• Clean Technology
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• v.28 no.4
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• pp.316-322
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• 2022

The flow pattern at the inlet of the catalyst layer in a selective catalytic reduction (SCR) system is one of the key parameters influencing the performance of the denitrification process. In the curved diffusing parts between the ammonia injection grids and the catalyst layers, guide vanes are installed to improve flow uniformity. In the present study, a numerical simulation has been performed to investigate the effect of the geometrical configuration of the guide vanes on the aerodynamic characteristics of a denitrification facility. This application has been made to the existing SCR process in a large-scaled coal-fired power plant. The flow domain to be solved covers the whole region of the flow passages from the exit of the ammonia injection gun to the exit of the catalyst layers. ANSYS-Fluent was used to calculate the three-dimensional steady viscous flow fields with the proper turbulence model fitted to the flow characteristics. The root mean square of velocity and the pressure drop inside the flow passages were chosen as the key performance parameters. Four types of guides vanes were proposed to improve the flow quality compared to the current configuration. The numerical results showed that the type 4 configuration was the most effective at improving the aerodynamic performance in terms of flow uniformity and pressure loss.

• Advances in aircraft and spacecraft science
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• v.9 no.5
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• pp.415-431
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• 2022

Secondary flows have a huge impact on losses generation in modern low pressure gas turbines (LPTs). At design point, the interaction of the blade profile with the end-wall boundary layer is responsible for up to 40% of total losses. Therefore, predicting accurately the end-wall flow field in a LPT is extremely important in the industrial design phase. Since the inlet boundary layer profile is one of the factors which most affects the evolution of secondary flows, the first main objective of the present work is to investigate the impact of two different inlet conditions on the end-wall flow field of the T106A, a well known LPT cascade. The first condition, labeled in the paper as C1, is represented by uniform conditions at the inlet plane and the second, C2, by a flow characterized by a defined inlet boundary layer profile. The code used for the simulations is based on the Discontinuous Galerkin (DG) formulation and solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Spalart Allmaras turbulence model. Secondly, this work aims at estimating the influence of viscosity and turbulence on the T106A end-wall flow field. In order to do so, RANS results are compared with those obtained from an inviscid simulation with a prescribed inlet total pressure profile, which mimics a boundary layer. A comparison between C1 and C2 results highlights an influence of secondary flows on the flow field up to a significant distance from the end-wall. In particular, the C2 end-wall flow field appears to be characterized by greater over turning and under turning angles and higher total pressure losses. Furthermore, the C2 simulated flow field shows good agreement with experimental and numerical data available in literature. The C2 and inviscid Euler computed flow fields, although globally comparable, present evident differences. The cascade passage simulated with inviscid flow is mainly dominated by a single large and homogeneous vortex structure, less stretched in the spanwise direction and closer to the end-wall than vortical structures computed by compressible flow simulation. It is reasonable, then, asserting that for the chosen test case a great part of the secondary flows details is strongly dependent on viscous phenomena and turbulence.

• Journal of the Institute of Convergence Signal Processing
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• v.24 no.2
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• pp.97-102
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• 2023

Numerical simulations have been performed to investigate the hydrodynamic characteristics of the rudder since they play an important role in naval architecture fields. Although some values such as hydrodynamics forces can be measured easily in the towing tanks, it is difficult to obtain the detailed information of the flow fields such as pressure distribution, velocity distribution, vortex generation from experiments. In the present study, the effects of hydrodynamic coefficients and Reynolds number acting on the rudder were studied by using Computational Fluid Dynamics(CFD). Ansys fluent, one of commercial CFD solvers, solves the Navier-Stokes equations and the k-epsilon turbulence model is selected for the viscous model to solve RANS equations. At first, drag coefficients and lift coefficient for different angle of attack are obtained by using a CFD commercial code for KCS rudder. Secondly, the 2-D lift coefficients and drag coefficients are compared with 3-D coefficients at the same conditions. Thirdly, the effects of Reynolds number on the hydrodynamic forces are investigated.

• 한국전산유체공학회:학술대회논문집
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• 1996.05a
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• pp.52-57
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• 1996

Mixing is most important for developing an electric washer which transforms angular momentum from rotating solid wall to laundry clothes inside it. For magnification of this mixing effect, some inventions are introduced to washing machine system, i. e., washing plate, washing rod, and even for washing cap in a model of a Korean manufacture. However, the previous efforts show dissatisfaction up till now. In this paper, a triumph to enhance mixing effects to increase washing performance is presented and verified by numerical investigation. The present model to simulate a washing tub is the simple circular cylinder with two endwall disks which is completely filled with a viscous liquid. The present improvement is to change mounting position of a bottom disk of the model cylinder. Therefore, the aim of this work just proposes a new idea, which is numerically inspected, to a producer of washing machine, In detail, this invention is alternating the mounting position of a rotating bottom disk. Actually skewed pulsator is placed in steady of a flat disk, so the two endwall disks at top and bottom are not in parallel. The angle between an inclined bottom disk and the horizontal plane is fixed as 5 degree and physical domain to consider poses a sliced cylinder. Flow fields in both a right circular cylinder and the present improved model are fully depicted by numerical integration on a body fitted nonorthogonal regular uniform grid system. Numerical data to explain flow structure are plotted for understanding of the effects of the inclined disk. Also enhanced mixing effects by the inclined rotating disk are gauged by accurate numerical data used in this work.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.235-242
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• 2017

A driving controller for active destruction protections can be applied to machinery, aerospace and military fields. In particular, this controller can be used to track and attack enemy flying objects through the active control. It is important to ensure reliability of the driving controller since its operation should be kept with precision to the target point. The temperature of the environment where the driving controller is used is about -32 C ~ 50 C (241~323 ). Heat generated in the driving controller should be maintained below a certain threshold (85 C (358 )) to ensure reliability; therefore, the study and analysis of the heat flow characteristics in the driving controller are required. In this research, commercial software Solid-Works Flow Simulation was used for the numerical simulation assuming a low Reynolds number turbulence model and an incompressible viscous flow. The goal of this paper is to design the driving controller safely by analyzing the characteristics of the heat flow inside of the controller composed of chips or boards. Our analysis shows temperature distributions for boards and chips below a certain threshold.

• Clean Technology
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• v.25 no.4
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• pp.324-330
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• 2019

The selective catalytic reduction system is a highly effective technique for the denitrification of the flue gases emitted from the industrial facilities. The distribution of mixing ratio between ammonia and nitrogen oxide at the inlet of the catalyst layers is important to the efficiency of the de-NOx process. In this study, computational analysis tools have been applied to improve the uniformity of NH₃/NO molar ratio by controlling the flow rate of the ammonia injection nozzles according to the distribution pattern of the nitrogen oxide in the inlet flue gas. The root mean square of NH₃/NO molar ratio was chosen as the optimization parameter while the design of experiment was used as the base of the optimization algorithm. As the inlet conditions, four (4) types of flow pattern were simulated; i.e. uniform, parabolic, upper-skewed, and random. The flow rate of the eight nozzles installed in the ammonia injection grid was adjusted to the inlet conditions. In order to solve the two-dimensional, steady, incompressible, and viscous flow fields, the commercial software ANSYS-FLUENT was used with the k-𝜖 turbulence model. The results showed that the improvement of the uniformity ranged between 9.58% and 80.0% according to the inlet flow pattern of the flue gas.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.29-41
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• 2008

The present paper provides a CFD analysis of diffraction problem for a ship with forward speed using an unsteady RANS simulation method, a WAVIS code. The WAVIS viscous solver adopting a finite volume method has second order accuracy in time and field discretizaions for the RANS equations. A two phase level-set method and a realizable ${\kappa}-{\varepsilon}$ turbulence model are adopted to compute the free surface and to meet the turbulence closure, respectively. To validate the capability of the present numerical methods for the simulation of an unsteady progressive regular wave, computations are performed for three grid sets with refinement ratio of ${\sqrt{2}}$. The main simulation is performed for a DTMB5512 model with a forward speed in a regular head sea condition. Validation of the present numerical method is carried out by comparing the present CFD results with available unsteady experimental data published in the 2005 Tokyo CFD Workshop: resistance, heave force, pitch moment, unsteady free surface elevations and velocity fields.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.6 s.144
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• pp.619-630
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• 2005

A two-frame PIV (Particle Image Velocimetry) technique is used to investigate the wake characteristics behind a marine propeller with 4 blades at high Reynolds number. For each of 9 different blade phases from $ 0^{\circ} $ to $ 80^{\circ} $, one hundred and fifty instantaneous velocity fields are measured. They are ensemble averaged to study the spatial evolution of the propeller wake in the region ranging from the trailing edge to one propeller diameter (D) downstream location. The phase-averaged mean velocity shows that the trailing vorticity is related to radial velocity jump, and the viscous wake is affected by boundary layers developed on the blade surfaces and centrifugal force. Both Galilean decomposition method and vortex identification method using swirling strength calculation are very useful for the study of vortex behaviors En the propeller wake legion. The slipstream contraction occurs in the near-wake region up to about X/D : 0.53 downstream. Thereafter, unstable oscillation occurs because of the reduction of interaction between the tip vortex and the wake sheet behind the maximum contraction point.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.1
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• pp.1-7
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• 2014

The present study numerically investigated the effect of the advance ratio on the wake characteristics of the marine propeller in the propeller open water test. Therefore, a wide range of the advance ratio(0.2${\kappa}-{\omega}$SST Model are considered. The three-dimensional vortical structures of tip vortices are visualized by the swirl strength, resulting in fast decay of the tip vortices with increasing the advance ratio. Furthermore, to better understanding of the wake evolution, the contraction ratio of the slip stream for different advance ratios is extracted from the velocity fields. Consequently, the slip stream contraction ratio decreases with increasing the advance ratio and successively the difference of the slip stream contraction ratio between J=0.2 and J=0.8 is about 0.1R.

• Advances in aircraft and spacecraft science
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• v.5 no.3
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• pp.363-383
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• 2018

One-dimensional (1D) models of incompressible flows, can be of interest for many applications in which fast resolution times are demanded, such as fluid-structure interaction of flows in compliant pipes and hemodynamics. This work proposes a higher-order 1D theory for the flow-field analysis of incompressible, laminar, and viscous fluids in rigid pipes. This methodology is developed in the domain of the Carrera Unified Formulation (CUF), which was first employed in structural mechanics. In the framework of 1D modelling, CUF allows to express the primary variables (i.e., velocity and pressure fields in the case of incompressible flows) as arbitrary expansions of the generalized unknowns, which are functions of the 1D computational domain coordinate. As a consequence, the governing equations can be expressed in terms of fundamental nuclei, which are invariant of the theory approximation order. Several numerical examples are considered for validating this novel methodology, including simple Poiseuille flows in circular pipes and more complex velocity/pressure profiles of Stokes fluids into non-conventional computational domains. The attention is mainly focused on the use of hierarchical McLaurin polynomials as well as piece-wise nonlocal Lagrange expansions of the generalized unknowns across the pipe section. The preliminary results show the great advantages in terms of computational costs of the proposed method. Furthermore, they provide enough confidence for future extensions to more complex fluid-dynamics problems and fluid-structure interaction analysis.