• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.349-352
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• 2010

A study is analyzed on the transient flow of supersonic diffuser and performed on the of supersonic diffuser with Computational Fluid Dynamic. The flow field of supersonic diffuser is calculated using Axisymmetric two-dimensional Navier-Stokes equation with $k-{\epsilon}$ turbulence model. The transient simulation is compared in terms of mach number and temperature of vacuum chamber according to the chamber pressure of starting transient on Liquid rocket engine.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.134-140
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• 1999

A three-dimensional CSCM upwind flux difference splitting Navier-stokes code with two-equation turbulence models was developed to predict the transonic flows in centrifugal compressor diffuser. The k-$\epsilon$ model of Abe et al. performed well in predicting the pressure distribution in the shock wave/turbulent boundary-layer interaction. Three turbulence models predicted the similar distribution of static pressure through the diffuser and showed a good agreement with the experimental results. The secondary flows in the corner were predicted well by these turbulence models. The pressure increase before the throat of the diffuser vane is important for the overall pressure recovery. As the mass flow rate increased the blockage decreased at the throat. The pressure coefficient distribution through the diffuser depended on the throat blockage not on the rotational speed of the impeller.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.469-475
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• 2003

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 differently according to the relative positions of tandem diffuser rows while the characteristics of impeller showed almost identical. 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.

• International Journal of Fluid Machinery and Systems
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• v.3 no.1
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• pp.91-101
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• 2010

Based on the one-dimensional stability analysis, the self-excited oscillation in hydraulic power generating systems was studied by a simple experiment and numerical simulation. It was shown that a cavity in a conical diffuser can cause surge. With the diffuser, a high amplitude and low frequency oscillation occurs at low cavitation number. This oscillation was not observed with the straight pipe. It was confirmed that the diffuser effect of the draft tube can be the cause of the full load surge in hydraulic power system. Numerical results were also analyzed to check the validity of the one-dimensional stability analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.349-354
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• 2005

There are various types of noise around us such as road traffic noise, aircraft noise and floor impact sound, equipment noise etc. Recently researches on the criteria to evaluate the noises have been progressed, however, researches on the noise criteria and evaluation method for the diffuser noise of HVAC are insufficient. dB(A) and NC values represented in ASHRAE guide book are applied as a noise criteria for diffuser noise, which have some problems like that the values between dB(A) and NC have deviation even if the sound is same one. Therefore, the evaluation method should be considered and proposed based on the subjective responses. From these reasons, this study aimed to analyze the evaluation factors for the diffuser noise of HVAC reflected on the subjective responses by surveying vocabularies and grouping them with factor analysis.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.4
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• pp.57-62
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• 2011

In this study, a experimental work to investigate the influence of a turbulent wake flow on the velocity distribution of a diffuser with PIV method. The turbulent wake is generated by a rectangular prism, which is installed at the inlet of a diffuser. The results show that the velocity recovery of the subsonic diffuser is dependent on the height and location of rectangular prism. It is found that a certain height of the rectangular prism to generate the turbulent wake give a better velocity recovery, compared with no rectangular prism.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.4
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• pp.328-334
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• 2006

Industrial electrostatic precipitators require a highly uniform velocity distribution in the collecting chamber. Increasing divergence angle of a diffuser makes a non-uniformity flow distribution characteristics on the diffuser exit. This paper provides CFD results of optimum positions and opening rates of perforated plates which were installed in the electrostatic precipitator. The considered divergence angels were 60 degree and 90 degree. In 90 degree diffuser, a blanking method was used.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.5
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• pp.357-366
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• 2001

In this paper, computer generated holographic diffuser with high diffraction efficiency and uniformity was designed by the modified iterative Fourier transform algorithm. Newly proposed method to design a CGHD is to flip and to combine BPHs or MPHs, so it makes the computation time decreased and it makes the reconstructed signal area enlarged. The designed sixteen phase holographic diffuser had the high diffraction efficiency of 85.20%, the uniformity of 2.43%, and the average signal to noise ratio of 18.97［㏈］. Also, we compared the CGHD with a 128 level pseudo random phase diffuser about the diffraction efficiency and the uniformity. The proposed diffuser can be provided good performance for a holographic diffuser and a next-generation display device.

• Journal of KSNVE
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• v.4 no.3
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• pp.377-384
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• 1994

This paper is an investigation of the performance of absorption diffusers to suppress the vent noise emitted when high pressure gas is throttled. First, experiment for the static performance is carried out. When there is no through-flow, the insertion loss has been obtained in terms of 1/3 octave band spectrum and the effect of the number of diffusers and the thickness of the absorption material on the static performance has been obtained. And the similarity in the spectrum of the static insertion loss is confirmed by comparing two similar models with different size. Second, the dynamic performance has been obtained by experiment using blow-down of compressed air from a storage tank through an orifice of diameter 10 mm. The back pressure by the diffuser is measured and compared with that of a single diffuser. It is found that the insertion loss of asingle diffuser is very low around 3 dB at high frequencies with negative value at low frequencies. By absorption material between the diffuser tubes, however, the performance is increased considerably. Without flow the static insertion loss increases by 3 - 4 dB by doubling the thickness or the density of the absorptionmaterial. With flow, however, the dynamic insertion loss increases. While, the back pressure by the diffuser is small enough to be neglected.

• International Journal of Fluid Machinery and Systems
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• v.3 no.3
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• pp.245-252
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• 2010

It's known that pump head of centrifugal impeller with lager blade outlet angle is kept higher in air-water two phase flow condition, though the efficiency in water single phase flow condition is inferior. In the present study, a centrifugal impeller with variable blade outlet angles, that has higher efficiencies in both water single phase flow and air-water two phase flow conditions, is proposed. And the performances of the centrifugal impeller with variable blade outlet angles were experimentally investigated in both flow conditions of single and two-phase. In addition, effects of installing diffuser vanes on the performances of centrifugal pump with movable bladed impeller were also examined. The results are as follows: (1) The movable bladed impeller that proposed in this study is effective for higher efficiency in both water single phase and air-water two phase flow conditions. (2) When diffuser vanes are installed, the efficiency of movable bladed impeller decreases particularly at large water flow rate in water single-phase flow condition; (3) The performances of movable bladed impeller are improved by installing of diffuser vanes in air-water two-phase flow condition at relatively small water rate. The improvement by installing of diffuser vanes however disappears at large water flow rate.