arXiv subjects

Zongmin Hu

Publications and source records attributed to Zongmin Hu.

5 recordsLinked to original sources

arXiv2026

Liquid-fueled Oblique Detonation Stabilized by a Transverse Jet

The role of a transverse liquid n-heptane jet in initiating and stabilizing liquid n-heptane oblique detonation waves (ODWs) in a confined model combustor was computationally investigated in the present work. The jet-to-inflow momentum ratio, J, was identified as the primary control parameter. Under steady inflow pressures, a weak jet with a small J fails to initiate an ODW; a slightly stronger jet ignites only a local near-normal detonation between the OSW and the separation shock wave without forming a developed ODW branch; a moderate jet establishes a standing detonation wave system consisting of an ODW, a near-normal detonation branch, and a separation shock wave; a large but still admissible J produces a wall-coupled ODW-Mach-stem configuration; and an excessive jet momentum destabilizes the ODW by pushing it out of the combustor into the external compression region. Under oscillatory inlet pressure, the standing ODW remains dynamically stabilized within the combustor through bounded, phase-dependent transitions between distinct combustion modes. At sufficiently large J, the transverse jet ceases to act as an effective stabilization actuator. The resulting dynamic-stabilization map reveals a finite operating window governed jointly by jet momentum and inlet-pressure fluctuation.

physics.flu-dyn↗

arXiv2025

Oscillating Detonation of Liquid Ammonia

Liquid ammonia is a promising carbon-free energy carrier, but its high volatility and low reactivity lead to detonation dynamics that differ significantly from those of liquid hydrocarbons. Using Eulerian-Lagrangian simulations, we revealed an oscillating detonation phenomenon driven by the flash boiling of ammonia. Specifically, intense endothermic evaporation and exothermic combustion periodically weaken and then restore the coupling between the shock front and the reaction zone. A delay differential equation (DDE) model is developed to describe this oscillatory behaviour. In this model, the shock response constraint is derived from the positive characteristic compatibility relation behind the shock front, and it is closed using delay-augmented relaxation models for evaporation and reaction progress variables. Normal-mode stability analysis of the DDE system shows that an oscillatory solution emerges when the evaporation and reaction timescales are comparable. Simulation data across different evaporation models, droplet diameters, and ambient temperatures collapse onto the theoretical frequency band predicted by the model.

physics.flu-dyn↗

arXiv2025

Liquid-fueled oblique detonation waves induced by reactive and non-reactive transverse liquid jets

This computational study demonstrates the formation of liquid-fueled oblique detonation waves (ODWs) induced by a liquid transverse jet, which is either reactive or non-reactive. The study employs an in-house two-phase supersonic reactive flow solver based on the rhocentralfoam framework of OpenFOAM. The findings emphasize the essential role of transverse jets in enabling successful ODW formation under conditions where detonation would otherwise fail. Specifically, the jet-inflow momentum ratio significantly influences the mechanisms of ODW formation. At lower momentum ratios, the oblique shock wave (OSW) induced by the jet is insufficient to directly initiate detonation. Instead, the atomized n-heptane jet increases the local fuel mass fraction, promoting low- and intermediate-temperature chemical reactions, which eventually lead to detonation. At higher momentum ratios, the OSW generated by the transverse jet is sufficiently strong to directly trigger detonation through intermediate-temperature chemistry, with the jet acting primarily as a combustion stabilizer rather than directly enhancing combustion. Comparative studies with non-reactive jets and wedge-strip configurations demonstrate that at higher momentum ratios, the dominant mechanism is the physical blocking effect of the jet, which generates a strong OSW capable of initiating detonation.

physics.flu-dyn↗

arXiv2024

Computational Investigation on the formation of liquid-fueled oblique detonation waves

Utilizing a two-phase supersonic chemically reacting flow solver with the Eulerian-Lagrangian method implemented in OpenFOAM, this study computationally investigates the formation of liquid-fueled oblique detonation waves (ODWs) within a pre-injection oblique detonation wave engine operating at an altitude of 30 km and a velocity of Mach 9. The inflow undergoes two-stage compression, followed by uniform mixing with randomly distributed n-heptane droplets before entering the combustor. The study examines the effects of droplet breakup models, gas-liquid ratios, and on-wedge strips on the ODW formation. Results indicate that under the pure-droplet condition, the ODW fails to form within the combustor, irrespective of the breakup models used. However, increasing the proportion of n-heptane vapor in the fuel/air mixture facilitates the ODW formation, because the n-heptane vapor rapidly participates in the gaseous reactions, producing heat and accelerating the transition from low- to intermediate-temperature chemistry. Additionally, the presence of on-wedge strips enhances ODW formation by inducing a bow shock wave within the combustor, which significantly increases the temperature, directly triggering intermediate-temperature chemistry and subsequent heat-release reactions, thereby facilitating the formation of ODW.

physics.flu-dyn↗

arXiv2024

A Dynamic Droplet Breakup Model for Eulerian-Lagrangian Simulation of Liquid-fueled Detonation

This study proposes a dynamic model to reflect the physical image of the droplet breakup process in two-phase detonation flows. This breakup model is implemented in a two-phase detonation solver developed based on an open-source computational fluid dynamic platform, OpenFOAM, and compared with three prevalent models (TAB, PilchErdman, and ReitzKH-RT model) under different droplet diameters in one- and two-dimensional detonation problems. The simulating results show that the present breakup model well predicts experimentally determined detonation parameters such as detonation velocities and post-wave temperature. In addition, the present model has the advantage of being free of the KH breakup time parameter, which is needed by the ReitzKH-RT model to fit the experimental data. The one-dimensional detonation simulations indicate that different breakup models have a slight impact on the detonation wave velocity because the droplet breakup process does not significantly affect the total heat release as long as it is sufficiently fast to sustain the detonation. However, the two-dimensional detonation simulations show that both the breakup model and the droplet initial diameter significantly affect the detonation cell size due to the different droplet distributions predicted by different models. The breakup length, which is the distance from the shock wave to the location at which sufficiently small child droplets appear, affects the chemical reaction zone thickness, which in turn affects the detonation cell size. A longer breakup length will result in a larger detonation cell size.

physics.flu-dyn↗