded in the plan-view which increases the crest length and the flow rate for a given channel width and an upstream flow depth. Nowadays, a labyrinth weir is an attractive alternative for those weirs that have a problem in passing the probable maximum flood. The three-dimensional flow pattern and unlimited geometric parameters provide a major challenge to the designers of these weirs. The present study aimed at determining discharge coefficients of sharp-crested triangular labyrinth weirs using the support vector machine (SVM). The results were compared with the experimental data. For this purpose, 123 laboratory test data including geometric and hydraulic parameters such as vertex angle (θ), magnification ratio (L/B), head water ratio (h/w), Froude number (Fr), Weber Number (We) and Reynolds number (Re) were used. The results showed that the SVM-based model produced the most accurate results when only three geometric parameters, e.g. (h/w, θ, L/B), were introduced as the input parameters (R2 = 0.974, Root mean square error [RMSE] = 0.0118, mean absolute error [MAE] =0.0112 and mean normal error [MNE] =0.017 for the test stage). Also, for these weirs, polynomials linear and nonlinear regression equations were presented. Finally, the discharge coefficient of sharp-crested triangular labyrinth weirs based on the Rehbock equation was evaluated and compared with the SVM using nonlinear and linear regression methods.
M. Eskandari, M. Heidarnejad, A. Egdernezhad,
Volume 27, Issue 3 (12-2023)
Abstract
The formation of vortices behind the gates of diversion dams is an operational challenge. Such vortices lead to vibration and corrosion in the gate, reducing the lifetime and raising the operational cost of the dam. This study investigated these vortices and their formation. It was found that the gate or cutoff wall was not the only explanation for the vortices; the closed side gates also contribute to vortex formation. Furthermore, an increase in the gate width reduced vorticity; the vortex size experienced a 200% reduction as the gate size increased by 200%. The cutoff wall diameter was another determinant. An increase in the cutoff wall diameter raised vorticity. The vortices increased by 50% as the wall diameter increased by 150%.
M. Karamdokht Bahbahani, M. Sajjadi, J. Ahadiyan, A. Parsaie,
Volume 28, Issue 1 (5-2024)
Abstract
One of the structures for regulating the water level in the irrigation and drainage ducts is the lopac gates, which are proposed as a structure for regulating and controlling the flow level. In this study, a new design of this type of structure has been proposed in which the gates are placed next to each other in pairs, and they are called multiple lopac gates. The objective of this research is to investigate the effective hydraulic parameters of the proposed structure and compare it in a case where a gate is used under the same conditions. All the simulations were modeled with 3 amounts of opening 30, 45, and 60 degrees and at 3 flow rates of 20, 40, and 60 liters per second and using Flow3d software, in these simulations, the number of mesh cells is 1000000 and RNG turbulence model is used. The results showed that the maximum shear stress was reduced by an average of 38% compared to the single gate mode in most tests at different openings and flow rates using multiple lopac gates, and the largest amount of this reduction was related to the opening of 45 degrees, and the flow rate is 40 liters per second with a value of 76%. Also, the forces acting on the gate at different flow rates and openings will be reduced by 150% on average. In the qualitative investigation of flow vortices, the investigations also showed that vortex range, length, and strength are reduced compared to the single gate mode when two gates are used, and the number of vortices increases compared to when a single valve.
