In this Ultrasonic Atomization CFD Analysis tutorial, we examine the physics of breaking liquid into mist using high-frequency vibration. This process uses a device called a transducer that vibrates thousands of times per second. These rapid movements create unstable waves on the surface of the liquid. Eventually, these waves release tiny, uniform droplets into the air. This method is critical for industries like medical nebulizers (inhalers) and metal powder manufacturing. However, testing these devices physically is expensive and difficult because the droplets are microscopic. To solve this, engineers use CFD simulation to visualize the breakup process. We rely on ANSYS Fluent because it accurately handles the complex interaction between air, water, and moving parts. This Ultrasonic Atomization fluent simulation provides a clear view of how droplets form without the need for high-speed cameras.

In this training, we focus on simulating the motion of the vibrating plate. We use a specific technique called Dynamic Mesh fluent with layering. This allows the bottom of our simulation domain to move up and down in a sine wave pattern, mimicking real-life physics. This Layering Dynamic mesh setup is the most accurate way to generate the pressure waves needed for atomization. For more lessons on moving boundaries, please check our Dynamic Mesh tutorials.

Figure 1: Development of a High-Power Ultrasonic System dedicated to Metal Powder Atomization used as the reference for the CFD simulation.

Simulation Process: Dynamic Mesh and VOF Model Settings

To perform this CFD simulation, we built a 3D rectangular geometry. The lower section contains the liquid (water), and the upper section contains gas (air). We created a high-density Structured Grid with a total of 5,856,000 cells. We selected hexahedral cells because they provide the best accuracy for tracking the interface between water and air. The most important setting in this project is the Layering Dynamic mesh fluent method. This feature allows ANSYS Fluent to add or remove layers of mesh cells automatically as the bottom plate vibrates. This ensures the mesh does not get distorted, even during fast motion.

We controlled the plate’s movement using a User Defined Function (UDF) written in C code. This script applies a sinusoidal velocity profile () to the bottom wall. To track the two fluids, we activated the Volume of Fluid (VOF) multiphase model. VOF calculates the volume fraction of water in every cell to determine the exact shape of the surface. We also enabled the Wall Adhesion option. This helps simulate how water sticks to the vibrating plate (contact angle), which affects how the waves start. By combining VOF with a custom UDF, we can simulate the realistic physics of the atomization process.

Figure 2: Structured Mesh grid of the 3D rectangular domain, showing high cell density to capture the liquid-gas interface.

Post-processing: Ultrasonic Atomization CFD Analysis of Droplet Formation

In this section, we review the results to see if the liquid successfully turns into mist. We use volume fraction contours to visualize the physics. Figure 3 shows the Volume Fraction Contours of the water. The dark teal area represents the main liquid pool. You can clearly see that the surface is not smooth. The vibration has caused capillary waves—sharp peaks and valleys on the water surface. This visual result confirms that our Dynamic Mesh fluent settings are correctly transferring energy from the moving plate to the fluid.

Higher up in the domain, we see the results of the breakup. The cyan and light-blue shapes represent the Droplet Formation zone. These colors show where the volume fraction is between 0.25 and 0.75, marking the edge of the droplets. The simulation captures the full “breakup chain.” First, we see “ligaments,” which are long, thin strands of water being thrown upward. Then, these ligaments snap into tiny spherical dots. This validates the Ultrasonic Atomization CFD Analysis method. We are successfully simulating the transition from Vibration → Wave Instability → Ligaments → Atomized Droplets.

Figure 3: Volume Fraction of Water Contours (VOF) illustrating the Ultrasonic Atomization CFD Analysis process, where the dark teal liquid surface breaks up into cyan droplets due to vibration.

Finally, we analyze the spatial distribution of the spray. The droplets are mostly located directly above the wave peaks. We observe that smaller, lighter droplets fly higher, while larger, heavier drops remain lower. This data is vital for manufacturing. If a company needs a finer mist for a medical device, they can use this simulation to adjust the frequency in the UDF. If they need a higher spray rate, they can increase the amplitude. This CFD Analysis allows engineers to optimize the atomizer design on the computer, ensuring the perfect droplet size before building the physical product.