Introduction
In many automotive and industrial applications, the performance of liquid spray nozzles can significantly affect efficiency, lubrication, combustion, or cooling. Despite their importance, engineers often rely on assumptions or trial-and-error testing, which can lead to sub-optimal results. For applications where liquid behavior is difficult to characterize, having accurate models is essential for making informed design decisions.
Anticipating how spray patterns change with minor geometric modifications can reduce uncertainty in the design process. This brief study demonstrates one approach to using CFD for rapid nozzle prototyping.
To showcase the capabilities of Ansys Fluent in modeling liquid sprays across various applications, a simple case study is presented. Both cases use the Volume of Fluid (VOF) model, as shown in the animation below, with identical solver settings to isolate the effect of nozzle geometry.
Could a small geometric change to the nozzle lead to more optimal spray distribution?
To find out, we used Ansys Fluent’s Volume of Fluid (VOF) model to simulate and compare the spray characteristics of two nozzle designs under identical operating conditions in our recent webinar.
Comparing Two Nozzle Geometries Under Identical Conditions
The two nozzle designs depicted below are used for this evaluation.
Case 1: Straight Nozzle Design
This design features a cylindrical outlet with sharp edges. The geometry allows the fluid to exit the nozzle along a more direct path, resulting in a relatively narrow spray pattern in the simulation.
Case 2: Rounded Nozzle Design
This version includes a smoother, rounded transition from the internal chamber to the nozzle throat. The modified geometry changes the way the fluid exits, producing a noticeably wider and more dispersed spray.
Both cases were simulated using the same transient setup over a 0.25-second interval, with all solver parameters held constant to isolate the influence of geometry alone. Within the simulation domain’s bounding box, normalized mass flux results are displayed at both the midplane and bottom surfaces for comparison, as shown below.
While this comparison focuses on qualitative differences in spray coverage, the same simulation method can be extended to evaluate more complex fluid interactions with CAD geometries. By extracting variables such as heat transfer coefficients, surface wetting behavior, or localized flow rates, this approach supports performance analysis across a wide range of engineering scenarios. When the final nozzle design or arrangement of multiple nozzles is not directly visible (E.g. oil nozzles within an engine or gearbox), simulations can offer critical insights into the impact of design decisions.
Midplane contours of the mass flux for both cases are shown and discussed in the following section.
Observations and Design Implications
- Straight Outlet (Case 1): Suitable for applications requiring a more focused spray pattern, such as targeted lubrication or fuel delivery.
- Rounded Outlet (Case 2): Better suited for applications that benefit from broader coverage, such as cooling, surface treatment, or agricultural spraying.
- Design Insights: Even small geometric changes, such as rounding a sharp edge, can significantly influence spray distribution. CFD modeling offers a practical method for evaluating these effects during early design phases. Asymmetric spray patterns are observed in both cases, which may result from the asymmetric inlet or provide insight into transient start-up behavior in these nozzle designs.
To summarize, these simulations illustrate how subtle geometric changes can be evaluated during early design phases to inform engineering decisions, especially when physical prototyping and testing are time-consuming, impractical, or costly.
See the Simulation in Action
To explore these results in more detail, including how the spray evolves over time and interacts with surrounding geometry, check out the full simulation walkthrough in our recent webinar with Dr. Ted Sperry. He’ll also cover tips for modeling pressure swirl atomizers and other complex spray systems in Ansys Fluent.
