Mustafa Gogus

Effect of spur dike length on the horseshoe vortex system and the bed shear stress distribution

ABSTRACT Turbulent flow structures forming around isolated spur dikes in a horizontal channel are investigated in this study. In the analysis detached eddy simulation is used under fully turbulent incoming flow conditions at a channel Reynolds number of 45,000. Changes in the structure of the horseshoe vortex system, bed shear stress and pressure standard deviation on the bed are investigated for three different spur dike lengths. In all of the cases the main horseshoe vortex undergoes bimodal oscillations, which leads to an amplification in the turbulence quantities such as turbulent kinetic energy and pressure fluctuations along its axis. The main horseshoe vortex disappears over a much shorter distance in the flow direction for the short spur dike than those of medium and long spurs. Large bed shear stress values and pressure standard deviation values observed around the tip of the spur dike, beneath the upstream part of the main horseshoe vortex and beneath the separated shear layers increase with the increasing length of the spur dike. Different from the long and medium spur dike, in the short spur dike case, it is shown that the secondary horseshoe vortex is as coherent as the main horseshoe vortex and it contains bimodal oscillations together with the main horseshoe vortex.

Assessment of sediment yield estimations for large watershed areas: a case study for the Seyhan, Demirköprü and Hirfanlı reservoirs in Turkey

Abstract Analyses of data from reservoir surveys and sediment rating curves are compared to predict sediment yield in three large reservoir watershed areas in Turkey. Sediment yield data were derived from reservoir sedimentation rates and suspended sediment measurements at gauging stations. The survey data were analysed to provide the volume estimates of sediment, the time-averaged sediment deposition rates, the long-term average annual loss rates in the reservoir storage capacity, and the long-term sediment yield of the corresponding watershed areas. Four regression methods, including linear and nonlinear cases, were applied to rating curves obtained from gauging stations. Application of the efficiency test to a power function form of a rating curve with nonlinear regression yielded the highest efficiency values. Based on the analysis of the sediment rating curves, sediment load fluxes were calculated by using average daily discharge data at each gauging station. Comparison of these two sediment yield values for each reservoir showed that the sediment yields from the suspended sediment measurements, SYGS, are 0.99 to 3.54 times less than those obtained from the reservoir surveys, SYRS. The results from the reservoir surveys indicate that all three reservoirs investigated have lost significant storage capacity due to high sedimentation rates.

Effects of Collars on Scour Reduction at Bridge Abutments

Bridge failures are generally resulted from scour of the bed material around bridge piers and abutments during floods. In this study, scour phenomenon around bridge abutments and collars, located at abutments as scour countermeasures, were experimentally investigated. Based on the results of 97 experiments conducted, the effect of various sizes of collars which were located around the abutments at different elevations, on the scour reduction at bridge abutments was determined. The results were compared with previous studies, and the effect of the sediment grain size on the performance of abutment collars was emphasized. It was noticed that when the collar width was increased and it was placed at or below the bed level, the reduction in the maximum local scour depth increases considerably. It was also seen that the change of the sediment size did not affect the optimum location of the collar at the abutment, which yields the maximum scour reduction around the abutment.

Effects of Antivortex Structures Installed on Trapezoidal Labyrinth Side Weirs on Discharge Capacity and Scouring

AbstractGreater or more constant discharge can be achieved at lower upstream water depths over the weir crest by increasing the effective lengths of labyrinth side weirs. Labyrinth weirs have uneve...

Formation of air-entraining vortices at horizontal intakes without approach flow induced circulation

The aim of this experimental study is to investigate the effects of hydraulic parameters on the formation of air-entraining vortices at horizontal intake structures without approach flow induced circulation. Six intake pipes of different diameters were tested in the study. The intake pipe to be tested was horizontally mounted to the front side of a large reservoir and then for a wide range of discharges experiments were conducted and critical submergences were detected with adjustable approach channel sidewalls. Empirical equations were derived for the dimensionless critical submergence as a function of the relevant dimensionless parameters. Available data is also checked for the possible scale effect. Then, these obtained equations were compared with the similar ones in the literature which showed a quite good agreement.

Geometry effect and generalization of velocity distribution in asymmetric compound channels

Nine different geometries with asymmetric rectangular compound cross-sections were tested in a laboratory flume in order to investigate effects of the geometry on the values of three different dimensionless velocity ratios. A generalized single variable regression model has been derived to predict each of the three dimensionless velocity ratios with high accuracy. Another set of the multiple-variable regression models has been derived using one additional dimensionless parameter which is the ratio of the upstream channel width to the main channel width. The application of several key statistics and validation procedures has indicated that the developed models predict the three mean dimensionless velocity ratios with high correlation coefficients.

Time Evolution of the Horseshoe Vortex System Forming around a Bridge Abutment

Scour forming around an isolated bridge abutment with curved end is investigated in this study. Clear water scour experiments are conducted for an abutment in a 25 m long sediment flume at a Reynolds number of 45000. 3D scour patterns forming around the abutments are obtained using an array of acoustic transducers along a grid refined up to 1–2 cm spacing at different stages of the scour. Detached Eddy Simulation (DES) is performed at the same channel Reynolds number for flat bed case (initiation of the scour) and for two deformed bed cases (intermediate stages of scour). Incoming flow in the simulations were fully turbulent containing unsteady velocity fluctuations. Variations in the structure and intensity of the horseshoe vortex system are investigated. At the initial stage of the scour the main and secondary horseshoe vortices undergo aperiodic bimodal oscillations. Those oscillations cause the horseshoe vortices to induce large bed shear stress values beneath them. As the scour hole starts forming secondary necklace vortex, HV2, gets closer to the primary necklace vortex, HV1, and merges with it at a location close to the abutment tip.