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How to Add Flow Tracers in FLOW-3D

Hydraulics, in a broad sense, deals with the mechanical properties of liquids. Types of applications include pipe flow, river flows, dam design, and pump design. In this example we will be looking at a hydraulic jump. A hydraulic jump occurs when a high velocity flow discharges into a lower velocity zone causing an abrupt rise in the fluid surface. Hydraulic jumps are used as energy dissipaters because the kinetic energy gets converted to potential energy and random kinetic energy eventually is dissipated as heat. In this simulation, we will look at how the flow mixes during the jump. A two-dimensional spillway with flood gates will be evaluated. This simulation was originally run for 120 seconds to obtain the flow pattern then a restart was done to add the tracer. The following steps were used in the setup:

  1. First, the location of the tracer needs to be determined. The location of the tracer will be placed at the top of the spillway. If the user knows how far along a given axis the tracer will be set, then this step can be skipped.
    1. Select the 2-D plane from which to probe for the placement of tracer. In this example, it is the x-z plane. This can be chosen by selecting the plane that will be facing into the page or facing out of the page indicated by + out of page – into page. Here it is the y icon shown in Figure 1-1a.
    2. Hold the Shift key + left click with mouse at the top of crest. The values at this point will be given in the lower left hand corner as shown in Figure 1-1c.
    3. Write down the x value. Along the x-direction, this is where the tracer will be placed. Figure 1 shows the process.
How to add flow tracers in FLOW-3D
Figure 1. Step 1 shows how to select the x-z plane, step 2 shows the location of shift-click to get probe point, and step 3 shows the x-direction location.
  1. Now that the location has been determined, we can add a baffle and define it as flux plane and a tracer.
    1. Right-click on Baffles > select Add. This will add a baffle region.
    2. Give the baffle a name, select Define as Flux Surface, and select Generate Tracer.
    3. Expand the Baffle region 1 tree
    4. Expand Definitions. Definitions describe the location along the axis to place the tracer. We determined this from step 1.
    5. Enter the value from step 1 in the x-coordinate.
    6. Limiters define the area of the tracer. If they are left blank then the extents will be defined according to the mesh (domain extents). If the user has several tracers in several locations then the extents or area of the tracer needs to be defined by limiters, in which case the user can locate positions same as section 1. For this example we will leave the limiters blank so they span to the mesh. Figure 2 shows the defined tracer.
Defining flow tracers in FLOW-3D
Figure 2. Defined tracer showing definition (location) and blank limiters to define tracer to mesh extents.
  1. Run the simulation.
  2. Post-process the results:
    1. Select the Analyze tab > 2-D tab.
    2. Select the open results file button.
    3. Select the flsgrf file.
    4. Select Tracer from flux surface #1 from the contour variables dropdown.
    5. Select no velocity vectors from vector types dropdown.
    6. Expand time frames. Figure 3 shows the 2-D tab with these steps.
    7. Select the Render button.
    8. Select multi from the drop-down menu. This will allow the user to show 4 time frames at once to see the evolution of the roll over mixing in a jump. Figure 4 shows the results for four different time frames. The order in which the user selects the time frames is the order in which they will appear.

Flow tracer postprocessing in FLOW-3D
Figure 3. 2-D setup for post-processing tracer results

 

Simulation results for flow tracers in FLOW-3D
Figure 4. Mixing layers of jump.

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