Interactions between liquid and vapor media are prominent in modern engineering systems such as combustion engines, cooling systems, and chemical reactors. The complex interactions between phases pose significant challenges for accurate mathematical modeling and simulation.
At FxLab, we focus on developing advanced methods for simulating multiphase flows using a unified formulation (Ly & Ihme, 2024) that emphasizes thermodynamic consistency between the liquid and vapor phases. The vapor-liquid phase-change regimes near critical conditions are modeled using cubic, real-fluid equations of state (EOS) (Ma et al., 2017). Addressing the physical effects across the interface, we employ a phase-field approach based on the diffuse interface theory of van der Waals to model these interfacial effects that are consistent with the vapor-liquid equilibrium in all temperatures and pressures.
This approach allows us to capture the intricate dynamics of phase transitions and interactions, providing a robust framework for simulating multiphase flows in various engineering applications. Our methods have been applied to a range of problems, including liquid injection in combustion engines (Ly & Ihme, 2024), shocks (Krisna et al., 2025), and cooling systems.
References
2025
-
Shock-Induced Vanishing Dynamics of Water-Droplet Interface
Benyamin Krisna, Nguyen Ly, and Matthias Ihme
In AIAA SCITECH 2025 Forum, Jan 2025
Novel combustion systems in aerospace propulsion systems as scramjets and rotating detonation engines utilize higher pressure conditions to achieve optimal thermodynamic efficiency. As a result, the combustion chamber pressure may affect the interface stability of water, one of the main combustion products. Although the immiscibility between the liquid water droplet and the ambiance guarantees the formation of the subcritical interface, its dynamics and impact is typically neglected in many simulations. These are even more prominent with interfacial dynamics due to transcritical effects that arise due to strong shocks inside the combustion chamber, which is typical in modern detonation engines. To elucidate this, we consider a shock of M=1.36 for a water/nitrogen system, where the post-shock liquid- and vapor-phase conditions (T_1=600 K and T_2=730 K) are fully transcritical with respect to the critical mixing point. In this work, we employ the Regularized Interface Method (RIM), since it is able to resolve both subcritical interfacial dynamics along with supercritical mixing dynamics. Vanishing and spontaneous emergence of the interface is observed, indicating the need of resolving the interfacial dynamics and effects.
2024
-
A regularized-interface method as a unified formulation for simulations of high-pressure multiphase flows
Nguyen Ly, and Matthias Ihme
Journal of Computational Physics, Dec 2024
The injection of multi-species fluids into high-pressure and high-temperature environments beyond the species’ critical points is commonly found in engineering applications. At these conditions, for immiscible species, both subcritical interfacial dynamics and supercritical mixing can coexist due to variations in temperature around the mixture critical point. The modeling of these complex transcritical phenomena for large-scale configurations is so far not possible. To address this issue, we propose the Regularized-Interface Method (RIM) as a unified formulation that can describe both sub- and supercritical processes as well as the transition between them. The proposed method is derived via filtering of the nanoscale interface-resolving formulation based on van der Waals’ linear gradient theory. Thus, this approach allows for the consistent modeling of interfacial dynamics that vanishes at supercritical conditions, while significantly reducing the temporal and spatial resolution constraints of the original nanoscale formulation. The resulting RIM formulation is examined in interface-capturing simulations of sub-, trans-, and supercritical fuel injection processes, involving droplets and jets. These results highlight the importance of resolving spatio-temporal transitions from subcritical interfacial dynamics to supercritical mixing in high-pressure multiphase simulations, in contrast to commonly employed diffused-interface methods, where interfacial dynamics are often neglected.
-
On the importance of species immiscibility in mixing-layer dynamics at supercritical pressures
Nguyen Ly, and Matthias Ihme
International Journal of Multiphase Flow, Nov 2024
The mixing dynamics of injected propellants is a key factor in determining the ignition performance and combustion-instability response of rocket engines, internal combustion engines, and gas turbines. A key source of uncertainty in the prediction of phase-exchange dynamics is the immiscibility of the injected propellants at supercritical pressure conditions, which induces liquid/vapor phase separation and surface-tension dynamics. While experimental observations indicate the presence of liquid/vapor interfacial structures, this interfacial dynamics is typically neglected in numerical analyses. To address this issue, the objective of the present study is to systematically evaluate the importance of species immiscibility on the phase-exchange dynamics of cryogenic LOX/GH2 mixing layers at typical rocket engine injection conditions. This is accomplished by comparing simulations of (i) a recently developed interface-capturing Regularized-Interface Method (RIM) formulation, and (ii) the commonly employed Diffuse-Interface Method (DIM) formulation. Analysis shows that the interfacial dynamics significantly impact the atomization and mixing of the propellants in the near-injector region, which is not captured by the DIM formulation. The findings of this study extend to other immiscible injection systems, such as LOX/kerosene and hydrocarbon-fuel/air, thereby highlighting the importance of resolving species immiscibility in simulating high-pressure combustion engines.
2017
-
An entropy-stable hybrid scheme for simulations of transcritical real-fluid flows
Peter C Ma, Yu Lv, and Matthias Ihme
Journal of Computational Physics, Nov 2017
Publisher: Elsevier
