• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2769-2774
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• 2007

In vacuum ejector-diffuser systems where a finite volume secondary chamber is used, the secondary jet exhibits transient characteristics during start-up. A steady state is achieved after some time in which mass entrainment prevails indefinitely inside the ejector, though there is no flow from the secondary chamber. An attempt is made in this work to study the infinite entrainment of secondary jet into the primary jet from a finite secondary chamber, with the help of a computational fluid dynamics method. The present study is also intended to identify the operating range of vacuum ejector-diffuser systems where the steady flow assumption can be applied without uncertainty. The results obtained show that the only condition in which an infinite mass entrainment is possible is the generation of a re-circulation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium at this point. Steady flow assumption is valid only after this point.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.36-44
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• 2000

The flow at the impeller exit is important to validate engineering design and numerical analysis of pumps. We installed axisymmetric collector instead of the volute casing, so there is no interaction between the impeller and casing. A hot-film probe and a high response pressure transducer are used to investigate the flow at impeller exit and vaneless diffuser region for design and off design flow rate. For a single suction centrifugal pump of low specific speed, the flow field such as velocity, flow angle, and total pressure are measured by traversing the probe across the vaneless diffuser. These data can be used for performance prediction, design, and numerical analysis of pumps.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1715-1719
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• 2004

An in-house supersonic ejector was designed to ensure low pressure and high speed scavenging of resonating cavity of chemical lasers. For given primary flow condition, 100g/s secondary mass flow rate was observed at the design pressure. Performance validation of a supersonic ejector system along with an investigation of effects of supersonic diffuser was conducted. Placement of diffuser at the secondary inlet further reduced diffuser upstream pressure to 1/4-1/5 relieving the local to the primary supply unit. In order to increase the secondary flow, we put two ejectors capable of removing 50g/s each of secondary flows together to deal with higher mass flow. Test of the parallel unit demonstrated the secondary flow rate was proportional to the numbers of individual units that were brought together. Additionally, flow calculations with a commercial code were carried out in every case of experiment and compared with results.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3104-3109
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• 2007

The present study has been carried out to investigate the pumping characteristics for different figures of inlet and outlet in diffuser/nozzle based on piezoelectric micropump. Piezoelectric micropump system consists of several parts like a pumping chamber, diffuser/nozzle, piezoelectric element and tubes. Parts of the micropump connected with diffuser/nozzle and tubes have been analyzed.. The magnified parts have been classified into two different models based on their resistance. These models have been further classified into six models with each one having three different angles at the magnified parts. Each model has been compared and analyzed using the simulation tool, namely, CFD-ACE depending on their flow rates and characteristics.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.66-69
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• 2009

New design configurations were developed based on the closed ventilation type igloo nozzle in contrast to the conventional open distribution type. To validate the enhanced performance, the prediction of the exhaust flow patterns of the igloo diffuser was carried out by both experimental and computational simulations. CFD provided detailed parametric studies that significantly reduced the amount of experimentation necessary to alter the design of existing the F-15K igloo exhaust diffuser.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.110-113
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• 2005

This paper presents flow regime maps of two-dimensional, planar diffusers with constant-area ducts at very low Reynolds numbers. They are obtained from numerical calculations using the commercial CFD program CFD-ACE+. The Reynolds numbers considered are 63, 105, and 210. For each Reynolds number, a wide range of geometric parameters of dimensionless diffuser length, which is a ratio of diffuser length to throat width, $1 and divergence half angle $1^{\circ}<\phi<50^{\circ}$ are selected to obtain steady-state solutions. These maps can be served as a guideline to designers for very low Reynolds number diffuser flows.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.344-352
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• 2006

Evacuation performance, starting transient, and plume blowback at diffuser breakdown of a straight cylindrical supersonic exhaust diffuser with no externally supplied secondary flow are investigated. Pressure records in the transitional periods are measured by a small-scale cold-gas simulator. Flow-fields evolving in the diffuser-type ejector are solved by preconditioned Favre-averaged Navier-Stokes equations with a low-Reynolds number $k-{\varepsilon}$ turbulence model edited for turbulence compressibility effects. The present RANS method is properly validated with measured static wall pressure distributions and evacuation level at steady operation as well as the pressure records during the transition regime.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.91-98
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• 2001

As the second part of the author's study, off-design behavior of the design and performance parameters in the low-solidity cascade diffuser in a centrifugal compressor is investigated. The experimental flange-to-flange compressor map serves the validity of application of the present CFD work to the detailed investigation of the low-solidity cascade diffuser. Some meanline design and performance parameters as well as three-dimensional internal secondary flow fields are studied when the flow rate is changed from deep choke to stall.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.645-645
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• 2009

In many practical applications of the centrifugal fan, the impeller-diffuser interaction noise is considered as a main source of fan noise. The housing for an electric motor is also expected to play an important role on noise propagation because of its complicated configuration. This study investigates the impeller-diffuser interaction noise and its sources by computing three-dimensional, incompressible flow field of the centrifugal fan in motor housing. The effect of motor case on fan noise characteristic is then investigated using the Brinkman penalization method, while the noise source associated with impeller-diffuser interaction is mathematically modeled. It is found that the present methodology combined with mathematical description of noise source provides a fairly good agreement with the experimental results, indicating that the motor housing has significant effect on noise characteristics. Finally, aeroacoustic noise prediction for various impeller-diffuser blade count ratios is conducted for noise reduction.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.303-306
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• 2007

A engineering analysis has been conducted to study operating characteristics of a supersonic exhaust diffuser simulating high altitude atmosphere from a flow-developing point of view. Emphasis is placed in the detail flow structure resulting from several design- and operating- parameters of the diffuser such as the area ratios of a exhaust nozzle to the diffuser, the vacuum chamber size, and jet pressure.