An Atomizer Spray CFD simulation is a fundamental engineering tool used to design the most critical components of combustion systems, such as those in gas turbines and jet engines. The goal of an atomizer is to break up a bulk liquid, like fuel, into millions of tiny droplets, a process called atomization. A Gas Turbine Combustor simulation often focuses on air-blast atomizers, which use a high-velocity stream of air to violently shatter a liquid sheet into a fine mist. The quality of this spray—specifically the size and distribution of the droplets—directly controls how efficiently and cleanly the fuel will burn.

This report details an Atomizer Spray fluent analysis that uses the powerful computational fluid dynamics software ANSYS Fluent to build a virtual prototype of this process. The simulation employs the specialized Air-Blast-Atomizer injection model to replicate the initial, violent breakup of the liquid fuel. It then uses a sophisticated Breakup DPM model (Discrete Phase Model) to track the life of each individual droplet as it travels, deforms, breaks apart, and evaporates. This type of Air-Blast-Atomizer model CFD study is essential for engineers. It allows them to see inside the chaotic spray and accurately predict droplet sizes, velocities, and evaporation rates, enabling them to perfect the atomizer’s design on a computer, which is far cheaper, faster, and safer than building and testing dozens of physical prototypes. For more DPM simulation tutorials, check our DPM CFD Tutorials.

Figure 1: Nozzle atomizer experimental visualization

Simulation Process: Modeling Air-Blast Atomization and Droplet Breakup

The simulation process for this Atomizer Spray CFD study was meticulously configured in ANSYS Fluent to capture the complete Multiphysics of the atomization process. The geometry of the combustor nozzle was designed with three distinct air inlets to generate the complex flow field needed for effective atomization: a central main air flow, a parallel co-flow to shape the spray, and a crucial swirling flow to create high shear. Because the nozzle is rotationally symmetric, a single wedge section was modeled with periodic boundary conditions to represent the full 360-degree geometry.

The liquid fuel was defined as methyl alcohol (CH3OH). The core of the simulation was the Discrete Phase Model (DPM), which was set up with two-way coupling. This means the gas phase affects the droplets (accelerating and heating them) and the droplets affect the gas phase (slowing it down and cooling it through evaporation). To ensure thermal accuracy, the latent heat of methanol was defined as temperature-dependent, allowing the model to calculate the correct energy needed for evaporation at any point in the combustor. The injection itself was configured using Fluent’s specialized Air-Blast-Atomizer injection model, which is designed to predict the initial droplet formation from a liquid sheet shattered by high-velocity air. To realistically model the droplet’s journey, the dynamic drag law model was selected, which accounts for the fact that real droplets deform from perfect spheres in high-speed flows. Finally, the TAB (Taylor Analogy Breakup) model was activated to simulate the critical physics of secondary breakup, where large droplets break into smaller ones. The species transport model was also enabled to track the mixing of the evaporated methanol vapor with oxygen from the air.

Post-processing: Story of a Fuel Droplet after injection

The simulation results tell a complete engineering story of a fuel droplet’s life, from its violent birth to its final disappearance into vapor. By following this journey, we can prove the effectiveness of the atomizer design. The life of the spray begins with a violent collision between liquid fuel and high-speed air. The velocity contour in Figure 3 shows the engine of this process. The swirling air inlet creates a powerful, high-velocity core of air that exits the nozzle at speeds up to 82.8 m/s. This is the “hammer” that the Air-Blast-Atomizer model uses to shatter the liquid methanol sheet into initial droplets. The velocity difference between this fast central core and the slower surrounding air creates intense shear forces that tear the liquid apart. The particle tracks in Figure 5 show the immediate result: a cone of droplets is formed, with the largest droplets (up to 52.5 microns) existing right at the nozzle exit where this primary breakup occurs.

Figure 2: The gas velocity contour from the CFD analysis, revealing the high-velocity (up to 82.8 m/s) swirling air core responsible for primary atomization.

Once born, the larger droplets are not stable. As they travel through the high-speed air, the aerodynamic forces acting on them cause them to deform. The TAB breakup model simulates this physics, treating each droplet like a tiny, oscillating water balloon. When the oscillations become too large, the droplet shatters into several smaller “daughter” droplets. This secondary breakup is clearly visible in the simulation. The particle diameter contour in Figure 4 shows a smooth map of this process. The red and orange zones near the nozzle show the larger parent droplets, while the green and blue zones further downstream show where the average droplet size has become much smaller (mostly 10 to 20 microns). The most important achievement of this simulation is the confirmation that the combination of primary and secondary breakup produces a very fine spray, with the vast majority of droplets being smaller than 26 microns. This is a critical result, as smaller droplets are essential for efficient combustion.

Figure 3: A smooth contour field showing the distribution of droplet Diameter [m] throughout the spray, as calculated by the DPM breakup model in Fluent.

Figure 4: Visualization of individual DPM particle tracks for methyl alcohol droplets from the atomizer spray simulation, colored by their diameter [m].

The final stage of the droplet’s life is its transformation into fuel vapor. The smaller droplets created by the TAB breakup model have a much higher surface-area-to-volume ratio, which means they evaporate incredibly quickly. The evaporation contour in Figure 6 shows exactly where this happens. The bright green and red areas, with evaporation rates up to 7.19e-09 kg/s·m³, represent a dense cloud of small, rapidly evaporating droplets right after the nozzle. As the spray travels downstream, the evaporation rate decreases simply because most of the liquid has already turned into vapor. The accuracy of this result is guaranteed by the use of a temperature-dependent latent heat model in Fluent.

Figure 5: DPM Evaporation-Devolatilization contour from the Fluent simulation, showing the mass transfer rate [kg/s·m³] as liquid methyl alcohol evaporates into a gas.