Hong-Gye Sung

Combustion Dynamics in a Model Lean-Premixed Gas Turbine with a Swirl Stabilized Injector

Unsteady numerical study has been conducted on combustion dynamics of a lean-premixed gas turbine with a swirl injector. A three-dimensional computation method utilizing large-eddy-simulation (LES) technique with finite rate chemical reaction was applied with the message passing interface (MPI) parallel architecture. The unsteady turbulent flame dynamics are carefully simulated so that the flow motion can be characterized in detail, showing fairly comparable results with the experimental data. It was observed that some fuel lumps escape from the primary combustion zone, and move downstream and consequently produce hot spots and large vortical structures in the azimuthal direction. The correlation between pressure oscillation and unsteady heat release is examined by the spatial Rayleigh parameter. In addition, it is shown that the complicate heat-release-structure can be precisely regenerated by means of modal analysis using proper orthogonal decomposition (POD).

Combustion of boron particles coated with an energetic polymer material

Elemental boron has attracted considerable attention as a potential high energetic material for explosives and propellants. However, its use has been hindered by its high vaporization temperature and surface oxide layer. In this study, boron particles were coated with glycidyl azide polymer (GAP) to improve their combustion characteristics. The coated particles were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy. XPS performed before and after Ar+ ion sputtering confirmed that the azide (−N3) group of GAP was positioned at the proximity of the boron surface. In addition, B@GAP particles could be decorated with metallic Ag (∼10 nm) nanoparticles. The combustion characteristics were examined using a newly designed pre-heated (1,800 K) drop tube furnace and a high speed camera. Two stages of combustion were observed for a dust cloud of GAP-coated boron particles. The burning time was estimated to be approximately 37.5 msec.

Preparation of TiO2-Decorated Boron Particles by Wet Ball Milling and their Photoelectrochemical Hydrogen and Oxygen Evolution Reactions

TiO2-coated boron particles were prepared by a wet ball milling method, with the particle size distribution and average particle size being easily controlled by varying the milling operation time. Based on the results from X-ray photoelectron spectroscopy, transmission electron microscopy, energy dispersive X-ray analysis, and Fourier transform infrared spectroscopy, it was confirmed that the initial oxide layer on the boron particles surface was removed by the wet milling process, and that a new B–O–Ti bond was formed on the boron surface. The uniform TiO2 layer on the 150 nm boron particles was estimated to be 10 nm thick. Based on linear sweep voltammetry, cyclic voltammetry, current-time amperometry, and electrochemical impedance analyses, the potential for the application of TiO2-coated boron particles as a photoelectrochemical catalyst was demonstrated. A current of 250 μA was obtained at a potential of 0.5 V for hydrogen evolution, with an onset potential near to 0.0 V. Finally, a current of 220 μA was obtained at a potential of 1.0 V for oxygen evolution.

Investigation of Thermophysical Properties of the Kerosene Using the Surrogate Model Fuel at Supercritical Conditions

For the study of thermophysical properties of kerosene for the liquid rocket and aviation fuels, the surrogate models are investigated. The density distributions based on the real gas equations of state(Soave modification of Redlich-Kwong and Peng-Robinson equation of state) and NIST SUPERTRAPP(extended corresponding state principle) are compared with the previous experimental results at supercritical conditions. The error range of thermophysical properties analyzed for the surrogate models as well. Peng-Robinson equation of state and extended corresponding state principle are especially accurate for the hydrocarbon fuels but the appropriate surrogate models need to be chosen to the operation conditions such as pressure and temperature.For the study of thermophysical properties of kerosene for the liquid rocket and aviation fuels, the surrogate models are investigated. The density distributions based on the real gas equations of state(Soave modification of Redlich-Kwong and Peng-Robinson equation of state) and NIST SUPERTRAPP(extended corresponding state principle) are compared with the previous experimental results at supercritical conditions. The error range of thermophysical properties analyzed for the surrogate models as well. Peng-Robinson equation of state and extended corresponding state principle are especially accurate for the hydrocarbon fuels but the appropriate surrogate models need to be chosen to the operation conditions such as pressure and temperature.

Fuel cell system for SUAV using chemical hydride - II. Lightweight fuel cell propulsion system

A 100 W fuel cell system using chemical storage method has been applied for a propulsion system of the SUAV(Small Unmanned Aerial Vehicle). A fuel cell and battery have been combined for both the small/light hydrogen generation control system and the hybrid power supply system. A small hydrogen generation device was implemented to utilize NaBH4 aqueous solution and dead-end type PEMFC system, which were evaluated on the ground and by the flight tests. The system pressurized at a 45kpa stably operates and get higher fuel efficiency. The pressure inside of the hydrogen generation control system was maintained at between 45 kPa and 55 kPa. The 100W fuel cell system satisfies the required weight and power consumption rate as well as the propulsion system, and the fuel cell system performance was demonstrated through flight test.

Experimental Study on Acoustic Attenuation Due to Solid Particles

ABSTRACT High-frequency pressure waves present in rocket motors can be dampened by solid or liquid particles produced from their propellant combustion depending on conditions. The present study conducted an experimental investigation into the effects of particle sizes, ambient gases, and pressure wave frequencies on the attenuation of acoustic energy. Aluminum oxide powders of single-peak broad distributions with average diameters of 5.1 μm, 7.6 μm, 16.5 μm, and 36.2 μm were used to simulate condensed particles in solid rocket combustion environment. Attenuation of excited pressure waves traveling through the fixed cylindrical volume full of particle-laden helium or nitrogen gas has been measured. The number densities of particles floating in gases have been determined by use of processing of images from a high-speed camera. It is observed that alumina particles surely have attenuation effects of pressure waves. The particles in helium show approximately two times greater pressure wave attenuation than those in nitrogen, which indicates the effect of gas density on the attenuation of pressure wave by particles. The optimal particle diameter for the maximal attenuation varies with the frequency of pressure wave. Pressure wave attenuation reaches maximal values at an average particle diameter of 7.6 μm in helium and 16.5 μm in nitrogen over frequencies. Particle diameters showing maximal attenuation become shifted and so do the attenuation characteristics for both cases of helium and nitrogen for high frequency waves greater than 2500 Hz.

Comparison of Hybrid RANS/LES Methods for Supersonic Combustion in a Model Scramjet Combustor

Numerical studies are carried out on the boundary layer behavior on a flat plate as well as on the non-reactive and reactive flows in a scramjet combustor to analyze the effects of various hybrid RANS/LES methods. Three hybrid RANS/LES methods are selected—an improved delayed detached eddy simulation, the l 2ω-detached eddy simulation, and the dynamic l 2ω-detached eddy simulation. The present method is based on the finite-volume approach on structured mesh, and the governing equations are treated using the Favre averaging approach. Inviscid fluxes are discretized using 5th order WENO schemes. Turbulent combustion is modeled as a level-set flamelet model. Based on the results from the flat plate and the non-reacting and reacting simulation, most of the hybrid RANS/LES methods show equivalent trends. However, dramatic differences are found in the calculations for the improved delayed detached eddy simulation and dynamic l 2ω-detached eddy simulation in terms of eddy capturing.

Application of Wind Tunnel Testing on the Dynamic Stability Derivatives of a Rocket Model

This paper described the wind tunnel testing apparatus and technique to acquire the dynamic stability derivatives of large slenderness ratio air vehicle such as the guided missiles or rockets. There have been few difficulties in conducting wind tunnel testing for slender long rocket due to the size limitation of the test section size and the installation of oscillation equipments. In this study, the dynamic stability balance was used as the wind tunnel technique for obtaining the dynamic stability derivatives. Through the wind tunnel testing, the experimental apparatus for slender air vehicle`s oscillation is established. The measured data showed that it is possible to acquire the dynamic stability derivatives of large slenderness ratio rocket, properly.

A Study on Operation Characteristics of Co-flow Fluidic Thrust Vector Control under Over-expanded Jet Condition

The purpose of this research is to investigate the operation characteristics of fluidic thrust vector control using injection of the control flow parallel to the main jet direction; Co-flow injection. The technique bases on the Coanda effect of flow. Both numerical and experimental studies were conducted to investigate operation parameters; flow structure, the jet deflection angle, and shock effects near the nozzle exit. While the total pressure of main jet is the range of 300 to 790 kPa, the total pressure of control flow varies from 120 to 200 kPa. The jet deflection angle and thrust coefficient have linear relation with the pressure ratio(PR) of main jet to control flow in 0.15

Numerical Analysis of a Model Scramjet Engine with Two Intake Side Walls and a Cavity Flame-Holder

A detailed 3D numerical simulation of the flow and H2-air mixing characteristics in a model scramjet engine with two intake-sidewalls and a cavity flame-holder was conducted. Turbulence closure was achieved by a model combining the low-Reynolds-number k-e twoequation model and Sarkar and Wilcox’s compressible turbulent correction model. The governing equations were solved numerically by means of a finite-volume, preconditioned flux-differencing scheme. Cases with and without intake side walls were considered. Intake side walls were found to strongly affect the inlet flow structure, which became more complex in the non-uniform flow field on the cross section perpendicular to the engine axis. The complex and non-uniform flow affected the H2-air mixing pattern inside the combustion chamber, unlike the pattern of the case without side walls. Mixing efficiency and fuel propagation rate were evaluated for the two cases with and without side walls. To verify the accuracy of the simulation, the computed wall pressure was compared with experimental data.