Performance comparison of four turbulence models (original) (raw)
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Due to the importance of channel flow characteristics in the water conveyance, the study of it is a noteworthy problem for hydraulics experts and much attempts has been accomplished for the modeling of the flow characteristics. One significant problem in this respect is the secondary-flow cells and their effect on flow specifications. Widespread experimental and analytical investigations have been accomplished on this phenomenon. However, researchers are trying to replace the expensive and time-consuming experimental approaches and ad-hoc analytical models with numerical simulation procedures using computational fluid dynamics (CFD). Selection of the proper turbulence model is one of the most important problems for this type of the numerical modeling. In the present study, after evaluating several turbulence models including k −ε , Shear Stress Transport (SST) and three versions of the Reynolds Stress Model (RSM) (i.e. LRR-IP, LRR-QI and SSG models), for the numerical simulation of the secondary-flow cells and their effects on trapezoidal channels flow, the more efficient model was selected. Available experimental data and theoretical model was used to validate the selected turbulence model. The results were validated in terms of the free water surface, depth-averaged velocity, and boundary shear stress. The results confirmed the performance and efficiency of SSG version of the Reynolds stress model for the numerical modeling of the secondary-flow cells.
A comparative study of turbulence models in a transient channel flow
Computers & Fluids, 2014
The performance of a number of low-Reynolds number turbulence models is evaluated against direct numerical simulations (DNS). All models are applied to an unsteady flow comprising a ramp-type excursion of flow rate inside a closed channel. The flow rate is increased linearly with time from an initial Reynolds number of 9308 (based on hydraulic diameter and bulk velocity) to a final Reynolds number of 29,650. The acceleration rate is varied to cover low, intermediate and high accelerations. It is shown that among the models investigated, the k-e models of Launder and Sharma (1974) and Chang et al. (1995) [28] and the c-Re h transition model of Langtry and Menter (2009) [38] capture well the key flow features of these unsteady turbulent flows. For the cases of low and intermediate acceleration rates, these three models yield predictions of wall shear stress that agree well with the corresponding DNS data. For the case of high acceleration, the c-Re h model of Langtry and Menter (2009) [38] and the k-e model of Launder and Sharma (1974) yield reasonable predictions of wall shear stress.
Application of Different Turbulence Models for Flow in Channels
Due to the rapid progress in computer hardware and software, CFD became a powerful and effective tool for implementation turbulence modeling in defined combustion mathematical models in the complex boiler geometries. In this paper the commercial CFD package, ANSYS FLUENT was used to model fluid flow through the boiler, in order to define velocity field and predict pressure drop. Mathematical modeling was carried out with application of Standard, RNG, and Realizable k-ε turbulence model using the constants presented in literature. Three boilers geometry were examined with application of three different turbulence models with variants, which means consideration of 7 turbulence model arrangements in FLUENT. The obtained model results are presented and compared with data collected from experimental tests. All experimental tests were performed according to procedures defined in the standard SRPS EN 303-5 and obtained results are presented in this paper for all three examined geometries. This approach was used for improving construction of boiler fired by solid fuel with heat output up to 35 kW and for selection of the most convenient construction.
2013
Fire field modelling (Computation Fluid Dynamics) has become more and more attractive as a critical design tool to meet Performance-based fire design on advanced modern buildings. This paper describes the application of Computational Fluid Dynamics (CFD) to predict velocities and temperature distributions induced by a fire in a Steckler's experimental data [1]. The experimental data of different fire loads is taken as case study for present investigation. The experiments of Steckler's compartment fire were conducted to investigate fire-induced flows through the opening in a compartment of size 2.8 m × 2.8 m × 2.18 m (height). The compartment has a doorway opening of 0.74 m × 1.83 m to account the ventilation condition. A porous gas burner is flushed at the floor in the centre of the room with the diameter of 0.3m in the compartment. With the above experimental data, simulation studies were performed with combustion modelling using commercial code of ANSYS CFX-5. The comparison of simulation results of fire field models with experimental domain for different strengths of fire 31.6, 62.9, 105.3 and 158.0 kW is reported. The boundary conditions of the simulation are kept constant, only fire strength is changed to see the performance of the CFD tool. The door centreline temperature, velocities and room corner temperatures are predicted and compared with experimental data as well as with FDS. The results are in good agreement with the experimental data.
Concept of Turbulence Modelling and Its Application in Open Channel Flow
2016
The foremost objectives of the particular study are to assess the working of the most popular RANS turbulence closure model in simulating river flows. For that reason, ANSYS-FLUENT package was used considering the simulation of uniform flows in straight channel with several different RANS turbulence closure models. Two approaches were used for the turbulent region and near-wall region, which are the standard k-ε model and a k-ω model respectively. On the other hand, Reynold Shear Model (RSM) is also studied upon and its pros and cons are taken into consideration with respect to the models like k-ε model and k-ω model. In comparison to the newly conducted experimental data under controlled system, models using ANSYS–FLUENT, a Computational Fluid Dynamics (CFD) code, are found to give suitable results. Computational Fluid Dynamics (CFD) is frequently used to as technique to investigate flow structures in developing areas of a flow field for the determination of velocity, pressure, she...
Empirical Formulation of Flow Characteristics in Trapezoidal Channels
Journal of The Institution of Engineers (India): Series A, 2016
Empirical relations for hydraulic jump characteristics, viz. sequent depth ratio (Y 2 /Y 1), efficiency of jump (E 2 /E 1) and relative length of jump (L j /Y 1) in trapezoidal channel with/without appurtenances are developed by introducing dimensionless Reynolds number, and neglecting the frictional effect for approach Froude number (varied between 2 and 10 under different conditions). Developed empirical models were also validated and compared with acquired experimental data as well as with literature data. Close fitness of the empirical models with appurtenances under varying dimensions, positions of baffle blocks provides accurate prediction of same for higher value of Froude number. Keywords Trapezoidal channel Á Hydraulic jump Á Energy dissipation Á Reynolds number Á Baffles q Density of water, Kg/m 3 l Dynamic viscosity of water, Ns/m 2 e Surface roughness, m h Side slope angle
Journal of Vibroengineering, 2016
In order to supply the required water for purposes such as irrigation, municipal and industrial consumptions, etc., human beings have always attempted to diverse water and construct large and small water intakes near the great rivers. Therefore, water diversion from the main path, water flow regime and the sediment transported by it change. This paper simulates the flow hydraulic in intake from the direct path of a rectangular channel and Navier-Stokes equations are solved by Finite-Volume Method (FVM) using the SSIIM2 software in which the flow velocity profiles near the surface of the water, the turbulent kinetic energy and hydrostatic pressure distribution in different sections of the main channels and intake at a constant discharge of 11 lit/sec, with the intake discharge ratio of 0.31, the inlet Froude number of 0.13 and various turbulence models were calculated in 3D mode and compared with the experimental results and there were a good agreement between the obtained values and the experimental results.
Study of Turbulence in Open Channels Using Two-Equation Models
2023
Prediction of the sediment transport in streams requires an accurate estimation of bed shear stress (for bed load) and eddy viscosity (for suspended load). In general, shallow water models employ empirical relationships to estimate the bottom shear stress. However, with the advancement of computing systems, the utilization of advanced turbulence models is getting common. In this paper, a number of model versions are reviewed based on their predictive abilities against the well-known bottom boundary layer properties in open channels and computational economy. Qualitative and quantitative comparisons have been made to infer that the choice of model versions should be based on the field application. For example, the bottom shear stress is very well predicted by the k- model whereas the cross-stream velocity profile and turbulent kinetic energy are predicted more efficiently by k- model versions. This study may be useful for researchers and practicing engineers in selecting a suitable two-equation model for calculating various bottom boundary layer properties.
Journal of Hydro-environment Research, 2020
Natural earth-bounded channel flows usually subject to various sidewall turbulences, i.e. in the form of secondary currents, due to non-constant channel shapes at different sections. This paper investigates an improved Shiono-Knight model (SKM) by combining it with a Multi-Zonal (MZ) method (proposed by Pu, 2019) to represent lateral flow turbulence and secondary currents in different shapes of open channel, i.e. rectangular and trapezoidal. By applying the proposed analytical model to both rectangular and trapezoidal channel flows, we have inspected different streamwise velocity characteristics across transverse direction generated by their sidewalls in order to provide crucial fundamental understanding to realworld natural flow system. The proposed model has also been validated via various experimental data conducted in national UK Flood Channel Facility (UK-FCF). It has been observed that the trapezoidal channel has created a larger sidewall zone where secondary current can affect flow velocity; however, the intensity of the secondary flow in trapezoidal channel has been found lesser than that of the rectangular channel. By improving the modelling of natural flow at sidewall, the studied approach could be adapted into different existing analytical models to improve their accuracy.