• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.1067-1071
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• 2004

In this paper, the characteristic of the regenerative pump is reviewed by the measurement and the analysis. The dominant noise sources are harmonic components of the rotating impeller frequency. The acoustic characteristics and the noise source position at the dump are identified. In order to reduce the high-level peak noise, the interior flow of the pump chamber is analyzed by CFD (Computational Fluid Dynamics). Acoustic pressure is calculated with Ffowscs Williams and Hawkings equation. As the result of the analysis new design of the pump chamber is recommended. The recommended pump is compared with original pump by evaluating the RMS value of a interior static pressure and the sound pressure level. The new pump chamber recommended by analysis results is proved by a process of the measurement. The overall SPL of a recommended pump is reduced about 3 dBA.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.213-217
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• 2008

This paper describes an application of centrifugal compressor optimization system, in which the blade profile of impeller is represented with NURBS(Non-Uniform Rational B-Spline) curve. A commercial CFD(Computational Fluid Dynamics) program named NUMECA fine/turbo was used to evaluate the performance of the whole centrifugal compressor flow passage including impeller and diffuser. The whole optimization design system was integrated based on iSIGHT, a commercial integration and optimization software, which provides a direct application of some optimization algorithms. To insure the practicability of optimization, the performance of centrifugal compressor under all condition was concerned during the optimizing process. That means a compositive object function considering the aerodynamic efficiency, pressure ratio and mass flow rate under different work condition was applied by using different weight number for different conditions. Using the optimization method described in this paper, an optimized design of the impeller blade of centrifugal compressor was obtained. Comparing to the original design, optimized design has a better performance not only under the design work condition, but also the off-design work condition including near stall and near choke condition.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.65-74
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• 2021

A key factor that governs the wave interferences of a submerged body is the dimensionless Froude number. Computational Fluid Dynamics (CFD) is used to describe the resistance force coefficients and the generated waves of two SUBOFF submarine models. Grid independence studies are performed on two cases, totally and shallowly submerged cases, with four sets of computing meshes. The highest peaks are marked by red points at given wavelengths, a line is fitted to those points with a least-squares approximation, and the half wake angle at multiple Froude numbers is defined between the fitted line and the centerline of the free surface. The results show that when the depth of the target is 1.1D, constructive interferences occur at Fn = 0.3 and 0.5, while destructive interference occurs at Fn = 0.35 with distortion of the waveform. The half wake angle is less than 19.47° because of the interference between the bow and stern wave systems.

• The KSFM Journal of Fluid Machinery
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• v.17 no.5
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• pp.43-53
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• 2014

This paper presents a the study on air curtain system of top and bottom bi-directional jet air discharge for blocking the spread of smoke in case of tunnel fire. The five kinds different air curtains of A, B, C, D, and E of models for various performance tested after manufactured. A results of the various performance test obtained the best efficiency from E model air curtain. And optimize the injection angle of the air curtain nozzle through the three-dimensional computational fluid dynamics (CFD) analysis and analyzed the effects of external pressure of tunnel. and also single factor design have been applied. At present, our attention is focused on the velocity distribution(flow width and flow position) of 1.5m on the ground in tunnel. Also, analyzed the influence of draft in the tunnel. Detailed effects of discharge angle of air curtain and velocity at nozzle exit are discussed.

• Ocean Systems Engineering
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• v.7 no.4
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• pp.435-460
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• 2017

The main objective of this study is to investigate the turning and zig-zag maneuvering performance of the well-known naval surface combatant DTMB (David Taylor Model Basin) 5415 hull with URANS (Unsteady Reynolds-averaged Navier-Stokes) method. Numerical simulations of static drift tests have been performed by a commercial RANS solver based on a finite volume method (FVM) in an unsteady manner. The fluid flow is considered as 3-D, incompressible and fully turbulent. Hydrodynamic analyses have been carried out for a fixed Froude number 0.28. During the analyses, the free surface effects have been taken into account using VOF (Volume of Fluid) method and the hull is considered as fixed. First, the code has been validated with the available experimental data in literature. After validation, static drift, static rudder and drift and rudder tests have been simulated. The forces and moments acting on the hull have been computed with URANS approach. Numerical results have been applied to determine the hydrodynamic maneuvering coefficients, such as, velocity terms and rudder terms. The acceleration, angular velocity and cross-coupled terms have been taken from the available experimental data. A computer program has been developed to apply a fast maneuvering simulation technique. Abkowitz's non-linear mathematical model has been used to calculate the forces and moment acting on the hull during the maneuvering motion. Euler method on the other hand has been applied to solve the simultaneous differential equations. Turning and zig-zag maneuvering simulations have been carried out and the maneuvering characteristics have been determined and the numerical simulation results have been compared with the available data in literature. In addition, viscous effects have been investigated using Eulerian approach for several static drift cases.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.11
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• pp.5384-5391
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• 2011

The computational fluid dynamics was analyzed for the pressure distribution, stream velocity distribution, stream line field, retention time and temperature distribution which are applied to the catalyst layer in the RCO reactor to derive the optimum operating condition of the heat condensing type catalytic oxidation (RCO) reactor. The results from the computational analysis revealed that the pressure loss due to the ceramic honeycomb in the catalytic bed of the reactor which is operating currently is not significant and the stream velocity (1.8~2.7 m/s) after the ceramic filter is working in stability without big channeling. To improve the stream velocity distribution of the air stream, it is necessary to extension of the connecting range between the plenum and catalytic bed inside the facility. However, the method of attaching the air stream guide vane or the perforated plate inside the reactor was not so effective.

• Journal of Korea Water Resources Association
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• v.37 no.3
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• pp.219-231
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• 2004

The use of air diffuser system to ameliorate the reservoir by breaking stratification is now widespread. This study focuses on the hydrodynamic behavior of bubble plumes, which is the major mechanism of destratification and their combined effect of adjacent plumes on destratification efficiency. By introducing 2-phase Computational Fluid Dynamics(CFD) technique, we could suggest the optimal diffuser spacing having optimal destratification efficiency by simply analyzing the complex destratification procedures varying with the seasonal stratification intensity and bubble flow rate. Lab experiments were also carried out to verify CFD model in thermally stratified fresh water which quite differs from former researches using salts. This study showed that the mixing efficiency strongly depends on the spacing of neighboring plumes. When diffuser spacing is lower than 1.5 times the depth, the combined effect is stronger; as Plume Number(PN) is increased, the efficiency is strongly affected by spacing. If the distance is shorter than the depth of water, the efficiency increases linearly in proportion to PN. Otherwise, the efficiency increases non-linearly. These findings suggest that the combined effect should be more quantitatively taken into consideration for design and operation of air-diffuser destratification system, and recommend that the optimal destratification efficiency will be when plume number is 1000 and the spacing between neighboring diffusers is 1.5 times the depth.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.561-568
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• 2020

A performance analysis was conducted according to changes in inflow velocity and the tip speed ratio of a portable horizontal-axis hydro turbine that can be used for marine leisure sports and outdoor activities by using the commercial computational fluid dynamics software ANSYS CFX. By using the analysis result and flow field analysis, the design was reviewed and the performance of the device was confirmed. In addition, data necessary to improve the performance of the hydro turbine were acquired by performing an additional performance analysis according to the variable blade pitch angle. The results among the numerical analysis cases show that the highest performance at all inflow velocities and blade pitch angles if achieved at a tip speed ratio of 4. The output power was found to be 30 W even under some conditions below the design flow rate. Among the numerical analysis cases, the highest output power (~ 85 W) and power coefficient (~ 0.30) were observed at an inlet flow rate of 1.5 m/s, a blade pitch angle of 3°, and a tip speed ratio of 4.

• Journal of Bio-Environment Control
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• v.17 no.2
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• pp.83-89
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• 2008

A wind tunnel test was conducted at Protected Horticulture Experiment Station of National Horticultural Research Institute in Busan to find the aerodynamic resistance and quadratic resistance coefficient of chrysanthemum in greenhouse. The internal plants of the CFD model has been designed as a porous media because of the complexity of its physical shapes. Then the aerodynamic resistance value should be input for analyzing CFD model that crop is considered while the value varies by crops. In this study, the aerodynamic resistance value of chrysanthemum canopy was preliminarily found through wind tunnel test. The static pressure at windward increased as wind velocity and planting density increased. The static pressure at leeward decreased as wind velocity increased but was not significantly affected by planting density. The difference of static pressure between windward and leeward increased as wind velocity and planting density increased. The aerodynamic resistance value of chrysanthemum canopy was found to be 0.22 which will be used later as the input data of Fluent CFD model. When the planting distances were $9{\times}9\;cm$, $11{\times}11\;cm$, and $13{\times}13\;cm$, the quadratic resistance coefficients of porous media were found to be 2.22, 1.81, and 1.07, respectively. These values will be used later as the input data of CFX CFD model.

• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.2
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• pp.72-78
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• 2022

A vacuum brazed cooling passage for an aircraft engine controller was designed. In order to predict the total pressure loss, which is the main design factor of the cooling passage, theoretical and numerical methods for the major loss and the minor loss considering the overall shape of the cooling passage are presented. This design and evaluation method can predict the pressure loss of the complex cooling passage shape for various flow conditions at the initial design step.