• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.33-45
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• 1997

Axisymmetric shear layers around a free jet is forced by co-flowing and counter-flowing secondary jets from/to an annular tube around the jet nozzle. The jet potential core extends far downstream with co-flowing secondary jets due to inhibited vortex developing and pairing. For counter-flowing cases, the axisymmetric shear layer around the jet transits from convective instability to absolute instability for velocity ratios R＝1.3～l.65 for the uniform velocity jets. Consequently, the jet potential core length increases and the turbulence level in the jet core is reduced significantly. The jets are controlled better with extension collars attached to the outer nozzle exit because the annular secondary flow is guided well by the extension collars. For the vectoring of jet, the annular tube around the jet is divided in two parts and the only one part is used for suction. The half suction makes the different shear layer around the jet and vectoring the jet by Coanda effect. The vectoring and turbulent components are varied significantly by the suction ratio. The experiments are carried out to investigate the characteristics of forced free jets using flow visualization, velocity and turbulence measurements.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2632-2637
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• 2007

Rotary performance and flow resistance induced by each element in suction nozzle of a vacuum cleaner with a double-blade rotary fan are investigated numerically and its relation with flow-induced noise and rotary performance is examined. Flow resistance and vorticity in suction nozzle are calculated and it is found that they are closely related with flow-induced noise. Gap between double blades, adoption of cross-flow fan, enlargement of flow inlet area, and optimization of blade number are tested for noise reduction. Finally, the effects of each method are verified experimentally. It is found that several combinations of the proposed methods can be adopted for noise reduction although the degree of reduction is not much.

• The KSFM Journal of Fluid Machinery
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• v.16 no.2
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• pp.21-26
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• 2013

Super-cavitating vehicle which is operating under water speeds up to 100m/s. In this process super-cavitation around body reduces frictional resistance. This paper introduces experimental study on different width of suction path as there is a warhead in the torpedo. Hydraulic performances of turbopump at non-cavitating condition does not display a significant differences depending on different width of suction path. However, cavitation performance of each model shows obvious differences in the same condition of experience. In case of radial inlet, the value of critical NPSH(which indicates 3% head drop) increases about 20% in comparison of axial inlet.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.208-211
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• 2006

Flow resistance induced by each element in suction nozzle of a vacuum cleaner with a rotary fan is investigated numerically and its relation with flow-induced noise is examined. Flow resistance and vorticity in suction nozzle are calculated and it is found that they are closely related with flow-induced noise. From numerical results, it is suggested that reduction of flow resistance effectively increases all-suction performance and decreases sound pressure level of noise generated in the suction nozzle.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.83-87
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• 2009

Ramjet engine is weak for low frequency combustion instability because of their long air flow passage. A model combustor which has fuel injector and V-gutter shaped flame holder was designed and fabricated in order to simulate a combustion mechanism of ramjet engine, and it could demonstrate combustion instability which might occur in ramjet combustor. The frequency of the instability was very similar to that of acoustic resonance frequency of combustor, and it proved that a typical combustion instability by thermo-acoustic coupling occurred.

• Journal of Wetlands Research
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• v.15 no.2
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• pp.215-222
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• 2013

In this study, the nutrient concentration changes along the hydrologic flow path of a free water surface flow constructed wetland (CW) treating agricultural stream runoff was investigated. Dry sampling was performed from April 2009 to November 2011 at five locations representing each treatment units of the CW. Grab water samples were analyzed for nitrogen forms such as total nitrogen (TN), total Kjeldahl nitrogen, nitrate, and ammonium; and phosphorus forms including total phosphorus (TP) and phosphate. Findings revealed that the physical properties such as temperature, dissolved oxygen and pH affected the TP retention in the CW. High nutrient reduction was observed after passing the first sedimentation zone indicating the importance of settling process in the retention of nutrients. However, it was until the 85% of the length of the CW where nutrient retention was greatest indicating the deposition of nutrients at the alternating shallow and deep marshes. TN and TP concentration seemed to increase at the final sedimentation zone (FSZ) suggesting a possible nutrient source in this segment of the CW. It was therefore recommended to reduce or possibly remove the FSZ in the CW for an optimum performance, smaller spatial allocation and lesser construction expenses for similar systems.

• Transactions of the KSME C: Technology and Education
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• v.2 no.2
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• pp.73-80
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• 2014

Drug delivery in human upper airway was studied by the numerical simulation of oral airflow. We created an anatomically accurate upper airway model from CT scan data by using a medical image processing software (Mimics). The upper airway was composed of oral cavity, pharynx, larynx, trachea, and second generations of branches. Thin sliced CT data and meticulous refinement of model surface under the ENT doctor's advice provided more sophisticated nasal cavity models. With this 3D upper airway models, numerical simulation was conducted by ANSYS/FLUENT. The steady inspiratory airflows in that model was solved numerically for the case of flow rate of 250 mL/s with drug-laden spray(Q= 20, 40, 60 mL/s). Optimal parameters for mechanical drug aerosol targeting of predetermined areas was to be computed, for a given representative upper airways. From numerical flow visualization results, as flow-rate of drug-laden spray increases, the drag spray residue in oral cavity was increased and the distribution of drug spray in trachea and branches became more homogeneous.

• Aerospace Engineering and Technology
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• v.4 no.2
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• pp.153-162
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• 2005

Through a preliminary design process, four design candidates for a 1.4MW class partial admission turbine have been chosen and the numerical analyses using a frozen rotor method are applied to estimate their performance. Each flow analysis result was compared with others and the optimum design was selected. Flow characteristics in the passages and some types of losses induced by shocks and wakes were found from calculation results. A new rotor blade was redesigned based on these calculations and this result is compared with previous one through flow analysis.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.481-487
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• 2005

A turbopump turbine consists of rotational part including a rotor and stationary part including nozzles and exit guide vanes, of which shape and relative position affect turbine performance owing to supersonic flows with prevailing unsteadiness. In this study, numerical 3-D flow calculations of the turbine with the different number of exit guide vanes and different relative position of each component are conducted and the effect of flow passage variations on turbine performance is analyzed.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.1
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• pp.51-62
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• 2017

A design optimization method is applied for the flow path design of RBCC engine, an important factor for the determining the propulsion performance operating at air-breathing mode. A design optimization was carried out to maximize the specific impulse of the RBCC engine by using a genetic algorithm based on the Kriging model. Results are analyzed using ANOVA and SOM. Design conditions of ramjet and scramjet mode are selected as Mach number 4 at 20 km altitude and Mach number 7 at 30 km, respectively. The optimized design presents that the specific impulse is increased by 7% and 10% on each condition than the baseline design.