• 설비공학논문집
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• 제6권4호
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• pp.325-336
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• 1994

A numerical simulation of velocity and temperature fields and Nusselt number distributions is performed by using the algebraic stress model (ASM) for the velocity profiles and low Reynolds number ${\kappa}-{\varepsilon}$ model and the algebraic heat flux model(AHFM) for turbulent heat transfer in a $180^{\circ}$ bend with a constant wall heat flux. In the low Reynolds number ${\kappa}-{\varepsilon}$ model, turbulent Prandtl number is modified by considering the streamline curvature effect and the non-equilibrium effect between turbulent kinetic energy production and dissipation rate. Every heat flux term presented in the transport equation of turbulent heat flux is reduced to algebraic expressions in a way similar to algebraic stress model. Also. in the wall region, low Reynods number algebraic heat flux model(AHFM) is applied.

• 대한기계학회논문집B
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• 제23권10호
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• pp.1229-1239
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• 1999

A computational study on unsteady compressible flows has been performed by adopting a low Reynolds number $k-{\omega}$ turbulence model in conjunction with dual time stepping scheme. An explicit four-stage Runge-Kutta scheme for the Navier-Stokes equations and an approximate factorization scheme for the $k-{\omega}$ turbulence model equations are used. Computational results obtained for blade surface pressure distributions in the process of rotor-stator interaction in a turbine stage are in good agreement with extant experimental data. The effects of the wake from the stator on the boundary-layer transition over the rotor blade surface are discussed by showing that high intensity turbulence of the stator wake induces an early transition.

• 설비공학논문집
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• 제13권7호
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• pp.588-594
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• 2001

The purpose of this study is to investigate the thermal and hydrodynamic characteristics of the channel in corrugated plate type heat exchangers numerically. Numerical work has been conducted using the Reynolds Stress Model(RSM) by utilizing the commercial finite-volume code, FLUENT. Based on this model, the dependence of heat transfer and friction factor on geometrical parameters have been investigated. It is found that larger corrugation angle give higher values of heat transfer coefficients and friction factors. As the reynolds number increases, the heat transfer coefficient also increases. It is also observed that the heat transfer coefficient reaches maximum while the friction factor stays relatively low at same corrugation angle. Through the analysis, it is found that the optimum corrugation angle for the heat exchanger performance exists. It is noted that the flow repulsions at the contact point of the two fluid streams make the low mixing more active for larger corrugation angle and high reynolds number.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.967-987
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• 2020

A numerical analysis is carried out for the marine propellers in open water conditions to investigate the effect of the wall treatments in model and full scale. The standard wall function to apply the low of the wall and the two layer zonal model to calculate the whole boundary layer for a transition phenomenon are used with one turbulence model. To determine an appropriate distance of the first grid point from the wall when using the wall function, a formula based on Reynolds number is suggested, which can estimate the maximum y+ satisfying the logarithmic law. In the model scale, it is confirmed that a transition calculation is required for a model scale propeller with low Reynolds number that the transient region appears widely. While in the full scale, the wall function calculation is recommended for efficient calculations due to the turbulence dominant flow for large Reynolds number.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.272-275
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• 2003

A mixed analytical/numerical method is developed here to solve the low Reynolds number kepsilon turbulence model. In this method the advection-diffusion part is solved numerically, while the source terms are split into two parts: one part is solved analytically and the next is solved numerically.

• 한국항공우주학회지
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• 제30권4호
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• pp.44-52
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• 2002

비정상, 비압축성 Navier-Stokes 코드를 이용하여, 저 레이놀즈수 유동에서 flapping 운동을 하는 익형의 공력특성을 수치해석적인 방법으로 연구하였다. 비정상 유동장의 효율적인 계산을 위하여, 개발된 코드는 MPI 프로그래밍 기법을 이용하여 병렬처리 되었으며, 난류 유동장의 계산을 위해 2방정식 난류모델의 하나인 k-$\omega$ SST 모델을 적용하였다. 익형의 3가지 운동모드 즉, pitching, plunging, flapping과 주파수 및 진폭의 변화 그리고 두께와 캠버의 변화에 의한 공력특성을 살펴보았고, 이를 위해 NACA4자 계열의 익형을 이용하였다. 해석 결과는 실험치와 비교하여 보았을 때 잘 일치하였으며, 각 운동모드에서의 공기역학적 특성을 파악할 수 있었다.

• 대한기계학회논문집B
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• 제24권2호
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• pp.316-323
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• 2000

A nonlinear low-Reynolds-number heat transfer model is developed to predict turbulent flow and heat transfer in separated and reattaching flows. The $k-{\varepsilon}-f_{\mu}$ model of Park and Sung (1997) is extended to a nonlinear formulation, based on the nonlinear model of Gatski and Speziale (1993). The limiting near-wall behavior is resolved by solving the $f_{\mu}$ elliptic relaxation equation. An improved explicit algebraic heat transfer model is proposed, which is achieved by applying a matrix inversion. The scalar heat fluxes are not aligned with the mean temperature gradients in separated and reattaching flows; a full diffusivity tensor model is required. The near-wall asymptotic behavior is incorporated into the $f_{\lambda}$ function in conjunction with the $f_{\mu}$ elliptic relaxation equation. Predictions of the present model are cross-checked with existing measurements and DNS data. The model preformance is shown to be satisfactory.

• 한국자동차공학회논문집
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• 제2권1호
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• pp.38-50
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• 1994

To improve the efficiency of internal combustion engines, it is necessary to understand mixed air-fuel in-cylinder flow processes accurately at intake and compression strokes. There is experimental and numerical methods to analyse in-cylinder flow process. In numerical method, standard $k-{\varepsilon}$ model with wall function was mostly adopted in in-cylinder flow process. But this type model was not efficiently predicted in the near wall region. Therefore in the present study, low Reynolds number $k-{\varepsilon}$ model was adopted near the cylinder wall and standard $k-{\varepsilon}$ model in other region. Also QUICK scheme was used for convective difference scheme. This study takes axisymmetric reciprocating model engine motored at 200rpm with a centrally located valve, incorporated 60 degree seat angie, and flat piston surface excluding inlet port. Because in-cylinder flow processes are undergoing unsteady and compressible, averaged cylinder pressure and inlet velocity at arbitrary crank angle are determined from thermodynamic analytic method and incylinder states at that crank angle are iteratively determined from the numerical analytic method.

• 대한기계학회논문집B
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• 제24권1호
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• pp.1-8
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• 2000

A modified low-Reynolds-number Reynolds stress model is developed for the calculation of drag-reducing turbulent flows induced by polymer injection. The results without polymer injection are compared with the results of direct numerical simulation to ensure the validity of the basic model. In case of drag reduction, profiles of mean velocity and Reynolds stress components, in two-dimensional channel flow, obtained with a proper value of viscosity ratio are presented and discussed. Computed mean velocity profile is in very good agreement with experimental data. And, the qualitative behavior of Reynolds stress components with the viscosity ratio is also reasonable.

• 한국전산유체공학회지
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• 제7권1호
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• pp.20-27
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• 2002

Flow over a circular cylinder is studied numerically using a turbulence model. Based on the κ-ε-f/sub μ/ model of Park and Sung[6], a new damping function is used. The efficiency of the strain dependent damping function is addressed for vortex-shedding flows past a circular cylinder. The mean velocity and Reynolds stresses are compared with available experimental data at Re/sub D/= 3900. Also, the computational results for the Strouhal number are evaluated at several Reynolds number. The predictions by κ-ε-f/sub μ/ model are in good agreement with the experiments.