Immersed Body Valve Simulation using Ansys CFD: Part 2
Introduction
In this session, we will explore the effects of valve motion on flow dynamics using Ansys CFD. We will build upon the previous technique demonstrated, focusing on the accuracy of the simulation as the valve moves.
Setup and Configuration
- Duplicate the existing setup and connect the solution to the new configuration for valve motion.
- Valve motion can be complex due to changes in flow topology as the valve opens and closes.
- Issues such as convergence and distorted mesh are common, but we aim to overcome these challenges.
Simulation Parameters
We will switch to a total pressure definition for the inlet, set at 2.8 and 2.6 for different conditions.
The benefit of using an immersed body is the ability to simulate motion by specifying:
- Displacement
- Speed and direction
- General motion
For this simulation, the valve will travel in the minus y-direction at a speed of 30 millimeters per second.
Analysis Type
We will conduct a transient analysis with the following settings:
- Initial condition: Flow moving through the valve
- Simulation duration: 1 second
- Time steps: 100 milliseconds each
Additional options include general motion and rigid body solutions, which can be explored later.
Simulation Execution
The simulation will use the previous results as initial conditions. We will perform 100 steps as the plunger moves downwards to seal the valve.
Note: The immersed solid is only affected by hydrodynamics, as other physics are not yet supported.
Results and Analysis
Upon completion, we will review the results to observe the interaction between moving parts and flow dynamics. The Immersed Boundary Method allows for complete flow sealing, unlike mesh deformation which changes topology.
Transient effects will be visible as the part moves. We will examine variables such as forces on the valve:
- Initial force: 8.89 Newtons
- Force when valve closes: 15 Newtons
This demonstrates how valve motion can be adjusted to control opening and closing.
Immersed Body Valve Simulation using Ansys CFD: Part 2 I should actually use the previous technique, which is more accurate. Instead, I want to now look at what happens when I move the valve. So I'm going to duplicate this, move it over here, and connect the solution to the solution here.
This will be valve motion. Let's open this up. Valve motion can be tricky. As the valve opens and closes, the topology of the flow can change. So, as the gaps get smaller or disappear, typically, you have issues with convergence and distorted mesh. We're going to try to overcome that.
What we can do here is switch to a total pressure definition for the inlet, which is 2. 869304. Now, the benefit of an immersed body is that we can make this moving. I can specify a displacement, speed, and direction or general motion.
So, let's say we're trying to close this valve, and we want this valve to travel in the minus y direction. We want to move this line somewhere down here. So, let's move it not quite 30 millimeters but at least 30 millimeters. We're going to plunge this thing all the way down here.
Let's turn this analysis from a steady state to transient. Our initial condition is a condition where the flow is moving through the valve. I'm going to run a total of one second and then do millisecond time steps. Probably do a hundred steps. That should give us a try and see if it works.
So, now it's a transient analysis, and we're going to do a hundred steps. We're going to specify a speed and direction.
Linear velocity will be 30 millimeters per second, and the direction will be in 0 -1 0. So, this will be moving at 30 millimeters per second, and you should get down there somewhere in one second. There are various set solver controls.
In addition to speed and direction, another very helpful option is general motion and rigid body solution. You can check that out later. I need to specify initial conditions and make sure I specify some sort of transient results. So, I'm going to save it at every time step.
I'm going to do a hundred of these. Immersive solid is only affected by hydrodynamics. Other immersive solid physics is not yet supported. That's fine. I just have hydrodynamics. In fact, I'm just going to plunge this plunger down and let it overlap and seal off the flow.
The reason I'm able to do this is because instead of velocity boundary, I've switched the boundary on the inlet side to total pressure. Let's give this a try. So, it's automatically going to use the previous set of results as the initial conditions.
We're going to do a hundred steps as we plunge that plunger downwards and seal off this valve. Simulation finished. Let's go back and do the next step. So, that's the first step. The second step is to do the third step. This is going to be the first step. The third step is to do the third step.
Simulation finished. Let's take a look at the results. This is at the end when we have filled in the flow. We can animate the results here. What this is showing you is the ability to have parts moving inside of a flow, seeing how the flow interacts with the part.
The best part about the Immerse Boundary method is that we can completely seal off the flow here, which is not applicable if just deforming the mesh because the mesh topology will change. And so it's not just a matter of a single part moving inside of a flow.
There are some transient effects as the part keeps moving down. Let's take a look at the types of variables we have for the result. You can see there are standard types of forces. We should be able to plot the forces on the valve as well, see if that's available, and in the y-direction.
Okay, so it's able to calculate how much force is on the valve if we switch to a different time step here, that's one of the earlier ones again, so that's 8.89 Newtons, and when the valve closes, it's almost 15 Newtons of force.
So, that shows you how we can adjust the the motion of the valve and have open and close you.
