• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.12
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• pp.1724-1733
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• 2003

This paper assesses the prediction performance of explicit algebraic stress and heat-flux models for reduction of heat transfer coefficient in a strongly-heated vertical tube. Two explicit algebraic stress models and four explicit algebraic heat-flux models are selected for assessment. Eight combinations of explicit algebraic stress and heat-flux models are used in predicting the turbulent gas flows with intense heating, which yields the significant property-variation. The results showed that the two combinations of GS-AKN and WJ-mAKN predicted the Nusselt number and the axial wall temperature variations well and that the predictions of Nusselt number with WJ-combinations spread in a wider range than those with Gs-combinations. WJ is the explicit algebraic stress model of Wallin and Johansson and GS is the model of Gatski and Speziale and that AKN is the explicit heat-flux model of Abe, Kondoh and Nagano and mAKN is the modified AKN.

• Journal of Mechanical Science and Technology
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• v.16 no.11
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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.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.1
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• pp.67-77
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• 2014

In this study, Explicit Algebraic Reynolds Stress Model (EARSM) which is based on the existing ${\kappa}-{\omega}$ model has been applied to the flow field analysis around ship hulls. Existing transport equations for the turbulent kinetic energy and the dissipation rate are used in almost the same form and anisotropy terms of Reynolds stresses are newly considered. The well-known KVLCC2 and KCS hull forms are selected as validation cases, which were also used in 2010 Workshop on CFD in Ship Hydrodynamics. In case of KVLCC2 double model, comparison of mean velocity distribution, turbulent kinetic energy, and Reynolds stresses near the propeller plane has been carried out and wave elevation and wave profiles have been additionally studied for KCS and KVLCC2 with free surface models. Some improved results for mean velocity distribution at the propeller plane have been obtained while there is little change in free surface wave profiles.

• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.889-894
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• 2001

In this study, the performances of various turbulence closure models are evaluated in the calculation of a transonic flow over axisymmetric bump. k-$\varepsilon$, explicit algebraic stress, and two Reynolds stress models, i.e., GL model proposed by Gibson & Launder and SSG model proposed by Speziale, Sarkar and Gatski, are chosen as turbulence closure models. SSG Reynolds stress model gives best predictions for pressure coefficients and the location of shock. The results with GL model also show quite accurate prediction of pressure coefficients down-stream of shock wave. However, in the predictions of mean velocities and turbulent stresses, the results are not so satisfactory as in the prediction of pressure coefficients.

• Advances in aircraft and spacecraft science
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• v.10 no.6
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• pp.521-543
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• 2023

Reynolds-averaged Navier-Stokes (RANS) models are extensively employed in industrial settings for the purpose of simulating intricate fluid flows. However, these models are subject to certain limitations. Notably, disparities persist in the Reynolds stresses when comparing the RANS model with high-fidelity data obtained from Direct Numerical Simulation (DNS) or experimental measurements. In this work we propose an approach to mitigate these discrepancies while retaining the favorable attributes of the Menter Shear Stress Transport (SST) model, such as its significantly lower computational expense compared to DNS simulations. This strategy entails incorporating an explicit algebraic model and employing a neural network to correct the turbulent characteristic time. The imposition of realizability constraints is investigated through the introduction of penalization terms. The assimilated Reynolds stress model demonstrates good predictive performance in both in-sample and out-of-sample flow configurations. This suggests that the model can effectively capture the turbulent characteristics of the flow and produce physically realistic predictions.

• Wind and Structures
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• v.23 no.6
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• pp.505-521
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• 2016

The objective of this study is to investigate numerically the effect of building roof shaps on wind flow and pollutant dispersion in a street canyon with one row of trees of pore volume, $P_{vol}=96%$. A three-dimensional computational fluid dynamics (CFD) model is used to evaluate air flow and pollutant dispersion within an urban street canyon using Reynolds-averaged Navier-Stokes (RANS) equations and the Explicit Algebraic Reynolds Stress Models (EARSM) based on k-${\varepsilon}$ turbulence model to close the equation system. The numerical model is performed with ANSYS-CFX code. Vehicle emissions were simulated as double line sources along the street. The numerical model was validated by the wind tunnel experiment results. Having established this, the wind flow and pollutant dispersion in urban street canyons (with six roof shapes buildings) are simulated. The numerical simulation results agree reasonably with the wind tunnel data. The results obtained in this work, indicate that the flow in 3D domain is more complicated; this complexity is increased with the presence of trees and variability of the roof shapes. The results also indicated that the largest pollutant concentration level for two walls (leeward and windward wall) is observed with the upwind wedge-shaped roof. But the smallest pollutant concentration level is observed with the dome roof-shaped.