• The KSFM Journal of Fluid Machinery
• /
• v.14 no.1
• /
• pp.55-60
• /
• 2011

Numerical analyses of a turbine redesigned to achieving the weight reduction by equipping square nozzles and the original turbine have been conducted and the results have been compared. The results show that the turbine with square section nozzles has more even flow distribution at the first row rotor inlet and less inactive areas but the loss induced by wake is increased. Despite the wake loss, the newly designed turbine shows better performance than the original one. It has also been found that the turbine performance can be improved by reshaping its stator and second row rotor.

• 한국신재생에너지학회:학술대회논문집
• /
• 2011.05a
• /
• pp.163.2-163.2
• /
• 2011

Due to global warming, the need to secure an alternative resource has become more important nationally. Due to the high tidal range of up to 9.7m on the west coast of Korea, numerous tidal current projects are being planned and constructed. To extract a significant quantity of power, a tidal current farm with a multi-arrangement is necessary in the ocean. The rotor, which initially converts the energy, is a very important component because it affects the efficiency of the entire system, and its performance is determined by various design variables. The power generation is strongly dependent on the size of the rotor and the incoming flow velocity. However, the interactions between devices also contribute significantly to the total power capacity. Therefore, rotor performance considering the interaction problems needs to be investigated for generating maximum power in a specific field. This paper documents the characteristics of wake induced by horizontal axis tidal current power turbine.

• International Journal of Ocean System Engineering
• /
• v.3 no.4
• /
• pp.169-174
• /
• 2013

The computational fluid dynamics software FLUENT is used to calculate and compare the hydrodynamic performance of the propeller-rudder system of a 42-m trawler, which is installed with a ducted propeller. The effects of rudder on the hydrodynamic performance of the ducted propeller and the wake flow behind the propeller are firstly investigated. In addition, the different rudder angles are also considered to further study the performance of this system.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2005.11a
• /
• pp.31-32
• /
• 2005

It is known that an oscillating airfoil can produce a driving force through the generation of a reversed $K\acute{a}rm\acute{a}n$ vortex street, and this can be expected to be a new highly effective propulsion system. We have been examined various conditions such as frequency number, amplitude in NACA 0010. As Strouhal number is greater than 0.08, wake profile with velocity deficit can be transformed into the wake with velocity excess. We also presented the experimental results on the unsteady vortices structure of the heaving airfoil at various parameters.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.10
• /
• pp.1229-1239
• /
• 1999

A computational study on unsteady compressible flows has been performed by adopting a low Reynolds number $k-{\omega}$ turbulence model in conjunction with dual time stepping scheme. An explicit four-stage Runge-Kutta scheme for the Navier-Stokes equations and an approximate factorization scheme for the $k-{\omega}$ turbulence model equations are used. Computational results obtained for blade surface pressure distributions in the process of rotor-stator interaction in a turbine stage are in good agreement with extant experimental data. The effects of the wake from the stator on the boundary-layer transition over the rotor blade surface are discussed by showing that high intensity turbulence of the stator wake induces an early transition.

• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.5-8
• /
• 2002

The issues associated with the application of CFD for ship design are addressed. It is quite certain that the CFD tools are very useful in evaluating hull forms a prior to traditional towing tank tests. However, the time-consuming pre-processing is an obstacle in the daily application of CFD tools to improve hull forms. The accuracy of computational modeling without sacrificing the usability of CFD system is also to be assessed. The wave generation is still predicted by using potential panel methods, while velocity profiles entering into propeller plane is solved using turbulent flow solvers. The choice of turbulence model is a key to predict nominal wake distribution within acceptable accuracy. The experimental data for CFD validation are invaluable to improve physical and numerical modeling. Other applications of CFD for ship design than hull form improvement are also given. It is certain that CFD can be a cost-effective tool for the design of new and better ships.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.12 s.243
• /
• pp.1313-1320
• /
• 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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11a
• /
• pp.318.2-318
• /
• 2002

Axial fans are widely used in heavy machines due to their ability to produce high flow rate fur cooling of engines. At the same time, the noise generated by these fans causes one of the most serious problems. This work is concerned with the low noise technique of discrete frequency noise. To calculate the unsteady resultant force over the fan blade in an unsymmetric engine room, Time-Marching Free-Wake Method is used. From the calculations of unsteady force on fan blades, noise signal of an engine cooling fan is calculated by using an acoustic similarity law. (omitted)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.104-109
• /
• 2000

The modes of oscillation and radiated acoustic fields of compressible flows over open cavities are investigated computationally. The compressible Navier-Stokes equations are solved for two-dimensional cavities with laminar boundary layers upstream. The high-order and high-resolution numerical schemes are used for the evaluation of spatial derivatives and the time integration. Physically correct numerical boundary conditions are implemented to produce time-accurate solutions in the whole computation domain. The computational domain is large enough to directly resolve a portion of the radiated acoutic field. The results show a transition from a shear layer mode, for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear layer mode is well characterized by Rossiter modes and these oscillations lead to intense upstream acoustic radiation dominated by a single frequency. The wake mode is characterized instead by a large-scale vortex shedding. Acoustic radiation is more intense, with multiple frequencies present.

• Journal of the Korean Society of Safety
• /
• v.10 no.1
• /
• pp.64-73
• /
• 1995

A preliminary study is performed in order to design an effective ventilation equipment for the control of possible pollutants in a workshop. To this end, the Patankar's SIMPLE methodology is used to investigate the flow characteristics of the contaminated thermal deflected jet which is encounted often in practical hood system. SIMPLE-Consistent algorithm is employed for the pressure-velocity coupling appeared in momentum equations. A two equation, k-$\varepsilon$ model is used for Reynolds stresses. The prediction data is compared well against the experimental results by Chang(1989). Considering the control of the wake due to its high turbulence together with the stagnant feature has been investigated in term of major parameters such as temperature and magnitude of the discharge velocity. Detailed discussions are made to reduce the size of the wake region which give rise to pollutant concentration stratification.