Janusz Urbański

Turbulence intensity and spatial scales of turbulence after hydraulic jump over scour hole in rectangular channel

Abstract The study presents experimental investigations of spatial turbulence intensity and scales of turbulent eddies (macroeddies) in a rectangular channel and the impact of the hydraulic jump on their vertical and streamwise distributions over a flat and scoured bed. The results of four tests and two different discharge rates are presented. Intensive mixing caused by the hydraulic jump has an impact on the instantaneous velocity, turbulence intensity and sizes of macroeddies, as well as their vertical and longitudinal distributions along the channel. The largest differences in turbulence characteristics were reported directly after the hydraulic jump, above the eroded bed. The interaction between the stream of the increased turbulence and the bed is a direct cause of formation of scour downstream water structures, which has a great effect on overall flow characteristics. The scour hole that arose downstream the jump moderated, in a small degree, the turbulence intensity at its end. Just next to the hydraulic jump only the small longitudinal relative sizes of macroeddies were present, while at the end of the analyzed reach, downstream of the scour, the relative scale reached around 1.5 depth of the stream.

Turbulent intensity and scales of turbulence after hydraulic jump in rectangular channel

Abstract Turbulent intensity and scales of turbulence after hydraulic jump in rectangular channel. Experimental research was undertaken to investigate the changes in spatial turbulence intensity and scales of turbulent eddies (macroeddies) in a rectangular channel and the influence of the hydraulic jump on vertical, lateral and streamwise distributions of relative turbulence intensity and scales of turbulent eddies. The results of three tests for different discharges are presented. An intensive turbulent mixing that arises as a result of a hydraulic jump has a significant effect on instantaneous velocity, turbulent intensities and sizes of eddies, as well as their vertical and longitudinal distributions. In the analysed case the most noticeable changes appeared up to 0.5 m downstream the hydraulic jump. In the vertical dimension such an effect was especially seen near the surface. The smallest streamwise sizes of macroeddies were present near the surface, maximum at the depth of z/h = 0.6 and from that point sizes were decreasing towards the bottom. The intensive turbulent mixing within the hydraulic jump generates macroeddies of small sizes.

The influence of morphological changes of small lowland river on discharge rate

Abstract The influence of morphological changes of small lowland river on discharge rate. The aim of the study was the comparison of the changes of cross-sections and longitudinal profile of the Mała river at the distance of 600 m. The paper presents the geometry changes of the river from field measurements made in 2013 in comparison with design assumptions from 1967 which were implemented in 1971. The four (available historical) cross-sections (hm 7+700, 7+800, 7+900, 8+000) and longitudinal profile (hm 7+700÷8+300) of the river were analysed and compared. The large scale of subsidence of the land surface on both banks was observed (even to 0.5 m). Probably it is the effect of peat shrinkage and mineralization processes of organic soils. The bottom of the Mała river was still located at the same altitude in sand deposits in the analysed period 1971-2013. The designed slope of bottom of the Mała river equals 0.7‰ (1967) and present slope (2013) was estimated to be around 1‰. The subsidence of peat layers on both river banks, changes in cross-sections’ parameters (present irregular shapes in comparison with designed trapezoidal cross-sections) caused the reduction of cross-sectional area and water discharge of about 40-50% in comparison with parameters designed in 1967 and made in 1971. Streszczenie Wpływ zmian morfologii koryta małej rzeki nizinnej na jej przepustowość. W pracy przedstawiono aktualne (2013) zmiany geometrii odcinka nizinnej rzeki Mała w stosunku do założeń projektowych (1967), zrealizowanych w 1971 roku. Analizą objęto cztery przekroje poprzeczne (hm 7+700, 7+800, 7+900, 8+000), dla których zachowały się materiały archiwalne oraz profil podłużny o długości 600 m (hm 7+700÷8+300). Przeprowadzone w 2013 roku badania terenowe wykazały znaczne obniżenie brzegów rzeki (nawet o około 0,5 m) w okresie 46 lat (osiadanie z racji procesów kurczenia i mineralizacji masy torfowej). Nie zaobserwowano natomiast znacznych zmian w rzędnych dna (podłoże piaszczyste). Projektowany spadek dna na analizowanym odcinku w 1967 roku wynosił 0,7‰, natomiast obecnie uległ nieco zwiększeniu i wynosi około 1‰. Pomimo przeprowadzanych okresowo prac konserwacyjnych analizowane przekroje poprzeczne obecnie różnią się swoim kształtem od projektowanych przekrojów trapezowych. Zmiany geometrii koryta na analizowanym odcinku rzeki wykazały również dużą zmienność pola powierzchni w poszczególnych przekrojach poprzecznych oraz zmniejszenie obecnie przepustowości analizowanego fragmentu rzeki o około 40-50% w stosunku do założeń projektowych z 1967 roku.

The length of the hydraulic jump on the basis of physical and numerical modeling

Abstract The outcomes of physical and numerical modeling of the sluice gate outflow are presented. The measured velocity distributions in verticals of a physical model were compared with results of numerical modeling, obtained using ANSYS Fluent software. The research goal was verification of suitability of the computational fluid dynamic (CFD) approach in determination of the hydraulic jump length at the outflow of the flow control structure. Studies were performed for the model of the sluice gate and stilling basin with two setups of baffle blocks: in one and two rows. The jump lengths were estimated by an analysis of vertical velocity profiles at the outflow. Two rows of baffle blocks in the stilling basin allowed to reduce the length of the hydraulic jump by 5–10%, comparing to the length with the single row of blocks. The computational fluid dynamic approach underestimated the length of the hydraulic jump by 4–7%, comparing to the physical model.