scholarly journals Morphological Patterns at River Contractions

Water ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1683
Author(s):  
Giuseppe Oliveto ◽  
Maria Cristina Marino
Keyword(s):  
Rectangular Channel ◽  
Experimental Investigations ◽  
Clear Water ◽  
Flow Conditions ◽  
Flow Area ◽  
Mobile Bed ◽  
Long Duration ◽  
The University ◽  
Working Section ◽  
Morphological Patterns

Sediment transport at river contractions is an important process of engineering concern which might occur when a river encounters a reduction in flow area because of either natural or artificial constraints. This paper focuses on the morphological patterns that are prone to form at and around the constriction of watercourses based on experimental investigations at laboratory scale. Experiments were carried out at the University of Basilicata, Italy, in a 1 m wide and 20 m long rectangular channel. The length of the working section extended up to 16 m, according to the length of the contraction model. Two nearly-uniform sediments were used as mobile bed, sand with median grain size d50 = 1.7 mm and gravel with d50 = 9.0 mm. The contraction length was either 0.5, 1.0, 2.0 or 3.0 m. Runs were carried out under steady flow and clear-water approach flow conditions. Typically, they were of long duration (up to 15 days) also to achieve an equilibrium state. New predictive equations are given on the temporal progress of: the maximum scour depth, the scour hole length, and the axial bed profile with emphasis on the processes of bed aggradation or degradation beyond the contracted region.

scholarly journals Effect of various flow, sediment and geometrical parameters on partially or fully submerged deck scour

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Müsteyde Baduna Koçyiğit ◽  
Onur Karakurt ◽  
Hüseyin Akay
Keyword(s):  
Maximum Depth ◽  
Geometrical Parameters ◽  
Flow Depth ◽  
Clear Water ◽  
Flow Conditions ◽  
Flow Area ◽  
Sediment Size ◽  
Scour Hole ◽  
Series Of Experiments ◽  
Hole Effect

AbstractThe effect of various parameters of flow, sediment and geometric features of the bridge on the depth and shape of the scour hole occurred underneath a bridge deck model without a pier was investigated by a series of experiments conducted in a flume under partially and fully submerged flow and clear water conditions. The experiments were performed with factors such as approach flow depth, discharge, sediment size, degree of submergence, girder location and depth. A total of 112 experiments were conducted for both partially and fully submerged flow conditions. The experimental data showed that the partially submerged flow increased the maximum depth of scour hole and affected the shape of the scour hole more when compared to the fully submerged flow. It was also noted that parameters that directly affected flow structure in the bridge opening such as girder height might significantly increase the maximum depth of scour hole. Effect of the distance between a single girder and the bridge edge was also tested by using three different girder location and it was found that as the distance increased, the depth of the scour hole decreased and the location of the maximum scour depth moved with the girder to where the contraction in the flow area occurred.

Research of the flow procedures in a pressure sewer system

2003 ◽  
Vol 47 (7-8) ◽  
pp. 351-356
Author(s):  
C. Dohse ◽  
H. Eckstädt
Keyword(s):  
Land Reclamation ◽  
Flow Conditions ◽  
Sewer System ◽  
Flow Meters ◽  
Initial Information ◽  
Pressure Pipe ◽  
Pumping Stations ◽  
Hydraulic Conditions ◽  
Measuring Section ◽  
The University

At the Institute of Land Reclamation, Hydrology and Sanitary Engineering of the University at Rostock the pressure and flow ratios are examined within a measuring section in the pressure dewatering system on the Darfl peninsula. The objective of the research project is the knowledge upgrade about the highly unsteady hydraulic conditions in a pressure sewer system. This paper firstly presents the method and the dimensioning of pressure dewatering systems, which can be done using either the peak effluent method or the statistical method; the examination program will be explained. The examination includes pressure difference measuring with two pressure meters and flow data measuring via magnetic-inductive flow meters. Additionally the pump running times of 15 pumping stations, as well as the compressor action of the pressure pipe rinsing station are continuously and temporarily recorded and saved. Finally the measuring results which provide initial information about the pressure and flow conditions in a pressure dewatering system will be presented. The effects of the rinsing, the low pressure differences, the air cushions, the seasonal differences as well as the daily development graphs of the wastewater production are all clearly visible.

Riprap Performance at Bridge Piers Under Mobile-Bed Conditions

1998 ◽  
Vol 1647 (1) ◽  
pp. 27-33 ◽  
Author(s):  
Carlos Toro-Escobar ◽  
Richard Voigt ◽  
Bruce Melville ◽  
Meng Chiew ◽  
Gary Parker
Keyword(s):  
Experimental Tests ◽  
Bridge Piers ◽  
Design Criteria ◽  
Research Groups ◽  
Clear Water ◽  
Pier Scour ◽  
Mobile Bed ◽  
Water Conditions ◽  
Improved Design ◽  
Flood Flow

Design criteria for riprap at bridge piers in rivers is based on the specification of a size, gradation, and cover that does not fail under an appropriately chosen flood flow. Experimental tests of riprap performance at bridge piers to date have relied on a configuration for which the ambient bed is not mobilized, that is, clear-water conditions. In the field, however, riprap is, as a rule, subjected to mobile-bed conditions during floods. Recent experiments by three cooperating research groups (University of Auckland, Nanyang University, and St. Anthony Falls Laboratory) indicate a heretofore unrecognized mechanism for riprap failure under mobile-bed conditions. When the flow is in the dune regime, the passage of successive dunes causes riprap that is never directly entrained by the flow to sink and disperse. Pier scour is realized as a consequence of these processes. In some cases, the depth of scour realized is not significantly less than that which would occur without riprap. When the riprap is fully underlain by a geotextile, edge effects can cause local removal of riprap, upturning of the geotextile, and general failure. When the riprap is underlain by a partial geotextile (i.e., one that covers an area less than the riprap), edge scour causes local sinking that anchors the geotextile. The sinking and dispersion of the rest of the riprap are greatly limited, and the riprap fails only when flow velocities are sufficient for direct entrainment. The experiments suggest improved design criteria for the installation of riprap in the field.

scholarly journals Experimental Investigations of Interactions between Sand Wave Movements, Flow Structure, and Individual Aquatic Plants in Natural Rivers: A Case Study of Potamogeton Pectinatus L.

Water ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 1166 ◽  
Author(s):  
Łukasz Przyborowski ◽  
Anna Łoboda ◽  
Robert Bialik
Keyword(s):  
Flow Velocity ◽  
Three Dimensional ◽  
Potamogeton Pectinatus ◽  
Sand Wave ◽  
Experimental Investigations ◽  
Cross Sectional ◽  
Bending Tests ◽  
Long Duration ◽  
Elevation Changes

Long-duration measurements were performed in two sandy bed rivers, and three-dimensional (3D) flow velocity and bottom elevation changes were measured in a vegetated area and in a clear region of a river. Detailed flow velocity profiles downstream and upstream of a single specimen of Potamogeton pectinatus L. were obtained and the bed morphology was assessed. Potamogeton plants gathered from each river were subjected to tensile and bending tests. The results show that the existence of the plants was influenced by both bottom and flow conditions, as the plants were located where water velocity was lower by 12% to 16% in comparison to clear region. The characteristics of the flow and sand forms depended on the cross-sectional arrangement of the river, e.g., dunes were approximately four times higher in the middle of the river than in vegetated regions near the bank. Furthermore, the studied hydrophytes were too sparse to affect water flow and had no discernible impact on the sand forms’ movements. The turbulent kinetic energy downstream of a single plant was reduced by approximately 25%. Additionally, the plants’ biomechanical characteristics and morphology were found to have adjusted to match the river conditions.

Effect of sand mining on the flow hydrodynamics around an oblong bridge pier

2021 ◽  
Author(s):  
Abhijit Lade ◽  
Jyotismita Taye ◽  
Bimlesh Kumar
Keyword(s):  
Rectangular Channel ◽  
Horseshoe Vortex ◽  
Bridge Piers ◽  
Hydraulic Structures ◽  
Complex Nature ◽  
Sand Mining ◽  
Mobile Bed ◽  
Turbulence Flow ◽  
First Case ◽  
Oblong Pier

Abstract Extraction of sand from riverbed has catastrophic repercussions on aquatic animalia habitat, water quality, and the environment. Alongside, physical alterations in the fluvial hydraulics arising on account of sand mining are also worthy of attention. Flows passing over the pits excavated in a channel have enhanced erosive propensity, which can be a cause of concern for the downstream hydraulic structures. The complex nature of flow interacting with the bridge piers after passing over a mining pit is not fully understood. Experiments were conducted to apprehend the effects of a dredged pit on the turbulence flow-field around an oblong pier. Flow was passed in an erodible sand bed rectangular channel having an oblong pier for the first case. In the second case, a pit was dredged in the mobile bed to replicate a mined channel, and the pier was subjected to the same discharge. The streambed at the approach of the pier experiences greater mean bed shear because of dredging. The amplification of the instantaneous bed shear beneath the turbulent horseshoe vortex (THSV) zone at the pier front is almost twice due to channel dredging. The findings can be useful in understanding the streambed instabilities around bridge piers in mining-infested channels.

An initial assessment of bed destabilization risk past vegetation patches using instrumented particles

2021 ◽  
Author(s):  
Yi Xu ◽  
Valyrakis Manousos ◽  
Panagiotis Michalis
Keyword(s):  
Initial Assessment ◽  
Flow Structures ◽  
Clear Water ◽  
Flow Conditions ◽  
Flow Parameters ◽  
Water Conditions ◽  
The Mean ◽  
Acoustic Doppler Velocimetry ◽  
Patch Density ◽  
Vegetation Patches

<p>Instream vegetation may alter the mean and turbukent flow fields leading to destabilizing riverbed surface, under certain flow conditions. In particular, recent research on instream vegetation hydrodynamics and ecohydrogeomorphology has focused on how energetic flow structures and bulk flow parameters downstream a vegetation may result in riverbed destabilization. This study, demonstrated the application of a 20mm novel instrumented particle in recording entrainment rates downstream simulated vegetation patches of distinct densities, at various distances downstream these. A patch of 6mm acrilic cylinders is used to simulate the emergent vegetation having the same diameter (12cm) and different porosities or densities (void volume equal to 1.25%, 3.15%, 6.25%, 11.25%, and 17.25%). The flow velocity near the instrumented particle is recorded using acoustic Doppler velocimetry (ADV) with appropriate seeding, under clear water conditions. Preliminary results are presented with focus on the effect of vegetation patch density on the flow field and subsequent effects on particle entrainment rates and implications for bed surface destabilisation.</p>

The Effects of Inlet Boundary Layer Condition and Periodically Incoming Wakes on Secondary Flow in a Low Pressure Turbine Cascade

2020 ◽  
Author(s):  
Tobias Schubert ◽  
Silvio Chemnitz ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
High Speed ◽  
Low Pressure ◽  
Experimental Investigations ◽  
Turbine Cascade ◽  
Flow Conditions ◽  
Low Pressure Turbine ◽  
Speed Flow ◽  
Unsteady Inflow

Abstract A particular turbine cascade design is presented with the goal of providing a basis for high quality investigations of endwall flow at high-speed flow conditions and unsteady inflow. The key feature of the design is an integrated two-part flat plate serving as a cascade endwall at part-span, which enables a variation of the inlet endwall boundary layer conditions. The new design is applied to the T106A low pressure turbine cascade for endwall flow investigations in the High-Speed Cascade Wind Tunnel of the Institute of Jet Propulsion at the Bundeswehr University Munich. Measurements are conducted at realistic flow conditions (M2th = 0.59, Re2th = 2·105) in three cases of different endwall boundary layer conditions with and without periodically incoming wakes. The endwall boundary layer is characterized by 1D-CTA measurements upstream of the blade passage. Secondary flow is evaluated by Five-hole-probe measurements in the turbine exit flow. A strong similarity is found between the time-averaged effects of unsteady inflow conditions and the effects of changing inlet endwall boundary layer conditions regarding the attenuation of secondary flow. Furthermore, the experimental investigations show, that all design goals for the improved T106A cascade are met.

Determination of the Flow Field in LP Steam Turbines

1986 ◽  
Author(s):  
J. Wachter ◽  
G. Eyb
Keyword(s):  
Flow Field ◽  
Measuring Equipment ◽  
Short Description ◽  
Test Stand ◽  
Steam Turbines ◽  
Flow Conditions ◽  
Flow Measurements ◽  
Last Stage ◽  
The University

Up to now the determination of flow conditions across the entire circumference in LP steam turbines appears to be a difficult undertaking. The difficulties are mainly caused by the condensing medium steam and by the limited access to the stage from outside. The Last Stage Test Stand at the University of Stuttgart is a suitable facility for flow measurements in the LP part of steam turbines. Besides a short description of the test stand itself, the measuring equipment and the newly developed methods for data acquisition and evaluation are presented. Finally the flow field behind the last stage is shown and the results interpreted.

Design Parameters and Practical Considerations in the Two-Phase Forced-Convection Cooling of Multi-Chip Modules

1992 ◽  
Vol 114 (3) ◽  
pp. 280-289 ◽  
Author(s):  
Christopher O. Gersey ◽  
Thomas C. Willingham ◽  
Issam Mudawar
Keyword(s):  
Forced Convection ◽  
Flow Rate ◽  
Rectangular Channel ◽  
Nucleate Boiling ◽  
Design Parameters ◽  
Two Phase ◽  
Chip Surface ◽  
Flow Area ◽  
Convection Cooling ◽  
Two Phase Cooling

Forced-convection boiling was investigated with a dielectric coolant (FC-72) in order to address some of the practical issues related to the two-phase cooling of multi-chip modules. The module used in the present study featured a linear array of nine, 10 × 10 mm2, simulated microelectronic chips which were flush-mounted along a 20-mm wide side of a rectangular channel. Experiments were performed with a 5-mm channel gap (distance between the chip surface and the opposing channel wall) at eight orientations spaced 45 degrees apart. Two other channel gaps, 2 and 10 mm, were tested in the vertical up flow configuration. For all these configurations, the velocity and subcooling of the liquid were varied from 13 to 400 cm/s and 3 to 36°C, respectively. Changes in orientation did not affect single-phase or nucleate boiling characteristics, but did have a major impact on CHF. Upflow conditions were found to be the best configuration for the design of two-phase cooling modules because of its inherently stable flow and relatively high CHF values. The CHF value for the most upstream chip in vertical upflow agreed well with a previous correlation for an isolated chip. Combined with the relatively small spread in CHF values for all chips in the array, this correlation was found to be attractive for design purposes in predicting CHF for a multi-chip array. To achieve a given CHF value, it is shown how the strong CHF dependence on velocity rather than flow area allows for a reduction in the required flow rate with the 2-mm, as compared to the 5-mm gap, which also required a smaller flow rate than the 10-mm gap. This reduction inflow rate was significant only with subcooled conditions corresponding to high CHF values.

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