Su-Hee Won

Numerical Investigation of Transverse Hydrogen Jet into Supersonic Crossflow Using Detached-Eddy Simulation

A three-dimensional unsteady reacting flowfield that is generated by transverse hydrogen injection into a supersonic mainstream is numerically investigated using detached-eddy simulation and a finite-rate chemistry model. Grid refinement with the grid-convergence-index concept is applied to the instantaneous flowfield for assessing the grid resolution and solution convergence.Validation is performed for the jet penetration height, and the predicted result is in good agreement with experimental trends. The results indicate that jet vortical structures are generated as the interacting counter-rotating vortices become alternately detached in the upstream recirculation region. Although the numerical OH distribution reproduces the experimental OH–planar-laser-induced fluorescence well, there are some disparities in the ignition delay times due to the restricted availability of experimental and numerical data. The effects of the turbulence model on combustion are identified by a comparative analysis of the Reynolds-averaged Navier–Stokes and detached-eddy simulation approaches. Their effects are quantified by the production ofH2O, which is the primary species of hydrogen combustion.

Three-Dimensional Dynamic Characteristics of Transverse Fuel Injection into a Supersonic Crossflow

Three-dimensional unsteady flowfield generated by transverse injection into a supersonic mainstream are simulated with a DES turbulence model. The grid refinement with GCI method is applied for the instantaneous and time-averaged flowfield to assess grid resolution and computational efficiency. Comparisons are made with experimental results to investigate the large-scale coherent structures and mixing characteristics. Results indicate that the DES simulations are of a good enough degree of agreement with the experiment. DES simulations replicate the instantaneous features and the predicted penetration height is comparable to experimental data with an acceptable error range. The eddy formation frequency is slightly overpredicted, probably due to inadequate turbulence intensity at the incoming and injector exit flowfield. The jet vortical structures are developed from the competing vortices in the recirculation region of upstream boundary.

Turbulent Combustion Characteristics in HyShot Model Combustor with Transverse Fuel Injection

This paper describes numerical efforts to investigate combustion characteristics of HyShot scramjet combustor, where gaseous hydrogen is transversely injected into a supersonic cross flow. The corresponding altitude, angle of attack, and equivalence ratio are 35-23 km, 0°, and 0.426 respectively. H2 and OH mass fraction show that the upstream recirculation region generated by the fuel injection has flame-holding effects. Twodimensional simulation reasonably predicts combustor inner pressure distribution and reveals periodic combustion characteristics of HyShot scramjet combustor. Altitude effects are also investigated and the strength of flow instability and subsonic boundary layer thickness affect the combustion efficiency according to altitudes. Frequency analyses provide the flow instability effects on the turbulent combustion in HyShot scramjet combustor.

DES Investigation of the Ignition of Hydrogen Transverse Jet into High Enthalpy Supersonic Crossflow

Unsteady three-dimensional reacting flowfield generated by transverse hydrogen injection into a supersonic mainstream is numerically investigated using DES and finite-rate chemistry model. Comparisons are made with experimental results to investigate the turbulent reacting flow physics. The numerical OH distribution describes well the experimental OH-PLIF result, while the numerical ignition delay time shows some disparity due to the restricted available experimental data. The intermittency phenomena are identified by the comparative analysis between RANS and DES. Those effects are also quantified by the temperature distributions along streamlines and superimposed OH mass fraction along with time.

Three-Dimensional Simulation of Ignition Transient in Hyshot Scramjet Configuration

HyShot scramjet combustor flowfield, where gaseous hydrogen is transversely injected into a supersonic cross flow, is simulated with DES turbulence and finite-rate chemistry model. The injection pressure is considered over a broad range which corresponds to equivalence ratio from 0.3 to 1.0. This work features detailed resolution of the flow and flame dynamics in the combustor, which was not typically available in most of the previous studies. Results indicate that the DES model is properly activated in the high equivalence ratio, where there exits the large scale eddies. The numerical pressure distribution shows that a high equivalence ratio causes a strong pressure wave generated by the explosive combustion. As a result of the strong pressure wave the combustor inner flowfield changes to the subsonic mode and converges to unstarting procedure.

A Partly Implicit Method for the Solution of Detailed Kinetics based on the Sensitivity Analysis

A partly implicit/quasi-explicit method is introduced for the solution of detailed chemical kinetics with stiff source terms based on the standard fourth-order Runge-Kutta scheme. Present method solves implicitly only the stiff reaction rate equations, whereas the others explicitly. The stiff equations are selected based on the survey of the chemical Jaconian matrix and its Eigenvalues. As an application of the present method constant pressure hydrogen-air combustion is considered with a detailed chemistry mechanism with NOx chemistry. The sensitivity analysis reveals that only the 4 species in NOx chemistry has strong stiffness and should be solved implicitly among the 13 species. The implicit solution of the 4 species successfully predicts the entire process with same accuracy and efficiency at half the price.

Numerical Analysis of Turbulent Combustion Flow in HyShot Scramjet Engine

This paper describes numerical efforts to investigate combustion characteristics of HyShot scramjet combustor, where gaseous hydrogen is transversely injected into a supersonic cross flow. The corresponding altitude, angle of attack, and equivalence ratio are 35-23km, 0°, and 0.426 respectively. H2 and OH mass fraction show that the upstream recirculation region generated by the fuel injection has flame-holding effects. Twodimensional simulation reasonably predicts combustor inner pressure distribution and reveals periodic combustion characteristics of HyShot scramjet combustor. Altitude effects are also investigated and the strength of instability and subsonic boundary layer thickness affect the combustion efficiency according to altitudes.

Numerical Simulation Study of Supersonic Combustion in Model Combustors

Air-fuel mixing and flame-holding are two important factors that have to be considered in the design of an injection system. Different injection strategies have been proposed with particular concern for rapid air-fuel mixing and flame-holding. Two representative injection techniques can be applied in a supersonic combustor. One of the simplest approaches is a transverse(normal) injection. The cavity flame holder, an integrated fuel injection/flameholding approach, has been proposed as a new concept for flame holding and air-fuel mixing in a supersonic combustor. This paper describes numerical efforts to characterize the flameholding and air-fuel mixing process of a model scramjet engine combustor, where hydrogen is injected into a supersonic cross flow and a cavity. The combustion phenomena in a model scramjet engine, which has been experimentally studied at University of Queensland and Australian National University using a free-piston shock tunnel, were observed around the separation region of the transverse injector upstream and the inside cavity. The results show that this flow separation generates recirculation regions which increase air-fuel mixing. Selfignition occurs in the separation-freestream and cavity-freestream interfaces.