## Fluids

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#### Simulating Centrifugal Pump in Fluent – How to Handle Stationary Walls

• Ya_Tang
Subscriber

Hello all,

I am a student who is currently trying to simulate blood flow through a centrifugal blood pump model, which was developed in an FDA project to assess numerical simulations. My plan is to simulate the blood flow through the pump model using the Sliding Mesh method in Fluent.

I divided the pump model into three fluid regions according to a method used in a scientific paper (https://doi.org/10.1016/j.apm.2022.05.016). Figure 1 shows these fluid domains.
I do not have any problems with the “Inlet Pipe” (the green body in Fig.1) or the “Volute, Diffuser, and Outlet Pipe” (the brown body in Fig. 1). However, my question is concerned with the “Rotary Region” (the teal body with orange surfaces in Fig. 1). This region contains the “Stationary Walls” (the orange surfaces in the Details of Rotary Region of Fig. 1) and the rotating “Pump Blades” of the FDA blood pump (the purple body in the Details of Rotary Region of Fig. 1).

Figure 1: The three parts of the flow region.

To simulate the pump rotation using the sliding mesh method, I needed to define the “Rotary Region” as a Rotating Fluid Cell Zone rotating at a constant speed of 3500 rpm, which is shown in Figure 2.

Figure 2: Setup of “Rotary Region” as a rotating cell zone in Fluent

Then, I set the “Pump Blade” inside the “Rotary Region” as a moving wall with a speed of 0 rad/s Relative to its Adjacent Cell Zone, as shown in Figure 3. So, the “Pump Blade” was now rotating at the same speed as the “Rotary Region”.

Figure 3: Fluent setup of the “Rotary Region’s” Pump Blade

For the “Stationary Walls” inside the “Rotary Region” (the orange surfaces in Fig. 1), I set them as moving walls with a rotational speed of 0 rad/s in the Absolute reference frame, which can be seen in Figure 4.

Figure 4: Fluent setup of the “Stationary Walls” in the “Rotary Region”

The simulation seemed to run well. However, I am not very sure about the effect of enforcing a speed of 0 rad/s in the Absolute Reference Frame in a Rotating Fluid Cell Zone.

Another way of dividing the flow region was to avoid including surfaces that needed to be specified as 0 rad/s moving walls in the Absolute Reference Frame within a Rotating Cell Zone, as shown in Fig. 5. In this figure, the key difference from the configuration in Figure 1 is about the Rotary Region #2 (yellow body in Fig. 5):

·         The Rotary Region #2 does not contain any Stationary Walls.

·         It is surrounded by fluid (the gray fluid zone/gap of the Volute, Diffuser, and Outlet Pipe in Fig. 5).

Figure 5: Alternative Configuration of the centrifugal pump model. The Inlet Pipe is the same as Fig. 1 and was excluded.

As you can imagine, the approach demonstrated in Fig. 5 is more tedious due to the need to create more interfaces. Also, small gaps exist between the Rotary Region #2 and the Stationary Walls (in Fig. 5). These small gaps are not good for meshing, especially for large element sizes.

In summary, my questions are:

1.      For the configuration shown in Fig. 1, what is the effect of enforcing a speed of 0 rad/s in the Absolute Reference Frame in a Rotational Cell Zone?

2.      Shall we use the configuration shown in Fig. 5 instead of that shown in Fig. 1?