• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.32 no.8
• /
• pp.118-128
• /
• 2004

Exhaust plume effects on longitudinal aerodynamics of missile were investigated by wind tunnel tests using a solid plume simulator and CFD analyses with both the solid plume and air jet plumes. Approximate plume boundary prediction technique was used to produce the outer shape of the solid plumer and chamber conditions and nozzle shapes of the air jet plumes were determined through plume modeling technique to compensate the difference in thermodynamic properties between air and real plume. From comparisons among turbulence models in case of external flow interaction with the air jet plume, Spalart-Allmaras model turned out to give accurate result and to be less grid-dependent. Effects induced by the plume were evaluated through the computations with Spalart-Allmaras turbulence model and the air jet plume to account for various ratios of chamber and ambient pressure and Reynolds number under the flight test condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.5
• /
• pp.71-78
• /
• 2002

Experiments have been performed using two-color PIV in hydrogen non-premixed flames with various conditions of coaxial air, which was classified into three cases with/without reaction. Mean velocity, turbulence intensity and Reynolds stress were analyzed using flow fields from PIV measurement First, the similarity of pure jet had a good agreement with previous results of other researchers. It was found that the decay of centerline velocity was proportional to $x^{-1}$ in coaxial air conditions. By normalizing axial distance with effective jet diameter defined by effective density, the data of centerline velocity collapsed a single line. And the radial profiles of mean velocity showed that they didn't become self-similar because the curves differed from each other as coaxial air velocity increased at fixed fuel velocity. Also, turbulence intensity became self-similar further downstream than mean velocity.

• Journal of Environmental Science International
• /
• v.32 no.8
• /
• pp.555-561
• /
• 2023

A study is to predict the effective pulsing distance following to the pulsing pressure, nozzle diameter, filtration velocity using numercial analysis techniques and use it as an efficient operation condition and economic data for on-line type pulse air jet bag filter. Filtration area 6 m² condition, calculate filter resistance coefficient for simulation through the primary experiments using coke dust. For CFD simulation, analysis pulsing characteristics about nozzle diameter, filtration velocity and pulsing pressure. The maximum pulsing length of on-line type pulse air jet bag filter, in 10mm nozzle, filtration velocity 1.5m/min and pulsing pressure 5 bar conditions, is 2,285 mm, maximum length is 76.2% of the total filter bag, which is sufficient to pulsing. In 12mm nozzle, pulsing pressure 5 bar and filtration area 1.22 m² conditions, the maximum pulsing length of on-line type pulse air jet bag filter is 1,744~2,952 mm, and the maximum length is 2,952 mm indicates pulsing air can be reached to the bottom of filter bag. When the nozzle diameter is increased 8mm to 10mm, maximum pulsing length is extended 40~47%, and increased 10mm to 12 mm, maximum pulsing length is extended 10~17%. For effective pulsing, over the 5bar of pulsing pressure and larger than 10 mm of nozzle diameter are required.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.48 no.3
• /
• pp.187-194
• /
• 2020

In this study, computational analyses are carried out to investigate the interference flows and the aerodynamic characteristics of a hit-to-kill intercepter due to lateral jets at medium altitude. In addition, the analyses are performed for air and multi-species gas used in the side jet. The results indicate that the position of the barrel shock are shifted upstream and the structure of the shock wave are changed for the multi-species jet when compared to the air jet. As a result, the high pressure region with multi-species jet moves forward and the pitching moment is higher under the same flow condition. Moreover, the inclusion of high temperature effects makes drastic changes in pressure distribution. The jet width is much bigger, and the jet diffuses over wider range in medium altitude than in low altitude, because of the low density of the freestream.

• Sleep Medicine and Psychophysiology
• /
• v.2 no.2
• /
• pp.146-155
• /
• 1995

Jet lag can be defined as the cumulative physiological and psychological effects of rapid air travel across multiple time zone. The consequences of jet lag include fatigue, general malaise, sleep disturbances, and reductions of cognitive and psychomotor performance, all of which have been documented in experimental biological and air crew personnel studies. Thus authors tried to study the jet lag of natural travellers by modified self reporting sleep log. Total 61 healthy travellers was studied for 3 days before and 7 days after jet-flights across seven to ten time zone. The eastbound travelling group was 38 persons, aged 19 -70 and westbound travelling group was 23 persons, aged 13 - 69. Sleep onset time, wake-up time, sleep latency, awakening frequency on night sleep, awakening duration on night sleep, sleepiness at wake-up and nap length were evaluated. Our results suggested that the 7 to 10 time zone shift gave significant influence to traveller's sleep-wake cycles. The date which subjective physical condition was recovered on was $5.16{\pm}1.50$ day after arrivals for eastbound, while for westbound, $4.91{\pm}1.62$ day. In eastbound travelling, sleep onset time became later than baselines and could not recover until 7th day. But in westbound, it became earlier than baseline and could recover until 6th day. The mean score of 24-hour sleepiness was greater in eastboumd than westbound. Therefore the eastbound travelling caused more sleep-wake cycle disturbance and daytime dysfunction than westbound travelling. In other parameters, there was no definite difference between east and westbound. From our results, it was suggested that the symptom severity of jet lag was dependent on the travelling direction. To demonstrate more definite evidence, large sized data collections and comparision by age difference were needed.

• Journal of the Korean Society of Combustion
• /
• v.5 no.1
• /
• pp.19-30
• /
• 2000

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 violation of the linear relationship between the flame volume and the flame reaction zone.

• Journal of Energy Engineering
• /
• v.20 no.2
• /
• pp.96-102
• /
• 2011

This research has been proceeded over the transition region(H/B=10) of two-dimensional impinging air jet system, in which square rods has been set up in front of heating surface in order to increase heat transfer. The objective of this research was to investigate the characteristics of heat transfer and air flow, in cases the clearance from rods to heating surface(C=1, 2, 4, 6 mm) and the width of rods(W=4, 6, 8 mm) changed. And this research compared the above with the experimentation without rods. As result, heat transfer performance was best under the condition of C=1 mm, and as the width is 8 mm, it is largely influenced by eddies and acceleration in case width of rods changed.

• 한국전산유체공학회:학술대회논문집
• /
• 1998.05a
• /
• pp.168-173
• /
• 1998

A numerical analysis of axisymetric backward facing step main nozzle flow in air jet loom has been accomplished. To obtain basic design data for an optimum main nozzle for an air-jet loom and to predict the transonic/supersonic flow, a characteristic based upwind flux difference splitting compressible Navier-Stokes method has been used. The wall static pressure of the main nozzle and the flow velocity changes in the nozzle tube were analyzed by changing air tank pressures and acceleration tube lengths. The flow inside the nozzle experiences double choking one at the needle tip and the other at the acceleration tube exit at tank pressures over $4kg_f/cm^2$. The tank pressure $P_t$ leading to the critical condition depends on the acceleration tube length; i.e, $P_t$ is higher for longer acceleration tubes. The $P_t$ value required to bring the acceleration tube exit to the critical condition is nearly constant regardless of acceleration tube length. The round needle tip shape might lead to less total pressure loss when compared with step shape.

• Nuclear Engineering and Technology
• /
• v.55 no.6
• /
• pp.2011-2017
• /
• 2023

Gas submerged jet is an outstanding thermohydraulic phenomenon in pool scrubbing of fission products during a severe nuclear accident. Experiments were performed on the hydraulic characteristics in the ranges of air mass flux 0.1-1400 kg/m²s and nozzle diameter 10-80 mm. The results showed that the dependence of inlet pressure on the mass flux follows a power law in subsonic jets and a linear law in sonic jets. The effect of nozzle submerged depth was negligible. The isolated bubbling regime, continuous bubbling regime, transition regime, and jetting regime were observed in turn, as the mass flux increased. In the bubbling regime and jetting regime, the air volume fraction distribution was approximately symmetric in space. Themelis model could capture the jet trajectory well. In the transition regime, the air volume fraction distribution loses symmetry due to the bifurcated secondary plume. The Li correlation and Themelis model showed sufficient accuracy for the prediction of jet penetration length.

• 연구논문집
• /
• s.23
• /
• pp.57-62
• /
• 1993

An experimental investigation was carried out to study the characteristics of concentration of a coaxial jet being tone excited and consisting of $CO_2$, and air. The concentration in a binary gas mixture was measured by using the hot-wire anemometer and flow visualization was performed by the schlieren technique. In the case of excited flow, it is found that acoustic energy is partially transferred to RMS concentration to enhance mixing.