• Journal of Advanced Marine Engineering and Technology
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• v.36 no.7
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• pp.894-901
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• 2012

For more efficient use of the high pressure water-jet in rehabilitation of the water pipes, we have studied the water-jet cleaning motion of the in-pipe robot with screw drive. The mathematical models of the water-jet in the straight and the curved pipe (90 degrees elbow), representative features of the water mains, were designed to understand the water-jet motion and simulations have been performed. Furthermore the experiments has been conducted to validate the simulations by using the prototype in-pipe robot in the 3-D pipeline. The simulation results show that the water-jet motion in the straight pipe has a constant water-jet interval, whereas the motion in the curved pipe is changed by its position. By the comparison of the simulation and the experimental results, we have demonstrated that the simulations successfully estimate the water-jet motion inside the water pipes. Therefore in-pipe robot operators can predict a water-jet motion for a target water pipe through the simulation and flexibly make a proper water-jet motion by changing the robot configurations before a cleaning work.

• Journal of the Korean Society of Combustion
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• v.22 no.3
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• pp.35-40
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• 2017

Jet aviation fuel is one of liquid fuel which are used in aircraft engines. Korean domestic jet fuel, called Jet A-1, is tested for measurement of ignition delay time by using a shock tube manufactured recently. The temperature varies from 680 to 1250 K and the pressure and equivalence ratio of Jet A-1/air are fixed 20 atm and 1.0, respectively, for this experiment. The ignition delay time data of Jet A-1 are compared with those of Jet A, which has similar properties to Jet A-1. The behavior of negative-temperature-coefficient (NTC) is observed in the temperature range 750-900 K. In addition, ignition delay time of iso-octane is measured, which is one of the surrogate components for jet aviation fuel. The experimental data are compared and validated with the previous results from the literatures. A surrogate fuel for the present Jet A-1 consists of 45.2% n-dodecane, 32.1% iso-octane, and 22.7% 1,3,5-trimethylbenzene. The predicted ignition delay time for the surrogate agrees well with the measured one for Jet A-1.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.18 no.2
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• pp.149-160
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• 2008

Bag-filter system has been widely used in industrial field to remove the particulate matters from the exhaust gas. The cylindrical type of bag-filter has been generally used. But it has many shortcomings. The reattachment of separated particles on the surface of bags could result in high pressure drop of bag-filter system and subsequent decrease of air flow rate since the cylindrical type bag-filter system should have the upward flow pattern. In addition, the supply of very high pressure pulse air jet to remove particulate matters on the surface of filter could result in a frequent rupture of bags. To overcome these shortcomings of the cylindrical type, the rectangular type was developed in the developed countries and imported to Korea. But, there was not many design data available to understand the mechanisms. Thus, the fundamental experiments were conducted in this study to get some ideas about the pulse jet cleaning of rectangular type bag filter system. The experimental factors are as follows; pulse distance, pulse duration, pulse interval, pulse pressure and pulse nozzle type. Experiments followed the factorial design method. With the shorter pulse distance, the distribution of pressure drops was relatively not uniform while the particulate removal efficiency was higher. With the longer duration of pulsing and the more number of pulse nozzle, the removal efficiency was higher and the pressure drop distribution was more uniform.

• Solar Energy
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• v.18 no.3
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• pp.217-228
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• 1998

The purpose of this research is to investigate the characteristics of static and total pressure distribution in the upward free water jet system impinged on a downward flat plate. The rectangular nozzle was used and its contraction and aspect ratio was five and about seven respectively. Experimental conditions considered were jet velocity, distance between nozzle and flat plate, height of supplementary water. It was founded that pressure distribution on the flat plate had the Gaussian curve when the pressure at stagnation point and impinging half width were chosen as the scaling parameters. The maximum pressure was shown at the stagnation point. The central impingement velocity decreased with the increment of distance between nozzle and flat plate, and its slop of decay was similar to that of chracteristics decay region in the three-dimensional free jet.

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

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.4
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• pp.48-54
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• 2005

An experimental study was carried out to investigate the effect of film cooling in the lab-scale liquid rocket engine using liquid oxygen(LOx) and Jet A-1(Jet engine fuel) as propellants. Film coolants(Jet A-1 and water) was injected through the film cooling injector. The outside wall temperature of the combustor and film cooled length were determined for chamber pressure, mixture ratio, and the different geometries(injection angle) with the percent film coolant flow rate. The loss of characteristic velocity was determined for the case of film cooling with water and Jet A-1. As chamber pressure increased, the outside wall temperature increased in the nozzle but unchanged over the 9 percent film coolant flow rate for the combustion chamber used in this study. Characteristic velocity wasn't affected with the mixture ratio over the 9 percent film coolant flow rate.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.3
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• pp.10-19
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• 1998

When an under-expanded supersonic jet impinges on an inclined flat surface, a complex flow structure is established due to the intersection between the flat surface and the shock system of the free jet. This study reports on an experimental results of flows due to under-expanded axisymmetric sonic jets impinging on flat plate. Plate inclination from $60^{\cire}$~$90^{\cire}$ were investigated by means of detailed measurements of the surface pressure and schlieren photograph and surface flow visualization. The schlieren photograph are consistent with the pressure distribution and the surface flow visualization pictures are clearly related to the pressure distributions. The maximum wall pressure is found to be large on the inclined plate than on the perpendicular plate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.1
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• pp.1-8
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• 2019

An experimental study is performed to observe the characteristics of the thrust vectoring control (TVC) of the supersonic jet using proportional control valves. It is observed that three different TVC characteristics exist as the nozzle pressure ratio varies. Strong hysteresis phenomena are also observed during the valve control for a certain range of the nozzle pressure ratio. It is also noticed that the secondary chamber pressure is one of the influencing parameters for the TVC. Therefore, a control algorithm utilizing the secondary chamber pressure coefficient as a predictor is applied to achieve the stable TVC avoiding the hysteresis. Consequently, the stable TVC with the maximum deflection angle of about 20-degree has been realized using the proportional control valves.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.2
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• pp.51-57
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• 2012

Base pressure at the base of high-speed jet has long been one of the important issues from both the view points of fluid dynamics as well as practical engineering applications. The base pressure characteristics of incompressible flows have been well known to date. However, the base pressure at transonic or supersonic speeds would be different due to the compressibility effects and shock waves. In the present paper, a CFD study has been performed to understand the base pressure characteristics at transonic and supersonic speeds, prior to experimental work. An emphasis is placed on the control of the base pressure using a simple orifice. A variety of supersonic jet plumes have been explored to investigate the flow variables influencing the base pressure. The results obtained were validated with existing experimental data and discussed in terms of the base pressure and discharge coefficient of the orifice.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1472-1479
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• 2003

An attempt to reduce supersonic jet noise is carried out by using two steady microjets in a round jet. The jet is issued from a round sonic nozzle with an exit diameter of 10 mm. Two micro-nozzles with an inside diameter of 1 mm each are installed on the exit plane at an angle of 45 relative to the main jet axis. Far-field noise was measured at 40 diameters off the jet axis. The angle between a microphone and the jet axis is 30 or 90$^{\circ}$. For an injection rate of 4-6% of the main jet, screech tones were completely suppressed by the microjets. The reduction in the overall sound pressure levels were 2.4 and 2.7 dB for 90 and 30 measuring directions, respectively. However, the enhancement of mixing/spreading of the jet by the microjet was negligible. The reduction of noise is probably due to distorted shock cell structures and/or deformed large scale vortical structures by the microjets.