Understanding how water droplets interact with the flow around hypersonic vehicles

During flight, hypersonic vehicles may encounter rain, hail, snow, or other water-based particles of different sizes and temperatures. The complex nose shapes of these vehicles create shocks in the air flow field that can break droplets up into smaller ones. To better understand how these can impact the vehicles’ surface, Prithvi Ramesh and Dorrin Jarrahbashi investigated how water droplet clouds interact with the hypersonic air flow fields around two types of canonical geometries.

Modeling droplet behavior in hypersonic flows is challenging because it involves multiple overlapping length and timescales, such as micro-sized droplets and meter-long nose tips. In this work, the authors employed a hybrid approach. They simulated the flow field with an Eulerian framework, which resolves the air flow around the vehicle, while tracking individual droplets with a Lagrangian approach. Integrating sub-models in the Eulerian framework allowed them to capture key multiphase interactions.

The simulations showed that the post-breakup droplets are likely to become entrapped and accelerate near the vehicle’s surface. This could disrupt the air flow around the vehicle and increase the possibility of droplet impact on the structure, especially if the droplets are large.

“This observation underscores the necessity of considering droplet breakup when estimating the impact force of particles on the vehicle’s surface,” said author Prithvi Ramesh. “Predicting air-droplet dynamics and their potential impacts on hypersonic vehicles is relevant not only to the development of the next generation of hypersonic vehicles, but also to deepening our understanding of the fundamental physics involved in multiphase flows under extreme conditions.”

Next, the authors will conduct more detailed simulations of individual droplets for a deeper understanding of droplet behavior in hypersonic flows.

Source: “Numerical analysis of droplet cloud interaction with a hypersonic flow field,” by Prithvi Ramesh and Dorrin Jarrahbashi, Physics of Fluids (2025). The article can be accessed at https://doi.org/10.1063/5.0270235 .