I. Jeung

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Analysis of NOx Emissions in Thrbulent Nonpremixed Hydrogen-Air Jet Flames with Coaxial Air

The characteristics of NOx emissions in pure hydrogen nonpremixed flames with coaxial air are ana... more The characteristics of NOx emissions in pure hydrogen nonpremixed flames with coaxial air are analyzed numerically for the three model cases of coaxial air flames classified by varying coaxial air velocity and/or fuel velocity. In coaxial air flames, the flame length is reduced by coaxial air and can be represented as a function of the ratio of coaxial air to fuel velocity. Coaxial air decreases flame reaction zone, resulting in reducing flame residence time significantly. Finally, the large reduction of EINOx is achieved by the decrease of the flame residence time. It is found that because coaxial air can break down the flame self-similarity law, appropriate scaling parameters, which are different from those in the simple jet flames, are recommended. In coaxial air flames, the flame residence time based on the flame volume produces better results than that based on a cube of the flame length. And some portion of deviations from the 1/2 scaling law by coaxial air may be due to the v...

The Estimation of Radiation Exposure for Arcsecond Pico Star Tracker (APST) in Low Earth Orbit

In general COTS components have radiation tolerance of 1-10 Krad/year and untested components whi... more In general COTS components have radiation tolerance of 1-10 Krad/year and untested components which are made up of silicon is estimated to have radiation tolerance up to 5 Krad. The primary idea of this paper is to estimate the Total Ionizing Dose (TID) of silicon and Single Event Upset (SEU) rates of the COTS components in LEO, using Space Environment Information System (SPENVIS) software. This analysis are performed for the orbital altitude of 400 to 600 km, inclination of 90° for one year. The result estimates that the target material silicon, without shielding acquired TID of 3.04 Mrad. The Aluminum shieling of 2mm and 3mm thickness reduces the TID to 3.04 Krad and 1.39 Krad respectively. The shielding of 2mm is optimum for COTS in LEO. At orbital inclination of 0°, 28° with a shielding of 2mm, the TID is 0.014Krad and 0.56 Krad respectively, but at 60° to 90° the TID increased to 3 Krad. The SEU rate varies for each device based on design, manufacturing technology, LET threshol...

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Numerical Study of Regular Start and Unstart Process of Superdetonative Speed Ram Accelerator

A numerical study was conducted to investigate the combustion phenomena of regular start and unst... more A numerical study was conducted to investigate the combustion phenomena of regular start and unstart processes based on ISL#s RAMAC 30 experiments with different diluent amounts in a ram accelerator. The initial projectile launching speed was 1800m/s which corresponded to the superdetonative speed of the stoichiometric mixture diluted with . In this study, it was found that neither shock nor viscous heating was sufficient to ignite the mixture at a low speed of 1800m/s, as was found in the experiments using a steel-covered projectile. However, we could succeed in igniting the mixtures by imposing a minimal amount of additional heat to the combustor section and simulate the regular start and unstart processes found in the experiments with an aluminum-covered projectile. The numerical results matched almost exactly to the experimental results. As a result, it was found that the regular start and unstart processes depended on the strength of gas mixture, development of shock-induced co...

Numerical Study of the Effect of Shock Strength on the Normal Start and Unstart Process in a Superdetonative Mode Ram Accelerator

Corresponding Author : In-Seuck Jeung Email : enjis@plaza.snu.ac.kr, Phone : +82-2-880-7387, FAX ... more Corresponding Author : In-Seuck Jeung Email : enjis@plaza.snu.ac.kr, Phone : +82-2-880-7387, FAX : +82-2-887-2662 Numerical Study of the Effect of Shock Strength on the Normal Start and Unstart Process in a Superdetonative Mode Ram Accelerator G.-W. Moon, I.-S. Jeung , J.-Y. Choi*, Friedrich Seiler, Gunther Patz, Günter Smeets, and Julio Srulijes Department of Aerospace Engineering, Seoul National Univesity, Seoul, 151-742, Korea *Department of Aerospace Engineering, Pusan National Univesity, Pusan, 609-735, Korea French-German Research Institute of Saint-Louis(ISL), Shock Tube Department, P.O.Box34, F68301, Saint Louis, France.

Numerical study of thermal choking process in a model scramjet engine

36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 2000

A numerical study was conducted to investigate the combustion phenomena of thermal choking proces... more A numerical study was conducted to investigate the combustion phenomena of thermal choking process in a model scramjet engine based on ANU's experiments. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations coupled with a Baidwin-Lomax turbulence model and detailed chemistry reaction equations of H/O/Nj based on the GRI-Mech. 2.11 were considered. The governing equations were discretized by a high order accurate upwind scheme and solved in a fully coupled manner with a fully implicit, time accurate integration method. In this study, it was found that thermal choking could be generated by strong turbulent mixing. Also, the vortex flow in a shear layer between fuel jet and air caused the mixing active. This increased the heat release by combustion and the flow in the downstream part of the duct changed into subsonic which propagated upstream along the duct, called thermal choking, followed by unstart,

Cavity Flame-Holder Experiments in a Model Scramjet Engine

14th AIAA/AHI Space Planes and Hypersonic Systems and Technologies Conference, 2006

Unexpected synchronous follicular lymphoma of paraaortic and pelvic lymph nodes in a patient with endometrial carcinoma: a case report

European journal of gynaecological oncology, 2011

Multiple neoplasms in a patient occur rarely. There has only been one case report about synchrono... more Multiple neoplasms in a patient occur rarely. There has only been one case report about synchronous endometrial carcinoma and follicular lymphoma of the paraaortic and pelvic lymph node (LN) until now. The patient was 64 years old and had vaginal spotting for four months. She was diagnosed with endometrioid endometrial carcinoma by endometrial biopsy. In intraoperative inspection, the whole paraaortic and pelvic LN had formed into a massive tumor bundle following the aorta and iliac vessels. The diagnosis was endometrial carcinoma FIGO Stage IB with synchronous follicular lymphoma Stage III. We performed adjuvant chemotherapy and radiotherapy. Currently, the patient has no evidence of recurrence for either carcinoma. Lymph node dissection was included in the staging and debulking operation of the endometrial carcinoma. An inaccurate result of the frozen section can not rule out metastasis of endometrial carcinoma and surgeons can fall into a dilemma regarding treatment.

Clinical analysis of borderline ovarian tumors

European journal of gynaecological oncology, 2011

The goal of this study was to evaluate the incidence and clinical features of borderline ovarian ... more The goal of this study was to evaluate the incidence and clinical features of borderline ovarian tumors (BOTS). We retrospectively performed chart reviews of 22 patients with BOTS who were diagnosed and treated in the university medical center from 1998 to 2009 inclusively. BOTS among ovarian pathology in our hospital were detected in 22 patients (1.79%). The mean age was 50 years, range (20-90). Post surgical FIGO staging was Stage I = 86.4%, and Stage II = 13.6%. The most common histologic subtype was mucinous (59%). Five patients (22.7%) had a unilocular cyst at ultrasonography. Conservative surgery was performed in 31.8%. One patient of them had normal spontaneous delivery after term pregnancy. Two patients had a recurrence. One patient with recurrent disease underwent transformation to invasive cancer and died 35 months after the initial diagnosis. Clinicians should warn patients about the early relapse of BOTS and these patients may need careful follow-up due to the possibilit...

Flowfield characteristics on a vent slot mixer in supersonic flow

Shock Waves, 2010

A research was conducted on a new mixing device referred as a "vent slot mixer", using experiment... more A research was conducted on a new mixing device referred as a "vent slot mixer", using experimental and computational methods. The experiment was conducted in a laboratory-scale supersonic wind-tunnel of Mach number 2. Inflow air was under atmospheric air condition, and hydrogen gas was used as fuel. In addition, the computational simulation approach was performed to support the experimental result. The vent slot mixer can directly entrain the main airflow into the recirculation region, inducing complex flow structures in the recirculation region. This also leads to gradual development of the shear layer to reduce the total pressure loss mainly induced by a recompression shock. Contrary to typical shear layers of step mixer, for the vent slot mixer, two-dimensional large-scale structures and weak shocks were clearly identified around the shear layer through experimental and computational methods. When the fuel was injected from one circular injector in the recirculation region, the high fuel concentration of the vent slot mixer was evenly distributed along the spanwise direction, but with the step mixer the fuel was highly concentrated along the Communicated by L. Bauwens. This paper is based on work that was presented at the 22nd International Colloquium on the Dynamics of Explosions and

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Effect of fuel injection location on a plasma jet assisted combustion with a backward-facing step

Proceedings of the Combustion Institute, 2011

Non-reacting and reacting experiments on the ignition by a plasma jet (PJ) torch were performed t... more Non-reacting and reacting experiments on the ignition by a plasma jet (PJ) torch were performed to understand the correlation between fuel injection location and combustion characteristics in unheated Mach 2 airflow. Fuel was injected through three sonic injectors in the recirculation region behind a backward-facing step: a parallel injector at 2mm from the bottom wall and two normal injectors at 2 and 9mm from the step wall. In order to mitigate the combustion pressure interaction with nozzle, an isolator was installed between the nozzle and combustor. The combustion performance of normal injection was little affected by the difference of fuel injection locations. Moreover, normally injected fuel was escaped not to be held in the recirculation region despite of low fuel injection rates. This led to lower combustion performance relative to the parallel injection which provided fuel not to leave the recirculation region. In this case, the role of the recirculation region was to fully hold fuel, and the PJ torch provided hot gases as a heat source and acted as a flame-holder to ignite fuel–air mixtures. In a low temperature inflow condition, combustible regions were constrained around the bottom wall where embedded with the PJ torch. When thermal choking occurred in the combustor, it induced shock train both in the combustor and isolator. Under this unstable condition, the combustion performance of the normal injection was lower than that of the parallel injection. This is because the normal injection led most fuel into low temperature incoming air-stream.

Trocar Site Herniation through a 5mm Trocar Site Following Removal of Drains after Gynecologic Laparoscopy

Journal of Minimally Invasive Gynecology, 2008

Effects of Fuel Nozzle Displacement on Pre-Filming Airblast Atomization

Journal of Engineering for Gas Turbines and Power, 1999

In gas turbine combustors, optimum arrangement between a fuel nozzle and a swirler/prefilmer modu... more In gas turbine combustors, optimum arrangement between a fuel nozzle and a swirler/prefilmer module must be sought to achieve satisfactory ignition and stability characteristics in addition to reduced level of emissions. However, due to thermal expansion of the combustor or misalignment of the fuel nozzle, the location of a fuel nozzle may vary. Displacement of a fuel nozzle may change the amount of fuel injected to the pre-filming device (usually the inner swirler wall) and the location of attachment, which in turn affects the thickness of pre-filming liquid sheet on the wall. As a result, the spray structure formed by pre-filming airblast atomization may be significantly changed. An experimental investigation is carried out to study the effects of fuel nozzle displacement on the structure of a spray formed by a dual orifice pressure atomizer and a counter-rotating dual swirler. The inner wall of the swirler is designed to be used as a pre-filming device. The behavior of droplets, ...

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Computational modeling of high pressure combustion mechanism in scram accelerator

Le Journal de Physique IV, 2000

A computational study was carried out to analyze a high-pressure combustion in scram accelerator.... more A computational study was carried out to analyze a high-pressure combustion in scram accelerator. Fluid dynamic modeling was based on RANS equations for reactive flows, which were solved in a fully coupled manner using a fully implicit-upwind TVD scheme. For the accurate simulation of high-pressure combustion in ram accelerator, 9-species, 25-step fully detailed reaction mechanism was incorporated with the existing CFD code previously used for the ram accelerator studies. The mechanism is based on GRI-Mech. 2.11 that includes pressure-dependent reaction rate formulations indispensable for the correct prediction of induction time in high-pressure environment. A real gas equation of state was also included to account for molecular interactions and real gas effects of high-pressure gases. The present combustion modeling is compared with previous 8-step and 19-step mechanisms with ideal gas assumption. The result shows that mixture ignition characteristics are very sensitive to the combustion mechanisms, and different mechanism results in different reactive flow-field characteristics that have a significant relevance to the operation mode and the performance of scram accelerator.

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A prospective comparison of vaginal stump suturing techniques during total laparoscopic hysterectomy

Archives of Gynecology and Obstetrics, 2009

Purpose We compared the incidence of vaginal cuV dehiscence and other surgical complications afte... more Purpose We compared the incidence of vaginal cuV dehiscence and other surgical complications after diVerent modes of suturing during total laparoscopic hysterectomy (TLH), and reviewed the characteristics of patients with complications. Methods We enrolled 248 patients undergoing TLH for benign diseases at Daejeon St Mary's Hospital of Korea from March 2007 through February 2009. We evaluated the clinical outcomes of diVerent vaginal cuV suture techniques during TLH: the widely used interrupted Wgure-of-eight suture and a two-layer running suture. Results All operations were completed successfully by laparoscopy. Three of 248 hysterectomies (1.2%) were complicated by vaginal cuV dehiscence. One of them belonged to the two-layer running suture group, and the others belonged to the interrupted Wgure-of-eight suture group. However, there was no statistically signiWcant diVerence in outcomes between the suture methods. One case of trocar site incisional herniation occurred. No ureteral, bladder, or major vascular injury occurred. The overall major complication rate including vaginal bleeding was 2.0% (5/248). Conclusions The two-layer running suture technique was safe and eVective for vaginal cuV suture during TLH, but there was no statistically signiWcant advantage over the widely used Wgure-of-eight suture method. Diabetes, cigarette smoking and pelvic adhesions produced statistically signiWcant increased risks of complication.

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Flowfield Characteristics of a Hypermixer Interacting with Transverse Injection in Supersonic Flow

AIAA Journal, 2012

ABSTRACT Nonreacting experiments were conducted at Mach 2 to understand the relationship between ... more ABSTRACT Nonreacting experiments were conducted at Mach 2 to understand the relationship between a wall-mounted alternating-ramp-wedge-type hypermixer and transverse injection compared with a step mixer. Experimental techniques such as schlieren visualization and stereoscopic particle image velocimetry were employed to study the three-dimensional flowfield with vortex structures induced by the interaction between the mixer and transverse injection. Without injection, the hypermixer creates a region that contains vortical motions. When a transverse jet is injected in the vortical region, flow parameters on mixing performance, such as the penetration height, vorticity, and turbulent stress, are improved. Three turbulent-stress components show relatively distinct distributions, and strong turbulent stresses are observed at the upper side of the jet plume. Turbulent-stress distributions are significantly associated with strain rate, which peaks along the sonic line of the jet plume.

Design and Experimental Verification of Two Dimensional Asymmetric Supersonic Nozzle

Journal of the Korean Society for Aeronautical Space Science

Most supersonic-flow test facility has axisymmetric nozzles or two-dimensional symmetric nozzles.... more Most supersonic-flow test facility has axisymmetric nozzles or two-dimensional symmetric nozzles. Compared to these nozzles, a two-dimensional asymmetric nozzle has advantages of reducing low cost for various Mach number testing and undesirable flow structure such as shock wave reflection because the nozzle part can be directly connected to the test section part in this type of nozzle. The two-dimensional asymmetric nozzle, which was Mach number 2, was designed for supersonic combustion experiment. And it was verified with the numerical analysis and visualization of Mach wave. This study suggested the practical method for design and verification of supersonic two dimensional asymmetric nozzles.

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Impulse-scaling in a laser-driven in-tube accelerator

Applied Physics A

ABSTRACT

Numerical study of hydrogen jet flames in supersonic flows - Effect of shock waves

34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit

A numerical study has been conducted to investigate the effect of shock waves on the mixing chara... more A numerical study has been conducted to investigate the effect of shock waves on the mixing characteristics and the recirculation zone of a hydrogen jet diffusion flame in a supersonic combustor. The general trends are compared with the experimental results obtained from the supersonic combustor at the University of Michigan. For the numerical simulation of supersonic diffusion flames, multi-species Navier-Stokes equations and detailed chemistry reaction equations of H 2-Air are considered. The k-co/k-8 blended two equation turbulent model is used. Roe's FDS method and MUSCL method are used for convection fluxes in governing equations. Numerical results show that the mixing and combustion efficiencies are enhanced by using the shock waves and are influenced by the location of shock waves. Also, it is found that the size of recirculation is elongated by the shock waves resulting in the improvement of flame stability. The flame shape of supersonic flames is different in the flame-tip; it is not closed but open as observed by the experiments.

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Effects of Injection Timing on the Lean Misfire Limit in an SI Engine

SAE Technical Paper Series

Numerical study on shockwave structure of superdetonative ram accelerator

Shock Waves, 2009

A numerical study was conducted to investigate shockwave and detonation structure of superdetonat... more A numerical study was conducted to investigate shockwave and detonation structure of superdetonative mode Ram Accelerator, based on ISL’s RAMAC30 II Shot225 experiment. Govern equation is discretized by Roe’s FDS and integrated by LU-SGS implicit time integration. H2/O2/CO2 detailed chemical reaction for high pressure was considered. By computation result, shockwave structure is determined by two separation bubble. Detonation wave is sustained by second separation bubble and second separation bubble is growing by pressure difference of detonation wave.

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