A Numerical Study of Turbulent Mixed Convection in a Smooth Horizontal Pipe

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Ahmed Faheem ◽  
Gianluca Ranzi ◽  
Francesco Fiorito ◽  
Chengwang Lei
Keyword(s):  
Richardson Number ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Hollow Core ◽  
Horizontal Pipe ◽  
Fully Developed Flow ◽  
Horizontal Pipes ◽  
Dimensionless Velocity ◽  
Hollow Core Slab

This paper presents a numerical study aimed at identifying a suitable turbulence model to describe the fully developed turbulent mixed convention of air in smooth horizontal pipes. The flow characteristics considered here are relevant to those typically observed in ventilated hollow core slab (VHCS) applications and, because of this, the adopted geometry and boundary conditions are represented by the Reynolds number and Richardson number of about 23,000 and 1.04, respectively. Empirical expressions available in the literature are used as reference to evaluate the accuracy of different turbulence models in predicting the dimensionless velocity (u+) and temperature (T+) profiles as well as the Nusselt number (Nu). Among the turbulence models considered, the standard and realizable k-ε models provide the best overall predictions of u+, T+, and Nu in the fully developed flow, and the former is recommended for the modeling of VHCS systems as it gives slightly better estimates of the Nu values.

A Numerical Procedure for Modelling the Thermal Performance of Ventilated Hollow Core Slabs

2016 ◽  
Vol 846 ◽  
pp. 12-17
Author(s):  
Ahmed Faheem ◽  
Gianluca Ranzi ◽  
Francesco Fiorito ◽  
Cheng Wang Lei
Keyword(s):  
Turbulence Model ◽  
Thermal Performance ◽  
Numerical Procedure ◽  
Turbulence Models ◽  
Experimental Measurements ◽  
Hollow Core ◽  
Horizontal Pipe ◽  
Dimensionless Velocity ◽  
Nusselt Numbers ◽  
Numerical Predictions

This paper presents a numerical procedure for modelling the thermal performance of ventilated hollow core slabs (VHCS). A turbulence model suitable for this purpose is identified first by considering a smooth horizontal pipe subjected to turbulent mixed convention conditions typical of VHCSs. Comparison of the fully-developed dimensionless velocity (u+) and temperature (T+) profiles as well as the Nusselt numbers (Nu) predicted by five different turbulence models against empirical expressions available in the literature shows that the Standard and Realisable k-ε models provide the best overall predictions of u+, T+ and Nu. Since the Standard k-ε model gives slightly better estimates of the Nu values, it is adopted to model the thermal performance of a VHCS geometry for which experimental thermal responses are reported in the literature. The numerical predictions of local temperatures within the VHCS agree well with the experimental measurements, and hence the Standard k-ε model is recommended here for the modeling of VHCSs.

Prediction of Confined Three-Dimensional Impinging Flows With Various Turbulence Models

1992 ◽  
Vol 114 (2) ◽  
pp. 220-230 ◽  
Author(s):  
T. M. Liou ◽  
Y. H. Hwang ◽  
L. Chen
Keyword(s):  
Richardson Number ◽  
Laser Doppler Velocimetry ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Quantitative Agreement ◽  
Computational Effort ◽  
Main Flow ◽  
Inlet Velocity ◽  
Impinging Flows

This paper deals with three-dimensional, turbulent, confined impinging flows. Various turbulence models are examined with reported laser-Doppler velocimetry data and flow-visualization photographs. The turbulence models considered are the k–ε, k–ε with the Richardson number correction for swirling and recirculating flows (k–ε w/scm), algebraic Reynolds stress (k–ε–A), and modified k–kl models. The k–ε and k–ε–A models are found to be superior to the k–ε w/scm and modified k–kl models in predicting the main flow characteristics. The k–ε–A model provides a better quantitative agreement with the experimental data than can be achieved with the k–ε model, however, less computational effort is spent with the k–ε model than with the k–ε–A model. Also, the effect of the inlet velocity profile on the characteristics of the confined impinging flows is addressed in this study.

scholarly journals Numerical Study of the Turbulent Flow from a Steam Dumping Pressurizer Relief Tank

Energies ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 4059
Author(s):  
Sen Zhang ◽  
Xiao-Wei Guo ◽  
Chao Li ◽  
Yi Liu ◽  
Ran Zhao ◽  
...  
Keyword(s):  
Turbulent Flow ◽  
Open Source ◽  
Complex Geometry ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Source Codes ◽  
Model Based ◽  
Eddy Simulation

Due to the complex geometry and turbulent flow characteristics, it is hard to simulate the process of steam dumping of the pressurizer relief tank (PRT). In this study, we develop a compressible fluid solver PRTFOAM to numerically study the turbulent flow dynamics from a PRT. The PRTFOAM is implemented based on the OpenFOAM and designed to be capable of integrating various turbulence models. Two representative Reynolds-averaged Navier–Stokes (RANS) models and a Smagorinsky–Lilly SGS model based on Large Eddy Simulation (LES) are coupled and tested with PRTFOAM. The case of a flow past a circular cylinder (Re = 3900) is tested and analyzed comprehensively as a benchmark case. Then, the turbulent steam dumping process in the full geometry of a PRT is analyzed and compared with ANSYS CFX and literature reports. In addition, we tested the WALE model based on the PRT steam dumping process. The results show that SST k-ω model and Smagorinsky–Lilly SGS model-based LES approach are more appropriate than the LRR model for PRT simulations. Moreover, it shows that the simulation results of Smagorinsky–Lilly SGS model and WALE model are basically consistent under the condition of PRT steam dumping process. Under this condition, the drawbacks of Smagorinsky–Lilly SGS model are not obvious. Furthermore, the comparison with CFX showed that our open source solver could be used to obtain better results in complex engineering cases. The design and testing results would provide guidance for further analysis of thermal-hydraulics in reactors based on open source codes.

scholarly journals Analysis of Flow Characteristics and Effects of Turbulence Models for the Butterfly Valve

2021 ◽  
Vol 11 (14) ◽  
pp. 6319
Author(s):  
Sung-Woong Choi ◽  
Hyoung-Seock Seo ◽  
Han-Sang Kim
Keyword(s):  
Turbulence Model ◽  
Dissipation Rate ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Flow Properties ◽  
Nominal Diameter ◽  
Large Pressure ◽  
Sst Model ◽  
Turbulence Effect ◽  
Valve Opening

In the present study, the flow characteristics of butterfly valves with different sizes DN 80 (nominal diameter: 76.2 mm), DN 262 (nominal diameter: 254 mm), DN 400 (nominal diameter: 406 mm) were numerically investigated under different valve opening percentages. Representative two-equation turbulence models of two-equation k-epsilon model of Launder and Sharma, two-equation k-omega model of Wilcox, and two-equation k-omega SST model of Menter were selected. Flow characteristics of butterfly valves were examined to determine turbulence model effects. It was determined that increasing turbulence effect could cause many discrepancies between turbulence models, especially in areas with large pressure drop and velocity increase. In addition, sensitivity analysis of flow properties was conducted to determine the effect of constants used in each turbulence model. It was observed that the most sensitive flow properties were turbulence dissipation rate (Epsilon) for the k-epsilon turbulence model and turbulence specific dissipation rate (Omega) for the k-omega turbulence model.

Numerical study of influence of casting speed on fluid flow characteristics in the four strand tundish

2021 ◽  
Author(s):  
Kridsanapong Boonpen ◽  
Pruet Kowitwarangkul ◽  
Patiparn Ninpetch ◽  
Nadnapang Phophichit ◽  
Piyapat Chuchuay ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Casting Speed ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Fluid Flow Characteristics

A numerical study on combined baffles quick-separation device

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ehsan Dehdarinejad ◽  
Morteza Bayareh ◽  
Mahmud Ashrafizaadeh
Keyword(s):  
Turbulent Flows ◽  
Separation Efficiency ◽  
Numerical Study ◽  
Turbulence Models ◽  
Complete Separation ◽  
Solid Particles ◽  
Flow Rates ◽  
Separation Device ◽  
Coupling Technique ◽  
Laminar And Turbulent Flows

Abstract The transfer of particles in laminar and turbulent flows has many applications in combustion systems, biological, environmental, nanotechnology. In the present study, a Combined Baffles Quick-Separation Device (CBQSD) is simulated numerically using the Eulerian-Lagrangian method and different turbulence models of RNG k-ε, k-ω, and RSM for 1–140 μm particles. A two-way coupling technique is employed to solve the particles’ flow. The effect of inlet flow velocity, the diameter of the splitter plane, and solid particles’ flow rate on the separation efficiency of the device is examined. The results demonstrate that the RSM turbulence model provides more appropriate results compared to RNG k-ε and k-ω models. Four thousand two hundred particles with the size distribution of 1–140 µm enter the device and 3820 particles are trapped and 380 particles leave the device. The efficiency for particles with a diameter greater than 28 µm is 100%. The complete separation of 22–28 μm particles occurs for flow rates of 10–23.5 g/s, respectively. The results reveal that the separation efficiency increases by increasing the inlet velocity, the device diameter, and the diameter of the particles.

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