3-D OPTIMUM ANALYSIS OF THE ENERGY DISSIPATING STRUCTURES IN SITILLING BASIN OF WEIRS BY USING COMPUTATIONAL FLUID DYNAMICS
SABİT BAĞLAMA DÜŞÜ YATAĞINDAKİ ENERJİ KIRICI YAPILARIN 3-D HESAPLAMALI AKIŞKANLAR DİNAMİĞİ İLE OPTİMUM ANALİZİ
Imran Sajid
Akdeniz University, Institute of Science, Antalya, Turkey
Kenan Büyüktaş*
Akdeniz University, Faculty of Agriculture, Department of Farm Structures and Irrigation, Antalya, Turkey
Ahmet Tezcan
Akdeniz University, Faculty of Agriculture, Department of Farm Structures and Irrigation, Antalya, Turkey
* Corresponding author: [email protected], +90 242 310 2489
Geliş Tarihi / Received: 15.10.2020 Kabul Tarihi / Accepted: 09.12.2020
Araştırma Makalesi/Research Article DOI: 10.38065/euroasiaorg.276
ABSTRACT
In this study, by using the Computational Fluid Dynamics Method (CFD), it was aimed to analyze the 5 different models of different positions of the energy dissipating structures planned in sipilling basin, according to the velocity and pressure of the water flowing from over a fixed weir body. Then, 4 different models which are created in the computer with real data of Type II model selected as Reference Model (Model 1) were compared. Model 2 has neither chut blocks nor energy dissipation blocks but has just end sill. Model 3 has a row chut block and end sill at the end of the stilling basin but has not got energy dissipation blocks. Model 4 has a row of energy dissipation blocks and end sill in the stilling basin but have not got chut blocks. Model 5 has a row chut block two row energy dissipating blocks in the stilling basin and end sill continuing along the body length at the end of the stilling basin. Different models were analyzed by using the Volume of Fluid (VOF) model in Ansys software. Then, flow patterns were created by determining the pressures, velocities and jump situations applied to energy dissipating blocks placed at different distances to the sipilling basin of the water flowing from over a fixed weir body. Thus, it has been attempted to determine the optimum model which is flow energy can dissipate the maximum among differently designed models. As a result of the simulation, Model 5 was found the optimum or best one among these five different models according to flow characteristics, in addition, the simulation’s output data obtained by Ansys Fluent matches with our Reference Model’s real data.
Keywords: Ansys-Fluent, energy dissipating structure, simulation, stilling basin.
ÖZET
Bu çalışmada, Hesaplamalı Akışkanlar Dinamiği Metodu (CFD) kullanılarak, sabit bir bağlama gövdesi üzerinden akan suyun hızına ve basıncına göre düşü yatağında planlanan enerji kırıcı yapıların farklı konumlandırılmış 5 farklı modelinin incelenmesi amaçlanmıştır. Daha sonra Referans Model (Model 1) olarak seçilen Tip II modelin gerçek akış verileri ile bilgisayarda oluşturulan 4 farklı modelin verileri karşılaştırılmıştır. Model 2'de ne şüt blokları ne de enerji kırıcı blokları vardır, ancak sadece düşü yatağının sonunda eşik vardır. Model 3’te, düşü yatağının başında bir sıra şüt bloğu ve düşü yatağının sonunda ise bir vardır, ancak enerji kırıcı blokları yoktur. Model 4’de, düşü yatağında bir sıra enerji kırıcı bloklar ve eşik vardır, ancak şut blokları yoktur. Model 5’de, düşü yatağının başında bir sıra şüt bloğu, iki sıra enerji kırıcı bloklar ve düşü yatağının sonunda gövde uzunluğu boyunca devam eden eşik vardır. Ansys yazılımında Akışkan Hacmi (VOF) modeli kullanılarak farklı modeller analiz edilmiştir. Daha sonra sabit bir bağlama
gövdesi üzerinden akan suyun düşü yatağına farklı mesafelerde yerleştirilen enerji kırıcı bloklara uygulanan basınç, hız ve sıçrama durumları belirlenerek akış modelleri oluşturulmuştur. Böylelikle, farklı tasarlanmış modeller arasında maksimum kırılabilen akış enerjisi olan optimum model belirlenmeye çalışılmıştır. Simülasyon sonucunda Model 5, akış özelliklerine göre bu beş farklı modelden optimum veya en iyisi olarak bulundu. Ayrıca Ansys Fluent tarafından elde edilen simülasyon çıktı verileri Referans Modelin gerçek verileriyle eşleşmiştir.
Anahtar Kelimeler: Ansys-Fluent, enerji kırıcı yapı, simülasyon, düşü yatağı. 1. INTRODUCTION
Weirs are fixed or movement structures that only cover to stream bed rather than water accumulate, that raise the water level, changes of flow direction, and take water as needed from the desired level. Fixed weirs are generally made with concrete or reinforced concrete and the water flow over from the body of weirs as similar to dam spillways. The high velocity and pressure of water flow over from the body of weirs cause abrasion or erosion of the stilling basin and stream bed in downstream. Thus, the stilling basin of weirs and its structures such as energy dissipators, chute blocks, and end sills which is made on stilling basin was very important in weirs planning (SHW 2012; Erkek and Ağıralioğlu 2013).
Energy dissipating structures are built in different sections such as stilling basin, damping basin etc. in order to prevent damage to the structure and the surrounding construction by breaking the energy of water flowing at a high velocity in a water structure. The flow energy is broken by these structures during the hydraulic jump that occurs when the flow passes from the flood regime to the river regime (SHW 2012; Erkek and Ağıralioğlu 2013).
When planning energy dissipating structures, some factors such as water flow, water surface profile, water depth in downstream, and stilling basin length should be taken into account (Aküzüm ve Öztürk 1996).
Analysis of behavior and hydraulic characteristics of flow over the dam spillway is a complicated task that takes lots of money and time in water engineering planning. To model, those hydraulic characteristics can be used several methods such as physical and numerical methods (Parsaie et al., 2015).
Recently, with advances in the field of computational fluid dynamics (CFD), a study on hydraulic characteristics of this structure with these techniques has been done (Chatila ve Tabbara 2004; Zhenwei et al., 2012))
In general, CFD is a method used to analyze all kinds of fluids and flows in different conditions. In this method, basically, three main equations (continuity, momentum, and energy equations) are taken as a basis and it is reached to pressure, velocity, temperature distribution, and many data depending on these parameters by solving these equations numerically (Ferziger and Peric, 2002). Chatila and Tabbara (2004), modeled as three dimensions of the Ogée-profiled spillway using the k-ε model in their studies and compared the x and y coordinates of the surface water with values obtained from the model. With this study, they determined the characteristic features of free surface flows. They observed close agreement with measured and numerical free surface profiles.
Nguyen and Nestmann (2004), have examined velocity, and turbulence status of the Rhine river with 1320 km length, which is one of the major rivers of Europe by using the K-ε model and VOF method according to water depth in a different distance of river.
Aydin et al. (2005), created models in Fluent software with three-dimensional analysis application in Kars Dam spillway and compared the spillway data with the hydraulic model obtained data. In the study done, they have seen that the results were close to each other. They also found that the
distribution of turbulence density on the surface of the water and the pressure distribution at the bottom of the channel was easily seen.
Tabbara et al. (2005), simulated flow over the stepped spillway in different cases by using ADINA. They predicted water surface profiles over the entire length of the spillway in close agreement with experimental results.
Kaya (2007), investigate of the energy dissipation rates of two-row energy dissipating blocks in stilling basin at laboratory study, he planned the distance opening is 0.04m and the sum of the energy dissipating block widths is to be 40-55% of the channel width and he changed the Froude number between 2.5 and 4.5 and the upstream water level between 0.10 and 0.26m. In the working result, it has been found that the best results were obtained when the distance between the two rows is as large as the block width.
Dursun and Öztürk (2009), in the study named the numerical analysis of damping ability of the flow energy of stepped spillways, they have used the CFD method to determine energy damping rates for different discharge canal base slopes. The results obtained at the end of the study were compared with the results of the experimental studies and they stated that the numerical analysis results are very close to the results obtained with experimental studies. They reported that 70-80% more energy damping in this type of spillways than classical spillways.
In this study, by using the Computational Fluid Dynamics Method (CFD), it was aimed to analyze the different placements of energy dissipating structures in a stilling basin of a fixed weir according to flow characteristic of water flows over this weir. For this, by using AutoCAD, Solid Works, and Ansys programs, fixed weir, stilling basin with different energy dissipating structures such as chute blocks, baffle blocks, and end sill was drawn in the computer environment. Then, flow patterns such as pressures, velocities, and hydraulic jumps applied of the water flow from weir body to energy dissipating structures placed at different distances and locations in the stilling basin were analyzed by the VOF model (Volume of Fluid) in Ansys Fluent Solution. Thus, it was determined the optimum model in which the energy of water dissipated the most among differently designed models.
2. MATERIAL AND METHOD 2.1. Material
In this study, weir stilling basins with different cross-sections were drawn in the computer, and energy dissipating structures were planned at different distances according to the hydraulic jump that will form in the stilling basin of the energy of the water flowing over the body. In the computer, for drawing shapes of a Reference Model and fixed weirs and their stilling basin which have 5 different cross-sections AutoCAD, Solidworks, Gambit, and ANSYS software were used. In addition, ANSYS-Fluent software is used for making the simulations for the created models. The defining to dam and spillway projecting software of General Directorate of State Hydraulic Works (pro-SHW) and “American Federal Highway Administration, Hydraulic Design of Energy Dissipators for Culverts and Channels, Hydraulic Engineering Circular (AFHA)” book that was obtained of the calculation results of Reference Model (Model 1) was used to compare of simulation results.
The Reference model structure’s (Model 1) all related dimensions and design values have been taken from AFHA. Also for the design of weirs and small dams pro-SHW used to calculate the Reference Model’s dimensions of energy dissipating structures and flow characteristics in the stilling basin that gives the same values as the book.
In the study, 5 different models were created as materials on the computer environment using AutoCAD and Solidworks software. Model 1 is the commonly preferred section by SHW and AFHA. This model which was selected as the reference model during the simulation has one-row
chut blocks after the body, one-row energy dissipating blocks in the middle of the stilling basin, and end sill continuing along the body length (Figure 1). The actual design calculation values and design parameters of the section selected as Reference Model in the study were given in Table 1 and Figure 1.
Table 1. The actual design calculation values of section selected as reference model (Model 1)
Parameters Values and units Parameters Values and units
Initial height from datum line Z0 = 30.5 m Water height at crest of weir h0 = 0.46 m Chut block height from datum
line Z1 = 26.7 m
Water height just before chut
blocks h1 = 0.322 m
End sill height from datum line Z2 = 26.7 m Height of hydraulic jump h2 = 2.98 m Height of downstream from
datum line Z3 = 29.15 m Water height of downstream h3 = 0.57 m
Flow Q = 11.8 m3 s-1 Height of chut block d1 = 0.32 m
Width of stilling basin B = 3.0 m Height of energy dissipating
blocks d2 = 0.56 m
Total length of stilling basin L = 20.5 m Height of end sill d3 = 0.45 m Initial flow velocity V0 =8.5 m s-1
Number of energy dissipating
blocks NB = 4.0
Flow velocity before energy
dissipating blocks V1 =12.2 m s
-1 Number of chut blocks N
C = 5.0 Flow velocity after end sill V2 =4.8 m s-1 Width of chut blocks W1 = 0.30 m
Froude number Fr = 6.9 Distance between chut block W2 = 0.30 m
Gravitational acceleration g = 9.81 m.s-2 Width of energy dissipating
blocks W3 = 0.38 m
Distance between energy
dissipating block W4 = 0.38 m LT =7.6 m LS = 4.9m 𝐹r1= 𝑉1 �g ∗ y1= 12.2 √9.81 ∗ 0.32= 6.9 LB / h2 = 2.7 LB = 2.7 * 2.98 m = 8m L= LT + LS + LB L= 20.5 m
Number of chut blocks 𝑁𝑐= 𝐵
2 ∗ 𝑑1=
3
2 ∗ 0.32 = 5 𝑝𝑖𝑒𝑐𝑒𝑠 Width and distance of chut blocks 𝑊1= 𝑊2= 𝐵
2 ∗ 𝑁𝑐=
3
2 ∗ 5 = 0.3 𝑚
Number of energy disipating blocks 𝑁𝐵= 𝐵
1.5 ∗ 𝑑2=
3
1.5 ∗ 0.56 = 4 𝑝𝑖𝑒𝑐𝑒𝑠 Width and distance of energy disipating block 𝑊3= 𝑊4= 𝐵
2 ∗ 𝑁𝐵 =
3
2 ∗ 4 = 0.38 𝑚
Figure 1. The actual designe parameters and values of the section selected as reference model (Model 1)
Model 2 is the model that has neither chut blocks nor energy dissipation blocks but it has just end sill. Model 3 is the model that has a row chut block and end sill at the end of the stilling basin but has not got energy dissipation blocks. Model 4 is the model that has a row of energy dissipation blocks and end sill in the stilling basin but have not got chut blocks. Model 5 is the model that has a row chut block, two-row energy dissipating blocks in the stilling basin, and end sill continuing along the body length at the end of the stilling basin (Figure 2).
a) Model 1 (Reference Model)
b) Model 2
c) Model 3
d) Model 4
e) Model 5
The screenshot of software (pro-SHW) used by SHW for the design of the weir is shown in Figure 3.
Figure 3. Pro-SHW software used by SHW
2.2. Method
In this study, weir stilling basins with different cross-sections were drawn in the computer, and energy dissipating structures were planned at different distances according to the hydraulic jump that will form in the stilling basin of the energy of the water flowing over the body. In the computer, for drawing shapes of a Reference Model and fixed weirs and their stilling basin which have 5 different cross-sections AutoCAD, Solidworks, Gambit, and ANSYS software were used. In addition, ANSYS-Fluent software is used for making the simulations for the created models. The defining to dam and spillway projecting software of General Directorate of State Hydraulic Works (pro-SHW) and “American Federal Highway Administration, Hydraulic Design of Energy Dissipators for Culverts and Channels, Hydraulic Engineering Circular (AFHA)” book that was obtained of the calculation results of Reference Model (Model 1) was used to compare of simulation results.
Then, flow characteristics such as velocity, depth, and total pressure of the Reference Model were compared with the simulation values obtained using the ANSYS-Fluent software. Model 1 used AFHA and SHW as Reference Model (Model 1) and then the values obtained after simulation were compared with the design values of Model 1. In addition, the Reference Model was also calculated by the software used by the SHW, and the results obtained were compared with the simulation model. Thus, it has been attempted to determine the cross-section that dissipates most of the energy between the different models designed. Design stages of the model contain steps such as the creation of model geometry, meshing, and determination of boundary conditions, determination of solution parameters, and the creation of flow patterns (Özdem,. 2007; Anonymus, 2013).
Gambit and Ansys software were used in creating of the geometry of the Reference Model as 3 dimensional. Since Ansys Fluent software accepts the analyzed area for flow characteristics as a
close object, therefore, the analyzed area where we want to analyze flow characteristic while passing the energy dissipating blocks are drawn as a close object.
In order to make simulations of the numerical models in the study and to get the closest results to the truth, a mesh (grid) was applied during the simulation for each model. Because the number of mesh to be defined directly affects the accuracy of the analysis to be made. Defining a large number of meshes increases the CPU time while increasing the accuracy of the analyzes, also. In this study, the 4 models created with Gambit software after defined to Ansys software were meshed between 1000000 and 1400000 according to a model by Finite Element Method (FEM) with varying (Figure 4). These values are the highest value determined according to the performance of the computer in which the analyzes are made.
After meshing, boundary conditions were determined to the software. The base of the stilling basin, both sidewalls, and the surface of the end sill were defined as Wall 1, Wall 2, and Wall 3 respectively. Also inlet from where water enters to this object and outlet where water leaves from the object were determined, moreover the upper surface of the object that is in touch with the atmosphere is determined as ambient in the software (Figure 5).
Figure 4. Meshing of Reference Model Figure 5. Boundray condition determination
For the determination of solution parameters, simulations were started with V=8.5 m.s-1 flow velocity and with h=0.46 m water height for all models. Entering different solution parameters such as that the gravitational acceleration is g = 9.81 m.s-2 and the density of ambient air mass is ρ = 1.225 kg.m-3 and roughness for concrete surfaces was taken as ks=0.001 m were defined to Fluent software.
Fluent is one of the most popular and suitable software of CFD that provides a wide range of advanced physical models for fluid flow and heat transfer including multiphase flow. It can exchange 2D and 3D dominant differential equations to algebraic equations by using the finite volume method. This software uses the volume of fluid (VOF) model to determine the free surface of the flow (Alhashimi, 2013).
Hirt and Nichols (1981) recommend that the Volume of Fluid model (VOF). That to determine the common surface of two fluid phases has been considered in many hydro-dynamic issues. Also, free-surface flow is very important in the hydraulic phenomena in the solution of the flow field. Various methods are used in determining the free surface, which is different relative to the prevailing view of solving the flow field.
In the VOF method, for each, a component volume of the cell is solved a differential equation, which ultimately amounts to a component volume of fluid is determined in each cell. In the flow field with the fixed network, is determined free surface based on the view O'Leary toward flow. Equations formulation are the basis on fluid volume models (VOF), based on the fact that two or more fluid phases that together they are not mixed. The purpose of this model is to find, the interface between phases in different parts of the domain. Although the basis of this theoretical model, is polyphase flows,, VOF model is not a polyphase model. For example, in the case of two-phase gas (air) and water, a series of momentum equations between the two two-phases is to be shared.
For each fluid phase is added to the model, in fact, one variable, into the solving process and this variable is the component volume of fluid in each of the calculated cells so that the sum volume of the fluid component in a cell is equal to the unit. In the case of two phases water and air component volume of fluid water or air can be considered as an added variable (Rassaei and Rahbar, 2014). Determining of solution parameters: Three-dimensional (3D) time-varying (unsteady) solution model which is the VOF model was chosen as models to Fluent. In the model, the first two phases were taken as water and air, respectively. The physical properties of these two phases were identified to Fluent software. In the VOF model, the k-ε turbulence model was used (Özdem, 2007; Anonymus 2013).
Launder and Spalding (1974) [18] proposed the standard k - ε model that was a semi-empirical model based on the model transport equations of the turbulent kinetic energy (k) and its dissipation rate (ε). 𝜕 𝜕𝑡(𝜌𝑘) + 𝜕𝑘 𝜕𝑥𝑖(𝜌𝑘𝑢𝑖) = 𝜕 𝜕𝑥𝑗��𝜇 + 𝜇𝑡 𝜎𝑘� 𝜕𝑘 𝜕𝑥𝑖� + 𝐺𝑘− 𝜌𝜀 𝜕 𝜕𝑡(𝜌𝜀) + 𝜕𝑘 𝜕𝑥𝑖(𝜌𝜀𝑢𝑖) = 𝜕 𝜕𝑥𝑗��𝜇 + 𝜇𝑡 𝜎𝜀� 𝜕𝜀 𝜕𝑥𝑖� + 𝑐𝜀1 𝜀 𝑘 𝐺𝑘− 𝑐𝜀2𝜌 𝜀2 𝑘 The eddy viscosity µt is written as follows:
𝜇𝑡 = 𝜌𝑐𝜇𝑘 2 𝜀
σkand σε are turbulence Prandtl numbers for k and ε respectively. The model constants as:
Cµ Cε1 Cε2 σk σε
0.09 1.44 1.92 1.00 1.30
A spillway model requires the presence of a free surface, representing the air-water interface. The VOF model is such an approach for accurately tracking the interface between immiscible liquids (Alhashimi, 2013).
The most suitable combination was determined by looking at significance levels between measured and simulated values. It was used in Equation 1 to determine the significance level between values [19]. The CRM is a measure of the tendency of the model to overestimate or underestimate the measurements. Positive values for CRM indicate that the model underestimates the measurements and negative values for CRM indicate a tendency to overestimate. For a perfect fit between observed and simulated data, values of CRM should equal 0 (Hagi-Bishow. and Bonnell,. 2000). Coefficient of Residual Mass (CRM),
Coefficient of Residual Mass (CRM), 𝐶𝑅𝑀 =∑𝑛𝑖=1∑𝑂𝑖− ∑𝑂𝑛𝑖=1𝑃𝑖
𝑖 𝑛
𝑖=1 ∗ 100
Eq.1
where Oi represent observed values, Pi is predicted values and n is number of samples.
3. RESULT AND DISCUSSION
3.1. Findings Related with Reference Model (Model 1)
The locations of levels of energy chut blocks, energy dissipating blocks and end sill in which were given belong to Model 1 cross-section which selected as a reference model in Figure 6.
Figure 6. The location of Model 1 selected as reference model.
In the study, the water velocity as V = 8.5 m.s-1 was started from x = 0, y = 3.8m and z = 1.5m coordinates. As can be seen from Fgure 6, after simulations, measurements have been taking from three different coordinates or positions of Model 1, while in four other models, measurements have been taken just before the chut blocks (x = 7m, y = 0.3m and z = 1.5m) and after end sill (x = 20.5m, y = 2.4m and z = 1.5m).
The geometry of the stilling basin of AFHA suggested and the section which was determined by SHW software was taken and compared with Model 1 as the reference model selected. Thus, the velocity values obtained from the simulation were compared with the calculated velocity values. In the following figures (Fig. 7 - Fig. 10) the variation of the velocity and water depth values obtained by the ANSYS-Fluent software at the same points was shown.
Figure 7. Changing of velocity values measured at 0th
coordinate with water height for Reference Model
Figure 8. Changing of velocity values measured at 7th coordinate with water height for Reference Model
Figure 9. Changing of velocity values measured at 20.5th
coordinate with water height for Reference Model
Figure 10. Changing of velocity values measured of
In the model calculations, the values of weir body height, water height, and water velocity in specific levels were calculated as below. In the 0th m coordinate (starting point), the body height of weir is 3.8m, the water height d=0.46m (d=0.46+3.8=4.2 m), the water velocity V= 8.5 m.s-1 (Figure 7). In the 7th m coordinate (just before chut blocks), the weir body height is 0.3m, the water height d=0.322m (d=0.3+0.322=0.622 m), the water velocity V= 11.8m.s-1 (Figure 8). In 20.5th m coordinate (after end sill), at 0 + 20.5 levels, the weir body height is 2.45m, the water height d=0.57m (d=0.57+2.45=3.02), the water velocity V=4.4 m.s-1 (Figure 9).
When Figure 10, which shows the variation of the measured velocity values of Reference Model with the body length is examined, it is seen that as the length of the weir body increases, the water velocity decreases and especially after the energy dissipating block the velocity decreases a lot. As will be understood from the figure, the water velocity decreases a little in the chut block which is located at 7.5 m of the stilling basin, and the water velocity decrease greatly after energy dissipating blocks located at the length of the 10th meter of the body.
Water flow pattern, changing of velocity values and velocity pattern belong to Reference Model were given Figure 11-12.
Figure 11. Water flow pattern belong to Reference
Model
Figure 12. Water velocity pattern belong to
Reference Model
Figure 11 shows the water flow, water presence, and hydraulic jump for Reference Model. The flow pattern varies from 0 to 1 and from blue to red. The red color shows the value of 1, which means full water presence, and other colors that have less than one value show that a decrease in water and occurs a jumping. The red color also gives an idea of water flow and water depth at each point throughout the section. Accordingly, when Figure 11 is examined, it is seen that the flow and water height did not change until the energy dissipating block, but after the energy dissipating blocks hydraulic jumps occurred so that the depth of water increased greatly and accordingly the water velocity decreased.
Figure 12 shows the changing of water velocity throughout the section of the body for the Reference Model. The water velocity varies from 0 to 12 m.s-1 and from blue to red. When Figure 13 is examined, it is seen that the water velocity has different values throughout the section. It is seen that velocity is increasing in places where it gets red color, and flow velocity is decreasing in places where it gets blue color. Especially after the energy dissipating blocks, the color changed from red to yellow, green, and blue, so this shows that there is a large decrease in the flow rate of the water.
Simulation values obtained from the Fluent software and calculated values that obtained from the calculation of AFHA and SHW were given in Table 2.
Table 2. Comparison of the simulation values obtained from the Fluent software with calculated values of AFHA and SHW. Points/coordinates taken measurements according to starting point d (m) Water height Velocity, V (m.s-1) Values of AFHA and SHW
Velocity, V (m.s-1) Values of simulation CRM 0 0.46 8.5 8.4 0.012 7 0.32 12.2 11.8 0.033 20.5 0.57 4.8 4.4 0.083
When Table 2 is examined, it was observed that the values obtained from SHW's spillway calculations with values obtained by simulation for the same coordinates were very close to each other. This shows that the closest result to real conditions can be achieved with the Fluent software which is a CFD method instead of modeling which takes a lot of time at the laboratory condition. So, other models used in this study were just designed and simulated.
3.2. Findings related with other Models
The flow pattern and velocity patterns belong to Model 2, Model 3, Model 4, and Model 5 were given in Figure 13-20. Figure 13 shows the water flow and Figure 14 shows the changing of water velocity during the section of the weir body for Model 2.
Figure 13. Water flow pattern belong to Model 2. Figure 14. Water velocity pattern belong to Model 2.
Figure 13 shows the water flow, water presence, and hydraulic jump for Model 2. The flow pattern varies from 0 to 1 and from blue to red. The red color shows the value of 1, which means full water presence and other colors that have less than one value shows that the decrease in water and occurs a jumping. When Figure 13 is analyzed, it can be seen that the flow of water and its depth does not change until the end sill but after the end sill, it appears that there is very little splash and therefore the depth of the water is slightly increased.
Figure 14 shows of water velocity throughout the section of the stilling basin for Model 2. The water velocity varies from 0 to 12 m.s-1 and from blue to red. When Figure 14 is analyzed, it is seen that the water velocity increases on inclined surfaces throughout the section and then does not change much until the end sill. While initially, the water velocity was 8.5 m.s-1, it reached 11.8 m.s-1 at the beginning of the stilling basin and fell below 8 m.s-1 after the end sill.
Figure 15 shows the water flow and Figure 16 shows changing of water velocity throughout the section of the stilling basin for Model 3.
Figure 15. Water flow pattern belong to Model 3. Figure 16. Water velocity pattern belong to Model 3.
Accordingly, when Figure 15 is analyzed, it can be seen that the flow of water does not change until shut blocks and there is no splash. While the water flow remains the same between the chut blocks and end sill it appears that water depth increases and as the water flow changes after the end sill. Figure 16 shows that the water velocity increases on inclined surfaces through section than decreases after chut bloks and then decreases much more after end sill. While initially, the water velocity was 8.5 m.s-1, it reached 11.8 m.s-1 at the beginning of the stilling basin and fell below 7 m.s-1 after the end sill.
Figure 17 shows the water flow and Figure 18 shows changing of water velocity through the section of the sitilling basin for Model 4.
Figure 17. Water flow pattern belong to Model 4. Figure 18. Water velocity pattern belong to Model 4.
When Figure 17 is examined, it can be seen that the flow of water does not change until energy dissipating blocks and there is no splash. But, because of occurring a big hydraulic jumping at energy dissipating blocks, it is seen that the water flow changes and water depth increases.
In Figure 18, it is seen that the water velocity increases on inclined surfaces until energy dissipating blocks than the water flow decrease dramatically because of occurring hydraulic jump and then, decreases much more after the end sill. While initially, the water velocity was 8.5 m.s-1, it reached 11.8 m.s-1 at the beginning of the stilling basin and fell below 7 m.s-1 after energy dissipating blocks, and then this value occurred it is below 6 m.s-1 after end sill.
Figure 19 shows the water flow and Figure 20 shows changing of water velocity throughout the section of the stilling basin for Model 5.
Figure 19. Water flow pattern belong to Model 5. Figure 20. Water velocity pattern belong to Model 5.
Accordingly, when Figure 19 is analyzed, it can be seen that the flow of water does not change until chut blocks and there is no jump. But because of occurring a hydraulic jump at 1-row energy dissipating blocks, it is seen that the water flow changes and as an increase of water depth. At the same shape, because of occurring a hydraulic jump again at 2-row energy dissipating blocks, it is seen that the water flow changes again and as increasingly more of water depth until the end sill. Figure 20 shows that the water velocity increases on inclined surfaces until energy dissipating blocks than the water flow decrease dramatically because of occurring hydraulic jump after energy dissipating blocks and then, decreases much more after the end sill. While initially, the water velocity was 8.5 m.s-1, it reached 11.8 m.s-1 at the beginning of the stilling basin. However, as the velocity of water decreases after chut blocks, and it has been observed that it continues by decreasing until the end sill. In addition, this value fell below 3 m.s-1 after energy dissipating blocks and end sill.
As a result of the simulation analysis, the comparisons of velocity and energy values before energy dissipating blocks with velocity and energy values after end sill belongs to all applied models were given in Table 3. In addition, the energy damping rates belong to Models and the velocity values after the end sill of the models were also given in Figure 21 and Figure 22.
Table 3. The flow velocity and energy comparisons of models
Model No Water height before chut blocks h1(m)
Water velocity just before chut blocks
V1(m/s)
Water height after end sill
h2(m) Water velocity after end sill V2(m/s) (V1 2 /2g)+h1 Amount of Energy E1(m) (V2 2 /2g)+h2 Amount of Energy E2(m) (E1 -E2)/E1 Model 1 0.3 11.8 0.57 4.4 7.40 1.56 0.79 Model 2 0.3 11.8 0.57 7.8 7.40 3.67 0.50 Model 3 0.3 11.8 0.57 6.8 7.40 2.93 0.60 Model 4 0.3 11.8 0.57 5.5 7.40 2.11 0.71 Model 5 0.3 11.8 0.57 2.4 7.40 0.86 0.88
Figure 21. The water velocity values after end sill of the
models
Figure 22. The energy damping rates belong to Models.
0 1 2 3 4 5 6 7 8 9 10
Model 1 Model 2 Model 3 Model 4 Model 5
F lo w v elo city ( m /s ) Applied models 0 10 20 30 40 50 60 70 80 90 100
Model 1 Model 2 Model 3 Model 4 Model 5
E ne rgy d am p ing ra te s ( % ) Applied models
When analyzed in Table 3 and Figure 21, the lowest velocity value after the end sill among the five different models was obtained from Model 5 with V2 = 2.4 m.s-1 and the highest value was obtained in Model 2 with V2 = 7.8 m.s-1. As also shown in Table 3 and Figure 22, it was determined that the highest energy damping rate was occurred in Model 5 and the lowest energy damping value was occurred in Model 2 among all Models.
Aydin (2005), created models in Fluent software with three-dimensional analysis application in Kars Dam spillway and compared the spillway data with the hydraulic model obtained data. In the study done, they have seen that the results were close to each other. They also found that the distribution of turbulence density on the surface of the water and the pressure distribution at the bottom of the channel was easily seen. As can be seen from the results of this study conducted, results were very similar between the two study.
Tabbara et al. (2005), simulated flow over the stepped spillway in different cases by using ADINA. They predicted water surface profiles over the entire length of the spillway in close agreement with experimental results.
Kaya (2003), investigate of the energy dissipation rates of two-row energy crushing blocks in energy stilling basin in a laboratory study, he planned the cover opening is 0.04m and the sum of the energy dissipating block widths is to be 40-55% of the channel width and he changed the Froude number between 2.5 and 4.5 and the upstream water level between 0.10 and 0.26m. In the working result, it has been found that the best results were obtained when the distance between the two rows is as large as the block width.
Dursun and Öztürk (2009), in the study named the numerical analysis of damping ability of the flow energy of stepped spillways, they have used the CFD method to determine energy damping rates for different discharge canal base slopes. The results obtained at the end of the study were compared with the results of the experimental studies and he stated that the numerical analysis results are very close to the results obtained with experimental studies. They reported that 70-80% more energy damping of this type of spillways than classical spillways.
Khan (2011), has reported that HAD is useful for simulating non-hydrostatic free surface flows in planning an energy dissipater structure in the event of sudden flooding into a water treatment plant. Savage and Johnson (2001), simulated flow over an ogee spillway using FLOW-3D software in 2D. The results of the numerical model including pressure on the spillway crest, water surface profile, and discharge coefficient of the spillway were in very good agreement with the experimental values.
Kaya (2003), investigate of the energy dissipation rates of two-row energy crushing blocks in energy stilling basin in a laboratory study, he planned the cover opening is 0.04m and the sum of the energy dissipating block widths is to be 40-55% of the channel width and he changed the Froude number between 2.5 and 4.5 and the upstream water level between 0.10 and 0.26m. In the working result, it has been found that the best results were obtained when the distance between the two rows is as large as the block width.
As can be seen from the literature, the results of this study are very similar to other studies. All results show that simulations and measurements were very close. This shows the accuracy of the study. However, there is no study that simulating the model we made. So, we could not compare the model results with the studies in the literature.
4. CONCLUSION
As a result of calculations and simulations made, the results which belong to the velocity distribution and energy damping rates obtained in different geometries of energy dissipating blocks in the stilling basin of 5 different models designed were given below..
The values obtained as a result of the simulation with the ANSYS-Fluent software of the drop pool and energy crusher block dimensions belonging to the Reference Model, which is a widely preferred model by SHW and American Federal Highway Administration compared with the actual values of the Reference Model (Model 1) and the results were very close to each other and the water flows were seen to have the same tendency. As the energy dissipating block geometries changed in all models, the velocity values, energy dissipating rates, and the forces coming into the blocks changed. It was determined that Model 5 is the model that reduces velocity most and the energy is the most dissipate. It was determined that the lowest energy dissipation rate occurred in the model which has not any block in the stilling basin (Model 2). The Reference Model (Model 1) was determined as the second model showing the best energy damping performance after Model 5. This study was shown that CFD can be used effectively in hydraulic models and hydraulic problems without regard to time and economic problems. It was observed that the results obtained for simulation in using Ansys-Fluent software were very satisfactory. With a large number of simulations to be carried out at different flow conditions over the water structures body or dam spillway, it can be determined the locations and sections of energy dissipating blocks or the dimensions of the stilling basin easily, so it can be earned economic and labor power during the application of the water constructions.
ACKNOWLEDGEMENTS
This research was supported by the Scientific Research Projects Unit of the Akdeniz University as with project number FYL-2016-1762. The authors would like to thank to Akdeniz University and 13th Regional Directorate of General Directorate of State Hydraulic Works for their support.
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