Dynamic Mesh Motion in Fluent - Piezoelectric Actuators 2

So in the second part of this video about using dynamic mesh motion and for modeling piezoelectric actuators, what we used previously that I showed the results in the first part of the video is that we used the constant density, the constant material properties for air and water liquids when using the volume of fluid method.

As you can see, constant density for air, constant density for water. But what we saw is that the velocity, the max velocity actually was quite high. So, some works we can do to work around that.

First of all, we can work on besides the mesh, we can work also on the material models available, different material models available in ANSYS.

For example, in air, for air besides constant density, we can use ideal gas models, and also for water, besides, in addition to the constant density, we can use compressible liquid.

So, when we use ideal gas, you will see that we have the other properties activated, thermal properties, and for water liquid, here we can use compressible liquid.

You can refer to the theory manual to see that what equations we are using for modeling density now, when instead of constant value, now we are using relation for the density. So in this way we consider compressibility for water liquid and hopefully we can see better results for the velocity.

About 55,000 cells and mesh quality is 0.8 above 0.8 which is very good you can see the mesh that we have it here materials air is constant density we use Compressible liquid for water. Let's initialize the model And patch water check where we have air and water at the beginning.

So the nozzles are half full. Run for the calculation check cases only for the mesh but we already know the mesh is good, good checking for VOF, running simulation for a hundred time steps. Thank you for watching! I'll be back when the solution is done. The solution is done.

Average velocity at the holes less than 30. Max velocity inside the domain is up to 120. Same also for the holes. Let's check the contours of the volume of the fluid to see about water. You can see it.

And we can compare these results with previous modeling that we had for constant air density and constant water density and you can see that for example how far these droplets are away from the nozzles. So let's look at the other animations.

Please be sure to correct any misspelled ANSYS product names as you transcribe, e.g., 'OptiSling' should be 'optiSLang'. So air coming in and now the wall are moving down and so push the water to exit these nozzles. Now we are in the second cycle of the prescribed motion of the walls.

And you see the how we model dynamic mesh motion using dynamic mesh motion features to model the motion, prescribed motion that we get it from the piezoelectric actuator.

And you can see that the air entering the domain are not the same as for every of these nozzles because it depends that where these nozzles are so the this first nozzles are different from the other nozzles.

Okay, so the good things is that when we using compressible fluid, okay, compressible liquid model for water, then the peak of the velocity reduced to about 120 which is much lower than what we had it before.

So this is very good, make it more reasonable and we are seeing that how far we can get the droplets away from the nozzles with the same prescribed motion, with same amplitude and same frequency for the motion. Next could be a change into the air. Let's see what happens if we use ideal gas.

So now we want to check ideal gas and liquid compressibility. As you can see here we have ideal gas for the air and compressible liquid for the water. Let's check the model's materials. Air is ideal gas, water liquid is compressible liquid.

We have to be sure that the boundary conditions now operating pressure set to zero and we applied 101 kPa atmospheric pressure here at the outlet boundary condition.

Go for solution, check case, only recommendations for the machine minimum orthogonality is 0.8 which is very good, number of cells is 55,000 cells, so let's start the solution. Adapting the necessities. Thank you for watching. Transcription by ESO. Translation by.

I will be back after the solution is finished. Solution done for 100 time steps. Average velocity at the holes is less than 25 m/s so far. Maximum velocity is not above 140 m/s. At the holes the maximum velocity is not above 100. Thank you for watching this video. I hope you enjoyed it.

Please share your opinion about the material models that I have been using in these two videos. In the first part, I used the constant density for both air and water. And then in this part, which is the second part, I use compressibility for water as you can see.

And then I consider the ideal gas for air. And you can see the effect of these changes into the average velocity and maximum velocity that we are getting in the domain. So these are all besides meshing that we also can work on that.

So hopefully in this video I can show you that the choice of the material model also can affect the results. That you can see for example for compressible water, you can see that how far the droplets can go away from these holes.

And maybe by different material modeling in ANSYS Fluent we can get a little bit different results and by comparing with the experimental data we can see that what model works better for us. In this part I want to check the effect of frequency of the prescribed motion for dynamic mesh.

So far what you have seen in this video and part 1 was for the prescribed motion when the frequency is 100 kHz. I want to show you another set of results that are for 200 kHz as you can see.

So, instead of only two cycles for 100 kHz, now we have four cycles for 200 kHz, and next is for 500 kHz that we have 10 cycles for the prescribed motion. Let's see the results. This is the model in ANSYS Fluent for Prescribed Motion of 200 kHz.

As I told you that I already used a profile that based on the curve that I showed you. So, okay here we have two parameters time and y component so we have vertical motion with frequency of 200 kilohertz, we have dynamic mesh same as before, I already ran this model, let's check the animation.

Okay, if I start to running this slowly, You can see that first going up, then going down, and you can see that the water jets that exiting the nozzles now again the next cycle that air coming in and then we can see.

So we are still in the first cycle, the motion is up and down vertically in 200 kilohertz.

So what we expect is that we see more water exiting the nozzles because now we have four cycles instead of two cycles during the 20 microsecond running and we expected to see more concentration of droplets above the nozzles. So now we are in the third, fourth cycle.

You can see that for sure we see much more about the droplets and they are going further away from the nozzle exits. So for sure we see the effect of the frequency on the number of the droplets and how far they can go away from the nozzles. Let's check next frequency.

This is the model for 500 kHz, same mesh, same condition for the mesh motion except that now we have 10 cycles during the 20 microseconds. Let's check the results. Let's just set the speed and start the animation. We see much more cycle. You can see that here.

As you can see that now instead of four cycle for 200 Kilohertz now we have 10 cycles for this one which is 500 kilohertz frequency. So we expected to see more and more. Now we finished the fifth, now this is the sixth cycle. And you see the effect of position, location of the droplets.

So we don't have uniform ejection of the liquid exiting the nozzles. If you don't have any wrote over nozzles, or hath the current nozzles having nozzles after the first float, you won't have the rules for your.

These are the result of a minimum foride ved Arrangement of the holes is also important, unless we have so many, like hundreds of holes that we can get close to the uniform distribution. But we still may not get it. So I just here compare the results for 100 kHz, 200 kHz, and 500 kHz.

So as you can see in 100 kHz, we have a much smaller number of the droplets and they are closer to the nozzles. But for 500 we have many more droplets and they are much away from the nozzles.

So in this video I showed you not only the effect of choice of the material model for air and water, Also, the effect of the frequency of the excitation of a piezoelectric that causes this wall motion or excitation of these holes that help us to just having the water droplets formation exiting this water pattern for water droplets from the nozzles.

And we have a kind of, if we have a controlled amplitude or controlled frequency, we can have a kind of controlled concentration for the droplets. So, again it can be used in a variety of applications, like prescribing drugs by inhaling for some patients.

So, hopefully I can show you how to use dynamic mesh motion in ANSYS for this kind of motion, wall motion that needs deformable mesh for piezoelectric actuator. Please contact us at https://ozeninc.com/contact for more information.