International Science Index
Studying the Effect of Froude Number and Densimetric Froude Number on Local Scours around Circular Bridge Piers
A very large percentage of bridge failures are attributed to scouring around bridge piers and this directly influences public safety. Experiments are carried out in a 12-m long rectangular open channel flume made of transparent tempered glass. A 300 mm thick bed made up of sand particles is leveled horizontally to create the test bed and a 50 mm hollow plastic cylinder is used as a model bridge pier. Tests are carried out with varying flow depths and velocities. Data points of various scour parameters such as scour depth, width, and length are collected based on different flow conditions and visual observations of changes in the stream bed downstream the bridge pier are also made as the scour progresses. Result shows that all three major flow characteristics (flow depth, Froude number and densimetric Froude number) have one way or other affect the scour profile.
Prediction for the Pressure Drop of Gas-Liquid Cylindrical Cyclone in Sub-Sea Production System
With the rapid development of subsea oil and gas exploitation, the demand for the related underwater process equipment is increasing fast. In order to reduce the energy consuming, people tend to separate the gas and oil phase directly on the seabed. Accordingly, an advanced separator is needed. In this paper, the pressure drop of a new type of separator named Gas Liquid Cylindrical Cyclone (GLCC) which is used in the subsea system is investigated by both experiments and numerical simulation. In the experiments, the single phase flow and gas-liquid two phase flow in GLCC were tested. For the simulation, the performance of GLCC under both laboratory and industrial conditions was calculated. The Eulerian model was implemented to describe the mixture flow field in the GLCC under experimental conditions and industrial oil-natural gas conditions. Furthermore, a relationship among Euler number (Eu), Reynolds number (Re), and Froude number (Fr) is generated according to similarity analysis and simulation data, which can present the GLCC separation performance of pressure drop. These results can give reference to the design and application of GLCC in deep sea.
A Two-Phase Flow Interface Tracking Algorithm Using a Fully Coupled Pressure-Based Finite Volume Method
Two-phase and multi-phase flows are common flow types in fluid mechanics engineering. Among the basic and applied problems of these flow types, two-phase parallel flow is the one that two immiscible fluids flow in the vicinity of each other. In this type of flow, fluid properties (e.g. density, viscosity, and temperature) are different at the two sides of the interface of the two fluids. The most challenging part of the numerical simulation of two-phase flow is to determine the location of interface accurately. In the present work, a coupled interface tracking algorithm is developed based on Arbitrary Lagrangian-Eulerian (ALE) approach using a cell-centered, pressure-based, coupled solver. To validate this algorithm, an analytical solution for fully developed two-phase flow in presence of gravity is derived, and then, the results of the numerical simulation of this flow are compared with analytical solution at various flow conditions. The results of the simulations show good accuracy of the algorithm despite using a nearly coarse and uniform grid. Temporal variations of interface profile toward the steady-state solution show that a greater difference between fluids properties (especially dynamic viscosity) will result in larger traveling waves. Gravity effect studies also show that favorable gravity will result in a reduction of heavier fluid thickness and adverse gravity leads to increasing it with respect to the zero gravity condition. However, the magnitude of variation in favorable gravity is much more than adverse gravity.
Scour Depth Prediction around Bridge Piers Using Neuro-Fuzzy and Neural Network Approaches
The prediction of scour depth around bridge piers is frequently considered in river engineering. One of the key aspects in efficient and optimum bridge structure design is considered to be scour depth estimation around bridge piers. In this study, scour depth around bridge piers is estimated using two methods, namely the Adaptive Neuro-Fuzzy Inference System (ANFIS) and Artificial Neural Network (ANN). Therefore, the effective parameters in scour depth prediction are determined using the ANN and ANFIS methods via dimensional analysis, and subsequently, the parameters are predicted. In the current study, the methods’ performances are compared with the nonlinear regression (NLR) method. The results show that both methods presented in this study outperform existing methods. Moreover, using the ratio of pier length to flow depth, ratio of median diameter of particles to flow depth, ratio of pier width to flow depth, the Froude number and standard deviation of bed grain size parameters leads to optimal performance in scour depth estimation.
Effects of Roughness on Forward Facing Step in an Open Channel
Experiments were performed to investigate the effects of roughness on the reattachment and redevelopment regions over a 12 mm forward facing step (FFS) in an open channel flow. The experiments were performed over an upstream smooth wall and a smooth FFS, an upstream wall coated with sandpaper 36 grit and a smooth FFS and an upstream rough wall produced from sandpaper 36 grit and a FFS coated with sandpaper 36 grit. To investigate only the wall roughness effects, Reynolds number, Froude number, aspect ratio and blockage ratio were kept constant. Upstream profiles showed reduced streamwise mean velocities close to the rough wall compared to the smooth wall, but the turbulence level was increased by upstream wall roughness. The reattachment length for the smooth-smooth wall experiment was 1.78h; however, when it is replaced with rough-smooth wall the reattachment length decreased to 1.53h. It was observed that the upstream roughness increased the physical size of contours of maximum turbulence level; however, the downstream roughness decreased both the size and magnitude of contours in the vicinity of the leading edge of the step. Quadrant analysis was performed to investigate the dominant Reynolds shear stress contribution in the recirculation region. The Reynolds shear stress and turbulent kinetic energy profiles after the reattachment showed slower recovery compared to the streamwise mean velocity, however all the profiles fairly collapse on their corresponding upstream profiles at x/h = 60. It was concluded that to obtain a complete collapse several more streamwise distances would be required.
The Effect of the Side-Weir Crest Height to Scour in Clay-Sand Mixed Sediments
Experimental studies to investigate the depth of the
scour conducted at a side-weir intersection located at the 1800 curved
flume which located Hydraulic Laboratory of Yıldız Technical
University, Istanbul, Turkey. Side weirs were located at the middle of
the straight part of the main channel. Three different lengths (25, 40
and 50 cm) and three different weir crest height (7, 10 and 12 cm) of
the side weir placed on the side weir station. There is no scour when
the material is only kaolin. Therefore, the cohesive bed was prepared
by properly mixing clay material (kaolin) with 31% sand in all
experiments. Following 24h consolidation time, in order to observe
the effect of flow intensity on the scour depth, experiments were
carried out for five different upstream Froude numbers in the range of
As a result of this study the relation between scour depth and
upstream flow intensity as a function of time have been established.
The longitudinal velocities decreased along the side weir; towards the
downstream due to overflow over the side-weirs. At the beginning,
the scour depth increases rapidly with time and then asymptotically
approached constant values in all experiments for all side weir
dimensions as in non-cohesive sediment. Thus, the scour depth
reached equilibrium conditions. Time to equilibrium depends on the
approach flow intensity and the dimensions of side weirs. For
different heights of the weir crest, dimensionless scour depths
increased with increasing upstream Froude number. Equilibrium
scour depths which formed 7 cm side-weir crest height were obtained
higher than that of the 12 cm side-weir crest height. This means when
side-weir crest height increased equilibrium scour depths decreased.
Although the upstream side of the scour hole is almost vertical, the
downstream side of the hole is inclined.
Prediction of Scour Profile Caused by Submerged Three-Dimensional Wall Jets
Series of laboratory tests were carried out to study the
extent of scour caused by a three-dimensional wall jets exiting from a
square cross-section nozzle and into a non-cohesive sand beds.
Previous observations have indicated that the effect of the tail water
depth was significant for densimetric Froude number greater than ten.
However, the present results indicate that the cut off value could be
lower depending on the value of grain size-to-nozzle width ratio.
Numbers of equations are drawn out for a better scaling of numerous
scour parameters. Also suggested the empirical prediction of scour to
predict the scour centre line profile and plan view of scour profile at
any particular time.
Characteristics of Hydraulic Jump
The effect of an abruptly expanding channel on the main characteristics of hydraulic jump is considered experimentally. The present study was made for supercritical flow of Froude number varying between 2 to 9 and approach to expanded channel width ratios 0.4, 0.5, 0.6 and 0.8. Physical explanations of the variation of these characteristics under varying flow conditions are discussed based on the observation drawn from experimental results. The analytical equation for the sequent depth ratio in an abruptly expanding channel as given by eminent hydraulic engineers are verified well with the experimental data for all expansion ratios, and the empirical relation was also verified with the present experimental data.
Experimental Study of Submersible Jet on Flow Hydraulic Parameters
Behavior of turbulent jet is relying on jet parameters,
environmental and geometric parameters. In this research, it has
attempt to Study effect of jet parameters of internal angle on
maximum effective length and velocity on centerline from nozzle
experimentally. Toward this end, four internal angles 30, 45, 60 and
90-degree are considered for this study in a flume with 600cm as
long, 100cm as high and 150cm in width. Various discharges were
used to evaluate effective length for a wide range of densimetric
Froude numbers F0, from 17.9 to 39.4 that is defined at the nozzle. As
a result, It is revealed that both velocity on centerline and effective
length decreases when nozzle angle decreased from 90° to 30°. The
results show that, for all range of Fr0 the Um/U0 ratio for nozzle with
α=90° on centerline increases 20% - 27% than nozzle with α=30° that
has lowest velocity on centerline than other nozzle.
Laboratory Experiments: Influence of Rainfall Characteristics on Runoff and Water Erosion
The study concerns an experimental investigation in
the laboratory of the water erosion using a rainfall simulator. We
have focused our attention on the influence of rainfall intensity on
some hydraulic characteristics. The results obtained allow us to
conclude that there is a significant correlation between rainfall
intensity and hydraulic characteristics of runoff (Reynolds number,
Froude number) and sediment concentration.
Investigation of Undular Hydraulic Jump over Smooth Beds
Undular hydraulic jumps are illustrated by a smooth
rise of the free surface followed by a train of stationary waves. They
are sometimes experienced in natural waterways and rivers. The
characteristics of undular hydraulic jumps are studied here. The
height, amplitude and the main characteristics of undular jump is
depended on the upstream Froude number and aspect ratio. The
experiments were done on the smooth bed flume. These results
compared with other researches and the main characteristics of the
undular hydraulic jump were studied in this article.
Influence of the Entropic Parameter on the Flow Geometry and Morphology
The necessity of updating the numerical models inputs, because of geometrical and resistive variations in rivers subject to solid transport phenomena, requires detailed control and monitoring activities. The human employment and financial resources of these activities moves the research towards the development of expeditive methodologies, able to evaluate the outflows through the measurement of more easily acquirable sizes. Recent studies highlighted the dependence of the entropic parameter on the kinematical and geometrical flow conditions. They showed a meaningful variability according to the section shape, dimension and slope. Such dependences, even if not yet well defined, could reduce the difficulties during the field activities, and also the data elaboration time. On the basis of such evidences, the relationships between the entropic parameter and the geometrical and resistive sizes, obtained through a large and detailed laboratory experience on steady free surface flows in conditions of macro and intermediate homogeneous roughness, are analyzed and discussed.
Evolution of Developing Flushing Cone during the Pressurized Flushing in Reservoir Storage
Sedimentation in reservoirs and the corresponding
loss of storage capacity is one of the most serious problems in dam
engineering. Pressurized flushing, a way to remove sediments from the reservoir, is flushing under a pressurized flow condition and
nearly constant water level. Pressurized flushing has only local
effects around the outlet. Sediment in the vicinity of the outlet openings is scoured and a funnel shaped crater is created. In this study, the temporal development of flushing cone under various
hydraulic conditions was studied experimentally. Time variations of
parameters such as maximum length and width of flushing and also
depth of scouring cone was measured. Results indicated that an
increase in flow velocity (and consequently in Froude number)
established new hydraulically conditions for flushing mechanism and
so a sudden growth was observed in the amount of sediment released
and also scouring dimenssions. In addition, a set of nondimensional
relationships were identified for temporal variations of flushing scour
dimenssions, which can eventuallt be used to estimate the development of flushing cone.