This study presents results of aerodynamic wing optimization under uncertainties. To consider uncertainties, an alternative strategy for reliability-based design optimization(RBDO) is developed. The strategy utilizes a single loop algorithm and a sequential approximation optimization(SAO) technique. The SAO strategy relies on the trust region-SQP framework which validates approximated functions at every iteration. Further improvement in computational efficiency is achieved by applying the same sensitivity of limit state functions in the reliability analysis and in the equivalent deterministic constraint calculation. The framework is examined by solving an analytical test problem to show that the proposed framework has the computational efficiency over existing methods. The proposed strategy enables exploiting the RBDO technique in aerodynamic design. For the aerodynamic wing design problem, the solution converges to the reliable point satisfying the probabilistic constraints.

A space launch vehicle departs the ground in a low speed, soon reaches a transonic and a supersonic speed, and then flies in a hypersonic speed into the space. Therefore, the design of a launch vehicle should include the prediction of aerodynamic characteristics for all speed regimes, ranging from subsonic to hypersonic speed. Generally, Empirical and analytical methods and wind tunnel tests are used for the prediction of aerodynamic characteristics. This research presents considerable factors for aerodynamic analysis of a launch vehicle using CFD. This investigation was conducted to determine effects of wake over the base section on the aerodynamic characteristics of a launch vehicle and also performed to determine effects of the sting which exist to support wind tunnel test model.

Drag prediction is sought for the aifoil having laminar and turbulent flow characteristics with CFD code being unable to predict transition to turbulent flow. Laminar flow simulation presents some insight to the transition position. Separate simulations with laminar and turbulent flow and their combination estimate the drag of the airfoil containing laminar and turbulent flow characteristics.

In the Smart UAV Development Program, one of the 21c Frontier R&D Program, the tiltrotor has been studied as the concept of vehicle. The tiltrortor aircraft take-off and land in rotary wing mode like conventional helicopter, and cruise in fixed wing mode like conventional propeller airplane. For the conversion of the flight mode from helicopter to airplane, the nacelle located at wing tip has to be tilted from about 90 degrees of helicopter mode to about 0 degree of airplane mode. In this study, the aerodynamic characteristics of the wing with tilted nacelle is investigated using computation fluid dynamics technique. In order to feature out aerodynamic interferences between wing and nacelle, the flow calculations are conducted for the wing and the nacelle separately and for the combined geometry of wing and nacelle, respectively. Through this computations, not only the aerodynamic data-base for the wing-nacelle is constructed but also its contribution to the configuration design of the wing-nacelle is anticipated.

A numerical investigation has been made for flows in an axisymmetric circular cylinder with a rotating cone located at the bottom of the container. The axisymmetric container is completely filled with a viscous fluid. Major parameter for the present research is the vertex angle of the cone, otherwise Reynolds number of fluid and aspect ratio of the vessel is fixed. Main interest is in vortex breakdown of meridional circulation by rotation of the cone with respect to the longitudinal axis of the cylinder. The method to this problem is numerically to integrate momentum and continuity equations on a generalized body fitted grid system. The pattern of vortex breakdown is quite different from that in a right circular cylinder with flat end wall disks. Flow visualization photographs of a preceeding work are compared with the present numerical results.

Numerical simulation of viscous compressible flow in turbomachinery cascade involves many problems due to the complex geometry of blade but also flow phenomena. In the present study, numerical investigations have been performed to examine the three-dimensional flow characteristics inside the transonic linear turbine cascades using a commercial code, FLUENT. Multi-block H-type grids are applied to the high-turning turbine rotor blades and comparisons with the experimental data and the numerical results have been done. In addition, the effects of turbulence models on the prediction of the endwall flows are analyzed in the sense of the flow compressibility.

This paper addresses a numerical simulation of the flow and heat transfer in a simplified model of helically coiled tube steam generator using a general purpose computational fluid dynamic analysis computer code. The steam generator model is comprised of a cylindrical shell and helically coiled tubes. A cold feed water entered the tubes is heated up, evaporates. and finally become a superheated steam with a large amount of heat transferred continuously from the hot compressed water at higher pressure flowing counter-currently through the shell side. For the calculation of tube side two-phase flow field formed by boiling, inhomogeneous two-fluid model is used. Both the internal and external turbulent flows are simulated using the standard k-e model. The conjugate heat transfer analysis method is employed to calculate the conduction in the tube wall with finite thickness and the convections in the internal and external fluids simultaneously so as to match the fluid-wall-fluid interface conditions properly. The numerical calculations are peformed for helically coiled tubes of steam generator at an integral type pressurized water reactor under normal operation. The effects of tube-side inlet flow velocity are discussed in details. The results of present numerical simulation are considered to be physically plausible based on the data and knowledge from previous experimental and numerical studies where available.

As the size and dimension of target problems in the field of computational engineering including CFD gets bigger and higher, it is needed to have more efficient and flexible data visualization environment in terms of software and hardware. Even though it is still manageable to use a mouse in controlling 3-dimensional data visualization, it would be beneficial to use 3-D input device for 3-D visualization. 'Data Glove' is one of the best 3-D input devices, because human hands are best tools understanding 3-D space. Signals coming from 'Data Glove' are analog and very sensitive to finger motions, so we decided to use a digital filter. This paper describes our experience and benefits of using data glove in controlling 3-Dimensional Postprocess Software.

Interaction between fluid flow and thermal radiation has received considerable attention due to its numerous applications in engineering field. In this case the thermofluid properties of radiating fluid vary with the variation of temperature field caused by absorption and emission of radiant heat. To analyze the radiation heat transfer in radiating fluid, the simultaneous solution of the radiative transfer equation (RTE) and the fluid dynamics equations is required. This means that the numerical procedure used for the RTE must be computationally efficient to permit its inclusion in the other submodels, and must be compatible with the other transport equations. The finite volume method (FVM) and the discrete ordinates method (DOM) are usually employed to simulate radiation problems in generalized coordinates. These two representative methods are examined and compared, especially in view of the numerical integration of the radiation intensity over solid angle. The FVM shows better accuracy than the DOM owing to less constraints of the selection of control angle.

An extension of our recently developed locally linear reconstruction scheme to 2 dimensional incompressible flow solver is presented. The solver is based on a semi-implicit fractional step method in which the convective term is discretized by Adams-Bashforth method and the diffusion term by Crank-Nicolson method. Several numerical examples are tested to demonstrate the mesh type independent accuracy of the solver, which include decaying vortex flow, square cavity flow, and flow around a circular cylinder. The above examples are solved on quadrilateral or hybrid meshes. For all numerical examples, we obtained reasonable results.

A new anisotropic mesh refinement method is proposed. The new method is based on a simple second order interpolation error indicator. Therefore, it is methodologically direct and intuitive as compared with traditional anisotropic refinement strategies. Moreover, it does not depend on the mesh type. The error indicator is face-wisely calculated for all faces in a mesh and the cell refinement type is determined by the configuration of face markings with a given threshold. For the sake of simplicity, an application for a poisson equation on a triangle mesh is considered. The error field and resultant mesh refinement pattern are compared and effects of the threshold selection are discussed. Applying anisotropic refinement with various thresholds, we observed higher convergence rates than those in the uniform refinement cases.

Substructuring methods are usually used in finite element structural analyses. In this study a multi-level substructuring algorithm is developed and proposed as a possible candidate for incompressible fluid solves. Finite element formulation for incompressible flow has been stabilized by a modified residual procedure proposed by Ilinca et.al.[5]. The present algorithm consists of four stages such as a gathering stage, a condensing stage, a solving stage and a scattering stage. At each level, a predetermined number of elements are gathered and condensed to form an element of higher level. At highest level, each subdomain consists of only one super-element. Thus, the inversion process of a stiffness matrix associated with internal degrees of freedom of each subdomain has been replaced by a sequential static condensation. The global algebraic system arising feom the assembly of each subdomains is solved using Conjugate Gradient Squared(CGS) method. In this case, pre-conditioning techniques usually accompanied by iterative solvers are not needed.

In two dimensional incompressible flows, a preconditioning technique called Hierarchical Iterative Procedure(HIP) has been implemented on a stabilized finite element formulation. The stabilization has been peformed by a modified residual method proposed by Illinca et. al.[3]. The stabilization which is necessary to escape from the LBB constraint renders an equal order formulation. In this paper, we increased the order of interpolation whithin an element up to cubic. The conjugate gradient squared(CGS) method is used for the outer iteration, and the HIP for the preconditioning for the incompressible Navier-Stokes equation. The hierarchical elements has been used to achieve a higher order accuracy in fluid flow analyses, but a proper efficient iterative procedure for higher order finite element formulation has not been available so far. The numerical results by the present HIP for the lid driven cavity flow showed the present procedure to be stable, very efficient and useful in flow analyses in conjunction with hierarchical elements.

A kinetic theory analysis is made of low-speed gas flows in microchannels. The Boltzmann equation simplified by a collision model is solved by means of a finite difference approximation with the discrete ordinate method. The method does not suffer from statistical noise which is common in particle based methods and requires much less amount of computational effort. Calculations are made for flows in simple microchannels and a microfluidic system consisting of two microchannels in series. The method is assessed by comparing the results with those from several different methods and available experimental data.

A kinetic theory analysis is made of low-speed gas flows around a micro-plate. The Boltzmann equation simplified by a collision model is solved by means of a finite difference approximation with the discrete ordinate method. The method does not suffer from statistical noise which is common in particle based methods and requires much less amount of computational effort. Calculations are made for flows around a micro-scale flat plate with a finite length of 20 microns. The method is assessed by comparing the results with those from several different methods and available experimental data.

This paper presents a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method (FDLBM). We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing the conventional FDLBM, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of $\alpha=23^0$. At a stand-off distance $\omega$, the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and th propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. The lattice BGK model for compressible fluids is shown to be one of powerful tool for computing sound generation and propagation for a wide range of flows.

Unsteady nonlinear wave motions on the free surface over a plane beach of constant slope are numerically simulated using a finite difference method in rectangular grid system. Two-dimensional Navier-Stokes equations and the continuity equation are used for the computations. Irregular leg lengths and stars are employed near the boundaries of body and free surface to satisfy the boundary conditions. Also, the free surface which consists of markers or segments is determined every time step with the satisfaction of kinematic and dynamic free surface conditions. Moreover, marker-density method is also adopted to allow plunging jets impinging on the free surface. The second-order Stokes wave theory and solitary wave theory are employed for the generation of waves on the inflow boundary. For the simulation of wave breaking phenomena, the computations are carried out with the plane beach of constant slope in surf zone. The results are compared with each other. The marker-density method is better then the hybrid method. Also they are compared with other existing experimental results. The Agreement between the experimental data and the computation results is good.

The interaction between the hypersonic free stream and the side jet flow at high altitudes is investigated by direct simulation Monte Carlo(DSMC) method. Since there is a great difference in density between the free stream and the side jet flow, the weighting factor technique which could control the number of simulation particles, is applied to calculate these two flows simultaneously. Chemical reactions are not considered in the calculation. For validation, the corner flow passing between a pair of plates that are perpendicularly attached is solved. The side jet flow is then injected into this comer flow and solution is found for the merged flow. Results are compared with the experiments. For a more realistic rocket model, the flow past a blunted cone cylinder shape is solved. The leeward or windward jet injection is merged with this flow. The effect on the rocket surface is observed at various flow angles. The lambda effect and the wake structure are found like low attitudes. High interaction between the free stream and the side jet flow is observed when the side jet is injected in the windward direction.

Flush inlet, which has been chosen for modem air vehicles to take advantage of structure compactness and small RCS, gives rise to some aerodynamic problems such as flow separation and distortion due to vortices which deteriorate the performance of both inlet and engine. In this study, pressure recoveries at inlet exit plane were evaluated through numerical analyses of 3D turbulent flow for various inlet shapes and flight conditions. Inlet shape was controlled by changing ramp angle and width of throat, and effects of mass flow rate and angle of attack were investigated.

A numerical study of underexpanded jet and impingement on a wall mounted at various distances from the nozzle exit is presented. The 3-dimensional Navier-Stokes equations and $\kappa-\omega$ turbulence equations are solved. The grids are constructed as overlapped grid systems to examine the distance effect. The DADI method is applied to obtain steady-state solutions. To avoid numerical instability such as the carbuncle that sometimes accompany approximate Riemann solver, the HLLE+ scheme is employed for the inviscid flux at the cell interfaces. A goal of this work is to apply a number of two-equation turbulence models based on the $\omega$ equation to the impinging jet problem.

The Numerical study has been carried out to investigate the effects of chemical reaction and thermal radiation on the rocket plume flow-field at various altitudes. The theoretical formulation is based on the Navier-Stokes equations for compressible flows along with the infinitely fast chemistry and thermal radiation. The governing equations were solved by a finite volume fully-implicit TVD(Total Variation Diminishing) code which uses Roe's approximate Riemann solver and MUSCL(Monotone Upstream-centered Schemes for Conservation Laws) scheme. LU-SGS (Lower Upper Symmetric Gauss Seidel) method is used for the implicit solution strategy. An equilibrium chemistry module for hydrocarbon mixture with detailed thermo-chemical properties and a thermal radiation module for optically thin media were incorporated with the fluid dynamics code. In this study, kerosene-fueled rocket was assumed operating at O/F ratio of 2.34 with a nozzle expansion ratio of 6.14. Flight conditions considered were Mach number zero at ground level, Mach number 1.16 at altitude 5.06km and Mach number 2.9 at altitude 17.34km. Numerical results gave the understandings on the detailed plume structures at different altitude conditions. The diffusive effect of the thermal radiation on temperature field and the effect of chemical recombination during the expansion process could be also understood. By comparing the results from frozen flow and infinitely fast chemistry assumptions, the excess temperature of the exhaust gas resulting from the chemical recombination seems to be significant and cannot be neglected in the view point of performance, thermal protection and flow physics.

Numerical simulations of supersonic impinging jet flows are carried out using the axisymmetric Navier-Stokes code. This paper focuses on the oscillatory flow features associated with the variation of the nozzle pressure ratio and nozzle-to-plate distance. Frequencies of the surface pressure oscillation from computational results are in accord with the measured impinging tones for various cases of nozzle-to-plate distance. The variation of this frequency with distance show a staging behavior. Computed results for the case of nozzle pressure ratio variation for a fixed nozzle-to-plate distance also demonstrate a staging behavior. These two seemingly different staging behaviors are found to obey the same frequency-distance characteristics when the frequency and the distance are normalized by using the length of the shock cell.

In the vortex particle method based on the vorticity-velocity formulation for solving the Wavier-Stokes equations, the unsteady, incompressible, viscous laminar flow over a NACA 0012 foil is simulated. By applying an operator-splitting method, the 'convection' and 'diffusion' equations are solved sequentially at each time step. The convection equation is solved using the vortex particle method, and the diffusion equation using the particle strength exchange(PSE) scheme which is modified to avoid a spurious vorticity flux. The scheme is improved for variety body shape using one image layer scheme. For a validation of the present method, we illustrate the early development of the viscous flow about an impulsively started NACA 0012 foil for Reynolds number 550.

Direct numerical simulations are peformed to investigate the physics of a spatially developing turbulent boundary layer flow suddenly subjected to spanwise oscillating electro-magnetic forces in the near-wall region. The Reynolds number based on the inlet momentum thickness and free-stream velocity is $Re_\theta=300$. A fully-implicit fractional step method is employed to simulate the flow. The mean flow properties and the Reynolds stresses are obtained to analyze the near-wall turbulent structure. It is found that skin-friction and turbulent kinetic energy can be reduced by the electro-magnetic forces. Instantaneous flow visualization techniques are used to observe the response of streamwise vortices to spanwise oscillating forces. The near-wall vortical structures are clearly affected by spanwise oscillating electro-magnetic forces.

In the present work, we have interests on the modification of parallel implemented with MPI(Message Passing Interface) programming method, 3-Dimensional, unsteady, incompressible Navier-Stokes equation solver to analyze the low-Reynolds number flow In order to accurate calculation aerodynamic coefficients in low-Reynolds number flow field, we modified the two-equation turbulence model. This paper describes the development and validation of a new two-equation model for the prediction of flow transition. It is based on Mentor's low Reynolds $\kappa-\omega$ model with modifications to include Total Stresses Limitation (TSL) and Separation Transition Trigger (STT)

Numerical analysis of a gaseous jet submerged in a liquid environment was carried out using the volume of fluid(VOF) method to simulate the kinematics of the gas-liquid interface. Two nozzle geometries were tested, one for Fanno tube and the other for converging diverging nozzle. Commercial code was used for the present calculation. Transient behavior of a gaseous jet since its start showed periodic nature of the jet, which was also observed in previous measurements.

The flow and the heat transfer about the cross-flow fin-tube heat exchanger in an out-door unit of a heat pump system has been numerically Investigated. Using the general purpose analysis code, FLUENT, the Navier-Stokes equations and the energy equation are solved for the three dimensional computation domain that encompasses multiple rows of the fin-tube. The temperature on the fin and tube surface is assumed constant but compensated later through the fin efficiency when predicting the heat-transfer rate. The contact resistance is also taken into consideration. The flow and temperature fields for a wide range of inlet velocity and fin-tube arrangements are examined and the results are presented in the paper. The details of the flow are very well captured and the heat transfer rate for a range of inlet velocity is in excellent agreement with the measured data. The flow solution provides the effective permeability and the inertial resistance factor of the heat exchanger if the exchanger were to be approximated by the porous medium. This information is essential in carrying out the global flow field calculation which, in turn, provides the inlet velocity lot the microscopic temperature-field calculation of the heat exchanger unit.

The pressure drop in a Venturi Scrubber is predicted using the Eulerian-Lagrangian Method, which is one of the numerical methods to solve the dispersed two-phase flow. KIVA-3V Code is modified to solve the coupled gas-liquid two-phase flow field. The liquid is assumed to be injected through the nozzles with the Rosin-Rammler drop size distribution. The computational results shows good agreement with the experimental data.

Aerodynamic characteristics of three-dimensional wings in ground effect for Aero-levitation Electric Vehicle(AEV) are numerically investigated for various ground clearances and wing spans at the Reynolds number of $2\times10^6$. Numerical results show that a sizeable three-dimensional flow separation occurs with formation of an arch vortex at the junction of main and vertical wings, and that this is conjectured a primary cause for the high lift-to-drag(L/D) reduction rate of the main wing, when the wing span is decreased. Improvements on L/D ratios of the wings with small spans are pursued by breaking the coherence of superimposed adverse pressure gradients at the wing junction.

In the present study a mesh generation program has been developed by using DXF file. The program consists of DXF file reading and mapping algorithm, which projects the 2-D mesh point onto the triangular surface constructed by nearest three points. The present program has been tested for mesh generations for the road tunnel ventilation analysis and analysis of lava movement in mountain area.

The HANARO, multi-purpose research reactor, 30 MWth open-tank-in- pool type, is under normal operation since it reached the initial critical in February 1995. The HANARO is planning to produce a fission moly-99 of radio isotopes, a mother nuclide of Tc-99m, a medical isotope and is under developing a target handling tool for loading and unloading it in a circular flow tube (OR-5). A guide tube is extended from the reactor core to the top of the reactor chimney for easily un/loading a target under the reactor normal operation. But active coolant through the core can be quickly raised up to the top of the chimney through the guide tube by jet flow. This paper is described an analytical analysis to calculate the hole size of a orifice inserted in the circular irradiation hole and to study the flow characteristics through the guide tube under reactor normal operation and loading the target. As results, the results show that the hole size of orifice was 31 mm of the inner diameter to suppress the guide tube jet flow and the coolant safely cooled the target of fission moly after inserting the orifice to the flow tube.

The HANARO, a multi-purpose research reactor of 30 MWth, open-tank-in-pool type, has been under normal operation since its initial criticality in February, 1995. The HANARO is composed of inlet plenum, grid plate, core channel with flow tubes and chimney. The reactor core channel is located at about twelve m (12 m) depth of the reactor pool and cold by the upward flow that the coolant enters the lower inlet of the plenum, rises up through the grid plate and the core channel and exit through the outlet of chimney. A guide tube is extended from the reactor core to the top of the reactor chimney for easily un/loading a target under the reactor normal operation. But active coolant through the core can be Quickly raised up to the top of the chimney through the guide tube by jet flow. This paper is described an analytical analysis to study the flow behavior through the guide tube under reactor normal operation and unloading the target. As results, it was conformed through the analysis results that the flow rate, about fourteen kilogram per second (14 kg/s) suppressed the guide tube jet and met the design cooling flow rate in a circular flow tube, and that the fission moly target cooling flow rate met the minimum flow rate to cool the target.

The initial conditions such as the film thickness and the void fraction at the onset of annular flow are required for the analytical dryout model. The Disturbance Wave Instability model(DWI model) is one of the model describing the Annular-to-Intermittent Flow regime Transition(AIFT). The experimental CHF conditions for the uniformly heated tube were compared with the predictions by the modified Levy model, for which the initial conditions at AIFT were estimated by the DWI model. For the flow through long tubes with small inlet subcooling, the effect of AIFT model on the dryout prediction was little. However, the use of DWI model gave better prediction of CHF in a short tube.

The objective of this work is not only to perform feasibility studies on the CFD (computational fluid dynamics) analysis for the capillary system design but also to provide an enhanced understanding of the autonomous capillary flow. The capillary flow is evaluated by means of the commercial CFD software of FLUENT, which includes the VOF (volume-of-fluid) model for multiphase flow analysis. The effect of wall adhesion at fluid interfaces in contact with rigid boundaries is considered in terms of static contact angle. Feasibility studies are first performed, including mesh-resolution influence on pressure profile, which has a sudden increase at the liquid/gas interface. Then we perform both 2D and 3D simulations and examine the transient nature of the capillary flow. Analytical solutions are also derived for simple cases and compared with numerical results. Through this work, essential information on the capillary system design is brought out. Our efforts and initial success in numerical description of the microfluidic capillary flows enhance the fundamental understanding of the autonomous capillary flow and will eventually pave the road for full-scale, computer-aided design of microfluidic networks.