• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.496-501
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• 2003

Reynolds averaged Wavier-Stokes simulations based on the Reynolds stress model was performed to investigated the effect of inlet flow angle on the distributions of the Reynolds stress tensor inside tip leakage vortex of a linear compressor cascade. Two different inlet flow angles ${\beta}=29.3^{\circ}$(design condition) and $36.5^{\circ}$(off-design condition) were considered. Stress tensor analysis, which transforms the Reynolds stress into the principal direction, was applied to show an anisotropy of the normal stresses. Whereas the anisotropy was highest in the region where the tip leakage vortex collides the suction side of the blade and tip leakage flow enters between blade tip of the pressure side and the endwall, it had the lowest value at the center of tip leakage vortex. It was also found that the magnitude of maximum shear stress at design condition was greater than that of off-design condition.

• Journal of Advanced Marine Engineering and Technology
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• 제35권7호
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• pp.930-937
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• 2011

The characteristics of mean velocity and turbulence have been analyzed in the circular open channel flow using PIV measurement data for a wide range of water depth. The measured data are fitted to a velocity distribution function over the whole depth of the open channel. Reynolds shear stress and mean velocity in wall unit are compared with the analytic models for fully-developed turbulent boundary layer. Both the mean velocity and Reynolds shear stress have different distributions from the two-dimensional boundary layer flow when the water depth increases over 50% since the influence of the side wall penetrates more deeply into the free surface. The cross-stream Reynolds normal stress also has considerably different distribution in view of its peak value and decreasing rate in the outer region whether the water depth is higher than 50% or not.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1522-1539
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• 2002

In the present study, an explicit algebraic stress model is shown to be the exact tensor representation of algebraic stress model by directly solving a set of algebraic equations without resort to tensor representation theory. This repeals the constraints on the Reynolds stress, which are based on the principle of material frame indifference and positive semi-definiteness. An a priori test of the explicit algebraic stress model is carried out by using the DNS database for a fully developed channel flow at Rer = 135. It is confirmed that two-point correlation function between the velocity fluctuation and the Laplacians of the pressure-gradient i s anisotropic and asymmetric in the wall-normal direction. Thus, a novel composite algebraic Reynolds stress model is proposed and applied to the channel flow calculation, which incorporates non-local effect in the algebraic framework to predict near-wall behavior correctly.

• 대한기계학회논문집B
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• 제28권8호
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• pp.902-909
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• 2004

A steady-state Reynolds averaged Navier-Stokes simulation was conducted to investigate the distribution of the Reynolds stress tensor inside tip leakage vortex of a linear compressor cascade. Two different inlet flow angles ${\beta}=29.3^{\circ}$(design condition) and $36.5^{\circ}$(off-design condition) at a constant tip clearance size of $1\%$ blade span were considered. Classical methods of solid mechanics, applied to view the Reynolds stress tensor in the principal direction system, clearly showed that the high anisotropic feature of turbulent flow field was dominant at the outer part of tip leakage vortex near the suction side of the blade and endwall flow separation region, whereas a nearly isotropic turbulence was found at the center of tip leakage vortex. There was no significant difference in the anisotropy of the Reynolds normal stresses inside tip leakage vortex between the design and off-design condition.

• Journal of Mechanical Science and Technology
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• 제14권1호
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• pp.93-102
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• 2000

The objective of the present study is to investigate the pressure-strain correlation terms of the Reynolds stress models for the three dimensional turbulent boundary layer in a $30^{\circ}$ bend tunnel. The numerical results obtained by models of Launder, Reece and Rodi (LRR) , Fu and Speziale, Sarkar and Gatski (SSG) for the pressure-strain correlation terms are compared against experimental data and the calculated results from the standard k-${\varepsilon}$ model. The governing equations are discretized by the finite volume method and SIMPLE algorithm is used to calculate the pressure field. The results show that the models of LRR and SSG predict the anisotropy of turbulent structure better than the standard k-${\varepsilon}$ model. Also, the results obtained from the LRR and SSG models are in better agreement with the experimental data than those of the Fu and standard k-${\varepsilon}$ models with regard to turbulent normal stresses. Nevertheless, LRR and SSG models do not effectively predict pressure-strain redistribution terms in the inner layer because the pressure-strain terms are based on the locally homogeneous approximation. Therefore, to give better predictions of the pressure-strain terms, non-local effects should be considered.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회(1)
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• pp.777-777
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• 2005

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.241-244
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• 2002

Large eddy simulation of a circular jet at the Reynolds number of 10000 is performed to investigate turbulence suppression effect with single frequency excitation at the non-dimensional frequency of 0.017. Instantaneous flow fields show that, with excitation, naturally occurring energetic vortices are suppressed through earlier saturation and breakdown of the shear layer vortices into fine grained turbulence. Due to the excitation, the Reynolds stresses are larger for the excited case near the jet and turbulence suppression begins afterward. The Reynolds normal stresses show largest suppression in the shear layer near the jet and in the centerline further downstream, while the Reynolds shear stress shows largest suppression in the shear layer at all the downstream locations.

• 한국전산유체공학회지
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• 제2권2호
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• pp.1-8
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• 1997

Two versions of anisotropic k-ε turbulence model are incorporated in the modified k-ε model of Sohn et al. to avoid the need for the experimental normal stress value in the model and applied to convergent and divergent flows with strong and adverse pressure gradients in the plane of symmetry of a body of revolution. The models are the nonlinear k-ε model of Speziale and the anisotropic model of Nisizima & Yoshizawa. All of the models yield satisfactory results for relatively complex flow on a plane-of-symmetry boundary layer. The results of the models are compared with those results of experimental normal stress value.

• 한국해양학회지
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• 제18권2호
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• pp.104-110
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• 1983

海洋 亂流境界層內 亂流運動量輸送의 斷續性 現象에 對하여 그 本質을 把握 하고 流體力學的 인 의미를 규명하기 위한 영구를 기원했다.또한 단속성 현상과 작비현상의 상호관계도 아울러 연구했다. 본 연구를 통해 난류경계층내에서도 중간층에 속하는 z/h=0.067층에서는 단속성의 크기가 평균난류운동량 수송의 408배의 달하고 상부층 즉 z/h=0.1층에서는 270배에 달함이 밝혀져,이제까지 보고되었던 Gordon(1974)이나 Heathersaw(1974)의 30배의 월등히 크다는 것이 새로운 사실이다. 일부 학자들은 단속성현상을 자기현상의 반영 또는 자기의 유통계의 부딪혀 나타나는 현상이라고 해석한바 있으나 (Gordon,1974; Heathersaw,1974),본 연구에서 밝혀진바에 의하면,이는 마찰 Reynolds 수가>$10^{5}$인 실제해양의 난류경계층내 난류운동의 특징이라는 사실이다.

• Wind and Structures
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• 제4권3호
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• pp.177-196
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• 2001

At present the most popular turbulence models used for engineering solutions to flow problems are the $k-{\varepsilon}$ and Reynolds stress models. The shortcoming of these models based on the isotropic eddy viscosity concept and Reynolds averaging in flow fields of the type found in the field of Wind Engineering are well documented. In view of these shortcomings this paper presents the implementation of a non-linear model and its evaluation for flow around a building. Tests were undertaken using the classical bluff body shape, a surface mounted cube, with orientations both normal and skewed at $45^{\circ}$ to the incident wind. Full-scale investigations have been undertaken at the Silsoe Research Institute with a 6 m surface mounted cube and a fetch of roughness height equal to 0.01 m. All tests were originally undertaken for a number of turbulence models including the standard, RNG and MMK $k-{\varepsilon}$ models and the differential stress model. The sensitivity of the CFD results to a number of solver parameters was tested. The accuracy of the turbulence model used was deduced by comparison to the full-scale predicted roof and wake recirculation zone lengths. Mean values of the predicted pressure coefficients were used to further validate the turbulence models. Preliminary comparisons have also been made with available published experimental and large eddy simulation data. Initial investigations suggested that a suitable turbulence model should be able to model the anisotropy of turbulent flow such as the Reynolds stress model whilst maintaining the ease of use and computational stability of the two equations models. Therefore development work concentrated on non-linear quadratic and cubic expansions of the Boussinesq eddy viscosity assumption. Comparisons of these with models based on an isotropic assumption are presented along with comparisons with measured data.