• Journal of Korean Port Research
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• v.14 no.3
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• pp.361-371
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• 2000

A demand of marine outfall system has been much increased for the effective disposal of the wastewater due to population and industrial development at the coastal areas. The outfall system discharges primary or secondary treated effluent into the coastline, or at the deep water, or between these two. The discharge is carried out by constructing a pipeline on the sea bed with a diffuser or with a tunnel, risers and appropriate. The effluent, which has a density similar to that of fresh water, rises to the sea surface forming plume or jet, together with entraining the surrounding salt water and becomes very dilute. Thus there have been growing interests about plume behaviour around the outfall system. Plume or jet discharged from single-port or multi-port diffuser might cause certain impacts on coastal environment. Near field mixing characteristics of discharged water field using CORMIX model have been studied for effective outfall design various conditions on ambient current, depth, flow rate, effluent concentration, diffuser specification, port specification etc.. This kind of analysis is necessary to deal with water quality problems caused by the ocean discharge. The analyzed result was applied to the Pusan Jungang effluent outfall system plan.

• KSTLE International Journal
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• v.3 no.2
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• pp.101-109
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• 2002

This paper presents the fabrication and performance inspection of a peristaltic micropump by flow simulation. The valve-less micropump using the diffuser/nozzle is consists of base plate, mid plate, top plate and connection tubes fur inlet and outlet. In detail, the base plate is composed of two diffuser nozzles and three chambers, the mid plate consists of a glass diaphragm for the volumetric change of the pumping chamber. The inlet and outlet tubes are connected at the top plate and the actuator fur pressing the diaphragm is located beneath the top plate. The micropump is fabricated on the silicon wafer by DRIE (Deep Reactive ion Etching) process. The pumping performances are tested by the pneumatic test rig and compared with the simulated results fur various dimensions of diffuser nozzles. The pumping characteristics of the micropump by the volumetric change at the pumping chamber is modeled and simulated by the commercial software of FLOW-3D. The simulated results shows that reverse flow is the inherent phenomena in the diffuser nozzle type micropump, but it can be reduced at the dual pumping chamber model.

• The KSFM Journal of Fluid Machinery
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• v.7 no.2 s.23
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• pp.27-34
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• 2004

The performance of a centrifugal compressor composed of an impeller, tandem diffuser rows and axial guide vanes has been predicted numerically and compared with available experimental results on its design rotational speed. The pitchwise-averaged mixing plane method was employed for the boundaries between rotor and stator to obtain steady state solutions. The overall characteristics showed difference according to the relative positions of tandem diffuser rows while the characteristics of impeller showed almost identical result. The numerical results agree with the measured data in respect of their tendency. It turned out that $0\%$ of relative positions is the worst case in terms of static pressure recovery and efficiency. According to the experimental results, some pressure fluctuations and malfunction of the compressor were observed for $75\%$ case. However, this numerical calculation using mixing plane method did not capture any of those phenomena. Thus, unsteady flow calculation should be performed to investigate the stability of the compressor caused by different diffuser configuration.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2000.11a
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• pp.85.2-93
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• 2000

A demand of marine outfall system have been much increased for the effective disposal of the wastewater due to population and industrial development at the coastal areas. The outfall system discharges primary or secondary treated effluent into coastline or at the deep water, or between these two. The discharge is carried out by constructing a pipeline on the sea bed with a diffuser or with a tunnel, risers and appropriate. The effluent, which has a density similar to that of fresh water, rises to the sea surface forming plume or jet, together with entraining the surrounding salt water and becomes very dilute. Thus there have been growing interests about plume behaviour around the outfall system. Plume or jet discharged from single-port or multi-port diffuser might cause certain impacts on coastal environment. Near field mixing characteristics of discharged water field using CORMIX model with has been studied for effective outfall design various conditions on ambient current, depth, flow rate, effluent concentration, diffuser specification, port specification etc.. This kind of analysis is necessary to deal with water quality problems caused by the ocean discharge. The analyzed vesult was applied to the Pusan Jungang dffluent outfall system plan.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2283-2296
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• 1995

Experiments of normal shock wave/turbulent boundary layer interaction were conducted in a supersonic diffuser. The flow Mach number just upstream of the normal shock wave was in the range of 1.10 to 1.70 and Reynolds number based upon the turbulent boundary layer thickness was varied in the range of 2.2*10$^{[-994]}$ -4.4*10$^{[-994]}$ . The wall pressures in streamwise and spanwise directions were measured for two test cases, in which the turbulent boundary layer thickness incoming into the supersonic diffuser was changed. The results show that the interactions of normal shock wave with turbulent boundary layer in the supersonic diffuser can be divided into three patterns, i.e., transonic interaction, weak interaction and strong interaction, depending on Mach number. The weak interactions generate the post-shock expansion which its strength is strong as the Mach number increases and the strong interactions form the pseudo-shock waves. From the spanwise measurements of wall pressure, it is known that if the flow Mach number is low, the interacting flow fields essentially appear two-dimensional, but they have an apparent 3-dimensionality for the higher Mach numbers.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.182-186
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• 2011

Ejector-diffuser system has long been used in many diverse fields of engineering applications and it has advantages over other fluid machinery, because of no moving parts and structural simplicity. This system makes use of high-pressure primary stream to entrain the low-pressure secondary stream through pure shear actions between two streams. In general, the flow field in the ejector-diffuser system is highly complicated due to turbulent mixing, compressibility effects and sometimes flow unsteadiness. A fatal drawback of the ejector system is in its low efficiency. Many works have been done to improve the performance of the ejector system, but not yet satisfactory, compared with that of other fluid machinery. In the present study, a mixing guide vane was installed at the inlet of the secondary stream for the purpose of the performance improvement of the ejector system. A CFD method has been applied to simulate the supersonic flows inside the ejector-diffuser system. The present results obtained were validated with existing experimental data. The mixing guide vane effects are discussed in terms of the entrainment ratio, total pressure loss as well as pressure recovery.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.6
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• pp.15-23
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• 2004

In order to investigate efficiency and flowfield charateristics of the intake-diffuser for the ship waterjet propulsion, new experimental verification technology was set up in the cavitation tunnel. 1-hole and 5-hole pilot tubes were designed and manufactured to measure the pressure and velocity distributions at intake-diffuser entrance and impeller inlet. The calibration of the 5-hole pilot tubes is conducted at the cavitation tunnel The cavitation inception occurs at the intake lip, and the occurrence position depends on IVR (Inlet Velocity Ratio) condition. The present experimental device will be applied sufficiently for the development of the design and performance improvement technologies.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.318-322
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• 2009

Supersonic ejectors are simple mechanical components, which generally perform mixing and/or recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for altitude testing of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser. This paper aims at the improvement of ejector-diffuser performance by focusing attention on reducing exhaust back flow into the test chamber, since alteration of the backflow or recirculation pattern appears as one of the potential means of significantly improving low supersonic ejector-diffuser performance. The simplest backflow-reduction device was an orifice plate at the duct inlet, which would pass the jet and entrained fluid but impede the movement of fluid upstream along the wall. Results clearly showed that the performance of ejector-diffuser system was improved for certain a range of system pressure ratios, where as there was no appreciable transition in the performance for lower pressure ratios and the orifice plate was detrimental to the ejector performance for higher pressure ratios. It is found that an appropriately sized orifice system should produce considerable improvement in the ejector-diffuser performance in the intended range of pressure ratios.

• Aerospace Engineering and Technology
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• v.11 no.2
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• pp.117-121
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• 2012

Upper stage propulsion system designed for operation in the upper atmosphere should be tested under nozzle full flow conditions to verify its performance on the ground. KARI has carried out high altitude simulation test of KSLV-I kick motor using cylindrical supersonic exhaust diffuser. Also cold and hot flow test for the sub-scaled diffuser have been conducted to verify the design of real scale diffuser and to study its operating characteristics. This paper deals with the results obtained from these high altitude simulation tests.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.291-294
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• 2006

Exhaust system of steam turbines consists of an annular diffuser and a collector and connects the last stage turbine and the condenser. The system is used to transfer the turbine leaving kinetic energy to potential energy while guiding the flow from turbine exit plane to the downstream condenser. In the steam turbine exhaust system, distorted pressure profile is arisen by the nonaxisymmetric collector structure at the diffuser outlet, and this distorted pressure is propagated to the last stage LP turbine exit plane through the diffuser, then the last stage LP turbine experiences asymmetric back pressure. It is known that the pressure recovery performance of diffuser is strongly influenced by diffuser inflow condition. In this study, the effect of exhaust system due to the changing of inlet flow condition is observed by using CFD, and the interaction of last stage LP turbine and exhaust system is investigated by using actuator disk model as modeling of turbine blade row of exhaust hood inlet.