• Wind and Structures
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• v.27 no.2
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• pp.101-109
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• 2018

Wall jet flow exists widely in engineering applications, including the simulation of thunderstorm downburst outflows, and has been investigated extensively by both experimental and numerical methods. Most previous studies focused on the scaling laws and self-similarity, while the effect of lip thickness and external stream height on mean velocity has not been examined in detail. The present work is a numerical study, using steady Reynolds-Averaged Navier Stokes (RANS) simulations at a Reynolds number of $3.5{\times}10^4$, of a turbulent plane wall jet with an external stream to investigate the influence of the wall jet domain on downstream development of the flow. The comparisons of flow characteristics simulated by the Reynolds stress turbulence model closure (Stress-omega, SWRSM) and experimental results indicate that this model may be considered reasonable for simulating the wall jet. The confined wall jet is further analyzed in a parametric study, with the results compared to the experimental data. The results indicate that the height and the width of the wind tunnel and the lip thickness of the jet nozzle have a great effect on the wall jet development. The top plate of the tunnel does not confine the development of the wall jet within 200b of the nozzle when the height of the tunnel is more than 40b (b is the height of jet nozzle). The features of the centerline flow in the mid plane of the 3D numerical model are close to those of the 2D simulated plane wall jet when the width of the tunnel is more than 20b.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.315-319
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• 2009

Investigation of the lateral force fluctuations in an axisymmetric overexpanded compressed truncated perfect (CTP) nozzle for the shutdown transient is presented. These nozzles experience side-loads during start-up and shut-down operations, because of the flow separation at nozzle walls. Two types of flow separations such as free shock separation (FSS) and restricted shock separation (RSS) shock structure occur. A two-dimensional unsteady numerical simulation has been carried out over an axisymmetric CTP nozzle to simulate the lateral force fluctuations in nozzle during shutdown process. Reynolds Averaged Navier-Stokes equations are numerically solved using a fully implicit finite volume scheme. Governing equations are solved by coupled implicit scheme. Two equation k-$\omega$ SST turbulence model is selected. Unsteady pressure is measured at four locations along the nozzle wall. Present pressure variation compared well with the experimental data. During shutdown transient, separation pattern varies from FSS to RSS and finally returns to FSS. Several pressure peaks are observed during the RSS separation pattern. These pressure peaks generate lateral force or side loads in rocket nozzle.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.174-175
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• 2005

The purpose of this study is focused on the analysis of 3D complex flow and performance characteristics of a centrifugal pump with volute casing. The numerical analysis was performed by commercial code CFX-10 according to the variation of flow rate, which is changing from 5.847$m^3$/min to 6.865$m^3$/min. The rated rotational speed of close type impeller is 1750rpm. Turbulence model, k-${\omega}$ SST was selected to guaranty more accurate prediction of flow separation. The ICEM-CFD 10, reliable grid generation software was also adapted to secure high quality grid generation necessary for the reliable numerical simulation. The experimental results such as static head, brake horse power and efficiency of the centrifugal pump were compared with the numerical analysis results. The simulated results are good agreement with the experimental results less 5$%$ error.

• The KSFM Journal of Fluid Machinery
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• v.13 no.5
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• pp.11-16
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• 2010

The development of lifting pumps that lift minerals to a mining vessel are one of the vital parts of the commercial mining process. The purpose of this study is to investigate internal flow and its effect on the performance of a mixed flow pump in order to improve the pump's performance. Numerical analysis was performed by commercial code of ANSYS CFX-11 based on flow rate and length of flexible hose. The rated rotational speed of the impeller is 1750rpm. For taking into account the turbulence, k-$\omega$ SST model was selected to guarantee more accurate prediction of flow separation. The simulated results are in good agreement with the experimental results and showed that its efficiency and the head of the pump are related mainly to the flow rate and the length of flexible hose. A lesser flow rate caused more secondary flow through the guide vane passage. The length of flexible hose and flow rate exert much more influence on the pump's performance than the shape of the flexible hose.

• The KSFM Journal of Fluid Machinery
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• v.13 no.6
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• pp.51-56
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• 2010

A numerical simulation is carried out to investigate the effect of flow rate variation and performance characteristics of double-suction centrifugal pump. Two types of pump which have different impeller inlet breadth and curvature of the shroud line consist of six blades impeller and shroud ring. Finite-volume method with structured mesh and $k-\omega$ Shear Stress Transport turbulence model was used to guaranty more accurate prediction of turbulent flow in the pump impeller. Total head, power and overall efficiency were calculated to obtain performance characteristics of two types of pump according to the variation of flow rate. From the results, impeller having smooth curve along the shroud line obtained good performance. The lower flow rate, the more circulation region, flow unsteadiness and complicate flow pattern are observed. Complicated internal flow phenomena through impellers such as flow separation, pressure loss, flow unsteadiness and performance are investigated and discussed.

• Advances in aircraft and spacecraft science
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• v.2 no.2
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• pp.169-182
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• 2015

Aeronautics engine cooling is one of the biggest problems that engineers have tried to solve since the beginning of human flight. Systems like radiators should solve this purpose and they have been studied extensively and various solutions have been found to aid the heat dissipation in the engine zone. Special interest has been given to air coolers in order to guide the air flow on engine and lower the high temperatures achieved by the engine in flow conditions. The aircraft companies need faster and faster tools to design their solutions so the development of tools that allow to quickly assess the effectiveness of an cooling system is appreciated. This paper tries to develop a methodology capable of providing such support to companies by means of some application examples. In this work the development of a new methodology for the analysis and the design of oil cooling systems for aerospace applications is presented. The aim is to speed up the simulation of the oil cooling devices in different operative conditions in order to establish the effectiveness and the critical aspects of these devices. Steady turbulent flow simulations are carried out considering the air as ideal-gas with a constant-averaged specific heat. The heat exchanger is simulated using porous media models. The numerical model is first tested on Piaggio P180 considering the pressure losses and temperature increases within the heat exchanger in the several operative data available for this device. In particular, thermal power transferred to cooling air is assumed equal to that nominal of real heat exchanger and the pressure losses are reproduced setting the viscous and internal resistance coefficients of the porous media numerical model. To account for turbulence, the k-${\omega}$ SST model is considered with Low- Re correction enabled. Some applications are then shown for this methodology while final results are shown in terms of pressure, temperature contours and streamlines.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.3
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• pp.123-129
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• 2018

In this study, CFD is used to compare and analyze the flow characteristics using reflected pressure wave during the intersection of two trains in straight tunnel. Two tunnels of different lengths; 600 m and 3,400 m were designed and numerical analysis of the flow characteristics of two tunnels carried out by setting the crossing state of the two trains at a constant velocity of 27 m/s form the center of the tunnel. The simulation model was designed using the actual tunnel and subway dimensions The train motion was achieved by using the moving mesh method. For the numerical analysis, $k-{\omega}$ standard turbulence model and an ideal gas were used to set the flow conditions of three-dimensional, compressible and unsteady state. In the analysis results, it was observed that the inside of the long tunnel without interference of the reflected pressure wave was maintained at a pressure lower than the atmospheric pressure and that the flow direction was determined by the pressure gradient and shear flow. On the other hand, the flow velocity in the short tunnel was faster and the pressure fluctuation was noted to have increased due to the reflected pressure wave, with more vortices formed. In addition, the flow velocity was noted to have changed more irregularly.

• 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.

• The KSFM Journal of Fluid Machinery
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• v.18 no.2
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• pp.60-66
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• 2015

Conjugate heat transfer analysis was performed to investigate the flow and cooling performance of the high pressure turbine nozzle of gas turbine engine. The CHT code was verified by comparison between CFD results and experimental results of C3X vane. The combination of k-${\omega}$ based SST turbulence model and transition model was used to solve the flow and thermal field of the fluid zone and the material property of CMSX-4 was applied to the solid zone. The turbine nozzle has two internal cooling channels and each channel has a complex cooling configurations, such as the film cooling, jet impingement, pedestal and rib turbulator. The parabolic temperature profile was given to the inlet condition of the nozzle to simulate the combustor exit condition. The flow characteristics were analyzed by comparing with uncooled nozzle vane. The Mach number around the vane increased due to the increase of coolant mass flow flowed in the main flow passage. The maximum cooling effectiveness (91 %) at the vane surface is located in the middle of pressure side which is effected by the film cooling and the rib turbulrator. The region of the minimum cooling effectiveness (44.8 %) was positioned at the leading edge. And the results show that the TBC layer increases the average cooling effectiveness up to 18 %.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.327-330
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• 2006

This paper represents the numerical analysis on effects of radius ratio in a concentric annulus with a rotating inner cylinder. The numerical model consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8mm, the numerical parameters are angular velocity and radius ratio. Also, the whole walls of numerical model have no-slip and the working fluid is used water at $20^{\circ}C$. The numerical analysis is assumed the transient state to observe the flow variations by time and the 3-D cylindrical coordinate system. The calculation grid adopted a non-constant grid for dense arrangement near the wall side of cylinder, the standard $k-{\omega}$ high Reynolds number model to consider the effect of turbulence flow and wall, the fully implicit method for time term and the quick scheme for momentum equation. The numerical method is compared with the experimental results by Wereley and Lueptow, and the results are very good agreement. As the results, TVF isn't appeared when Re is small because of the initial flow instability is disappear by effect of the centrifugal force and viscosity. The vortex size is from 0.8 to 1.1 for TVF at various $\eta$, and the traveling distance for wavy vortex have the critical traveling distance for each case.