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.
Computational fluid dynamics; FLUENT; Workbench; Diffuser; Butterfly valve
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.
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.
Shape of flow channel:
Boundary conditions:
Double-click Shortcut Workbench 17.0.
The window Unsaved Project—Workbench, Fig. 5.3, opens.
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.
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.
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.
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.
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.
Surfaces are created from Sketches by performing the following steps.
From the DesignModeler Main Menu, select Concept → Surfaces from Sketches → Details View.
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.
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.
Then velocity vectors of air flow in the diffuser appear in the window, as seen in Fig. 5.42.
By using the [A] Zoom to Area button, enlarge the graphics of air flow in the diffuser as seen in Fig. 5.43.
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.
Shape of flow channel:
Boundary conditions:
Double-click Shortcut Workbench 17.0
The window Unsaved Project—Workbench appears
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.
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.
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.
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.
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.
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.
Then velocity vectors of air flow in the butterfly valve appear in the window as seen in Fig. 5.77.