Xingjian Wang

Counterflow Diffusion Flames of Oxygen and N-Alkane Hydrocarbons (CH4-C16H34) at Subcritical and Supercritical Conditions

This article presents an investigation of counterflow diffusion flames of oxygen and n-alkanes (CH4-C16H34) over the entire thermodynamic fluid regime and a wide range of flow strain rates. The formulation incorporates fundamental thermodynamics and transport theories, along with detailed chemistry. An improved two-point flame-controlling continuation method is employed to capture the complete flame response along the S-curve. Two selected members of the n-alkane family, methane and n-heptane, are studied in detail. The results confirm that the flame thickness () and the global heat-release rate () of oxygen/hydrocarbon systems are closely related to the pressure-weighted strain rate, and . The latter correlation is further modified to account for the pressure effect on peak flame temperature, for the oxygen/methane system, for the oxygen/n-heptane system. The inlet temperature appears to have a negligible effect on flame characteristics. General similarities are developed in the mixture-fraction space in terms of flame temperature, species concentrations, flame thickness, and heat-release rate for all pressures under consideration. This suggests that the flame behaviors at high pressure can be evaluated by their counterpart at low pressure. The common features for the n-alkane family are identified. The flame properties of a given hydrocarbon fuel can be predicted from those of another hydrocarbon fuel at the same flow conditions. The results contribute to the establishment of a tabulated chemistry library for the modeling of supercritical combustion of oxygen and hydrocarbon fuels.

Supercritical Mixing and Combustion of Liquid-Oxygen/ Kerosene Bi-Swirl Injectors

The mixing and combustion characteristics of liquid-oxygen/kerosene bi-swirl injectors are investigated under the supercritical conditions typical of contemporary rocket engines. The basis of the study is a large-eddy simulation technique combined with a unified treatment of real-fluid thermodynamics. The turbulence/chemistry interaction is treated using a laminar flamelet library approach. Emphasis is placed on the near-field flow and flame development downstream of the inner swirler. The flame is found to be stabilized by two counter-rotating vortices in the wake region of the liquid-oxygen post, which is covered by the kerosene-rich mixture. The width of the kerosene annulus is found to significantly affect the injector behavior. A wider annulus induces a larger spreading angle of the liquid-oxygen stream, which intercepts the kerosene stream in a more efficient way. Increasing the annulus width, however, imposes a wake region in a broader zone. The resultant flame becomes relatively unstable if the fl...

Supercritical Combustion of General Fluids in Laminar Counterflows

A counterflow configuration is considered to study flame responses of laminar diffusion flames for general fluid mixtures over the entire thermodynamic regimes. Both subcritical and supercritical temperatures and pressures are included. A unified treatment of thermophysical properties based on fundamental thermodynamic theory and extended corresponding state principle is incorporated into the flame calculations in an opposed flow field. A two-point temperature-controlling continuation method is applied to treat the singularity problem at the turning points on the folded S-shaped curve. The resultant numerical scheme is capable of studying laminar counterflow flame structures over the entire S-curve at any fluid state with detailed chemical mechanism. Both oxygen/hydrogen and oxygen/methane flames are investigated over a broad range of pressures from 0.5 atm to 200 atm. The strain rate varies from a small value to the maximum value (up to 2.0×10 8 s -1 ) in extinction state. The effects of oxygen injection temperature on the flame structure are also discussed in detail.

Comprehensive Study of Cryogenic Fluid Dynamics of Swirl Injectors at Supercritical Conditions

A comprehensive study is conducted to enhance the understanding of swirl injector flow dynamics at supercritical conditions. The formulation is based on full-conservation laws and accommodates real...

Geometric Effects on Liquid Oxygen/Kerosene Bi-Swirl Injector Flow Dynamics at Supercritical Conditions

A systematic study is carried out to investigate the flow dynamics and mixing of liquid oxygen/kerosene bi-swirl injectors at supercritical conditions. The theoretical framework is based on the ful...

A Three-Dimensional Analysis of Swirl Injector Flow Dynamics at Supercritical Conditions

1 Graduate Research Assistant, Georgia Institute of Technology, Email: xwang343@gatech.edu. 2 Mechanical Engineer, GE Global Research Center, Niskayuna, NY, 12309 3,4 Postdoctoral fellow, School of Aerospace Engineering 5 William R. T. Oakes Professor and Chair, School of Aerospace Engineering, Fellow AIAA. 1 American Institute of Aeronautics and Astronautics A Three-Dimensional Analysis of Swirl Injector Flow Dynamics at Supercritical Conditions

Supercritical Injection and Mixing Characteristics of Liquid Oxygen/Kerosene Bi-Swirl Injectors

A numerical study is carried out to investigate the mixing and atomization characteristics of liquid oxygen/kerosene swirl coaxial injectors at supercritical conditions. The numerical scheme is based on fullconservation laws and accommodates real-fluid thermodynamics and transport theories over the entire range of fluid states. Turbulence closure is achieved using large eddy simulation. A grid independence study was first conducted to ensure accurate numerical resolution and underlying flow physics. The mixing characteristics and flow dynamics were discussed in depth. Various geometric parameters, including recess region, post thickness, and kerosene annulus width, are examined to explore their influence on mixing efficiency and flow dynamics. The recess region enhances the interaction of liquid oxygen and kerosene and improves the mixing efficiency. A larger post thickness or larger annulus width imposes a higher spreading angle of the liquidoxygen film and intercepts the kerosene film in a broader area, thereby facilitating mixing in the recess region. But the flow structures in the recess region become more complicated and the mixture ratio in the vicinity of the injector post is close to stoichiometric, which leads to the potential overheating in case of combustion. An appropriate selection of the post thickness, recess length, and annulus width must be carefully made for the optimum injector performance. The present study provides important information for injector design and underlying flow physics.

Supercritical fluid flow dynamics and mixing in gas-centered liquid-swirl coaxial injectors

Gas-centered, liquid-swirl coaxial injectors similar to those used in the main chambers of oxidizer-rich staged-combustion engines are investigated computationally, in terms of supercritical fluid flow dynamics and mixing. Gaseous oxygen (GOX) is axially directed through a center post at a temperature of 687.7 K. Kerosene is tangentially introduced into the outer coaxial swirler at a temperature of 492.2 K. The mean chamber pressure of 253.0 bars substantially exceeds the thermodynamic critical pressures of oxygen and kerosene. The end of the GOX post is recessed from the entrance of the taper region, which is connected downstream to an open domain. A wide range of recess lengths (and correspondingly, fuel shielding collar lengths) is considered to determine the dependence of flow characteristics on this geometric parameter. Special attention is given to the regions downstream of the GOX post end and in the taper section, where primary mixing occurs. Instantaneous and time-averaged flow properties, as well as mixing effectiveness, are examined. Results indicate that the recess length plays a critical role in determining the flow evolution and mixing behaviors. In a fully recessed injector without fuel shielding, the initial kerosene/GOX interaction resembles a swirling transverse jet into a crossflow, and flow recirculation occurs near the kerosene injection slit and the head end. In other injectors with fuel shielding, the kerosene flow is predominantly axial before it enters the mixing zone; the coflow kerosene and GOX streams expand radially and recirculate in the wake of the GOX post. Flow unsteadiness arising from the fluid injection and mixing and vorticity production in the boundary layer of the GOX stream, along the wall of the fuel passage, and at the kerosene/GOX interface cause the development of salient vortical structures in the downstream flowfield. The geometric changes at the entrance of the taper region and at the injector exit further alter the flow dynamics, inducing multiple toroidal recirculation zones and secondary vortex structures.Gas-centered, liquid-swirl coaxial injectors similar to those used in the main chambers of oxidizer-rich staged-combustion engines are investigated computationally, in terms of supercritical fluid flow dynamics and mixing. Gaseous oxygen (GOX) is axially directed through a center post at a temperature of 687.7 K. Kerosene is tangentially introduced into the outer coaxial swirler at a temperature of 492.2 K. The mean chamber pressure of 253.0 bars substantially exceeds the thermodynamic critical pressures of oxygen and kerosene. The end of the GOX post is recessed from the entrance of the taper region, which is connected downstream to an open domain. A wide range of recess lengths (and correspondingly, fuel shielding collar lengths) is considered to determine the dependence of flow characteristics on this geometric parameter. Special attention is given to the regions downstream of the GOX post end and in the taper section, where primary mixing occurs. Instantaneous and time-averaged flow properties, as wel...

An Efficient Surrogate Model for Emulation and Physics Extraction of Large Eddy Simulations

ABSTRACT In the quest for advanced propulsion and power-generation systems, high-fidelity simulations are too computationally expensive to survey the desired design space, and a new design methodology is needed that combines engineering physics, computer simulations, and statistical modeling. In this article, we propose a new surrogate model that provides efficient prediction and uncertainty quantification of turbulent flows in swirl injectors with varying geometries, devices commonly used in many engineering applications. The novelty of the proposed method lies in the incorporation of known physical properties of the fluid flow as simplifying assumptions for the statistical model. In view of the massive simulation data at hand, which is on the order of hundreds of gigabytes, these assumptions allow for accurate flow predictions in around an hour of computation time. To contrast, existing flow emulators which forgo such simplifications may require more computation time for training and prediction than is needed for conducting the simulation itself. Moreover, by accounting for coupling mechanisms between flow variables, the proposed model can jointly reduce prediction uncertainty and extract useful flow physics, which can then be used to guide further investigations. Supplementary materials for this article, including a standardized description of the materials available for reproducing the work, are available as an online supplement.

Evolution and transition mechanisms of internal swirling flows with tangential entry

The characteristics and transition mechanisms of different states of swirling flow in a cylindrical chamber have been numerically investigated using the Galerkin finite element method. The effects of the Reynolds number and swirl level were examined, and a unified theory connecting different flow states was established. The development of each flow state is considered as a result of the interaction and competition between basic mechanisms: (1) the centrifugal effect, which drives an axisymmetric central recirculation zone (CRZ); (2) flow instabilities, which develop at the free shear layer and the central solid-body rotating flow; (3) the bouncing and restoring effects of the injected flow, which facilitate the convergence of flow on the centerline and the formation of bubble-type vortex breakdown; and (4) the damping effect of the end-induced flow, which suppresses the development of the instability waves. The results show that the CRZ, together with the free shear layer on its surface, composes the basi...