• International Journal of Naval Architecture and Ocean Engineering
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• 제9권6호
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• pp.677-692
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• 2017

A numerical approach based on a potential flow method is developed to simulate the unsteady interaction between propeller and rudder. In this approach, a panel method is used to solve the flow around the rudder and a vortex lattice method is used to solve the flow around the propeller, respectively. An iterative procedure is adopted to solve the interaction between propeller and rudder. The effects of one component on the other are evaluated by using induced velocities due to the other component at every time step. A fully unsteady wake alignment algorithm is implemented into the vortex lattice method to simulate the unsteady propeller flow. The Rosenhead-Moore core model is employed during the wake alignment procedure to avoid the singularities and instability. The Lamb-Oseen vortex model is adopted in the present method to decay the vortex strength around the rudder and to eliminate unrealistically high induced velocity. The present methods are applied to predict the performance of a cavitating horn-type rudder in the presence of a 6-bladed propeller. The predicted cavity patterns compare well with those observed from the experiments.

• 대한기계학회논문집B
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• 제29권12호
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• pp.1313-1320
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• 2005

In this investigation, we studied the wake interactions incurred by two nearby spheres at Re=300. We considered all possible arrangements of the two spheres in terms of the distance between the spheres and, the angle inclined with respect to the flow direction. It turns out that significant changes in shedding characteristics are noticed depending on how the two spheres are positioned. In this study, not only quantitative changes in the key physical parameters such as force coefficients and shedding frequencies, but also qualitative changes in shedding patterns are analyzed and reported.

• Journal of Advanced Marine Engineering and Technology
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• 제36권3호
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• pp.358-367
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• 2012

A study on tidal turbine using CFD simulation has been an economical and reliable method. However, large flow fields with multi-turbine arrays require high computer performance. Actuator disc theory therefore is widely applied. Actuator disc is the concept that imitates actual turbine by means of an energy absorption disc which has the same dimension and characteristics. Turbines installed in array may have disturbance effects on one another. Thus, the subject of this study is to analyze the far wake of these tidal turbines and compare to single turbine case. The main objects are to analyze two turbines positioned longitudinally at different spaces.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.705-710
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• 2004

In the present study, a transient incompressible viscous turbulent flow is simulated for the automotive torque converter with moving mesh technique. For the analysis, entire torque converter flow passages are modeled. Computed torque ratio, capacity factor and efficiency show a good agreement with the experiment data. The flow instabilities characterized by back-flow and wake etc. appeared in some cascade passages are shown to be Propagating along tangential direction. These flow patterns are mainly influenced by the pump and turbine blade passing and can't be predicted through conventional steady simulation with a mixing plane approach. The understanding of the unsteady flow characteristics in a torque converter achieved in the present study may lead to the optimal design of a torque converter.

• 한국유체기계학회 논문집
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• 제9권5호
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• pp.36-41
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• 2006

In the present study, a transient incompressible viscous turbulent flow is simulated for the automotive torque converter with moving mesh technique. For the analysis, entire torque converter flow passages are modeled. Computed torque ratio, capacity factor and efficiency show a good agreement with the experiment data. The flow instabilities characterized by back-flow and wake etc. appeared in some cascade passages are shown to be propagating along tangential direction. These flow patterns are mainly influenced by the pump and turbine blade passing and can't be predicted through conventional steady simulation with a mixing plane approach. The understanding of the unsteady flow characteristics in a torque converter achieved in the present study may lead to the optimal design of a torque converter.

• 한국해양공학회지
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• 제29권6호
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• pp.427-435
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• 2015

This paper provides the numerical results of a simulation of the flow around a propeller working beneath the free surface. A finite volume method is used to solve the unsteady Reynolds averaged Navier-Stokes (URANS) equations, where the wave-making problem is solved using a volume-of-fluid (VOF) method. The numerical analysis focuses on the propeller wake structure affected by the free surface, where we consider another free surface boundary condition that treats the free surface as a rigid wall surface. The propeller wake under the effect of these two free surface conditions shows a reduction in the magnitude of the longitudinal and vertical flow velocities, and its vortical structures strongly interact with the free surface. The thrust and torque coefficient under the free surface effect decrease about 3.7% and 3.1%, respectively. Finally, the present numerical results show a reasonable agreement with the available experimental data.

• Advances in aircraft and spacecraft science
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• 제7권6호
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• pp.537-551
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• 2020

Investigation of leading edge impingement cooling for first stage rotor blades in an aero-engine turbine, its effect on rotor temperature and trailing edge wake loss have been undertaken in this study. The rotor is modeled with the nozzle for attaining a more accurate simulation. The rotor blade is hollowed in order for the coolant to move inside. Also, plenum with the 15 jet nozzles are placed in it. The plenum is fed by compressed fresh air at the rotor hub. Engine operational and real condition is exerted as boundary condition. Rotor is inspected in two states: in existence of cooling technique and non-cooling state. Three-dimensional compressible and steady solutions of RANS equations with SST K-ω turbulent model has been performed for this numerical simulation. The results show that leading edge is one of the most critical regions because of stagnation formation in those areas. Another high temperature region is rotor blade tip for existence of tip leakage in this area and jet impingement cooling can effectively cover these regions. The rotation impact of the jet velocity from hub to tip caused a tendency in coolant streamlines to move toward the rotor blade tip. In addition, by discharging used coolant air from the trailing edge and ejecting it to the turbines main flow by means of the slot in trailing edge, which could reduce the trailing edge wake loss and a total decrease in the blade cooling loss penalty.

• 해양환경안전학회지
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• 제27권7호
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• pp.1106-1115
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• 2021

본 연구에서는 80k Bulk carrier의 저항성능 향상을 목적으로 선미부에 1개의 핀을 부착해 선미 유동을 제어하였고, 저항성능 및 반류의 변화를 분석하였다. 부착된 핀은 직사각형 단면을 가지며, 길이와 폭, 두께는 고정된 채 길이 및 흘수 방향 부착 위치와 유선에 대한 각도만 변화가 있었다. 나선 및 핀이 부착된 선체에 대한 모형 스케일에서의 CFD 해석이 수행되었고, 그 결과를 실선 확장 후 비교하였다. 핀은 프로펠러로 유입되는 빌지 볼텍스의 경로를 선미 트랜섬 쪽으로 변화시켰고, 이는 프로펠러 상부와 선미부의 압력을 증가시켰다. 이로 인해 선체의 압력저항 및 전 저항이 감소되었으며, 감소율은 핀의 부착 위치가 선미 및 선저와 가까울수록 높았다. 또한 핀은 공칭반류를 감소시켰는데 핀의 각도가 커질수록 반류의 변화가 컸고, 전 저항 저감률은 최대가 되는 특정 각도까지만 비례하였다. 대상 선박에 단일 핀을 부착했을 시의 최대 전 저항 저감률은 약 2.1 %였고, 선미로부터 수선간장의 12.5%, 선저로부터 흘수의 10 % 위치에 14°의 각도로 부착됐을 때이다.

• 한국화재소방학회논문지
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• 제27권6호
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• pp.64-69
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• 2013

본 연구에서는 엔진 나셀 화재를 모사하고 이전의 실험결과를 보충하기위해 이차원 둔각물체 주위의 반응유동장에 대하여 수치해석을 수행하였다. Direct numerical simulation (DNS) 기반의 fire dynamic simulator (FDS)를 이용하여 반응유동장의 특성을 조사하였고, 실험결과와의 비교를 통해 화학반응식을 결정하였다. 산화제는 공기를 사용하였고, 연료는 메탄을 사용하였다. 동축류와 대향류 분사 모두의 경우에 화염의 안정성이나 모양은 둔각물체 주위의 와 강도와 크기에 크게 영향을 받았다. 동축류 분사의 경우 계산에 통한 화염소화한계를 결정하였는데 연료유속이 커질수록 공기의 유속 또한 커지는 경향이 있었고, 그 속도들 또한 기존의 실험결과와 잘 일치함을 볼 수 있었다. 유동장 특성에 대한 화학반응의 효과를 고찰하기 위해 반응이 없는 경우를 계산하여 비교하였다. 모든 경우에 비반응 유동장에 비해 반응 유동장의 후류와는 크기도 감소하고 세기도 감소함을 볼 수 있었는데 이는 반응에 의한 후류의 온도증가가 유체의 밀도 및 모멘텀을 감소시켰기 때문으로 판단된다.

• 대한조선학회논문집
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• 제49권5호
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• pp.440-446
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• 2012

A twisted cylinder has been newly designed by rotating the elliptic cross section along the spanwise direction in order to reduce the drag and vorticies in wake region. The flow around the twisted cylinder at a subcritical Reynolds number (Re) of 3000 is investigated to analyze the effect of twisted spiral pattern on the drag reduction and vortex suppression using large eddy simulation (LES). The instantaneous wake structures of the twisted cylinder are compared with those of a circular and a wavy cylinder at the same Re. The shear layer of the twisted cylinder covering the recirculation region is more elongated than that of the circular and the wavy cylinder. Successively, vortex shedding of the twisted cylinder is considerably suppressed, compared with those of the circular and the wavy cylinder. Consequently, the mean drag coefficient and the fluctuating lift of the twisted cylinder are less than those of the circular and the wavy cylinder.