Adam Kozioł

Measurements of 3D Turbulence Structure in a Compound Channel

Experimental research was undertaken to investigate the changes in spatial turbulence intensity, water turbulent kinetic energy, the time and spatial macro-scale, scales of turbulent eddies (macro- and microeddies) in a compound channel. Three tests for two various roughness values were realized. The surface of the main channel bed was smooth and made of concrete, whereas the floodplains and sloping banks were covered by cement mortar composed of terrazzo. Instantaneous velocities were measured with the use of a three-component Acoustic Doppler Velocimeter (ADV). The distributions of relative turbulence intensity (u′/U, v′/U, w′/U) in the main channel and on the floodplains were presented. It was found that the longitudinal (u′/U) and transverse (v′/U) turbulence values decreased from the bottom upwards to the floodplain elevation (z/h = 0.56) in the main channel, but remained constant above the floodplain level. Vertical relative turbulence intensity (w′/U) increased going up from the bottom until z/h = 0.15, decreased until about z/h = 0.7, and then increased again upwards to the water surface. The distributions of relative turbulence intensities were described with regression equations. The distributions of turbulent kinetic energy at different water depths were described by regression equations. Vertical distributions of turbulent kinetic energy on the floodplains and over the banks of the main channel were divided into three zones. Over the bottom of the main channel, four zones were determined, containing the middle zone of the flow field divided into two zones of different trends. Measurements of instantaneous velocities are used to investigations of the longitudinal sizes of the smallest eddies (Kolmogorov’s microscale). Presented analyses were based on the already published results.

Three-Dimensional Turbulence Intensity in a Compound Channel

AbstractExperimental research was undertaken to investigate the changes in spatial turbulence intensity in a compound channel and the influence of rigid, emergent floodplain vegetation on turbulence intensity. Five tests for two various roughness values of floodplains were realized. In the first series of experiments (three tests), the surface of the main channel bed was smooth and made of concrete, whereas the floodplains and sloping banks were covered by cement mortar composed of terrazzo. In the second set of experiments (two tests), emergent vegetation (trees) on the floodplains, modeled by aluminum pipes, was added. Instantaneous velocities were measured with the use of a three-component acoustic Doppler velocity meter. The influence of floodplain trees, on the distributions of relative turbulence intensity (u′/U, v′/U, w′/U) in the main channel and on the floodplains was presented. It was found that the longitudinal (u′/U) and transverse (v′/U) turbulence values decreased from the bottom upward to t...

Scales of turbulent eddies in a compound channel

Experimental research was undertaken to investigate the changes in scales of turbulent eddies (macro- and microeddies) in a compound channel and the influence of rigid, emergent floodplain vegetation on scales of turbulent eddies. The results of eight tests for different roughness conditions (smooth bed, rough bed) and with a tree system on the floodplains from two earlier studies are presented. The increase of the channel roughness resulted in a decrease of longitudinal sizes of macroeddies in the whole channel. Trees on the floodplains resulted in disintegration of the sizes of macroeddies, making values of sizes more uniform. A more significant decreasing influence on sizes of macroeddies in the whole channel was exerted by an increase of the main channel sloping bank roughness, having a higher effect than a twofold decrease in the floodplain trees density. The microeddies’ sizes are larger in the main channel centreline than on the floodplains and the smallest ones were present in the main channel/floodplain interface.

The Kolmogorov’s microscale eddies in a compound channel

Abstract The Kolmogorov’s microscale eddiesin a compound channel. Investigations of the longitudinal sizes of the smallest eddies (Kolmogorov’s microscale) presented in the paper are based on measurements of instantaneous velocities in a hydraulic laboratory in a compound trapezoidal channel with different roughness conditions (smooth bed, rough bed) and with trees system on the floodplains. Sizes of the smallest eddies varied in the ranges of 0.08 to 0.48 mm. The changes of longitudinal sizes of the floodplain microeddies are not caused by: the increase of floodplain roughness, the presence of trees, but only when the main channel bed is smooth, and they are also not caused by the increase of roughness of the main channel sloping banks. However, the increase of the size of the floodplain microeddies is influenced by trees, when the roughness of the floodplains and the main channel sloping banks are identical. The increase of microeddies size in the main channel is influenced by: the increase of the main channel sloping banks roughness, by the presence of trees on the floodplains, but only when the roughness of the floodplains and the main channel sloping banks are identical. Microeddies are larger in the main channel centerline than on the floodplains, and the smallest ones were present in the main channel/floodplain interface. The calculated values of microeddies reached decimal parts of a millimeter, and that is why it is difficult to prove vital changes of their values, caused by bed roughness and floodplain trees influence Streszczenie Mikrowiry Kołmogorowa w korycieo złożonym przekroju poprzecznym. W artykule przedstawiono długości podłużnych mikrowirów (mikroskala Kołmogorowa) w strumieniu w korycie o złożonym przekroju poprzecznym. Długości mikrowirów obliczono na podstawie szybkości dyssypacji energii i lepkości cieczy. Do określenia szybkości dyssypacji wykorzystano analizę funkcji gęstości spektralnej, wyznaczonej na podstawie pomierzonych w laboratorium hydraulicznym chwilowych prędkości w korycie o złożonym przekroju poprzecznym dla dwóch różnych szorstkości powierzchni dna koryta i rozmieszczonych drzew na przyległych terenach zalewowych. Na zmiany podłużnych długości mikrowirów na terenie zalewowym nie wpływa: wzrost chropowatości powierzchni terenów zalewowych, występowanie drzew ale kiedy powierzchnia koryta głównego jest gładka, wzrost chropowatości powierzchni skarp koryta głównego. Natomiast na wzrost długości mikrowirów na terenie zalewowym wpływają drzewa kiedy powierzchnie terenów zalewowych i skarp koryta głównego są identyczne. Na wzrost długości mikrowirów w korycie głównym wpływa: wzrost chropowatości powierzchni skarp koryta głównego, występowanie drzew na terenach zalewowych ale kiedy powierzchnie terenów zalewowych i skarp koryta głównego są identyczne. Mikrowiry są większe w osi symetrii koryta głównego niż na terenach zalewowych, a najmniejsze w płaszczyźnie rozdziału pomiędzy obiema częściami koryta. Obliczone wartości mikrowirów są rzędu dziesiątych części milimetra, więc trudno mówić o istotnych zmianach wartości w wyniku wpływu chropowatość powierzchni dna i obecności drzew na terenach zalewowych.

Turbulent kinetic energy of water in a compound channel

Turbulent kinetic energy of water in a compound channel The aim of the experimental research was the determination of water turbulent kinetic energy changes in a compound channel without and with rigid, emergent, vegetation existing on floodplains. Two tests for two various roughness of floodplains were realized. In the first test the surface of the main channel bed was smooth and made of concrete whereas the floodplains and sloping banks were covered by cement mortar composed with terrazzo. In the second test the covering of the floodplains was left as in the first test but additionally emergent vegetation (trees) growing on the floodplains were modeled by aluminium pipes. Instantaneous velocities were measured with use of a three-component acoustic Doppler velocity meter (ADV). The influence of trees, located on floodplains, on the distributions of turbulent kinetic energy in the main channel and on the floodplains were presented. The distributions of turbulent kinetic energy at different water depths were described by regression equations. Vertical distributions of turbulent kinetic energy on the floodplains and over the banks of the main channel were divided into three zones. Over the bottom of the main channel, four zones were determined, containing the middle zone of the flow field divided into two zones of different trends. Turbulentna energia kinetyczna strumienia wody w korycie o złożonym przekroju poprzecznym Celem badań eksperymentalnych było wyznaczenie zmian turbulentnej energii kinetycznej strumienia wody w korycie o złożonym przekroju poprzecznym, bez sztywnej i ze sztywną niezanurzoną roślinnością znajdującą się na terenach zalewowych. Wykonano dwa doświadczenia dla dwóch różnych wariantów chropowatości powierzchni terenów zalewowych. W pierwszym doświadczeniu powierzchnia dna koryta głównego była gładka, a skarpy koryta głównego i tereny zalewowe pokryte były lastryko na zaprawie cementowej. W drugim doświadczeniu dodatkowo na terenach zalewowych rozmieszczono roślinność wysoką (drzewa), którą zmodelowano aluminiowymi rurkami. Pomiar trzech składowych chwilowych prędkości wykonywano sondą akustyczno-dopplerowską ADV. Przedstawiono wpływ drzew z terenów zalewowych na rozkłady turbulentnej energii kinetycznej w korycie głównym i na terenach zalewowych. Rozkłady turbulentnej energii kinetycznej w funkcji głębokości opisano równaniami regresji. Rozkłady turbulentnej energii kinetycznej w pionie na terenach zalewowych i nad skarpami koryta głównego podzielono na trzy strefy, natomiast nad dnem koryta głównego wydzielono cztery strefy, przy czym w strefie środkowej pola przepływu są dwie strefy o różnych trendach.

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 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.

Identification of vegetation parameters for compound channel discharge as inverse problem

Abstract In recent years many sophisticated models for discharge capacity of compound channels with vegetation have been developed. Despite the mature state of knowledge in this field, in a practice the simplest methods prevail and most of hydraulic models are based on the Manning formula. One of the reasons is that more complex methods require detailed characteristics on vegetation. The present study demonstrates that this issue can be solved by treating all such necessary variables as parameters to be identified in a sense of an inverse problem, using techniques of optimization. With a flume experiment as a case study, four models of a uniform flow were identified: Pasche, Mertens as complex methods, divided channel method (DCM) with Manning and Darcy–Weisbach equations as techniques used in a practice. Results showed that parameters for all methods can be found on the basis of minimization of model residuals, with the restriction that because of the larger number of parameters in complex methods, more observations are required. Methods of Pasche and Mertens with identified parameters provided a much better explanation of water depths than the Manning or Darcy–Weisbach based on the DCM. It is surprising that significant discrepancies between identified parameters and their real measured values were recorded. Even more, an almost perfect fit was obtained for different parameter sets.