• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.6
• /
• pp.771-787
• /
• 1998

A Navier-Stokes code with a modified low Reynolds number k-.epsilon. turbulence model was used to study the unsteady transitional boundary layer flow due to rotor-stator interaction. The modification, proposed by Launder, to improve prediction of stagnation flows was incorporated to the low Reynolds number k-.epsilon. turbulence model by Fan-Lakshminarayana-Barnett. Numerical solution is shown to capture well the calmed laminar flow as well as the wake induced transitional strip due to rotor-stator interaction and shows improvement, in terms of onset of transition and its length, over previous Euler/boundary layer solution. The turbulent kinetic energy shows local maximum along the upstream rotor wake in the wake induced transitional strip and this characteristics is observed untill the end of transition. The wake induced strip also shown apparent even in the laminar sublayer as the upstream rotor wake penetrates inside the boundary layer.

• Journal of ILASS-Korea
• /
• v.1 no.3
• /
• pp.37-50
• /
• 1996

Computational fluid dynamics was used to optimize an A/C duct. Three dimensional flow analysis in an automotive A/C duct was performed computationally using various turbulence models and compared numerical predictions such as outlet flow split, surface pressure distribution along the duct to experimental data. Additionally, we studied the effect of location variation of 2nd branch on exit flow ratio and could find optimal location of 2nd branch. The design of an A/C duct was modeled and calculated to enhance the airflow distribution in each outlet using the STAR-CD computational fluid dynamics software. In results, modified $k-\varepsilon$ turbulence model allows a successful prediction of static pressure distribution particulary at around strong curvature but little improvement flow split. In the future, adoption of CFD to design an A/C duct with modified $k-\varepsilon$ model will bring benefits of producing more accurate prediction, and also give designers more detail information much more than now.

• The KSFM Journal of Fluid Machinery
• /
• v.3 no.2 s.7
• /
• pp.15-23
• /
• 2000

The present work describes the prediction method for the unsteady flow field and the acoustic pressure field of a ducted axial fan. The prediction method is comprised of time-marching free-wake method, acoustic analogy, and the Kirchhoff-Helmholtz BEM. The predicted sound signal of a rotor is similar to the experiment one. We assume that the rotor rotates with a constant angular velocity and the flow field around the rotor is incompressible and inviscid. Then, a time-marching free-wake method is used to model the fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The newly developed Helmholtz-Kirchhoff BEM lot thin body is used to calculate tile sound field of the ducted fan. The ducted fan with 6 blades is analysed and the sound field around the duct is calculated.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.60 no.2
• /
• pp.56-62
• /
• 2011

The purpose of the present study is to examine prediction of perceived usefulness of learning, school support and learning flow on academic satisfaction, academic achievement and absenteeism in computer education of engineering college. To meet the purpose of the present study, D university was chosen and, two surveys were conducted among the engineering students enrolled in the computer application class. The results of this study through multiple regression analysis indicated that perceived usefulness of learning and school support predicted significantly on satisfaction(${\beta}$ = .53, ${\beta}$ = .21), In addition, perceived usefulness of learning and learning flow predicted significantly on achievement(${\beta}$ = .23, ${\beta}$ = .24), but absenteeism didn't predict significantly on any variables in this study. The results of this study suggested that perceived usefulness of learning, school support and learning flow should be considered as the important elements for designing instructional courses to enhance students' satisfaction and achievement in college education.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.42 no.3
• /
• pp.213-220
• /
• 2014

A program that predicts trajectories of projectiles influenced by the interference flow field of helicopters is developed. The interference flow field are computed using a compressible inviscid solver in conjunction with an actuator disc model. The trajectories are predicted using 6-DOF (Degree of Freedom) equations as well as an alternative form of modified point mass equations of motion. The method for the interference flow field prediction method are validated with ROBIN(ROtor Body INteraction) model. A Sierra international bullet and a 105mm projectile are used to validate the trajectory method. Trajectories of a Sierra International bullet and a HYDRA 70 rocket firing from a helicopter are predicted.

• Journal of computational fluids engineering
• /
• v.11 no.4 s.35
• /
• pp.32-38
• /
• 2006

The objective of this study is to evaluate the prediction accuracy of development large eddy simulation(LES) program for turbulent flow behind a bluff-body. The LES solver was implemented on parallel computer consisting 16 processors. To verify the capability of LES code, the results were compared with those of Reynolds Averaged Navier-Stokes(RANS) using standard ${\kappa}-{\varepsilon}$ model as well as experimental data. The results showed that the LES and RANS qualitatively well predicted the experimental results, such as mean axial, radial velocities and turbulent kinetic energy. In the quantitative analysis, however, the LES showed a better prediction performance than RANS. Specially, the LES well described characteristics of the recirculation zones, such as air stagnation point and jet stagnation point. Finally, the unsteady phenomena on the Bluff-body, such as the transition of recirculation region and vorticity, was examined with LES methodology.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2007.11a
• /
• pp.389-392
• /
• 2007

The study focused on the flow-supply characteristics of the liquid oxidizer $N_2O$ reserved in a tank without any pressurization devices. It was taken accounted that the change of material properties to temperature in the oxidizer tank and the discharge coefficients of both liquid and gas for more precise prediction of the supply mass-flow rate of $N_2O$ oxidizer. To validate the prediction model derived in the study, the experiments were conducted and compare with the theoretical results.

• The KSFM Journal of Fluid Machinery
• /
• v.20 no.2
• /
• pp.17-25
• /
• 2017

Prediction of performance and operating characteristics of a state-of-the-art ultra-supercritical (USC) steam turbine is an important issue in many ways. Theoretical and empirical correlation equations, developed a few decades ago, have been widely used in commercial programs for a prediction of performance. To improve of these correlation equations and apply them to the high pressure turbine of a USC steam turbine, computational fluid dynamic analysis was carried out and correlation equations to calculate efficiency variation of each stage were made. Both fluid dynamic characteristic and thermodynamic performance was analyzed for the development of the correlation equations. In particular, the impact of flow addition through an overload valve (OLV) between stages was examined throughly. The trend of pressure drop due to the flow mixing by the OLV flow addition was analyzed and an efficiency correlation equation considering the OLV flow was also made.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.7 no.4
• /
• pp.589-599
• /
• 1995

The frictional pressure drop of a capillary tube flow is experimentally investigated for pure refrigerants such as R32, R125, and R134a and refrigerant mixtures such as R32/R134a(30/70 by mass percent), R32/R125(60/40), R125/R134a(30/70), and R32/R125/R134a(23/25/52). The binary interaction parameters for the calculation of viscosities of refrigerant mixtures are found based upon the data in the open literature. Several homogeneous flow models predicting the viscosity of two-phase region are compared to select the best model. Cicchitti's equation is known to be the most adequate for the prediction of the viscosity for refrigerant mixtures, which is used in the analysis of adiabatic capillary flows. A model for the prediction of the frictional pressure drop of single and two-phase flow is developed for refrigerant mixtures in this study. This model may be used to design and analyze the performance of a capillary tube in the refrigerating system.

• Journal of Mechanical Science and Technology
• /
• v.16 no.8
• /
• pp.1144-1153
• /
• 2002

A hybrid performance prediction method is proposed in the present study. A channel diffuser is divided into four subregions: vaneless space, semi-vaneless space, channel, and channel exit region. One-dimensional compressible core flow and boundary layer calculation of each region with an incidence loss model and empirical correlation of residuary pressure recovery coefficient of a channel predict the performance of diffusers. Three channel diffusers are designed and tested for validating the developed prediction method. The pressure distributions from an impeller exit to the channel diffuser exit are measured and discussed for various operating conditions from choke to nearly surge conditions. The strong non-uniform pressure distribution which is caused by impeller-diffuser interaction is obtained over the vaneless and semi-vaneless spaces. The predicted performance shows good agreement with the measured performance of diffusers at a design condition as well as at off-design conditions.