5

Analysis for fluid dynamics

Abstract

Various fluids such as air and liquid are used as an operating fluid in a blower, a compressor and a pump. The shape of flow channel often determines the efficiency of these machines. In this chapter, the flow structures in a diffuser and the channel with a butterfly valve are examined by using FLUENT, a computational fluid dynamics (CFD) programme of Workbench. In this chapter, two calculation examples are presented: the flow in a diffuser and the channel flow with a butterfly valve. In addition, the drawing software DesignModeler is used to draw a geometry for analysis in this chapter.

Keywords

Computational fluid dynamics; FLUENT; Workbench; Diffuser; Butterfly valve

5.1 Introduction to FLUENT

Various fluids such as air and liquid are used as an operating fluid in a blower, a compressor and a pump. The shape of flow channel often determines the efficiency of these machines. In this chapter, the flow structures in a diffuser and the channel with a butterfly valve are examined by using FLUENT, which is a computational fluid dynamics (CFD) programme of Workbench. A diffuser is usually used for increasing the static pressure by reducing the fluid velocity and the diffuser can be easily found in a centrifugal pump, as shown in Fig. 5.1.

Fig. 5.1
Fig. 5.1 Typical machines for fluid.

5.2 Analysis of flow structure in a diffuser

5.2.1 Problem description

Analyse the flow structure of an axisymmetric conical diffuser with diffuser angle 2θ = 6 degrees and expansion ratio = 4, as shown in Fig. 5.2.

Fig. 5.2
Fig. 5.2 Example 5.1, Axisymmetrical conical diffuser.

Shape of flow channel:

  • 1. Diffuser shape is axisymmetric and conical, diffuser angle 2θ = 6 degrees, expansion ratio = 4;
  • 2. Diameter of entrance of the diffuser DE = 0.2 m;
  • 3. Length of straight channel for entrance: 4.5 DE = 0.9 m;
  • 4. Length of diffuser region: 9.55 DE = 1.91 m; and
  • 5. Length of straight channel for exit: 50.0 DE = 10.0 m.
  • Operating fluid: Air (300 K)
  • Flow field: Turbulence
  • Velocity at the entrance: 20 m/s
  • Reynolds Number: 2.54 × 105 (assumed to set the diameter of diffuser entrance to a representative length)

Boundary conditions:

  1. 1. Velocities in all directions are zero on all walls.
  2. 2. Pressure is equal to zero at the exit.
  3. 3. Velocity in the y direction is zero on the x axis.

5.2.2 Create a model for analysis using Workbench

5.2.2.1 Select kind of analysis

Double-click Shortcut Workbench 17.0.

The window Unsaved Project—Workbench, Fig. 5.3, opens.

  1. 1. Drag the [A] Fluid Flow (Fluent) button into the [B] Project schematic window as shown in Fig. 5.4.
  2. 2. Save this project as diffuser by clicking [C] File.
Fig. 5.3
Fig. 5.3 Unsaved Project—Workbench window.
Fig. 5.4
Fig. 5.4 Launch Fluid Flow (Fluent) software.

5.2.2.2 Preparation for DesignModeler to create a geometry for analysis

  1. 1. Double-click [D] Geometry in the Project Schematic window. Then the Graphics window of DesignModeler opens, as shown in Fig. 5.5.
  2. 2. To change from a 3D screen to a 2D screen, place a cursor on the arrow of the z direction and then the arrow is highlighted. Click [A] the arrow in the z direction and then the screen is changed from 3D to 2D, as shown in Fig. 5.6.
  3. 3. Click the [A] Tree Outline button on the left-hand side of the Graphics window and select Schetching → Settings. Fig. 5.7 then opens.
  4. 4. Check the Show in 2D box in Grid and input 5 m to the Major Grid Spacing box. Input 10 to the Minor Steps per Major box. The Graphics window is then changed, as shown in Fig. 5.8.
Fig. 5.5
Fig. 5.5 DesignModeler window.
Fig. 5.6
Fig. 5.6 2D window of DesignModeler.
Fig. 5.7
Fig. 5.7 Sketching Toolboxes.
Fig. 5.8
Fig. 5.8 Graphics window with grids.

5.2.2.3 Create a wire frame for diffuser

To draw a diffuser for analysis, the method using the drawing software, DesignModeler, is described in this section. The dimensions of the diffuser are described in Section 5.2.1.

  1. 1. Click the Graphics window and enlarge the grid by scrolling up the scrollwheel of the mouse.
  2. 2. Select Sketching Toolboxes → Draw → Polyline (see Fig. 5.9). By using the Polyline command, the upper half of the diffuser is described with approximate dimensions because the diffuser treated in this section is axisymmetric.
  3. 3. Click Polyline and the Pencil mark appears on the Graphics window. Click the left mouse button at the approximate position of the window and move the Pencil mark to the next position to draw the shape of the diffuser. When the first quadrangle is drawn, click the right mouse button and click Open End in the context menu. The start point to draw the quadrangle in the clockwise direction is the bottom left corner. Then describe the next quadrangle and finally the approximate model is drawn as shown in Fig. 5.10.
  4. 4. Make constraints on the drawn lines by using the commands of Vertical and Horizontal in Sketching Toolboxes.
Fig. 5.9
Fig. 5.9 Draw commands in Sketching Toolboxes.
Fig. 5.10
Fig. 5.10 Wire frame drawing for a diffuser described in the window.

Click Sketching Toolboxes → Constraints → Vertical. Click four vertical lines.

Click Sketching Toolboxes → Constraints → Horizontal. Click three horizontal lines on the centre line and two horizontal lines corresponding to the diffuser wall. Then the shape of the diffuser is changed as seen in Fig. 5.11.

  1. 5. Use the commands of dimensions to input the dimensions of the diffuser.
Fig. 5.11
Fig. 5.11 Wire frame drawing after the Constraints commands were conducted.

Click Sketching Toolboxes → Dimensions → Vertical.

Pick two horizontal parallel lines at the inlet of the diffuser and then move the mouse to the left. Click the left mouse button at the proper position and the variable V1 indicating the dimension appears as shown in Fig. 5.12. Pick two horizontal parallel lines at the outlet and the variable V2 appears.

Fig. 5.12
Fig. 5.12 Setting of the dimensions for the drawing.

Click Sketching Toolboxes → Dimensions → Horizontal.

Pick two vertical parallel lines at the inlet and the variable H3 appears. Conduct the same procedures for the vertical lines and the variables H4 and H5 appear as shown in Fig. 5.13.

Fig. 5.13
Fig. 5.13 Wire frame drawing of the diffuser after the Dimensions commands were completed.

Click the cursor on the Details View button and the table as shown in Fig. 5.14 appears. Change the values of H3, H4, H5, V1, and V2 according to the shape of flow channel. Click [A] the row H3 and input 0.9 to the left column and click the Return button. Then input the following values to the columns in turn.

  • H3 → 0.9, H4 → 1.91, H5 → 10, V1 → 0.1, V2 → 0.2.
Fig. 5.14
Fig. 5.14 Input Details View table.

5.2.2.4 Create surfaces for diffuser

Surfaces are created from Sketches by performing the following steps.

From the DesignModeler Main Menu, select Concept → Surfaces from Sketches → Details View.

  1. 1. The Details View table, Fig. 5.15, opens.
  2. 2. Click the [A] Base Object button and click [B] Sketch1. Then click the [C] Apply button.
  3. 3. Click [D] Operation and change from Add Material to Add Frozen.
  4. 4. Click the Generate button and the Graphics window is changed as seen in Fig. 5.16.
  5. 5. Select Tree Outline → + button of 3 Parts, 3 Bodies. Fig. 5.17 opens.
  6. 6. Press the Ctrl button on the keyboard and click [A] three Surface Body commands. Click the right mouse button and click Form New Parts in the drop-down list. Then Fig. 5.18 opens, in which 3 Parts, 3 Bodies is changed to [B] 1 Part, 3 Bodies.
Fig. 5.15
Fig. 5.15 Procedure of making surfaces from Sketch1.
Fig. 5.16
Fig. 5.16 Surfaces of the diffuser.
Fig. 5.17
Fig. 5.17 Tree Outline window.
Fig. 5.18
Fig. 5.18 Tree Outline window.

5.2.3 Create mesh in surface for diffuser

  1. 1. Double-click [A] Mesh in the Project Schematic window of Fig. 5.19. Then the Meshing window as shown in Fig. 5.20 opens, after clicking the arrow in the z direction.
  2. 2. Click [A] Mesh in the Outline window and the Details of ‘Mesh’ table opens, as seen in Fig. 5.21.
  3. 3. Select Sizing → Size Function. Curvature is changed to [B] Adaptive (see Fig. 5.22).
  4. 4. Click [C] Edge →, [D] Mesh Control, then click Sizing in the pull-down list. Then the Details of ‘Sizing’ table appears, as seen in Fig. 5.23.
Fig. 5.19
Fig. 5.19 Launch Mesh software.
Fig. 5.20
Fig. 5.20 2D drawing for meshing.
Fig. 5.21
Fig. 5.21 Details of ‘Mesh’ table.
Fig. 5.22
Fig. 5.22 Preparation for meshing.
Fig. 5.23
Fig. 5.23 Details of ‘Sizing’ table.

Press the Ctrl key and select [E] two horizontal lines of the diffuser at the inlet. Click the No Selection button of Geometry and then the Apply button. The Details of ‘Edge Sizing’ table as seen in Fig. 5.24 appears.

  1. 5. Click Type in Details of ‘Edge Sizing’ of the frame shown in Fig. 5.25. Change [G] Element Size to Number of Divisions. Input [H] 10 in the Number of Divisions box. Change Soft to Hard in the Behavior box.
  2. 6. Click Mesh Control and then click Sizing in the pull-down list. Press the Ctrl key and select two lines of the diffuser area. Click the No Selection button of Geometry and then the Apply button. Click Type in Details of ‘Edge Sizing’. Change Element Size to Number of Divisions. Input 20 in the Number of Divisions box. Change Soft to Hard in the Behavior box.
  3. 7. In the same way of step 6, click Mesh Control and then select Sizing in the pull-down list. Press the Ctrl key and select two horizontal lines at the outlet. Click the No Selection button of Geometry and then the Apply button. Click Type in Details of ‘Edge Sizing’. Change Element Size to Number of Divisions, and input 80 in the Number of Divisions box. Change Soft to Hard in the Behavior box. Then the drawing in the window is changed as seen in Fig. 5.26.
  4. 8. Next, the meshes of four vertical lines are controlled. In the vertical lines, the mesh distance is not the same interval and set to be shorter, as it is closer to the outside wall of the diffuser. Click Mesh Control → Sizing in the pull-down list. Press the Ctrl key and select three lines: the second, third, and fourth lines of the diffuser area from the left end. Click the No Selection button of Geometry, and then the Apply button. Click Type in Details of ‘Edge Sizing’. Change Element Size to Number of Divisions. Input 50 in the Number of Divisions box. Change Soft to Hard in the Behavior box. Click Bias Type and select [- - --- -----]. Input 5 in the Bias Factor box.
  5. 9. Click Mesh Control and select Sizing in the pull-down list. Select one line, the first line of the diffuser area from the left end. Click the No Selection button of Geometry, then click the Apply button. Click Type in Details of ‘Edge Sizing’. Change Element Size to Number of Divisions, and input 50 in the Number of Divisions box. Change Soft to Hard in the Behavior box. Click Bias Type and select [- - --- -----]. Input 5 in the Bias Factor box and then click the Reverse Bias button. Click the first line in the window and click the Apply button in the Reverse Bias box. Then the Outline window is changed as seen in Fig. 5.27.
  6. 10. Click Mesh Control → Face Meshing in the pull-down list. Press the Ctrl key and select three areas of the diffuser. Click the Apply button of Geometry in the Details of ‘Face Meshing’ window. The window as seen in Fig. 5.28 appears.
  7. 11. Click [A] Generate Mesh and then [B] Show Mesh. Then the window as seen in Fig. 5.29 appears by enlarging the drawing.
Fig. 5.24
Fig. 5.24 Details of ‘Edge Sizing’ table.
Fig. 5.25
Fig. 5.25 Details of ‘Edge Sizing’ table.
Fig. 5.26
Fig. 5.26 Drawing of the diffuser in the window.
Fig. 5.27
Fig. 5.27 Outline window.
Fig. 5.28
Fig. 5.28 Drawing of the diffuser after Face Meshing command.
Fig. 5.29
Fig. 5.29 Created mesh.

5.2.4 Boundary conditions

In this section, boundary conditions listed in problem description are set.

From the Outline window, click Model (A3) with the right mouse button. Select Insert → Named Selection.

  1. 1. From the Outline window, click Model (A3) with the right mouse button. Click Insert and then Named Selection. Click the vertical line of the diffuser at the inlet, then click the Apply button in the Geometry box.
  2. 2. Click the right mouse button on the word Selection in the Outline window. Click the Rename button. Change the name from Insert to Inlet.
  3. 3. From the Outline window, click Model (A3) with the right mouse button. Click Insert and then Named Selection. Press the Ctrl key and click three lines of the diffuser outside the wall. Click the Apply button in the Geometry box.
  4. 4. Click the right mouse button on the word Selection in the Outline window. Click the Rename button. Change the name from Selection to Wall.
  5. 5. From the Outline window, click Model (A3) with the right mouse button. Click Insert and then Named Selection. Click the vertical line at the outlet of the diffuser. Click the Apply button in the Geometry box.
  6. 6. Click the right mouse button on the word Selection in the Outline window. Click the Rename button and change the name from Selection to Outlet.
  7. 7. From the Outline window, click Model (A3) with the right mouse button. Click Insert and then Named Selection. Press the Ctrl key and click three center lines of the diffuser. Click the Apply button in the Geometry box.
  8. 8. Click the right mouse button on the word Selection in the Outline window. Click the Rename button and change the name from Selection to Axis. The Outline window is changed as seen in Fig. 5.30.
  9. 9. Right-click on the Setup command of the Fluid Flow (Fluent) box in the Project Schematic window. Click Edit in the pull-down list. Click OK in the Fluent Launcher window and then Fig. 5.31 appears.
Fig. 5.30
Fig. 5.30 Outline window.
Fig. 5.31
Fig. 5.31 Setup window.

5.2.5 Setup for solution and excursion of the analysis

  1. 1. Check [A] Axisymmetric in the Task Page window.
  2. 2. Click [B] Models in the Tree window, and the frame shown in Fig. 5.32 appears. Double-click [C] Energy-off, check Energy Equation and click OK.
  3. 3. Click Viscous—Laminar, check k-epsilon (2 eqn) and click OK.
  4. 4. Click [D] Materials and confirm that Fluid is air.
  5. 5. Click [E] Boundary Conditions, and Fig. 5.33 appears. Click Inlet in Zone and then Velocity-Inlet in the pull-down list, and Fig. 5.34 appears. Input [A] 20 in the Velocity Magnitude (m/s) box and click OK.
  6. 6. Click Boundary Conditions then Outlet in Zone. Click Pressure-Outlet in the pull-down list and Fig. 5.35 appears. Confirm [A] that Gauge Pressure (pascal) is zero. Click [B] Thermal and confirm [C] that Backflow Total Temperature (k) is 300 in Fig. 5.36. Click the OK button.
  7. 7. In a similar way to step 6, click Boundary Conditions then Wall in Zone. Click Wall in the pull-down list and Fig. 5.37 appears. Confirm that Stationary Wall and No Slip are checked. Click Thermal and confirm that Heat Flus (w/m2) is 0. Click the OK button.
  8. 8. Click Solution Initialization in the Tree window. Click the Initialize button in the Tree Page window.
  9. 9. Click Calculation Activities.
  10. 10. Click Run Calculation, and Fig. 5.38 appears. Input [A] 200 in the Number of Iterations box and click the Calculate button. Fig. 5.39 appears when the calculation is done. Click OK.
Fig. 5.32
Fig. 5.32 Setup procedure using Tree window.
Fig. 5.33
Fig. 5.33 Tree window.
Fig. 5.34
Fig. 5.34 Velocity inlet window.
Fig. 5.35
Fig. 5.35 Pressure Outlet window.
Fig. 5.36
Fig. 5.36 Pressure Outlet window.
Fig. 5.37
Fig. 5.37 Wall window.
Fig. 5.38
Fig. 5.38 Task Page window.
Fig. 5.39
Fig. 5.39 Information window.

5.2.6 Postprocessing

  1. 1. Click [A] Graphics in the Tree window, and Fig. 5.40 appears. Click [B] Vectors and then the [C] Set Up button. Fig. 5.41 appears. Click the [D] Display button.
Fig. 5.40
Fig. 5.40 Tree window.
Fig. 5.41
Fig. 5.41 Vectors window.

Then velocity vectors of air flow in the diffuser appear in the window, as seen in Fig. 5.42.

Fig. 5.42
Fig. 5.42 Calculated result window with velocity vectors.

5.2.6.1 Create XY plot of air flow at a cross section of the diffuser

By using the [A] Zoom to Area button, enlarge the graphics of air flow in the diffuser as seen in Fig. 5.43.

  1. 1. Click [A] Plots in the Tree window. Click [B] XY Plot in Task Page and then the Set Up button. Then Fig. 5.44 appears.
  2. 2. Input [A] 0 to the X box and [B] 1 to the Y box. Click [C] New Surface → Line/Rake. Fig. 5.45 appears.
  3. 3. Click [A] Select Points with Mouse. According to the comment, select two points [B], [C] by clicking the right mouse button, as seen in Fig. 5.46. The Line/Rake Surface window appears (see Fig. 5.47).
  4. 4. Input [A] -3.0 to the x0 and x1 boxes, [B] 0 to the y0 box, and [C] 0.2 to the y1 box. Click the [D] Create button.
  5. 5. Click [A] line-6 of Surfaces in Fig. 5.48. Click the [B] Plot button, and Fig. 5.49 appears.
Fig. 5.43
Fig. 5.43 Enlarged view of calculated result with velocity vectors.
Fig. 5.44
Fig. 5.44 Solution XY Plot window.
Fig. 5.45
Fig. 5.45 Line/Rake Surface window.
Fig. 5.46
Fig. 5.46 Selection method of two points for XY Plot.
Fig. 5.47
Fig. 5.47 Line/Rake Surface window.
Fig. 5.48
Fig. 5.48 Solution XY Plot window.
Fig. 5.49
Fig. 5.49 Calculation result with XY Plot.

5.3 Analysis of flow structure in a channel with a butterfly valve

5.3.1 Problem description

Analyse the flow structure around a butterfly valve as shown in Fig. 5.50. The butterfly valve has a metal disc mounted on a rotational rod. In operation, the valve can be opened incrementally to control flow rate. In addition, by rotating the disc a quarter turn, the valve can be fully open or closed.

Fig. 5.50
Fig. 5.50 Flow channel with a butterfly valve. (From http://www.kitz.co.jp/product/bidg-jutaku/kyutouyou/index.html.)

Shape of flow channel:

  1. 1. Diameter of flow channel DE = 0.06 m.
  2. 2. Diameter of a butterfly valve DE = 0.06 m.
  3. 3. Tilt angle of a butterfly valve α = 30 degrees.
  • Operating fluid: water
  • Flow field: turbulent
  • Velocity at the entrance: 0.01 m/s

Boundary conditions:

  1. 1. Velocities in all directions are zero on all walls.
  2. 2. Pressure is equal to zero at the exit.
  3. 3. Velocity in the y direction is zero on the x axis.

5.3.2 Create a model for analysis using Workbench

5.3.2.1 Select kind of analysis (Fluent)

Double-click Shortcut Workbench 17.0

The window Unsaved Project—Workbench appears

  1. 1. Drag the Fluid Flow (Fluent) button into the Project schematic window.
  2. 2. Save this project as valve by clicking File.

5.3.2.2 Preparation for DesignModeler to create a geometry for analysis

  1. 1. Double-click Geometry in the Project Schematic window. Then the Graphics window of DesignModeler opens.
  2. 2. To change from a 3D screen to a 2D screen, place a cursor on the arrow of the z direction and then the arrow is highlighted. Click the arrow in the z direction; the screen is changed from 3D to 2D.
  3. 3. Click the Tree Outline button on the left-hand side of the Graphics window, then select Schetching → Settings.
  4. 4. Check the Show in 2D box and input 0.5 m to the Major Grid Spacing box. Input 10 to the Minor Steps per Major box.

5.3.2.3 Create a wire frame for a butterfly valve

To draw a butterfly valve for analysis, DesignModeler is described in this section. The dimensions of the valve are described in Section 5.3.1.

  1. 1. Click the Graphics window and enlarge the grid by scrolling up the wheel button of the mouse (see Fig. 5.51).
  2. 2. Select Schetching Toolboxes → Draw → Rectangle. By using the Rectangle command, the channel of the valve is described with approximate.
  3. 3. Select Schetching Toolboxes → Draw → Rectangle by 3 Points. Click Rectangle by 3 Points and the Pencil mark appears on the Graphics window. Click the left mouse button at the approximate position in the channel and move the Pencil mark to the next two positions to draw the shape of the valve. Then the lines as seen in Fig. 5.52 are created.
  4. 4. Use the Dimensions command to input the dimensions of the valve.
Fig. 5.51
Fig. 5.51 Graphics window with grids.
Fig. 5.52
Fig. 5.52 Wire frame drawing of a flow channel with a butterfly valve.

Click Sketching Toolboxes → Dimensions → Vertical.

Pick two horizontal parallel lines at the inlet of the channel and then move the mouse to the left. Click the left mouse button at the proper position and the variable V1. Pick the bottom horizontal line and the lowest point of the edge of the valve and the variable V2 appears.

Click Sketching Toolboxes → Dimensions → Horizontal.

Pick two vertical parallel lines at both end of the channel and the variable H3 appears. Pick the vertical line at the outlet of the channel and the lowest point of the edge of the valve and the variable H4 appears.

Click Sketching Toolboxes → Dimensions → Length/Distance.

To determine the length of the valve, click two parallel end lines of the valve and the variable L5 appears. In the same way, click two parallel lines of the valve to determine the thickness of the valve and the variable L6 appears.

Click Sketching Toolboxes → Dimensions → Angle.

To determine the angle of the valve, click the bottom line first and then the line of the valve towards the outlet of the channel. The variable A7 appears.

Click Details View and input the following values of the Dimensions:7 table, as seen in Fig. 5.53.

  • A7 → 60, H3 → 0.2, H4 → 0.1441, L5 → 0.06, L6 → 0.002, V1 → 0.06, V2 → 0.0035.
Fig. 5.53
Fig. 5.53 Wire frame drawing after Dimensions commands and Details View table.

5.3.2.4 Create a surface for a channel with a butterfly valve

Select Sketching Toolboxes → Modeling → XYPlane → Sketch1. Highlight the geometry of Sketch1 in the Graphics window.

Select Concept → Surfaces from sketches → Generate. Then a surface is made in Sketch1 as seen in Fig. 5.54.

Fig. 5.54
Fig. 5.54 Wire frame drawing after making a surface.

5.3.2.5 Create meshes for a channel with a butterfly valve

  1. 1. Double-click [A] Mesh in the Project Schematic window of Fig. 5.55. Then the Meshing window opens, as shown in Fig. 5.56. Click the arrow [A] in the z direction.
  2. 2. Click [B] Mesh in the Outline window and the Details of ‘Mesh’ table opens, as seen in Fig. 5.57.
  3. 3. Select Sizing → Size Function. Curvature is changed to [A] Adaptive (see Fig. 5.58).
  4. 4. Click [B] Edge, [C] Mesh Control and then Sizing in the pull-down list. The Details of ‘Sizing’ table then appears as seen in Fig. 5.59.
Fig. 5.55
Fig. 5.55 Launch Mesh software.
Fig. 5.56
Fig. 5.56 Meshing window with 3D view.
Fig. 5.57
Fig. 5.57 2D drawing and Details of ‘Mesh’ table.
Fig. 5.58
Fig. 5.58 Details of ‘Mesh’ table.
Fig. 5.59
Fig. 5.59 Details of ‘Sizing’ table.

Press the Ctrl key and select [D] two horizontal lines of the wall of the channel. Click the No Selection button of Geometry and then the Apply button. The Details of ‘Edge Sizing’ table appears, as seen in Fig. 5.60.

  1. 5. Click Type in Details of ‘Edge Sizing’ of Fig. 5.60. Change [E] Element Size to Number of Divisions. Input [F] 200 in the Number of Divisions box.
  2. 6. Click Mesh Control → Sizing in the pull-down list. Press the Ctrl key and select two vertical lines at the inlet and outlet of the channel. Select two lines for the valve surfaces. Click the No Selection button of Geometry, then the Apply button. Click Type in Details of ‘Edge Sizing’ and change Element Size to Number of Divisions. Input 40 in the Number of Divisions box and click Bias Type → - -- ---- -- - → Bias Option → Bias Factor. Input 4 in the Bias Factor box.
  3. 7. Click Mesh Control → Sizing in the pull-down list. Press the Ctrl key and select two lines at the valve edges. Click the No Selection button of Geometry and then the Apply button. Click Type in Details of ‘Edge Sizing’. Change Element Size to Number of Divisions. Input 2 in the Number of Divisions box.
  4. 8. Click Mesh Control and then select Face Meshing in the pull-down list. Select a surface of the channel and click the No Selection button of Geometry, then the Apply button. Click method in the Details of ‘Face Meshing’ table and change to Quadrilaterals.
  5. 9. Click Generate Mesh → Show Mesh. Then Fig. 5.61 appears.
Fig. 5.60
Fig. 5.60 Details of ‘Edge Sizing’ table.
Fig. 5.61
Fig. 5.61 Drawing with created mesh.

5.3.3 Boundary conditions

In this section, boundary conditions listed in the problem description are set.

From the Outline window, click Model (A3) with the right mouse button. Click Insert then Named Selection.

  1. 1. From the Outline window, click Model (A3) with the right mouse button, then Insert → Named Selection. Click the vertical line of the channel at the inlet. Click the Apply button in the Geometry box.
  2. 2. Click the right mouse button on the word Selection in the Outline window. Click the Rename button. Change the name from Insert to Inlet.
  3. 3. From the Outline window, click Model (A3) with the right mouse button, then Insert → Named Selection. Click the vertical line at the outlet of the diffuser. Click the Apply button in the Geometry box.
  4. 4. Click the right mouse button on the word Selection in the Outline window. Click the Rename button and change the name from Selection to Outlet.
  5. 5. From the Outline window, click Model (A3) with the right mouse button, then Insert → Named Selection. Press the Ctrl key and select two horizontal lines of the channel and four lines of the butterfly valve. Click the Apply button in the Geometry box.
  6. 6. Click the right mouse button on the word Selection in the Outline window. Click the Rename button. Change the name from Selection to Wall. The Outline window is changed, as seen in Fig. 5.62.
  7. 7. Right-click on the Setup command of the Fluid Flow (Fluent) box in the Project Schematic window. Double-click Setup and then Fig. 5.63 appears. Click OK and Fig. 5.64 opens.
Fig. 5.62
Fig. 5.62 Changed Outline window.
Fig. 5.63
Fig. 5.63 Fluent Launcher window.
Fig. 5.64
Fig. 5.64 Tree and Mesh windows.

5.3.4 Setup for solution and excursion of the analysis

  1. 1. Confirm the following conditions of Solver in the Task Page window: Pressure-Based, Absolute, Steady, and Planer.
  2. 2. Click [A] Models in the Tree window, as seen in Fig. 5.65. The Task Page window appears. Double-click [B] Energy-off, check Energy Equation and click the OK button.
  3. 3. Double-click [C] Viscous—Laminar and check k-epsilon (2 eqn). Click OK.
  4. 4. Click [D] Materials and double-click Fluid. Fig. 5.66 opens.
Fig. 5.65
Fig. 5.65 Tree window.
Fig. 5.66
Fig. 5.66 Create/Edit Materials window.

Click [A] Fluent Database, and Fig. 5.67 opens. Select [B] water-liquid in the Fluent Fluid Materials table and click [C] Copy then [D] Close. Click [E] Change/Create in the Create/Edit Materials window, then click Close.

  1. 5. Click [A] Boundary Conditions in the Tree window, and Fig. 5.68 appears. Click [B] inlet in Zone and select Velocity-Inlet in the pull-down list. Fig. 5.69 appears. Input [C] 0.01 in the Velocity Magnitude (m/s) box, and then OK.
  2. 6. Click Boundary Conditions and then Outlet in Zone. Click Pressure-Outlet in the pull-down list, and Fig. 5.70 appears. Confirm [A] that Gauge Pressure (pascal) is zero. Click [B] Thermal and confirm that [C] Backflow Total Temperature (k) is 300 in Fig. 5.71. Click the OK button.
  3. 7. In a similar way to step 6, click Boundary Conditions then Wall in Zone. Click Wall in the pull-down list, and Fig. 5.72 appears. Confirm that Stationary Wall and No Slip are checked, and click Thermal. Confirm that Heat Flus (w/m2) is 0 and click the OK button.
  4. 8. Click Solution Initialization in the Tree window. Click the Initialize button in the Tree Page window.
  5. 9. Click Calculation Activities.
  6. 10. Click Run Calculation, and Fig. 5.73 appears. Input [A] 200 in the Number of Iterations box and click the [B] Calculate button. Fig. 5.74 appears when the calculation is done. Click OK.
Fig. 5.67
Fig. 5.67 Fluent Database Materials window.
Fig. 5.68
Fig. 5.68 Task Page of Boundary Conditions window.
Fig. 5.69
Fig. 5.69 Velocity Inlet window.
Fig. 5.70
Fig. 5.70 Pressure Outlet window.
Fig. 5.71
Fig. 5.71 Pressure Outlet window.
Fig. 5.72
Fig. 5.72 Wall window.
Fig. 5.73
Fig. 5.73 Task Page of Run Calculation window.
Fig. 5.74
Fig. 5.74 Information of Calculation complete window.

5.3.5 Postprocessing

  1. 1. Click [A] Graphics in the Tree window, and Fig. 5.75 appears. Click [B] Vectors and [C] Set Up. Fig. 5.76 appears. Input [D] 4 to the Scale box and click the [E] Display button.
Fig. 5.75
Fig. 5.75 Task Page of Graphics window.
Fig. 5.76
Fig. 5.76 Vectors window.

Then velocity vectors of air flow in the butterfly valve appear in the window as seen in Fig. 5.77.

Fig. 5.77
Fig. 5.77 Calculation results window.
..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset