Standard Wall Function Research Articles

Enhancing Thermal–Hydraulic Performance in Nuclear Reactor Subchannels with Al2O3 Nanofluids: A CFD Analysis

In this paper, the performance of aluminum-based nanofluids with a possible application in pressurized water reactors is numerically investigated. A 605 mm long 4-rod array square (2 × 2) subchannel geometry with a uniform heat flux of 50 kW/m2 has been used in CFD simulation. This analysis has been carried out using the RNG k-epsilon turbulence model with standard wall function in ANSYS FLUENT 2022R1. The impact of various flow conditions and nanofluid concentrations has been examined. The effects of variable velocities on nanofluid performance have been studied using different Reynolds numbers of 20,000, 40,000, 60,000, and 80,000. The analysis was conducted with Al2O3/water nanofluid concentrations of 1%, 2%, 3%, and 4%. A comparison of the Nusselt number based on five different correlations was conducted, and deviations from each correlation were then presented. The homogeneous single-phase mixer approach has been adopted to model nanofluid characteristics. The result shows a gradual enhancement in the heat transfer coefficient with increasing volume concentrations and Reynolds numbers. A maximum heat transfer coefficient has been calculated for nanofluid at maximum volume concentrations (ϕ = 4%) and highest velocities (Re = 80,000). Compared to the base fluid, heat transfer was enhanced by a factor of 1.09 using 4% Al2O3. The Nusselt number was calculated with a minimal error of 3.62% when compared to the Presser correlation and the maximum deviation has been found from the Dittus–Boelter correlation (13.77%). Overall, the findings suggest that aluminum-based nanofluids could offer enhanced heat transfer capabilities in pressurized water reactors.

Impact of inlet air momentum on flameless combustion

Impact of inlet air momentum on flameless combustion characteristics was investigated numerically. Changing the inlet air momentum was achieved using different inlet air nozzle diameters (12, 10, 8 and 6 mm). The mixture mixing and recirculation ratio were obtained and evaluated. A Three-dimensional model was computed using ANSYS fluent. The computations were carried out using RNG k- ε with standard wall function for turbulence modelling. The GRI-EDC model was used to simulate the interaction between turbulence and chemical kinetic. The predicted results were validated against experimental data of small-scale flameless burner. The results showed that, reducing the air nozzle diameter from 12 to 6 mm increased the inlet air momentum, leading to an increase in the recirculation ration by more than 300% of its value at 12 mm. As a result, the O2 concentration decreased in the mixture at burner tip and supports flameless mode creation. The influence of inlet air momentum on combustion species (OH, HC, CO, and NO) were reported. It was concluded that increasing inlet air momentum reduces the greenhouse gases due to the decrease in reaction temperature and mixture dilution. Moreover, Transient radicals (OH and HC) decreased with increasing the inlet air momentum which supports the flame disappearance.

A parametric investigation of Dual-throat nozzle bypass channel configurations for advanced Aviation applications

The Bypass Dual-Throat Nozzle (BDTN) has garnered growing attention due to its remarkable thrust vectoring capabilities. This type of nozzle boasts broad application prospects as it achieves deflection control of the jet stream merely through regulating the opening and closing of bypass channels. Our comprehensive study delves deeply into the intricate parameterization of the bypass channel within the BDTN. Research has demonstrated that utilizing Fluent software in conjunction with the Realizable k-epsilon turbulence model, standard wall functions, and the Sutherland formula for viscosity coefficient approximation can yield a relatively accurate representation of the vector flow field structure within the BDTN. Following the validation of the numerical computation methodology employed in this study, we have investigated the influence of factors such as bypass channel radius, precise valve positioning, and actuation direction on the nozzle's vectoring performance. Key findings indicate that, due to the relatively small proportion of secondary flow, the radius of the bypass channel has minimal impact on the thrust vector angle. The positioning of the valve and its opening direction are critical in determining the thrust vector angle, requiring careful consideration during the design and optimization process. Fully opening the bypass channel does not necessarily yield the maximum thrust vector angle. Moreover, the total pressure, velocity, position, and direction of the secondary flow within the bypass channel exert a more profound influence on the nozzle's vector performance compared to the mere presence of the secondary flow itself. Notably, the forward opening method of the valve emerges as the preferred choice, as it facilitates more precise later vector control.

CFD assessment of internal Vapor/Liquid separator in an ebullated bed reactor (EBR) for heavy oil hydroprocessing

The ebullated-bed reactor (EBR) is an important system used in the upgrading of heavy oil residue into valuable light products in petroleum refinery operations. The assessment of the gas separation region hydrodynamics is very significant to investigate the performance of EBR. An advanced understanding of EBR fluid dynamics will help in improving the design of existing and future commercial units. For this reason, the development of a computational fluid dynamics (CFD) model is very challenging, where understanding the fundamentals of fluid dynamics in EBR is carried out using a three dimensional model and the turbulence model with a standard wall function in cup geometric design. The two models were used to analyze the influence of operational parameters such as recycle ratio, and inlet velocity on gas fraction recycled and separation efficiency. Moreover, the prediction of the regime transitions occurring in the freeboard region of the EBRs was achieved using the two aforementioned models. The results of the fluid dynamics behavior revealed that the inlet velocity has a substantial effect on gas fraction recycled and separation efficiency. The liquid mean residence time scale provided a valuable efficiency result for the separation within the range of expected mean residence times. This investigation, therefore, provided a good framework for the evaluation of future design and gave a better understanding of gas and liquid flow patterns in EBR.

Roughness constant selection for atmospheric boundary layer simulations using a k-ω SST turbulence model within a commercial CFD solver

Transit of an atmospheric boundary layer (ABL) profile within computational fluid dynamics (CFD) simulations is often hindered through unintended streamwise gradients in the flow resulting in ABL inhomogeneity. Within Reynolds-Averaged Navier–Stokes (RANS) turbulence modeling in Ansys Fluent, user-defined wall functions are not available for the k–ω class of RANS models as a remedy to this problem. Instead, the practitioner is required to use the sand–grain roughness property for ground surface roughness calibration, and specify a roughness height and roughness constant, Cs, accordingly. To-date, no clear guidance on their selection is available that can accommodate both high and low roughness terrains. To overcome this, a straightforward and practical calculation is presented for the roughness constant based on the standard wall function implementation. When this calculation is synthesized with other best-practice guidelines, it is possible to reliably model transiting ABL profiles based on wind-tunnel data whilst minimizing effects due to ABL inhomogeneity.

Assessment of heat transfer capabilities of some known nanofluids under turbulent flow conditions in a five-turn spiral pipe flow

Abstract In this study, the thermo-flow behaviours of the spiral tube were examined using water and some nanofluids such as TiO2, Al2O3, Fe2O3, CuO, ZnO, and CeO2. The computational flow dynamic modelling of the spiral coiled tube was performed with ANSYS 20 software program. The k–ε model with a standard wall function was used to simulate the thermo-flow characteristics. The solution of the governing equations was performed using the discretization method of finite volume. The study was carried out considering the case of fluid-to-fluid heat transfer in turbulent conditions. The influence of different key design parameters such as Reynolds number, different nanofluids, and flow arrangements was of main interest. The volume concentration of the nanofluids is 1%. The experiments were performed at different Reynolds ranges (9,000, 14,000, 20,000, and 25,000). The outlet temperature values, heat transfer coefficient, coefficient of friction, Nusselt number values of water, and nanofluids were found and compared. It was found that the outlet temperature, heat transfer coefficient, and Nusselt number values of water were the lowest, while the coefficient of friction value was the highest compared to the nanofluids. Among the nanofluids, CeO was found to have the highest outlet temperature, heat transfer coefficient, and Nusselt number value, as well as the lowest coefficient of friction value. TiO2 was found to have the lowest outlet temperature (T out), the heat transfer coefficient value, and the highest coefficient of friction value. Al2O3 was found to have the lowest Nusselt number. In addition, Nusselt number values were obtained at different Dean numbers of water (2,200, 3,400, 4,900, 6,100, 7,350, and 8,600) and found to be compatible with previous studies. In addition, the coefficients of friction values of water at different velocities (0.18, 0.24, 0.41, 0.71, 0.95, 1.07, and 1.18) were obtained and found to be compatible with previous studies.

Analysis of open channel flow with various layered vegetation using CFD, considering different near-wall treatment methods

PurposeThe purpose of this paper is to investigate the impact of near-wall treatment approaches, which are crucial parameters in predicting the flow characteristics of open channels, and the influence of different vegetation covers in different layers.Design/methodology/approachAnsys Fluent, a computational fluid dynamics software, was used to calculate the flow and turbulence characteristics using a three-dimensional, turbulent (k-e realizable), incompressible and steady-flow assumption, along with various near-wall treatment approaches (standard, scalable, non-equilibrium and enhanced) in the vegetated channel. The numerical study was validated concerning an experimental study conducted in the existing literature.FindingsThe numerical model successfully predicted experimental results with relative error rates below 10%. It was determined that nonequilibrium wall functions exhibited the highest predictive success in experiment Run 1, standard wall functions in experiment Run 2 and enhanced wall treatments in experiment Run 3. This study has found that plant growth significantly alters open channel flow. In the contact zones, the velocities and the eddy viscosity are low, while in the free zones they are high. On the other hand, the turbulence kinetic energy and turbulence eddy dissipation are maximum at the solid–liquid interface, while they are minimum at free zones.Originality/valueThis is the first study, to the best of the author’s knowledge, concerning the performance of different near-wall treatment approaches on the prediction of vegetation-covered open channel flow characteristics. And this study provides valuable insights to improve the hydraulic performance of open-channel systems.

Rheology-based wall function approach for wall-bounded turbulent flows of Herschel–Bulkley fluids

Modeling fully developed turbulent flow for Herschel–Bulkley (HB) fluids in pipes is a long-standing challenge. Existing semi-empirical, theoretical, and numerical methods are either inconsistent with experimental data or are validated for low Reynolds numbers. This study focuses on validating a novel approach using rheology-based wall functions within Reynolds-averaged Navier–Stokes solvers. Simulations of wall shear stress and velocity profiles were conducted across a wide range of Reynolds numbers using a single-phase HB fluid, with measurements taken both upstream and downstream of a 90° pipe bend. Two turbulence closure models, the k–ε model and the Reynolds stress model, were employed with the wall function implemented as a specified shear boundary condition. Results demonstrate significant improvements over the Newtonian-based models, such as standard wall function by Launder–Spalding or with available semi-empirical models, achieving strong statistical correlations and minimal deviation (from the experimental findings) at high Reynolds numbers. The study also examines the utility of the wall viscosity Reynolds number and assesses the reliability of semi-empirical models for HB fluids. These findings offer valuable insights for enhancing modeling accuracy in complex fluid flow scenarios, with potential applications spanning industries like mining, chemical processing, petroleum transportation, and sanitation systems, providing practical alternatives to costly experimental procedures in pipe systems.

Study on the sensitivity of steam ejector simulation to wall treatment methods

Considering the importance of turbulence model and wall treatment to steam ejector simulation, the influence of five wall treatment methods on numerical results was studied based on the realizable k-ε turbulence model (RKE). Combined with experimental data and SST turbulence model, the prediction of complex flow phenomena inside the ejector, including shock wave and reflux, by different wall treatment methods is discussed. The results show that under the numerical simulation conditions, the enhanced wall treatment method (EWT) combined with the RKE model can better predict the injection coefficient of the steam ejector, and the relative error compared with the experimental data is 5.3%. The standard wall function method (STWF) ignores the influence of the viscous bottom layer, resulting in inaccurate simulation of the internal flow phenomenon of the injector, and the injection coefficient calculated by the simulation is 10.2% higher than the experimental value. The results of the non-equilibrium wall function (NWF) method are relatively indifferent to the experimental values, and are not recommended when simulating steam ejectors.

CFD analysis and aerodynamic effects of add-on devices on an audi TT vehicle model

Environmental issues and increased fuel prices are driving automotive manufacturers to develop more fuel-efficient vehicles with lower emissions. Due to the limitations of conventional wind tunnel experiments and rapid developments in computer hardware, considerable efforts have been invested to study vehicle aerodynamics computationally. The ANSYS computer software package is employed, and 3D computer model cars are designed by the SolidWorks software. The Fluent subpackage is used to evaluate the aerodynamic behavior. This paper concentrates on the prediction of lift and drag for the car body using Computational Fluid Dynamics (CFD) on three different models of vehicles for simulation without any devices, with a rear wing or spoiler, and with vortex generators. Turbulence modeling was done with the realizable k-ε model using standard wall functions. The computational results for the three models are provided. The drag and lift coefficients that we have found are 0.4142 and 0.4338, respectively; compared with model 2, they are 0.4585 and 0.0387, and for model 3, they are 0.3971 and 0.3858, respectively. Model 2 has shown that the aerodynamic drag has increased from 0.4142 to 0.4585, which is a 10.69% drag increment. In addition, it showed an increase in negative lift by reducing the lift coefficient from 0.4338 to -0.0387, which is a 91.07% lift reduction by comparing with model 1. Similarly, model 3 has shown that the aerodynamic drag is reduced from 0.4142 to 0.3971, which is a 4.12% drag reduction, and it also showed an increase in negative lift by decreasing the lift coefficient from 0.4338 to 0.3858, which is a 11.06% lift reduction.

Experimental and Numerical Estimation of the Aerodynamic Forces Induced by the Wind Acting on a Fast-Erecting Crane

The current work concerns the problem of estimating the aerodynamic forces and moments induced by the wind on the fast-erecting 63K crane by Liebherr. In the first step, scaled sectional models of the tower truss and horizontal jib truss are prepared for experimental analysis in an aerodynamic tunnel. Next, the aerodynamic forces and moments are measured in the aerodynamic tunnel. It is assumed that the direction of the wind changes from 0° to 180° in 15° steps for both of the studied sectional models. The experimental tests are carried out for two levels of turbulence intensity. In the case of the model of the vertical part of the studied crane, the turbulence intensities are assumed to be equal to 3% and 9%. In the case of the horizontal crane jib, they are 3% and 12%, respectively. In the second step, a CFD analysis is performed with the use of Ansys Fluent R22 software. The standard k-ε model with a standard wall function of the turbulent flow is utilized. The airflow around the studied structures is modeled with the use of polytetrahedral cells. A relatively good agreement between the numerical and experimental results is observed. The obtained values are compared to the appropriate standard, namely PN-ISO 4302.

Numerical Study of Fluid Mixture Characteristics at 90° Angles with Variations of Standard Wall Functions on the k-ε Turbulence Model

A numerical study has been carried out to determine the characteristics of fluid mixtures with different temperatures at 90° angles using ANSYS Fluent Computational Fluid Dynamics (CFD). The variation of the turbulence model used is k-ε, which is standard, RNG, and Realizable with the Near Wall Treatment method of Standard Wall Functions. The simulation domain is 90° angled with 2 perpendicular inputs and one output. The first step is to do a grid independence analysis with different mesh variations to get a proportional mesh. The research object is focused on section 6 with a distance of 35 cm before the flow output or located at 105 cm from the coordinate center. Validation was carried out by comparing temperature and velocity magnitude in research from S.N. Sridhara in section 6. It was found that the standard k-ε turbulence model was the best compared to the other variations. This gives a good idea of the distribution and flow behavior of the fluid which can be used for efficient elbow design.

Numerical study on wind pressure characteristics of Chinese yurt building under downburst wind

SummaryInner Mongolia is a high‐frequency thunderstorm region in China, and the downburst caused by the thunderstorm weather is a severe threat to buildings. In order to study the influence of downburst on the wind pressure characteristics of the yurt building, the wind field model of the yurt building under downburst is established based on the computational fluid dynamics method, and the effect of the wall treatment method and turbulence model on the numerical simulation of wind pressure of the yurt building under downburst is analyzed. The results demonstrate that the maximum positive pressure at the windward side of the yurt building occurs at 3/4 of the yurt building height under downburst, and the maximum negative pressure at the roof of the yurt building appears at the center of the roof. Compared with the experimental results, the Shear Stress Transport (SST) k‐ω model is suitable for simulating both sides of the yurt building, while the Reynolds Stress equation Model (RSM) is suitable for simulating the windward side, roof, and leeward of the yurt building. The enhanced wall treatment is appropriate for simulating the remaining sides of the yurt building while the standard wall function is appropriate for simulating both sides of the building.

Revisiting RANS turbulence modelling used in built-environment CFD simulations

The strong commitment of European Union (EU) to energy efficiency and the increasing energy prices will put pressure on the building sector to find solutions that are simultaneously very low-level or nearly zero energy-consuming, efficient, thermally comfortable and disease free. In the pursuit of such solutions, Computational Fluid Dynamics (CFD) has been used, with great success, in predicting and optimizing built-environment flows. Nonetheless, it is known that the choice of the turbulence model and the way in which it treats the near wall region, influences the quality of the yielded results. A set of experimental three-dimensional particle image velocimetry (3D PIV) data is used to assess the predictive ability of six turbulence models, commonly used in built-environment simulations, together with two new variants of the turbulence model k−ε−v‾2−f. The phenomena variables, inside a 1:30 lab-scale room, with an emulated occupant were computed for two different ventilation strategies, displacement and mixing. Only the k-ε RNG VisEff and the original ‘code-friendly’ variant of the k−ε−v‾2−f (LKM) coherently described the two simulated flows. Furthermore, it was not unequivocal that obeying the dimensionless wall distance (Y+) less than 1 rule, for the first grid node, guaranteed the enhancement of the computed results. The integration of the Standard Wall Functions (SWF) with the k−ε−v‾2−f (LKM) turbulence model proved to yield more accurate and less grid-dependent results than the stand-alone k−ε−v‾2−f (LKM) model, showing, simultaneously, a predictive ability similar to that of the k-ε RNG VisEff model, despite the lower computational complexity of the latter.

Demonstration of RANS models with wall functions in the spectral element code Nek5000

The spectral element based computational fluid dynamics (CFD) code Nek5000 has been traditionally used for high-fidelity applications, such as direct numerical simulation (DNS) and large eddy simulation (LES). These techniques require very fine numerical resolution to accurately capture turbulent fluctuations which can be prohibitively expensive for users without access to leadership class computing facilities. For broader application and adoption, significant effort has been invested to develop Reynolds-averaged Navier–Stokes (RANS) capabilities in Nek5000.This work presents details of the implementation and demonstration of the standard wall functions for the k – τ model in Nek5000. Results using the wall-modeled approach are compared to a wall-resolved approach for cases with negligible pressure gradient, viz., channel flow, pipe flow and flow in a reactor subchannel. Results show reasonably good agreement between the two approaches for friction factor and Nusselt number. Some expected differences are identified near the wall. These cases demonstrate the potential for significant computational savings by using much coarser meshes for the wall-modeled approach, with only minor differences between the predicted result. Additionally, several Reynolds numbers up to 1,000,000 are demonstrated for pipe flow and predicted friction factors and Nusselt numbers compared well to available correlations, with the worst below 10%. As the Reynolds number is increased, better agreement is observed between the correlations and the wall-modeled approach. In addition, flow in a molten salt fast reactor (MSFR) core is considered which features an adverse pressure gradient and flow separation. It showcases the inability of standard wall functions to accurately predict flows with adverse pressure gradients. The results, however, match reasonably well in trend in regions of the flow where the boundary layer is attached. Ongoing research is dedicated to include a pressure gradient correction to wall functions to improve the accuracy of flows with separation or reattachment and adverse or favorable pressure gradients.

Numerical and Experimental Determination of the Wind Speed Value Causing Catastrophe of the Scissor Lift

The current work is devoted to the numerical determination of the wind speed value, which can cause the overturning of the mobile elevating work platform of the scissor lift type. In the first step of the analysis, the scaled model of the real vehicle is prepared. In the second step, the model is used in the aerodynamic tunnel to determine the aerodynamic force values and moment, which act on the vehicle. The three different configurations of the work platform are considered, namely: (a) The work platform raised to the maximum height with an additional bridge extended, (b) the work platform raised to the maximum height, and (c) the work platform half raised. In each position, the direction of the wind is changed from the range from 0° to 180° with an increment equal to 15°. In the next step of the analysis, the CFD simulations are carried out. The ANSYS Fluent R22 software is used. As a model of turbulent airflow, the standard k-ε with standard wall function is adopted. The obtained experimental results are used to verify the numerical model. A very good agreement between the results of the experiment and the results of numerical simulations is obtained. As the main result of the numerical study, the values of the tipping moment and corresponding wind speed that cause the overturning of the analyzed real scissor lift are determined. It occurred that the lowest value of the wind speed is obtained for the first variant of the vehicle configuration V1crt = 22.315 m/s for the angle of the wind speed direction β = 30° and the highest one for the third variant V3crt = 34.534 m/s and β = 15°, without any persons on the work platform. The presence of human beings on the work platform is also considered.

Diffusion simulation and risk assessment model establishment of chlorine gas leakage based on terrain conditions

This study researches the impact of terrain factors on chlorine gas diffusion processes based on SLAB model. Simulating the law of wind speed changing with altitude by calculating the real-time speed with vertical height combing actual terrain data, and integrating the influence of terrain on wind speed by using Reynolds Average Navier-Stokes (RANS) algorithm, K-turbulence model, and standard wall functions, then plotting the gas diffusion range in the map with terrain data according to the Gaussian-Cruger projection algorithm and dividing the hazardous areas according to the public exposure guidelines (PEG). The accidental chlorine gas releases near Lishan Mountain, Xi'an City, were simulated by the improved SLAB model. The results show that there are obvious differences analyzing contrastively the endpoint distance and area of chlorine gas dispersion under real terrain condition and ideal condition at different times; it can be found that the endpoint distance of the real terrain conditions is 1.34km shorter than that of the ideal conditions at 300s with terrain factors, and also the thermal area is 3,768,026m2 less than that of the ideal conditions. In addition, it can predict the specific number of casualties within different levels of harm at 2min after chlorine gas dispersion, and casualties are constantly changing over time. The fusion of terrain factors can be used to optimize the SLAB model, which is expected to provide an important reference for effective rescue.

Numerical study of perforated obstacles effects on the performance of solar parabolic trough collector.

The current work presents and discusses a numerical analysis of improving heat transmission in the receiver of a parabolic trough solar collector by introducing perforated barriers. While the proposed approach to enhance the collector's performance is promising, the use of obstacles results in increased pressure loss. The Computational Fluid Dynamics (CFD) model analysis is conducted based on the renormalization-group (RNG) k-ɛ turbulent model associated with standard wall function using thermal oil D12 as working fluid The thermo-hydraulic analysis of the receiver tube with perforated obstacles is taken for various configurations and Reynolds number ranging from 18,860 to 81,728. The results are compared with that of the receiver without perforated obstacles. The receiver tube with three holes (PO3) showed better heat transfer characteristics. In addition, the Nusselt number (Nu) increases about 115% with the increase of friction factor 5-6.5 times and the performance evaluation criteria (PEC) changes from 1.22 to 1.24. The temperature of thermal oil fluid attains its maximum value at the exit, and higher temperatures (462.1K) are found in the absorber tube with perforated obstacles with three holes (PO3). Accordingly, using perforated obstacles receiver for parabolic trough concentrator is highly recommended where significant enhancement of system's performance is achieved.

Assessment of RANS turbulence model performance in tight lattice LWR fuel subchannels

Reynolds-averaged Navier–Stokes simulations have been performed of the turbulent flow (Re=48000) through a tight lattice (P/D=1.194) subchannel typical of those found in nuclear thermal–hydraulic applications. A wide range of turbulence models (linear eddy-viscosity, non-linear eddy-viscosity and stress-transport) and the use of different near-wall treatments, including low-Re models, standard wall-functions and the more advanced analytical wall-function, have been considered. Results indicate that only those models capable of reproducing some degree of stress anisotropy are able to correctly predict the presence of secondary motion and only the low-Re near-wall treatment was able to reproduce the correct qualitative behaviour of the wall shear stress along the rod surface, in agreement with experimental results by Hooper (1980). They also demonstrate both the failure of the standard wall-function approach in reproducing flows with significant near-wall convection and pressure-gradient effects, and the limitations of using linear eddy-viscosity approaches in flows with even moderate anisotropic effects. Although models utilizing a low-Re near-wall approach demonstrated superior overall performance, the analytical wall-function tested offers improvements over the standard ‘log-law’ based formulation.

Development of heat transfer correlation of turbulent forced convection in subchannels with rough surfaces based on CFD

Changes in roughness caused by crud deposits on the surface of nuclear fuel rods can impact the convective heat transfer characteristics of the fuel assembly. Therefore, it is necessary to establish Nusselt number correlations to estimate the heat transfer in subchannels with different surface roughness. In this paper, an analytical Nusselt number of rough round tubes was first driven by integrating the product of the wall temperature and velocity distribution functions. Then, the realizable k-ε turbulence model with the standard wall function is verified using the Dittus-Boelter correlation for smooth tubes, the analytical Nusselt number correlation for the rough tubes, and Markcozy bundle heat transfer correlation for smooth subchannels, respectively. Finally, the convective heat transfer in different rough subchannels is calculated using the verified realizable k-ε turbulence model. And a new single-phase heat transfer correlation for the rough subchannels is proposed based on the CFD results.