• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.152-155
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• 2008

In this paper, the effect of modification of geometric variables on the performance of a centrifugal compressor blade has been studied numerically. The compressor contains six main blades and six splitter blades. Reynolds averaged Navier-Stokes (RANS) equations with shear stress turbulence (SST) model are discretized by finite volume approximations and solved on hexahedral grids for flow analysis. The design variables from blade lean angle at tip and middle of the blade have been modified. The isentropic blade efficiency and pressure have been predicted with the variation of the variables. Frozen rotor simulation is performed and adiabatic wall condition has been used. One of the six blades of compressor has been used for simulation to reduce the computational load. Optimum number of meshes has been selected by grid-dependency test, and this is used for all the simulations with changing geometric variables. The detailed flow analysis results have been reported as well as the effects of the variables.

• Journal of Mechanical Science and Technology
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• 제18권12호
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• pp.2273-2283
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• 2004

The vortical flows over sharp-edged delta wings with and without a leading edge extension have been investigated using a computational method. Three-dimensional compressible Reynolds-averaged Navier-Stokes equations are solved to provide an understanding of the effects of the angle of attack and the angle of yaw on the development and interaction of vortices and the aerodynamic characteristics of the delta wing at a freestream velocity of 20 m/s. The present computations provide qualitatively reasonable predictions of vortical flow characteristics, compared with past wind tunnel measurements. In the presence of a leading edge extension, a significant change in the suction pressure peak in the chordwise direction is much reduced at a given angle of attack. The leading edge extension can also stabilize the wing vortex on the windward side at angles of yaw, which dominates the vortical flows over yawed delta wings.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.181-189
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• 1998

A numerical study based on the three-dimensional Reynolds averaged Navier-Stokes equations is presented to analyze the transonic flowfield through two-stage axial compressor. Explicit four-step Runge-Kutta scheme is used for solution algorithm, and local time step and implicit residual averaging are introduced for enhancing the convergency. Artificial dissipation model is adopted to assure the stability of solution. The solver is coupled with Baldwin-Lomax model to describe turbulence. To avoid calculating the unsteady flow, a mixing process is modeled at a station between rotating and stationary blade rows. Results show a variety of important physical phenomena. Comparison of the flowfields with and without tip clearance shows that the effect is considerable in this flowfield. Comparisons with experimental data carried out to validate the calculational results show reasonable agreements. Some remedies are also suggested to improve the revealed problems.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.704-708
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• 2000

A new efficient numerical method for computing unsteady, incompressible flows, DRANS (Decoupled Reynolds-Averaged Navier-Stokes), is presented. To eliminate the restriction of CFL condition, a fully-implicit time advancement in which the Crank-Nicolson method is used fer both the diffusion and convection terms. is adopted. Based on decomposition method, the velocity-turbulent quantity decoupling is achieved. The additional decoupling of the intermediate velocity components in the convection term is made for the fully-implicit time advancement scheme. Since the iterative procedures for the momentum, ${\kappa}\;and\;{\varepsilon}$ equations are not required, the components decouplings bring fourth the reduction of computational cost. The second-order accuracy in time of the present numerical algorithm is ascertained by computing decaying vortices. The present decoupling method is applied to turbulent boundary layer with local forcing.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.781-785
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• 2003

This work presents a numerical analysis of two-phase natural circulation flow in reactor cavity under external vessel cooling. Steady, incompressible, three-dimensional Reynolds-averaged Navier-Stokes equations for multiphase flows with zero equation turbulence model are solved to predict the shear key effect on the circulation rate of cooling water and the distribution of void fraction according to the different mass flow of inlet air. Results show that shear key has a positive effect on the circulation rate of cooling water and induce a local increase of void fraction below the shear key, but not remarkably.

• 한국유체기계학회 논문집
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• 제11권2호
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• pp.46-54
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• 2008

This study presents a numerical optimization to optimize an axial flow fan blade to increase the efficiency. The radial basis neural network is used as an optimization method with the numerical analysis by Reynolds-averaged Navier-Stokes equations using SST model as turbulence closure. Four design variables related to airfoil maximum camber, maximum camber location, leading edge radius and trailing edge radius, respectively, are selected, and efficiency is considered as objective function which is to be maximized. Thirty designs are evaluated to get the objective function values of each design used to train the neural network. Optimum shape shows the efficiency increased by 1.0%.

• 한국유체기계학회 논문집
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• 제19권2호
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• pp.16-20
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• 2016

Design optimization of a transonic compressor rotor(NASA rotor 37) was carried out using response surface method(RSM) which is one of the optimization methods. A numerical simulation was conducted using ANSYS CFX by solving three-dimensional Reynolds-averaged Navier Stokes(RANS) equations. Response surfaces that were based on the results of the design of experiment(DOE) techniques were used to find an optimal shape of blade which has the maximum aerodynamic performance. Two objective functions, viz., the adiabatic efficiency and the loss coefficient were selected with three design configurations to optimize the blade shape. As a result, the efficiency of the optimized blade is found to be increased.

• International Journal of Fluid Machinery and Systems
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• 제10권3호
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• pp.227-239
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• 2017

The accuracy of turbulence models for the Reynolds-Averaged Navier-Stokes (RANS) equations in rough-wall flows is evaluated using data from large-eddy simulations (LES) of boundary layers with favourable and adverse pressure gradients. Some features of the flow (such as flow reversal in the roughness sublayer) cannot be captured accurately by any model, due to the fundamental model formulation. In mild pressure gradients most RANS models are sufficiently accurate for engineering applications, but if strong favourable or adverse pressure gradients are applied (especially those leading to separation) the model performance rapidly degrades.

• International Journal of Aeronautical and Space Sciences
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• 제14권3호
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• pp.210-214
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• 2013

The sensitivity of transonic flow past a Whitcomb airfoil to deflections of an aileron is studied at free-stream Mach numbers from 0.81 to 0.86 and vanishing or negative angles of attack. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver using the $k-{\omega}$ SST turbulence model. The numerical study demonstrates the existence of narrow bands of the Mach number and aileron deflection angles that admit abrupt changes of the lift coefficient at small perturbations. In addition, computations reveal free-stream conditions in which the lift coefficient is independent of aileron deflections of up to 5 degrees. The anomalous behavior of the lift is explained by interplay of local supersonic regions on the airfoil. Both stationary and impulse changes of the aileron position are considered.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.473-478
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• 2004

This work presents the Thermal Hydraulic analysis has been performed for a 19-pin wire-spacer fuel assembly using three-dimensional Reynolds-averaged Navier-Stokes equations. SST model is used as a turbulence closure. The whole fuel assembly has been analyzed for one period of the wire-spacer using periodic boundary condition at inlet and outlet of the calculation domain. The overall results far a preliminary calculation show a good agreement with the experimental observations. It has been found that the major unidirectional flows are the axial velocity in sub-channels and the peripheral sweeping flows and the velocities are found to be following a cyclic path of period equal to the wire-wrap pitch. The temperature is found to be maximum in the central region and also, there exist a radial temperature gradient between the fuel rods. The major advantage of performing this kind of analysis is the prediction of thermal-hydraulic behavior of a fuel assembly with much ease.