• Journal of Korea Water Resources Association
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• v.54 no.11
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• pp.1011-1019
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• 2021

This study presents numerical simulations of submerged jump and washed-out jump resulted from the flow over the embankment type weir. Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are solved with the k-𝜔 SST turbulence model. Validations are carried out using the experimental results in the literature, revealing that computed roller shape, free surface, and mean velocity are in good agreement with measured data. The volume fractions of water of the submerged jump and washed-out jump are compared, and the characteristics of the two flows from the double-averaged volume fractions of water are presented. The condition under which the transition occurs from the submerged jump to washed-out jump is presented by the relation between the relative embankment length and submergence factor via numerical simulations by changing the weir length, discharge, and tailwater depth.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.3
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• pp.270-281
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• 2018

Application of the LeMoS hybrid (LH) URANS/LES method for the wake parameters prediction is considered. The wake fraction coefficient is calculated for inland ship model M1926 under shallow water conditions and compared to results of PIV measurements. It was shown that due to lack of the resolved turbulence at the interface between LES and RANS zones the artificial grid induced separations can occur. In order to overcome this drawback, a shielding function is introduced into LH model. The new version of the model is compared to the original one, RANS $k-{\omega}$ SST and SST-IDDES models. It is demonstrated that the proposed modification is robust and capable of wake prediction with satisfactory accuracy.

• International Journal of Fluid Machinery and Systems
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• v.9 no.2
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• pp.119-128
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• 2016

This work presents the numerical investigation of an unsteady cavitating flow around a balancing drum of a multistage pump. The main attention is focused on the cavitation phenomena, which occur in the rear part of the drum clearance, cause the erosion of the drum material and influence the pressure losses and the flow rate through the clearance. The one-way coupling of the URANS equations and the full Rayleigh-Plesset equation is employed to analyse the flow field as well as the dynamics of cavitating bubbles. The numerical simulations show that the erosion processes are highly influenced by shaft vibrations, namely by periodic deformations of the annular clearance in time. The calculated results are verified by erosion tests on a real pump.

• Journal of computational fluids engineering
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• v.13 no.3
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• pp.35-43
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• 2008

A methodology for the simulation of compressible high Reynolds number flow over rigid and moving bodies on a structured Cartesian grid is described in this paper. The approach is based on a modified version of the Brinkman Penalization method. To avoid oscillations in the vicinity of the body and to simulate shcok-containing flows, a Weighted Essentially Non-Oscillatory scheme is used to discretize the spatial flux derivatives. For high Reynolds number viscous flow, two turbulence models of the two-equation Menter's SST URANS model and a two-equation Detached Eddy Simulation are implemented. Some simple flow examples are given to assess the accuracy of the technique. Finally, a moving grid capability is demonstrated.

• Journal of computational fluids engineering
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• v.10 no.4 s.31
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• pp.1-11
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• 2005

A numerical study of the evaluation of turbulence models for thermal striping phenomenon is performed. The turbulence models chosen in the present study are the two-layer model, the shear stress transport (SST) model and the V2-f model. These three models are applied to the analysis of the triple-jet flow with the same velocity but different temperatures. The unsteady Reynolds-averaged Navier-Stokes (URANS) equation method is used together with the SIMPLEC algorithm. The results of the present study show that the temporal oscillation of temperature is predicted by the SST and V2-f models, and the accuracy of the mean velocity, the turbulent shear stress and the mean temperature is a little dependent on the turbulence model used. In addition, it is shown that both the two-layer and SST models have nearly the same capability predicting the thermal striping, and the amplitude of the temperature fluctuation is predicted best by the V2-f model.

• International Journal of Fluid Machinery and Systems
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• v.5 no.1
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• pp.18-29
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• 2012

This paper deals with the CFD analysis of cavitating flow in the mixed-flow pump with the specific speed of 1.64 which suffers from a high level of noise and vibrations close to the optimal flow coefficient. The ANSYS CFX package has been used to solve URANS equations together with the Rayleigh-Plesset model and the SST-SAS turbulence model has been employed to capture highly unsteady phenomena inside the pump. The CFD analysis has provided a good picture of the cavitation structures inside the pump and their dynamics for a wide range of flow coefficients and NPSH values. Cavitation instabilities were detected at 70% of the optimal flow coefficient close to the NPSH3 value (NPSH3 is the net positive suction head required for the 3% drop of the total head of the pump).

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.200-208
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• 2007

A methodology for the simulation of compressible high Reynolds number flow over rigid and moving bodies on a structured Cartesian grid is described in this paper. The approach is based on a modified version of the Brinkman Penalization method. To avoid oscillations in the vicinity of the body and to simulate shcok-containing flows, a Weighted Essentially Non-Oscillatory scheme is used to discretize the spatial flux derivatives. For high Reynolds number viscous flow, two turbulence models of the two-equation Menter's SST URANS model and a two-equation Detached Eddy Simulation are implemented. Some simple flow examples are given to assess the accuracy of the technique. Finally, a moving grid capability is demonstrated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.512-519
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• 2009

Flow pulsation in the gap connecting with two parallel channels is investigated by RANS and URANS approaches. The two parallel channels are connected by a small channel called for a gap. The parallel channels are designed to have different cross section area with its ratio of 0.5. Computations are conducted using a CFX 11.0 code. The bulk Reynolds number is 60,000. Predicted results are compared with the previous experimental data. Mean velocity profile at the center of gap region are compared with experiments for its validation. Spectral analysis on the lateral velocity in the center of the gap was performed. Auto correlation for the axial-flow velocity pattern was presented. The unsteady structure of the flow pulsation was visualized in the region of the gap in the parallel channel.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.142-147
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• 2005

A numerical study of evaluation of turbulence models for thermal striping phenomenon is performed. The turbulence models chosen in the present study are the two-layer model, the shear stress transport (SST) model and the V2-f model. These three models are applied to the analysis of the triple jet flow with the same velocity but different temperature. The unsteady Reynolds-averaged Navier-Stokes (URANS) equation method is used together with the SIMPLE algorithm. The results of the present study show that the temporal oscillation of temperature is predicted only by the V2-f model, and the accuracy of the mean velocity, the turbulent shear stress and the mean temperature is a little dependent on the turbulence model used. The the two-layer model and the SST model shows nearly the same capability of predicting the thermal striping and the amplitude of the temperature fluctuation is predicted best by the V2-f model.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.601-604
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• 2008

The flow pulsation of two parallel channels is investigated using RANS and URANS approaches. The parallel channels are connected with a small gap and have different cross section areas. The ratio of a right side area and a left side area ($A_R$ / $A_L$) is 0.5. Computations are conducted using a CFX code. Turbulence models adopted for RANS are Reynolds stress model and Shear Stress Transport (SST) model. The bulk Reynolds number is 60,000. Predicted results are compared with the experimental result of Lee et al. and show the flow pulsation with the frequency of about 100 Hz at the center of the gap.