Baffle Blocks Research Articles

Stepped chute energy dissipation structure downstream of a low-level river crossing for embankment protection

A low-level river crossing is an economic means of providing access for lower-order roads during high-frequency flood events. Conventionally, culverts are employed to enable the flow to traverse the road, albeit with allowance for overtopping. This overtopping flow from the approach roads, however, possesses the potential to cause erosion of the downstream embankment, thereby jeopardising the foundational integrity of the structure. A physical modelling study was undertaken to investigate the hydraulic performance of stepped chutes in terms of flow patterns, air-water flow properties, and energy dissipation. Various types of stepped chutes were investigated, namely horizontal steps with a chute wall, horizontal steps without a chute wall but with riprap placed directly downstream of each chute, step-inclined steps (backward sloping), steps with pooled cascades, and steps with baffle blocks. Notably, chutes with horizontal steps were the most efficient configuration in terms of relative energy dissipation. Furthermore, this research culminated in the formulation of a new regression formula to establish a quantifiable relationship between the required step length and the overflow depth and discharge, thereby offering a valuable tool for design purposes.

Hydraulic jump in a circular stilling basin by using angled baffle blocks

The present study aims to evaluate characteristics of the hydraulic jump formed in a circular stilling basin with baffle blocks. Baffle blocks improve performance of the hydraulic jump and stabilize its position in the basin. In addition to experimental modeling, theoretical relationships were derived to determine the sequent depth ratio and the relative energy loss in circular stilling basins with baffle blocks, deriving a relationship for estimating the force imposed by the blocks. Based on the results of the present study, baffle blocks in a stilling basin improve the characteristics of a circular hydraulic jump such as the sequent depth ratio and relative energy loss. Furthermore, increasing the obstruction ratio and the sequent radius ratio decrease the sequent depth ratio. Furthermore, an increase in the sequent radius ratio led to an increase in the relative energy loss. Also, the results show that the relative length of a circular hydraulic jump is significantly smaller than that of the classical hydraulic jump (CHJ). Error analysis on the measured data and the developed theoretical relationships indicated that the theoretically obtained results compare well with the present experimental data.

Numerical investigation of hydraulic jumps with USBR and wedge-shaped baffle block basins for lower tailwater

Abstract The stilling basin of the Taunsa barrage is a modified form of the United States Bureau of Reclamation (USBR) Type-III basin, which consists of baffle and friction blocks. Studies revealed uprooting of baffle blocks due to their vertical face. Additionally, the literature highlighted issues of rectangular face baffle blocks: less drag, smaller wake area, and flow reattachment. In contrast, the use of wedge-shaped baffle blocks (WSBBs) is limited downstream of open-channel flows. Therefore, this study developed numerical models to investigate the effects of USBR and WSBB basins on the hydraulic jump (HJ) downstream of the Taunsa barrage under lower tailwater conditions. Surface profiles in WSBB and modified USBR basins showed agreement with previous studies, for which the coefficient of determination (R2) reached 0.980 and 0.970, respectively. The HJ efficiencies reached 57.9 and 58.6% in WSBB and modified USBR basins, respectively. The results of sequent depths, roller length, and velocity profiles in the WSBB basin were found more promising than the modified USBR basin, which further confirmed the suitability of the WSBB basin for barrages. Furthermore, WSBB improved flow behaviors in the basin, which showed no fluid reattachment on the sides of WSBB, increased wake regions, and decreased turbulent kinetic energies.

Numerical investigation of hydraulic jump for different stilling basins using FLOW-3D

Abstract Stilling basin of the Tuansa barrage is a modified form of the United States Bureau of Reclamation (USBR) Type-III basin, which includes impact baffle and friction blocks. Soon after the barrage's operation, baffle blocks were found to be uprooted. Additionally, previous studies also highlighted the issues of rectangular baffle blocks, i.e., less drag, smaller wake zone, and flow reattachment. On the contrary, the use of wedge-shaped splitter blocks is found limited downstream of diversion barrages. Therefore, this study focuses on the hydraulic effects of wedge-shaped splitter blocks on hydraulic jump (HJ) and energy dissipation using FLOW-3D and confirms its suitability downstream of the diversion barrage. The study mainly investigated the free surface profiles, roller lengths, relative energy losses, velocity profiles, and turbulent kinetic energies for three different stilling basins. The results of free surface profiles indicated that new basins stabilised the HJ and produced smaller lengths of HJ. The results also showed that as the flow increased, the roller lengths decreased in the new basins. Similarly, with an increase in the flow, the relative energy loss increased in new basins. Furthermore, within HJ, and at the basins' end, the results showed higher decay of velocity and turbulent kinetic energy in the new basins.

THE INFLUENCE OF THE CHANNEL BED RECTANGULAR CONFIGURATION ON SEDIMENT TRANSPORTATION

Sediment transport is the movement of organic and inorganic particles caused by gravity, a moving fluid’s force, the wind, and ice motion. Sediment deposition degrades dams’ safety, leading to environmental pollution and channel area reduction. This study describes the effect of the weir height and spacing of used and non-used rectangular configuration structures on sediment transport rates in an open channel. This project was created using a rectangular open channel (30 cm wide and 60 cm deep). A sharp-crested weir was installed in the channel, and the rectangular wooden configurations were fixed in specific locations on each weir to reduce the bedload transportation rate and sediment motion. The weir heights were different (0.25B, 0.35B, 0.45B, and 0.55B, where B is the channel width). Also, the spacing between the baffle blocks (S) was set to 4Y, 8Y, 12Y, and 16Y, where Y was the maximum water depth without installing blocks and weirs. The results showed that the maximum transported bedload for the lowest weir was 1.4 kg/min, but only 4.4 × 10-3 kg/min was transported for the weir 16.5-cm high with baffle blocks. Using long baffle blocks yielded a worse result than using no blocks. The sediment-transport rate increased to 1.66 kg/min for the 7.5-cm weir due to block configurations. In conclusion, the obtained result contradicts the predicted result, as using baffle blocks increased the sediment transportation rate.

Experimental Investigation of Energy Dissipation in Ogee Spillway Using New Distributions of Dissipation Blocks

Ogee spillway is the most important structure used to get rid of excess water during flood. Scouring phenomenon occurring in the downstream region due to high energy dissapation is an envitable. This study aims to reduce the amount of scour occurred at the downstream stilling basin of the ogee spillway by using three dissipation energy blocks namely as baffle, triangle and stepped blocks. A new distribution was proposed for each type of dissipated block, which varied between one row, two rows, and three rows. The flow and scour experimental tests were carried out under Froude numbers ranging from 2.5 to 8.5. During the tests, sequent depths and transverse velocities distribution were measured. The results showed that the used blocks appeared with good results in minimizing flow velocities and sediment scouring within the stilling basin in accordance with proposed distributions, especially with the range of Froude number 4.5-8.5. Also, The stepped block is characterized by reducing the flow velocities compared to the baffle block and triangle block, as it can be seen that there is a decrease in velocities up to 0.85% for all used distributions (A1, A2, A3, B1, B2, and C1).

Experimental and numerical modeling of various energy dissipater designs in chute channels

Energy dissipater in the stilling basin is a structure designed to protect downstream of the spillway from erosion and scour by reducing flow energy in the energy dissipation pool. Energy dissipation pool is an important element of hydraulic structures as a transition between the high-velocity flow and the sensitive tail water. The aim of this study is to investigate the energy dissipation ratios of baffle blocks which constructed in Type III stilling basin with different geometric shapes by using physical and numerical modeling methods. In all types of baffle blocks, the block heights and widths are chosen equally, and the total baffle block lengths are designed to be 50% of the stilling basin width. Energy dissipation ratio of the baffle blocks in 4 different geometric shapes was determined in 3 different layouts as single row, two rows and two rows without threshold structure, in a total of 12 different designs and 7 different flow rates are tested. In addition, these experimental studies were tested in the FLOW-3D software program, and the results of experimental and numerical studies were compared. As a result of the study, it was determined that the T-shaped energy-dissipating block had the highest energy dissipation ratio, and it was observed that the results obtained from the experimental studies and the FLOW-3D software were similar to each other with in the range of 5%.

Study on the Hydraulic Characteristics of the Trapezoidal Energy Dissipation Baffle Block-Step Combination Energy Dissipator

The step-type energy dissipator is widely used to construct small- and medium-sized reservoirs with its high energy dissipation rate. In order to further improve its air entrainment characteristics and energy dissipation, and reduce the influence of cavitation, in this paper, we added a trapezoidal energy dissipation baffle block at the convex corner of the traditional step to form a trapezoidal energy dissipation baffle block-step combination energy dissipator. We used a combination of hydraulic model experiments and numerical simulation to study the hydraulic characteristics. The results showed that the trapezoidal energy dissipation baffle block-step combination energy dissipator initial entrainment point, with the increase in flow rate, gradually moved backward. A step horizontal surface pressure change in the cavity recirculation area showed a prominent “V” shape; in front of the trapezoidal energy dissipation baffle block, there was a rising trend, and in the energy dissipation baffle block gap, there was a declining trend. The step vertical surface pressure showed a decreasing trend, and negative pressure appeared near the convex angle. The cross-section velocity distribution presented a trend of being small at the bottom and large at the surface, with a large velocity gradient in the longitudinal section of the energy dissipation baffle block and a small velocity gradient in the longitudinal section of the nonenergy dissipation baffle block. The energy dissipation rate reached more than 70% within the test range, and the energy dissipation rate gradually decreased with the increase in the flow rate. The combined energy dissipator is conducive to reducing the cavitation hazard and improving the energy dissipation effect, providing a reference for engineering design and existing step energy dissipators to remove risks and reinforcement.

Thermodynamic performance evaluation of an indoor designed solar air heater duct equipped with V-down baffle blocks having racetrack-shaped staggered openings of varying aspect ratio – an experimental study

ABSTRACT 1This paper presents the thermodynamic performance assessment of an indoor-designed solar air heater (SAH) duct with its absorber affixing the racetrack perforated 45o V-down baffle blocks in staggered holes array. The experimentation work encompasses studying the effect of parameters like – the mass flow rate of air () and the hole aspect ratio (w/d) of baffle blocks on the air temperature rise (), the energy (), the exergy () and the thermohydraulic () efficiencies of the duct under turbulent airflow conditions. The open area ratio (Φ), relative roughness height (e/H) and relative roughness pitch (p/e) of the baffle blocks are maintained constant in this study. The result showed drastic improvement in the performance assessing parameters due to ‘w/d‘ affecting the heat transfer and friction characteristics significantly in the duct. Increasing ‘w/d’ at lower airflow rate results in a uniform downfall of ‘’, and ‘’. At an increased flow rate, the energy and exergy efficiencies decrease. The exergy destruction and pressure drop show non-monotonous variations with the hole-aspect ratio. The smallest hole aspect ratio (w/d of 1.04) baffle blocks outperform in all assessment segments providing maximum values as 14.86oC, 96.81%, 17.46% and 93.95%, respectively, for the air temperature rise, the energy, the exergy and the thermohydraulic efficiency.

Study On Scouring and Protection of USBR-III Type Downstream of Spillway

Abstract. In the downstream part of the spillway building, especially in the flood way, occurs phenomenon of changing flow conditions from super critical to sub critical which causes a hydraulic jump and used by energy absorbers to reduce flow energy. The hydraulic jump in the floodway causes scouring of the bottom, particularly in the unprotected downstream spillway. Using 3 different dimensional baffle block models provides three different discharge variations in four flow simulations. Based on the results of the analysis and planning of the baffle block, it is found that the effectiveness in protecting the downstream scour of the spillway, namely baffle block dimensions of 1:1, 1:3 and 1:5. The three models of baffle blocks are used to determine the change in channel cross-section, scour pattern, scour volume and flow parameters that occur in downstream of spillway. The results showed that without baffle block was 32.80%, 1:1 baffle block was 43, 24%, 1:3 baffle block was 10.01% and 1:5 baffle block was 47.77%. The results of the drainage simulation showed that the higher the water level and the velocity of the flow at the bottom of the channel, the less the flow will be and will not be able to lift the bottom material of the channel

ASSESSMENT OF FLOW CHARACTERISTICS ALONG THE HYDRAULIC PHYSICAL MODEL OF A DAM SPILLWAY

Water flowing over a spillway has a very high kinetic energy because of the conversion of the entire potential energy to kinetic energy. This circumstance results in damage or significant erosion at the toes of the spillways, weir bed, and downstream of a river. To solve this problem, the water flow velocity must be minimised. Physical modelling was implemented to this conundrum in order to modify the current energy dissipating structure, the stilling basin, to enhance energy dissipation as much as achievable by downstream velocity reduction. Baffle blocks were adopted as the modification in this study because these are widely used to stabilize the jumps, shorten its length, and maximize energy dissipation. A selection of baffle arrangements was evaluated by positioning them in the stilling basin’s mid-span to identify the most effective outcome in minimizing downstream velocity. From the findings, it was clearly shown the arrangement of baffles blocks at the stilling basin impacts velocity reduction in various discharge cases. The formation of cross-waves was also assessed at the discharge channel at every discharge value with its relative distance from the sump and the width of the channel prior to the site. For discharge situations of 70.0 L/s and 100.0 L/s, modifications to the Type II stilling basin were recommended. Furthermore, constriction, expansion, or curvature should be avoided in chute spillways identical to the dam spillway to limit cross-wave generation and other unfavourable flow behaviours

Artificial Control Against Unstable Flow in Submerged Jump Below Single or Multiple Gates

For the formation of submerged hydraulic jump with a large submergence, a high velocity flow below a sluice gate is located near the bottom. When the main flow lifts to the water surface from the channel bottom, in some cases, the main flow is periodically deflected. In this case, it might be difficult for swimming fishes to migrate upstream through the hydraulic structure, even if the fish passage is installed at the downstream of the structure. Therefore, there is a need to the periodically deflected flow must be changed to a stabilized flow. In this study, the installation of baffle blocks with asymmetrical length at the downstream of sluice gates was proposed in order to disappear a periodically deflected flow in submerged hydraulic jump. The experiments yield that the periodically deflected flow can be disappeared. The artificially controlled flow has been confirmed by time averaged velocity and the velocity with time series.

Comparison of oxygen transfer efficiency using new types of baffle blocks

Oxygen is needed in water to maintain the natural ecological balance and the health of organisms. The amount of dissolved oxygen (DO) in water can be increased naturally in different ways. In particular, some hydraulic structures are designed so reoxygenation of water occurs spontaneously over a short distance and in a short time. Baffled chutes are designed to dissipate the energy of flow in irrigation systems, wastewater systems and stormwater systems. Staggered baffle blocks placed in a chute channel not only dissipate the energy of the water but also allow free oxygen transition between the water–air surface by means of hydraulic jumps. While water flows over, between and around the blocks, air bubbles are entrained into the water. The entrained air bubbles in the flow start to dissolve within the chute and the DO concentration in the water thus increases. In this study, the amount of DO was determined for baffle blocks with six different geometric shapes, different flow discharges and angle variations (10° ≤ α ≤ 56°). The oxygen transfer efficiency of the new baffle blocks designed in this study was found to be very effective. Different block types were found to have greater oxygen transfer efficiency for chutes with different slopes.

THE EFFECTIVENESS NUMBER OF BAFFLE BLOCKS TO REDUCE ENERGY IN TUKUTAHA TRANSITION CHANNELS

One of the causes of damage to the weir structure is scouring. Scouring may occur along the weir channel. Scouring occurs due to the high flow velocity and high specific energy. One of the methods used to reduce specific velocity and energy is by installing baffle blocks in parts that have high-velocity and energy. The addition of baffle blocks is carried out at a place that has a high-velocity, namely the transition channel. To see the effect of baffle block variation on velocity and energy, a study was conducted. The study was conducted with four baffle block type models. The type 0 model is a baffle block installation pattern based on the initial design. Type 1 model is designed based on the planning of The Colorado State University (CSU) rigid boundary basin. Type 2 model is designed by reducing the number of baffle blocks from the initial design of 102 baffles to as many as 75 baffles. while the 3 channel type model transitions without baffle blocks. Based on the analysis of % energy loss in the transition channel, the type 0 model produces the largest energy loss. The type 0 model at maximum discharge has a % energy loss 10.821% greater than the type 1 model, 14.889% greater than the type 2 model and 33.02 % greater than the type 3 model.

The application of baffle block in mitigating TDGS of dams with different discharge patterns

Total dissolved gas supersaturation (TDGS) caused by high-dam discharge leads to gas-bubble trauma or even death in fish and has become an active research area because of global concern regarding this issue. It is important to use engineering measures to reduce the TDGS level to protect the fish habitat and water environment. As there are different mechanisms for TDGS generation by discharge, the application of mitigation measures needs to be investigated. In this study, three dams in which bottom flow, surface flow and trajectory jet used for energy dissipation were simulated to analyze the characteristics of TDGS generation and distribution. The simulated results show that the generation and distribution of TDGS is affected by bubble-water mass transfer. Consequently, a mitigation measure in which baffle blocks installed downstream of the spillway was proposed to change transport bubbles to low-pressure regions. The simulated results showed this engineering measure reduced TDGS by 5.2% and 13.1% for dams with bottom flow and trajectory jet, respectively. This study serves as a reference for the characteristics of TDGS generation and the design of TDGS mitigation measures.

Experimental study of parametric influence on heat transfer and friction in a rectangular duct having V-down baffle blocks with staggered racetrack-shaped openings

ABSTRACT This paper presents the detailed study of parameter’s effect on Nusselt number (Nu), friction factor (f), and thermohydraulic performance parameter (η) of a rectangular duct through experiments using 45° V-down baffle blocks with staggered racetrack-shaped perforation geometry. The parameters investigated are the relative roughness height (e/H), relative pitch (p/e), and flow Reynolds number (Re). The results show that the secondary air jets issuing through racetrack-shaped perforations of baffle blocks with staggered holes strongly affect the duct’s flow pattern. The Nusselt number values show ups and downtrend with variation in the relative pitch and relative roughness height of the baffle blocks at all Reynolds number. The friction factor decreases with increased spacings but with variations up to a p/e value of 6 for different e/H of baffle blocks. The baffle block having e/H of 0.7 at p/e of 2 shows a maximum 456% rise in Nusselt number and an increase of 39 times in friction factor over the smooth duct. Baffle blocks having e/H of 0.5 and p/e of 4 obtain a 100% rise in thermohydraulic performance parameter value than the value for e/H of 0.6.

Flow Characteristics of Stilling Basin, Case Study: Karian Dam, Central Java Province

The hydraulic jump is a process is to reduce most of the energy that occurs in spillway. It can also raises the water level in the lower reaches. A very large energy flow that must be reduced so as not to endanger the end of the dam’s overflow channel. The dissipation structure, such as stilling basin at the end of the spillway, plays a role in reducing kinetic energy flow before the flow enters the river. This paper aims to analyse the effect of the baffle block along with the layout of the stilling bed. The experiment was comparing the stilling basin without and with a baffle block, where hydraulic jump intently occurs with variation of flow rate from Q50 to QPMF. This research results that stilling basin with baffle block with a bucket angle of 23.33°has the most effective variation among the others compared to Lj and Hj values. Lj/H1 and H2/H1 has linear relationship with Froude Number (Fr), which is the higher discharge rate, the higher Lj/H1, H2/H1 and Fr value they obtain.

Efficiencies assessment of an indoor designed solar air heater characterized by V baffle blocks having staggered racetrack-shaped perforation geometry

The outcome of an experimental study carried to maximize the thermal efficiency of a rectangular section solar air heater duct having V-baffle blocks with staggered racetrack-shaped openings are presented in this paper. The investigation encompasses the methodology to determine first the baffle blocks' optimum parameters yielding the thermohydraulic performance factor (η) value greater than unity and then finalizing the 'best optimum parameters' that maximize the duct's thermal (ηth) and effective (ηeff) efficiencies. The thermal and fluid flow characteristics are studied under a constant heat flux at the duct's top wall for turbulent airflow condition. The effect of relative roughness height (e ⁄H) ranging from 0.4 to 0.7, relative pitch (p ⁄e) ranging from 2 to 10 and Reynolds number (Re) ranging from 5000 to 15000 are investigated on 45° V-baffle blocks with apex pointing both in downstream and upstream directions. The result shows that the air jets issuing through racetrack openings intensify the turbulence in the wake of baffle blocks leading to a substantial rise in Nusselt number (Nu) and friction factor (f) relative to smooth duct. The V-down baffle blocks obtain the maximum enhancement of Nusselt number and friction factor over the smooth duct with range 1.358 to 4.559 and 4.03 to 39.07, respectively. The V-down baffle blocks' parameters, e/H of 0.5, p/e of 4 and Re of 13021, provides a maximum value of thermohydraulic performance factor as 1.435. V-up baffle block with e/H of 0.7, p/e of 6 at Re of 12,322 reports the highest thermal and effective efficiencies values as 96.6% and 91.8%, respectively.

Influence of A Fully Angle Baffled Floor on Scour behind A Hydraulic Structure.(Dept.C)

Baffle blocks are used to dissipate the energy of water flow, which pass under gales or over weirs. In this paper, a fully angle baffled apron of a heading-up structure is experimentally studied. Two arrangements are considered. Baffle's height, flow discharge, and downstream water depth are the considered variables. Obtained results from eighty-one runs are graphically represented to illustrate the effect of the suggested systems. The suggested systems are easy to be added to the existed structures without changing their floors. Present results are compared with previous ones for single and double lines of angle baffles.

Laboratory study of stilling basin using trapezoidal bed elements

When designing dam spillway structures, the most significant consideration is the energy dissipation arrangements. Different varieties of baffle blocks and stilling basins have been used in this context. However, the hydraulic jump form of stilling basin is considered to be the most suitable. The main objective of this research was to introduce four different baffle block shapes (models arranged from A to D, installed at slopes 0.00, 0.04, 0.06 and 0.08 in the stilling basins). To illustrate the consequences for the qualities of pressure-driven bounce, each model was attempted in the bowl. The trials applied Froude numbers between 6.5 and 9.2. The puzzle square model D provided the best outcomes compared to the models A, B, C and smooth. Model D with different models at inclines 0.00, 0.04, 0.06 and 0.08 was used to consider the impacts of perplex hinders on water driven-bounce when bed slants were changed. When the model D baffle used instead of a smooth bed at 0.08 slope, the reduction in y2 / y1 reached 12.8%, and Lj / y1 was 18.9%. Among the different bed slopes, a normal decrease in y2 / y1 ranged from approximately 10.3%, whereas the normal decrease in Lj / y1 was about 13.8% when the model D baffle was used instead of the model A baffle with a horizontal slope bed of 0.00. The results show that the new shapes led to a decrease in sequent profundity proportion and length of jump proportion; however, the energy dissipation proportion increased.