• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.3
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• pp.1-8
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• 2013

In this study, we performed three-dimensional CFD analysis to investigate the effect of the rotor blade sweep of a partial admission supersonic turbine on the stage performance and the flow field. The computations are conducted for three different sweep cases, No sweep(NSW), Backward sweep(BSW), and Forward sweep(FSW), using flow analysis program, FLUENT 6.3 Parallel. The results of the BSW model show reduced mass flow rates of tip leakage and increased total-to-static efficiency. The strength of leading edge bow shock was decreased a little with BSW model. And the BSW model also shows a good performance around the hub region compared to other models.

• Bulletin of the Society of Naval Architects of Korea
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• v.20 no.3
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• pp.1-16
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• 1983

In this paper a discrete-vortex-method(DVM) is presented for investigating the hydromechanics of the planar hydrofoils performing the undulatory motion which can be related to fish propulsion with carangiform mode. This is an extention of the authors previous work(1981) on the 2-dimensional hydrofoil. The applicability and accuracy of the present method are shown by means of comparing the calculated lifts and moments, and their distributions over the planforms with those in available references, for aspect ratio 1.0 and 2.0 rectangular hydrofoils and a swept-back hydrofoil of aspect ratio 2.0 from reduced frequency 0.1 to 0.5. The agreement is considered good. To assure the applicability of the DVM to the study of the propulsive performance of the oscillating planar hydrofoils, the convergence tests are performed. The mean thrust(in pure heave, this is wholly due to leading-edge suction), the mean power to maintain the motion and the hydromechanical efficiency are calculated for the rectangular hydrofoil of aspect ratio 8.0 and these are compared with the calculations by Chopra & Kambe(1977) and Lan(1979) for the same cases.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.6 s.150
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• pp.656-666
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• 2006

Numerical analysis using the FLUENT is performed for the 138K LNG carrier of the MOERI. In this study, results according to the number and also the type of the grid, different turbulent models, variations of y+ are compared with experiments and computational results from the WAVIS. RSM model gives good result in comparison with other models, and the more the number of grid increase, the better the resistance converges to the constant value. Additionally, it is confirmed that the resistance and wake distributions vary with the change of y+, and O-O type grid yields better wake distributions than that of O-H type. Average velocity distributions and velocity profiles are mainly in accord with experiments and computational results of the WAVIS, however, present results in the region of transom and tip of leading edge of the rudder are poor for the lower velocity components comparing with that of the WAVIS.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.5
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• pp.273-281
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• 2013

In this paper, the effects of bow deck shape on the green water are studied by numerical and experimental method. Varying the deck shapes to triangular, elliptic and circular, the thickness and advancing velocity of green water leading edge are compared using numerical method. Also the motion, the pressure on the vertical wall and the height on the deck of green water are compared among the three bow deck shapes in the heave and pitch motion free condition by experimental method. To remove the effects of the difference of motions among the deck shapes, numerical simulations are performed varying the deck shape with the same motion. In the same motion condition, smallest impulsive pressure occurred in the condition of elliptic deck shape.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.4
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• pp.403-410
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• 2008

This paper describes the optimization of the rudder section by the genetic algorism based on VLM(Vortex Lattice Method) and panel method. The developed propeller-rudder analysis program has been validated by comparing with experimental data. The research extends to optimize the anti-erosion rudder section of the large container ship. The object function is the amount of pressure at leading edge of rudder which is closely related with erosion phenomena. The optimized rudder has been compared with conventional rudder with NACA 0021 section by analyzing with the developed program. The finally optimized section has low and mild pressure distribution in comparison with the NACA rudder. The experiments is expected to be carried out for the validation of the present optimization and more parametric study of section geometry is also expected to be conducted in the near future.

• The KSFM Journal of Fluid Machinery
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• v.17 no.1
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• pp.28-34
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• 2014

This paper presents the performance enhancement of a double-inlet centrifugal blower by the shape optimization of an impeller. Two design variables, a number of blade and a length of chord, are introduced, and analyzed by a response surface method. Three-dimensional compressible Navier-Stokes equations are used to analyze the blower performance and the internal flow of the blower. Throughout the numerical simulation of the blower, blower efficiency can be increased by reducing separation flow generating from the blade leading edge of a blade pressure surface. It is noted that recirculation flow observed inside the blade passage induces low velocity region, thus increases pressure loss. Efficiency and pressure of the optimum blower are successfully increased up to 3% and 3.9% compared to those of reference blower at the design flow condition, respectively. Detailed flow field inside the blower is also analyzed and compared.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.12
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• pp.645-653
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• 2017

Thermal and flow modeling and fin structure optimization were performed to reduce the weight of an electrical device with a staggered fin. First, a numerical model for thermal and flow characteristics was suggested, and then, the model was verified experimentally. Using the verified model, improvement in cooling performance of the cooling system through the staggered fins was predicted. As a result, 87.5% of total heat generated was dissipated through the cooling fins, and a thermal island was observed in the rotor because of low velocity of the internal air flow through the air gap. In addition, it was confirmed that the staggered fin improves the cooling performance but it also increases the total pressure drop within the cooling system, by maximizing the leading edge effect. Based on this analysis result, the effect of each design parameter on the thermal and flow characteristics was analyzed to select the main optimal design parameters, and multi-objective optimization was performed by considering the cooling performance and the fin weight. In conclusion, the optimized fin structure improved the cooling performance by 7% and reduced the fin weight by 28% without any compromise of the pressure drop.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.8-17
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• 2002

In this paper, the computational analysis of open-water characteristics for three model propellers(P4119, P4842 and 3 podded propeller of KRISO) is done by using a viscous-flow method based on Reynolds-Averaged Navier-Stokes equations. The results are presented for open-water performances, blade-section pressures, and circumferentially-averaged velocity profiles for the all three propeller models. Overall close agreements with available experimental data are shown. However, some discrepancies are also found in the pressure near the leading edge of the propeller blade and the open-water performance of the podded propellers.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.14-24
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• 2011

In this paper, design optimization for mixed-flow pump impellers and diffusers has been studied using a commercial computational fluid dynamics (CFD) code and DOE (design of experiments). We also discussed how to improve the performance of the mixed-flow pump by designing the impeller and diffuser. Geometric design variables were defined by the vane plane development, which indicates the blade-angle distributions and length of the impeller and diffusers. The vane plane development was controlled using the blade-angle in a fixed meridional shape. First, the design optimization of the defined impeller geometric variables was achieved, and then the flow characteristics were analyzed in the point of incidence angle at the diffuser leading edge for the optimized impeller. Next, design optimizations of the defined diffuser shape variables were performed. The importance of the geometric design variables was analyzed using $2^k$ factorial designs, and the design optimization of the geometric variables was determined using the response surface method (RSM). The objective functions were defined as the total head and the total efficiency at the design flow rate. Based on the comparison of CFD results between the optimized pump and base design models, the reason for the performance improvement was discussed.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.33-46
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• 2011

Concave surface boundary-layer flows are subjected to centrifugal instability which results in the formation of streamwise counter-rotating vortices. Such boundary layer flows have been experimentally investigated on concave surfaces of 1 m and 2 m radius of curvature. In the experiments, to obtain uniform vortex wavelengths, thin perturbation wires placed upstream and perpendicular to the concave surface leading edge, were used to pre-set the wavelengths. Velocity contours were obtained from hot-wire anemometer velocity measurements. The most amplified vortex wavelengths can be pre-set by the spanwise spacing of the thin wires and the free-stream velocity. The velocity contours on the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices. Three different vortex growth regions can be identified. The occurrence of a secondary instability mode is also shown as mushroom-like structures as a consequence of the non-linear growth of the streamwise vortices. Wall shear stress measurements on concave surface of 1 m radius of curvature reveal that the spanwise-averaged wall shear stress increases well beyond the flat plate boundary layer values. By pre-setting much larger or much smaller vortex wavelength than the most amplified one, the splitting or merging of the streamwise vortices will respectively occur.