• Journal of Power System Engineering
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• 제13권4호
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• pp.31-37
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• 2009

The purpose of this numerical study was to investigate performance characteristics for cooling tower axial fans with sweep. Performance data for the fans with various sweep angles were obtained in terms of the setting angle at a constant flow rate. Viscous flow calculations were carried out to obtain Performance data of the total pressure rise and hydraulic efficiency. A solution of the Ffowcs Williams-Hawkings equations was used to calculate the sound pressure level at three times fan diameter away from the fan. The calculated performance data well represented performance characteristics of the cooling tower axial fan. The total pressure rise and hydraulic efficiency at the same setting angle decreased with sweep angle. Sound pressure level slightly decreased for the fan with a sweep angle of 10 degree. No significant effect of the sweep geometry was found on the sound pressure level.

• Bulletin of the Korean Mathematical Society
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• 제48권2호
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• pp.397-412
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• 2011

In this paper, the equation of the transient Stokes flow of an incompressible viscous fluid is studied. Growth and decay estimates are established associating some appropriate cross sectional line and area integral measures. The method of the proof is based on a first-order differential inequality leading to an alternative of Phragm$\'{e}$n-Lindell$\"{o} $f type in terms of an area measure of the amplitude in question. In the case of decay, we also indicate how to bound the total energy.

• Journal of computational fluids engineering
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• 제8권4호
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• pp.34-40
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• 2003

The effect of nose radius on aerodynamic heating is investigated by using the Navier-Stokes code extended to thermochemical nonequilibrium airflow, Spherical blunt bodies, whose nose radius varies from 0.O03048 m to 0.6096 m, flying at Mach 25 at an altitude of 53.34 km are considered. Comparison of heat flux at stagnation point with the solution of Viscous Shock Layer and Fay-Riddell are made. Results show that the flow for very small radius is in a nearly frozen state, and therefore the heat flux due to diffusion is smaller than that due to translational energy. As the radius becomes larger, the portion of heat flux by diffusion becomes greater than that of heat flux by translational temperature and approaches to a constant value.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.178-183
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• 2000

An efficient Newton-GMRES algorithm is presented for computing two-dimensional steady compressible viscous flows on unstructured hybrid meshes. The scheme is designed on cell-centered finite volume method which accepts general polygonal meshes. Steady-state solution is obtained with pseudo-transient continuation strategy. The preconditioned, restarted general minimum residual(GMRES) method is employed in matrix-free form to solve the linear system arising at each Newton iteration. The incomplete LU fartorization is employed for the preconditioning of linear system. The Spalart-Allmars one equation turbulence model is fully coupled with the flow equations to simulate turbulence effect. The accuracy, efficiency and robustness of the presently developed method are demonstrated on various test problems including laminar and turbulent flows over flat plate and airfoils.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.66-72
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• 2000

Aerodynamic sensitivity analysis is performed for the Navier-Stokes equations coupled with two-equation turbulence models using a discrete adjoint method and a direct differentiation method respectively. Like the mean flow equations, the turbulence model equations are also hand-differentiated to accurately calculate the sensitivity derivatives of flow quantities with respect to design variables in turbulent viscous flows. Both the direct differentiation code and the adjoint variable code adopt the same time integration scheme with the flow solver to efficiently solve the differentiated equations. The sensitivity codes are then compared with the flow solver in terms of solution accuracy, computing time and computer memory requirements. The sensitivity derivatives obtained from the sensitivity codes with different turbulence models are compared with each other. Using two-equation turbulence models, it is observed that a usual assumption of constant turbulent eddy viscosity in adjoint methods may lead to seriously inaccurate results in highly turbulent flows.

• Transactions of the Korean Society of Mechanical Engineers
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• 제7권2호
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• pp.175-185
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• 1983

When a circular cylinder near the plane fluid-interface of different viscosities is in parallel and normal motion, solutions of the Oseen equation are obtained. Classical image method with Faxen's integral form is used to satisfy the boundary conditions on the plane interface. Coefficients of drag and lift increase as a cylinder approaches to the interface. But drag-coefficients of parallel motions with viscosity-ratio less than unity are decreased slightly. They show monotonic increase with Reynolds number in case of parallel motion, but minimum values of drag coefficients in normal motion are appeared. On the other hand Stokes' solution are obtained by taking limits of low Reynolds number except the case of parallel motion with viscosity-ratio not equal to infinity.

• Journal of the Korean Society for Precision Engineering
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• 제20권5호
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• pp.171-179
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• 2003

An Amplitude Proportional Friction Damper (APFD) is considered in order to improve the characteristics of Coulomb friction damper. The frictional force is proportional to the amplitude in APFD system and the system is non-linear as is Coulomb damper system. A free vibration analysis on the 1-DOF system has made to demonstrate the characteristics of the APFD system. The results show that APFD system has similar damping characteristics to the viscous damper. Also, the solution for the response of a base-excited system with APFD is developed through the application of a Fourier series to represent the frictional force of APFD. It is assumed that no stick-slips occur during any portion of the steady-state oscillation.

• Journal of the Korean Society of Safety
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• 제13권4호
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• pp.3-8
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• 1998

The vortex particle method, which includes viscous effects, consists of diffusion of boundary vorticity and creation of the vortex particles, convection, particle strength exchange, and particle redistribution. Accuracy of the boundary element method is very important since it creates the particles around the body at every time step. A boundary element method based on source panel was investigated as part of computation of unsteady separated flows by rising the vortex particle method. The potential flows were computed around a circular cylinder and a square cylinder. The results around the circular cylinder were compared with the exact solution, and the distribution of vorticity, in particular near the sharp comers of the square cylinder, is scrutinized for different number of panels.

• Journal of the Korean Mathematical Society
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• 제45권3호
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• pp.645-681
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• 2008

The Navier-Stokes system for heat-conducting incompressible fluids is studied in a domain ${\Omega}{\subset}R^3$. The viscosity, heat conduction coefficients and specific heat at constant volume are allowed to depend smoothly on density and temperature. We prove local existence of the unique strong solution, provided the initial data satisfy a natural compatibility condition. For the strong regularity, we do not assume the positivity of initial density; it may vanish in an open subset (vacuum) of ${\Omega}$ or decay at infinity when ${\Omega}$ is unbounded.

• Bulletin of the Korean Mathematical Society
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• 제50권5호
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• pp.1737-1751
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• 2013

An efficient and stable point collocation scheme based on a meshfree method is studied for the stationary incompressible Navier-Stokes equations. We describe the diffuse derivatives associated with the moving least square method. Using these diffuse derivatives, we propose a point collocation method to fit in solving the Navier-Stokes equations which improves the stability of the direct point collocation scheme. The convergence of the numerical solution is investigated from numerical examples. The driven cavity ow and the backward facing step ow are implemented for the reliability of the scheme. Also, the viscous ow on complicated geometry is successfully calculated such as the ow past a circular cylinder in duct.