Baffle Blocks Research Articles

CHARACTERISTIC OF CONTRACTION AND DISCHARGE COEFFICIENT FOR FLOW UNDER SLUICE GATE

The contraction coefficient (Cc) and discharge coefficient (Cd) always rise in flow while sluice gate operated with variation of open gate and discharge (Q). This experimental research used prototype model made from fiberglass (horizontal channel), sluice gate installed on it. Two models of trapezoid baffle block installed as three rows, specified location 25 cm after sluice gate pair using sill with different dimension. Water depth (y) and velocity (v) were measured during each running test then Froude number, contraction coefficient (Cc) and discharge coefficient (Cd) were calculated. The result showed that trapezoid baffle block model T2 (used no sill, sill 2 cm and sill 2.7 cm, Fr = 0.11 - 0.75) gives the better performance modelling of Cc and Cd in term of the initial Froude number with R2 = 0.8086 (Cc) and R2 = 0.8273 (Cd).

A PHYSICAL HYDRAULIC MODEL TEST TO SOLVE THE PROBLEM ON SPILLWAY DAM

This research studies about the hydraulic performance and and the problem solving alternativesof spillway design at Fila Tukutaha Dam, Alor District Indonesia. Flow water passing over the spillway of adam typically has a large amount of energy, must be dissipated safely before the floodwaters rejoin to thenatural river system. Therefore, energy dissipation takes place at the downstream end of the chuteway. Thestilling basin at the end of the chute way is commonly used to dissipate energy from the spillway and slow thewater velocity to protect the downstream river channel from erosion and damage. The methodology ofexperiment consists of physical modeling in the Hydraulic and Coastal Engineering Laboratory of CivilDepartement, Sepuluh Nopember Institute of Technology. The discharge design was analyzed by hydrologicalrouting formula over the spillway. The methods include Bernoulli’s formula equation for the steeply slopedchannel, the standard step formula for calculating the energy equation on the transition channel, and the USBRtype 2 for designing the stilling basin. From the experimental result, cross-flow was reduced by adding thehexagonal baffle block on the transition channel, and the effectiveness of stilling basin was occurred by placingthe abrupt rise in the downstream area.

Quantitative analysis of trapezoid baffle block sloping angles on oxygen transport and performance of proton exchange membrane fuel cell

Increasing the power density of proton exchange membrane (PEM) fuel cell without extra cost through flow channel design is an effective method to achieve cost and compact requirement of its commercialization for vehicles. PEM fuel cell power or current density is mainly limited by oxygen transport to the reacting sites in the cathode porous electrode. Inserting baffle blocks in the flow channel of PEM fuel cell can effectively enhance the oxygen transport and fuel cell performance. However, existing researches on the structure design of baffle blocks are still insufficient, especially for the design of baffle block sloping angles. In this study, the influence of the trapezoid baffle block sloping angles on the convective and diffusive oxygen transport and performance of PEM fuel cell is quantitatively investigated using a three-dimensional numerical model. The results indicate that larger leading angle of the baffle block leads to a higher gas velocity component in the vertical direction, hence enhances the convective oxygen transport effect; but it reduces the convection area, as well as the oxygen delivery efficiency in the channel. Larger trailing angle of the baffle block induces the back-flow phenomenon at the rear of the baffle block, which causes the loss of gas pressure and worse oxygen transport. Both the baffle block sloping angles are carefully designed, and it demonstrates that the trapezoid baffle blocks with both the leading and trailing sloping angles of 45° show the best oxygen transport and fuel cell performance.

The Effects of Different Shaped Baffle Blocks on the Energy Dissipation

Stilling basins can be defined as energy dissipaters constructed of the irrigation systems. This study aims at investigating the performance of the new seven baffle blocks design in terms of reducing the dimensions of stilling basins in irrigation systems. In order to assess the hydraulic efficiency of a new model for baffle block used in stilling basins, a Naval Research Laboratory (NRL) has conducted. The results of this study demonstrate that the performance of the new baffle block, in term of hydraulic jump length reduction and hydraulic energy dissipation, it's better than standard blocks. However, the ratios of the drag resistance attributed to the new baffles block (FB / F2) have been larger than that applied on the normal block. It was found that the new block dissipates the energy by 9.31% more than the concrete block, and decreases the length of the hydraulic jump by 38.6% in comparison with the standard blocks. However, the new block maximizes the drag force ratio by 98.6% in comparison with the standard baffle blocks. The findings indicated that in terms of energy reduction and dissipation in the length of the hydraulic jump, the new block is superior to the other kinds.

Investigating the Effects of the Block Geometries and Sidewall Divergences on the Local Scour Downstream of Baffled Chute Spillways

Due to the lack of any specific study about the sidewalls and other blocks’ changes in the case of hydraulic and scour downstream, the present study was conducted to investigate this issue. For this purpose, drainage projects and spillway chutes, as well as many baffle block chutes, were designed and constructed with the parallel sidewalls and trapezoidal shape using the U.S. Bureau of Reclamation (USBR) instructions. Three divergence ratios of ((b1/b2) = 1.45, 1.75, and 2.45), a parallel sidewall of (b1/b2 = 1), and also three geometry blocks including trapezoidal USBR, trihedral, and semicircle blocks were applied and tested in the hydraulic laboratory using a baffle chute with the slope of (2 : 1), (H : V). The material used in this study was sediment sand with a uniform grain size of d50 = 1.2 mm, 15 cm of thickness, and 2 m of length. The experiment was conducted with seven different discharges in lasting condition, and the flow characteristic and scour hole dimensions were measured. The results revealed that in comparison with the USBR blocks, changes in the baffle sidewall and block shape made an approximate 50% reduction in the maximum depth of the scour hole. Thus, increasing the divergence ratio from 1 to 2.45 had a significant effect on reducing the maximum depth and the topographic shape of the scour hole. According to the range mentioned in the literature for the Weber number, the scale effect was negligible for the chute with baffle blocks. Generally, it can be concluded that the sidewall changes also can make a reduction in the number of overbaffle blocks, causing a reduction in the construction cost.

Experimental Investigation of the Characteristics of Hydraulic Jump in a Diverging Stilling Basin with an Adverse Slope Using Baffle Blocks

Experimental Investigation of the Characteristics of Hydraulic Jump in a Diverging Stilling Basin with an Adverse Slope Using Baffle Blocks

Modelling Equation of Contraction Coefficient (Cc) and Discharge Coefficient (Cd) for Flow under Sluice Gate Using Cubic Baffle Block and Sill

Modelling Equation of Contraction Coefficient (Cc) and Discharge Coefficient (Cd) for Flow under Sluice Gate Using Cubic Baffle Block and Sill

Utjecaj hrapavosti na spregnutu dubinu kod vodnih skokova na neravnoj podlozi

Hydraulic jump is an important phenomenon in open channel flows such as rivers and spillways. Hydraulic jump is mainly used for kinetic energy dissipation at the downstream side of a spillway with the assist of baffle blocks. It has been demonstrated that corrugated or rough beds show considerably more energy dissipation than smooth beds. The experimental research evaluating the effect of crushed stones on the hydraulic jump is presented in this paper. Five different-size sets of crushed stones were used. Results show that the effect of rough bed does not increase after a certain height of crushed stone is reached.

Effects of Different Shaped Baffle Blocks on the Energy Dissipation and the Downstream Scour of a Regulator

The scouring problem caused by the flow movement in the downstream areas of hydraulic structures is an issue that keeps its actuality. In order to prevent these scouring to occur in the downstream, various typed energy dissipaters are placed on the downstream of the hydraulic structures. Factors such as sediment type, the velocity of the stream, and flow regime play an important role in scouring. In order to prevent scouring, the flow’s energy must be dissipated before meeting the sediment. In this study, it is aimed to reduce the amount of scour occurred at the downstream of the weir by using energy dissipaters with different geometries. The flow and scouring events on the weir were modeled in two dimensions using Computational Fluid Dynamics (CFD). The findings were compared for different downstream conditions and the results were discussed in this respect.

Forced Hydraulic Jump in a Diverging Stilling Basin Using Angled Baffle Blocks

AbstractThe effect of angled baffle blocks for improving hydraulic jump characteristics in a gradually diverging stilling basin with an adverse bed slope was investigated experimentally. Baffle blo...

Effect of baffle block configurations on characteristics of hydraulic jump in adverse stilling basins

The construction of stilling basin with adverse slope change the characteristics of hydraulic jump such as sequent depth ratio, length of jump ratio, length of roller and energy dissipation ratio, consequently the dimensions of stilling basin are changed, also using baffle blocks with different configurations develop these characteristics. In this study different shapes of baffle block (models (A), (B), (C) and (D)) installed in the stilling basins at adverse slopes (- 0.03, - 0.045, - 0.06) in addition to horizontal bed, all these models are tested in the stilling basin to show their effects on the characteristics of hydraulic jump, the experiments applied for the range of Froude number (Fr1) between 3.99 and 7.48. The baffle block model (D) showed good results when compared with models (B) and (C), therefore it used with arrangement of (single and double row) and compared with baffle block model (A) at slopes (0, - 0.03, - 0.045, - 0.06) to study the effects of baffle blocks on hydraulic jump when bed slopes are changed. In general using baffle block caused a reduction in sequent depth ratio, length of jump ratio and the length of the roller, but the energy dissipation ratio increased.

Die structure optimization for hollow aluminum profile

The whole aluminum profile extrusion process, especially the welding stages, for an upside beam on the train, was simulated by using FEM (Finite Element Method) combined with a mesh reconstruction technology in the welding zone. According to the simulation results, the deformation of the extrudate head, the velocity distribution on the cross-section of the extrudate at the die exit and the pressure in the welding-chamber were analyzed. The die structure was optimized to avoid the phenomena of ‘die blocked’ and bad weld quality. By modifying the structures of the second welding-chamber, the bearing length and baffle block height, the velocity uniformity at the die exit was improved and as a result, the phenomena of ‘die blocked’ was avoided. By modifying the port-bridge structure, the welding-chamber pressure was improved, and consequently, the welding quality was improved.

Evaluation of Boundary Dam spillway using an Autonomous Sensor Fish Device

Fish passage conditions over spillways are important for the operations of hydroelectric dams because spillways are usually considered as a common alternative passage route to divert fish from the turbines. The objectives of this study were to determine the relative potential of fish injury during spillway passage both before and after the installation of baffle blocks at Boundary Dam, and to provide validation data for a model being used to predict total dissolved gas levels. Sensor Fish were deployed through a release system mounted on the face of the dam in the forebay. Three treatments, based on the lateral position on the spillway, were evaluated for both the baseline and post-modification evaluations: Left Middle, Right Middle, and Right. No significant acceleration events were detected in the forebay, gate, or transition regions for any release location; events were only observed on the chute and in the tailrace. Baseline acceleration events observed in the chute region were all classified as strikes, whereas post-modification events included strike and shear on the chute. While the addition of baffle blocks increased the number of severe events observed on the spillway chute, overall fewer events were observed in the tailrace post-modification. Analysis of lateral positioning of passage indicated that the Right Middle treatment was potentially less injurious to fish based on relative frequency of severe events at each location. The construction of baffle blocks on the spillway visibly changed the flow regime. Prior to installation the flow jet was relatively thin, impacting the tailrace as a coherent stream that plunged deeply, possibly contributing to total dissolved gas production. Following baffle block construction, the discharge jet was more fragmented, potentially disrupting the plunge depth and decreasing the time that bubbles would be at depth in the plunge pool. The results in this study support the expected performance of the modified spillway chute: the addition of the baffle blocks generally lessened the depth and impact of entry. This study provides information that can be used to help design and operate spillways for improving fish passage conditions.

Turbulence measurements in submerged hydraulic jumps with baffle blocks

Laboratory measurements of turbulence in submerged hydraulic jumps with blocks downstream of a sluice gate are presented. As observed previously two flow regimes were distinguished; the deflected surface jet (DSJ) and the reattaching wall jet (RWJ) regimes. In the DSJ regime considerable turbulent kinetic energy (TKE) was generated just downstream of the blocks and the rate of dissipation of TKE was found to be very high resulting in a rapid decay of TKE. In the RWJ flow regime the magnitude of both the TKE and the dissipation rate were considerably lower but because the TKE decayed more slowly higher levels of TKE persisted farther downstream. This study provides insights into the production and dissipation of turbulence in submerged flows and helps to explain why a submerged jump with blocks with a low submergence factor; i.e., the DSJ flow regime, is as effective as a free jump in dissipating energy.

Length prediction of non-aerated region flow at baffled chutes using intelligent nonlinear regression methods

Baffled chutes are used in irrigation systems, storm water systems, wastewater canal chutes, river training, and drop structures for energy dissipation. Two flow regions occur on the flow surface of baffled chutes. These are black water and white water regions. Knowing the location of the inception point where white water begins to appear on the surface is important for determination of the non-aerated flow region. Thus, cavitation damage can be prevented. In this study, 160 laboratory test results have been used for determining black water length (i.e., length of the non-aerated region) of baffled chutes with stepped, wedge, trapezoidal, and T-shaped baffle blocks. The obtained observation data have been analyzed by well-known soft computing methods such as artificial neural networks (ANN), curve fitting (CF), non-linear regression (NLR) and special extreme learning machine (ELM). The methods’ performance in mapping input data to the output were compared. The mean regression errors calculated by the curve fitting model, ANN, NLR and ELM are obtained as 2.5, 8.0, 11.25 and 0.8 %, respectively. The experimental results show that ELM’s nonlinear system modeling capability is superior to ANN, NLR, and CF.

Efficiency of the Nam Theun 2 hydraulic structures on water aeration and methane degassing

Release of hypolimnetic water from man-made reservoirs can be a problem for downstream rivers. These effects can be significant mainly during the first years after the reservoir impoundment, especially in thermally stratified reservoirs favouring the release of anoxic methane-rich water. In tropical areas, higher temperatures decrease the oxygen solubility and enhance chemical processes responsible for the rise of reduced compounds. The Nam Theun 2 Reservoir was first filled in 2008. It experienced hypolimnetic deoxygenation and significant methane concentrations during the first 2 years. Dedicated structures to oxygenate water and degas methane were designed during the study phase. The overall aerating and degassing effects of these hydraulics structures varied from very good to moderate. Results depend on the continuous water quality improvement with time as well as on the limited range of upstream oxygen and methane concentrations tested. The hollow jet valve and the concrete tooth shaped structure were very efficient together with downstream natural turbulence in aerating/degassing compared to the staggered baffle blocks. Contrary to other structures, the efficiency of the baffle blocks structure is reduced with high discharges. The aeration weir showed a moderate efficiency in supplying oxygen to the water due to the high upstream oxygen saturations (close to 100%). However, it was very efficient for methane degassing even at low concentrations. Hydraulics structures of the Nam Theun 2 project are an efficient, reliable and low maintenance way to improve oxygen content and to degas methane.

Experimental Study for Energy Dissipation Using Stilling Basin with One and Two Consecutive Drops

The scour at downstream of hydraulic structures is one of the major concern in its stability analysis and operation .The excess energy existing immediately downstream of such structures has to be controlled. Hence, it is necessary to design and install a device for dissipating excess energy in order to prevent downstream scour. The drop structures is one of the commonly structures used for dissipating excess energy.In the present study an experimental approach is employed through which different types of stilling basin with different heights were tested using one drop and two consecutive drops. Moreover the effect of the end sill and baffles with different heights and different bed slopes was investigated. The hydraulic parameters involved were measured experimentally using a model of straight drop installed in the available (S6) multi-purpose flume in the fluid mechanics lab at the Civil Engineering Department, University of Garyounis.Results showed that, for one drop the presence of end sill reduced the length of the jump by a small value approximately 4%with an increase of relative energy loss by a small value. The increase of relative baffles block height increases the optimum relative height of drop (w/y1=6), and the relative energy loss .For two consecutive drops it was found that the most value of energy loss takes place in the second basin. The presences of end sill at the end of second basin increases the performance of second basin by small value approximately 5%. It is also shown that increasing the relative height of baffles blocks lead to increases in the relative energy loss (within the ranges considered in this study), and the optimum relative baffle block height hb/y1=0.77 to 1.7 and bed slope is 1/50

Laminar Nanofluid Flow Over Periodic Two Dimensional Rectangular Baffled Channels

Forced convection of laminar nanofluid flow in a periodic baffled channel is numerically studied. The governing equations of the problem are continuity, momentum and energy equations which are discretized using finite volume method (FVM). The upper and lower walls of the test section are kept at a constant temperature. Two distinct baffle shapes are studied, which are diamond baffle and vertical flat plate baffle. Different half tip angles of the diamond baffle (5°, 10° and 15°) and different block ratios (BR = 0.1 H, 0.3 H and 0.5 H) for both diamond and vertical flat plate baffles are pondered. Four varied types of nanofluids are employed as working fluids which are Al 2O2, CuO, SiO2, and ZnO dispersed in pure water as a base fluid. Different concentrations of nanoparticles (1% to 4%) and different diameters of nanoparticles (30 nm to 80 nm) are used. The range ofReynolds number varied from 100 to 1200. The numerical results state that with the increase in the height and the decrease in the angle of the baffle and also the increase of the volume fraction and the decrease of the nanoparticle diameter, the Nu number increases and so does the friction factor. Among all of the four studied nanofluids, SiO2-water with 4% volume fraction and 30 nm diameter of the nanoparticles shows the highest heat transfer and thermal enhancement of the system.

Mean Flow in a Submerged Hydraulic Jump with Baffle Blocks

AbstractThe flow in a submerged hydraulic jump with three-dimensional (3D) baffle blocks was experimentally studied. An incoming jet with varying supercritical Froude numbers was deflected with one or two rows of 3D baffle blocks for different downstream water depths. Depending on the submergence factor, two flow regimes were observed for which the time-averaged 3D velocity field was measured with an acoustic Doppler velocimeter (ADV). Measurements were conducted at different stations located both upstream and downstream of the blocks and above the crest of the blocks. Velocity measurements were made in a plane located at the center of the middle block (i.e., the centerplane of the flume) and, also, in a plane located at the midpoint between the blocks (off-centerplane). The mean flow pattern was found to be significantly different for the two flow regimes. In the deflected surface jet (DSJ) regime, which occurred at low submergence factors, the major flow features were a small surface roller upstream of ...

Analysis of Supercritical Flow In Suddenly Expanding Channel

The experimental analysis is carried out to study the variation of flow characteristics namely sequent depth ratio (Y2 / Y1), Relative height of jump (hj / Y1), relative energy loss (EL / E1), Efficiency (E2 / E1), Relative length of jump (Lj / Y1) and relative length of roller (Lr / Y1) of the hydraulic jump for suddenly expanding channel for different B1 / B2 (expansion) ratio. Dimension of baffle blocks and end sill are also considered as the third variable. Explanations of the variation of these characteristics with approach Froude number is presented based on experiments. Empirical models are presented using Buckinham's π-theorem; these models are tested, validated and compared with other authors result. Modifications in energy dissipation as a result of application of appurtenances are obtained showing usefulness to its dimensions.