• 항공우주시스템공학회지
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• 제2권2호
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• pp.20-27
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• 2008

The characteristics of compressible flow are different from those of incompressible flow from the mathematical and physical point of view. Therefore, the way to solve the flowfield is different between compressible flow and incompressible flow. In general, density-based numerical algorithm is mainly used for compressible flow solver development. On the other hand, incompressible flow solver prefers to use pressure-based numerical algorithm. In this research, a compressible Navier-Stokes flow solver is developed by means of extending from pressure-based incompressible numerical algorithm to handle both compressible and incompressible flows using the same flow solver. The present flow solver is tested at various speed ranges and compared with the solutions of density-based compressible flow solver. Numerical results show a good agreement between two flow solvers.

• Interaction and multiscale mechanics
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• 제5권1호
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• pp.27-40
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• 2012

The two-dimensional incompressible flow of a linear viscoelastic fluid we considered in this research has rapidly oscillating initial conditions which contain both the large scale and small scale information. In order to grasp this double-scale phenomenon of the complex flow, a multiscale analysis method is developed based on the mathematical homogenization theory. For the incompressible flow of a linear viscoelastic Maxwell fluid, a well-posed multiscale system, including averaged equations and cell problems, is derived by employing the appropriate multiple scale asymptotic expansions to approximate the velocity, pressure and stress fields. And then, this multiscale system is solved numerically using the pseudospectral algorithm based on a time-splitting semi-implicit influence matrix method. The comparisons between the multiscale solutions and the direct numerical simulations demonstrate that the multiscale model not only captures large scale features accurately, but also reflects kinetic interactions between the large and small scale of the incompressible flow of a linear viscoelastic fluid.

• 한국전산유체공학회지
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• 제13권2호
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• pp.27-41
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• 2008

An unstructured hybrid mesh flow solver has been developed for the simulation of three-dimensional steady and unsteady incompressible flow fields. The incompressible Navier-Stokes equations with an artificial compressibility method were discretized by using a node-based finite-volume method. For the unsteady time-accurate computation, a dual-time stepping method was adopted to satisfy a divergence-free flow field at each physical time step. An implicit time integration method with local time stepping was implemented to accelerate the convergence in the pseudo-time sub-iteration procedure. The one-equation Spalart-Allmaras turbulence model has been adopted to solve high-Reynolds number flow fields. The flow solver was parallelized to minimize the CPU time and to overcome the computational overhead. This method has been applied to calculate steady and unsteady flow fields around submarine configurations and a 3-D infinite cylinder. Validations were made by comparing the predicted results with those of experiments or other numerical results. It was demonstrated that the present method is efficient and robust for the prediction of steady and unsteady incompressible flow fields.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.614-617
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• 2008

An unstructured hybrid mesh flow solver has been developed for the simulations of three dimensional steady and unsteady incompressible flow fields. The incompressible Navier-Stokes equations with an artificial compressibility method were discretized by using a node-based finite-volume method. For the unsteady time-accurate computation, a dual-time stepping method was adopted to satisfy a divergence free flow field at each physical time step. The one equation Spalart-Allmaras turbulence model has been adopted to solve the high-Reynolds number flow fields. This method has been applied to calculate the steady flow fields around submarine configurations and unsteady flow fields around a 3-D infinite cylinder.

• 대한기계학회논문집
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• 제19권9호
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• pp.2237-2248
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• 1995

In incompressible flow which has multi-length scale, it has a very important effect which dependent variables are used for adaptive grid generation. Among many length scales in incompressible flow, the dependent variables used for the adaptive grid generation should be able to represent the feature of the concerned system. In this paper, by using vorticity and stream function, in addition to velocity components, the smoother and more stable grid generation is possible and these four flow properties represent each scale. The adaptive grid generation for a lid-driven cavity flow with $N_{re}$ =3200 using four flow properties such as velocity components, vorticity, stream function is performed, and the usefulness of using vorticity and stream function as the indicator for adaptive grid generation is shown.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.78-85
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• 2011

The Vortex-In-Cell(VIC) method combined with panel method is applied to the analysis of incompressible unsteady viscous flow. The dynamics of resulting flow is governed by the vorticity transport equation in Lagrangian form with vortex particle representation of the flow field. A regular grid which is independent to the shape of a body is used for numerical evaluation based on immersed boundary technique. With an introduction of this approach, the development and validation of the VIC method is presented with some computational results for incompressible viscous flow around two or three dimensional bodies such as wing section, sphere, finite wing and marine propeller.

• 한국항공우주학회지
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• 제49권6호
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• pp.449-456
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• 2021

본 연구에서는 저마하수 예조건화 기법이 적용된 기존 압축성 해석자의 해석 범위를 최소한의 수정으로 비압축성 유동해석이 가능하도록 확장하는 전략을 제시하였다. 이를 위해 압축성 총 에너지 방정식과 동일한 형태의 에너지 방정식을 사용하였다. 이러한 에너지 방정식은 비압축성 지배방정식인 연속방정식, 열에너지 방정식과 역학적 에너지방정식의 선형 조합을 통해 얻어진다. 이렇듯 압축성 방정식과 동일한 형태를 갖는 비압축성 지배방정식에 시간 전진 기법을 적용하기 위해 Turkel의 가상 압축성 기법을 적용하였다. 또한 Roe 평균이 공통의 압축성/비압축성 지배방정식에서 모두 유효함을 보였다. 압축성 해석자에 위 내용을 적용하여 비압축성 해석이 가능하도록 확장하는 과정은 본래의 압축성 해석자를 이용한 압축성 해석에 아무런 영향이 없다. 확장된 해석자를 통한 비압축성 해석 검증을 위해 비점성, 층류 그리고 난류 유동에 대한 순차적 해석을 수행하였다.

• 한국전산유체공학회지
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• 제4권1호
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• pp.53-61
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• 1999

Two-dimensional, unsteady, incompressible and compressible Navier-Stokes codes are developed for the computation of the viscous turbulent flow over high-lift airfoils. The compressible code involves a conventional upwind-differenced scheme for the convective terms and LU-SGS scheme for temporal integration. The incompressible code with pseudo-compressibility method also adopts the same schemes as the compressible code. Three two-equation turbulence models are evaluated by computing the flow over single and multi-element airfoils. The compressible and incompressible codes are validated by predicting the flow around the RAE 2822 transonic airfoil and the NACA 4412 airfoil, respectively. In addition, both the incompressible and compressible code are used to compute the flow over the NLR 7301 airfoil with flap to study the compressible effect near the high-loaded leading edge. The grid systems are efficiently generated using Chimera overlapping grid scheme. Overall, the κ-ω SST model shows closer agreement with experiment results, especially in the prediction of adverse pressure gradient region on the suction surfaces of high-lift airfoils.

• 한국전산유체공학회지
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• 제17권2호
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• pp.35-41
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• 2012

This paper presents incompressible Navier-Stokes solution algorithm for 2D Free-surface flow problems on the Cartesian mesh, which was implemented to run on Graphics Processing Units(GPU). The INS solver utilizes the variable arrangement on the Cartesian mesh, Finite Volume discretization along Constrained Interpolation Profile-Conservative Semi-Lagrangian(CIP-CSL). Solution procedure of incompressible Navier-Stokes equations for free-surface flow takes considerable amount of computation time and memory space even in modern multi-core computing architecture based on Central Processing Units(CPUs). By the recent development of computer architecture technology, Graphics Processing Unit(GPU)'s scientific computing performance outperforms that of CPU's. This paper focus on the utilization of GPU's high performance computing capability, and presents an efficient solution algorithm for free surface flow simulation. The performance of the GPU implementations with double precision accuracy is compared to that of the CPU code using an representative free-surface flow problem, namely. dam-break problem.

• 반도체디스플레이기술학회지
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• 제7권3호
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• pp.55-58
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• 2008

The objective of this research is to design, manufacture and test a mass flow controller capable of measuring compressible as well as incompressible fluid flows based on a 'bucket and stop-watch' method. The basic principle behind such a system is the measurement of time, where the time taken to fill and empty a bucket of known volume is measured. This device should be able to handle fluid flows in the range of 0.1 ml/min to 10 ml/min within an accuracy of ${\pm}$1%. For the flow meter to be able to compete with established designs, it must be not only comparable in cost and robustness, but also very accurate and reliable as well.