Numerical Modeling Of Flow Field Research Articles

Numerical modelling of flow field at shaft spillways with the marguerite-shaped inlets

By decreasing the entrained air flow discharge and improving the hydraulic characteristics of vertical shaft spillways, Marguerite-shaped inlets (MSIs) can mitigate the effects of swirling flow surrounding their inlet. The hydraulic and hydrodynamic characteristics of flow around MSIs under orifice flow regime were numerically investigated, applying different geometrical parameters. This inlet configuration can decrease the strength of swirling flow and increase the flow discharge through the shaft. The finite-volume method and the re-normalisation group k–ε turbulence model were employed to solve the governing equations of motion in a cylindrical coordinate system and a two-phase air–water flow on the water free-surface. Increasing the height and length of the blades of the MSIs was found to increase the area of the barriers against swirling flow, weaken the swirling flow strength, engender a more uniform flow and lower the water free-surface level. Extremely long or high blades, however, resulted in an intense collision of the flow with the spillway and increased the water free-surface level and the swirling flow strength at the MSI.

Numerical Modeling of Flow Field in Three Types of Vortex Settling Basins

AbstractVortex settling basins (VSBs) are efficient and economical structures that use free-surface vortex strength to remove sediment particles from flow. In this study, computational fluid dynami...

Numerical modelling of flow field at shaft spillways with circular piano-key inlets

Shaft spillways are commonly provided with adequate submergence to avoid air entrainment and swirling flows. However, other structural approaches can also be considered for this purpose if the required approach flow conditions cannot be met. Optimising the inlet shape, for example by installing a circular piano-key (CPK) inlet over the shaft spillway, is an economic way of reducing air entrainment and the swirling flow strength. In this study, numerical modelling was performed to investigate the flow field around a shaft spillway with a CPK inlet. The effects of the CPK inlet in increasing the performance of a simple shaft spillway under orifice control flow – an unfavourable flow condition for the operation of hydraulic systems – was examined. Given its special configuration, a CPK inlet reduces the swirling flow strength and significantly increases flow discharge through the shaft. The finite-volume method was used to solve the governing differential equations of motion in a cylindrical coordinate system. A two-phase air–water flow was applied on the water free surface along with a standard k–ε turbulence model. The effects of different CPK geometries on the hydraulic characteristics of flow were also investigated. The results showed that CPK inlets significantly increase the flow discharge and reduce the turbulent flow intensity compared with a simple shaft or even a morning glory spillway. To maximise the efficiency of vertical shaft spillways, optimal geometries of the CPK inlets were derived.

Effect of fish scale texture on friction performance for reciprocating pair with high velocity

PurposeThis paper aims to study the frictional performance of reciprocating pair with high velocity by using hydrodynamic lubrication principle and fish scale textured piston model.Design/methodology/approachBased on the idea of function characteristic approximation and coordinate change, a mathematical representation model of imitating fish scale texture pit section is established. According to the principle of dynamic pressure lubrication of the textured fluid, a three-dimensional numerical model of flow field for fish scale texture is established without considering cavitation. Numerical analysis of the model carp scale texture unit by orthogonal experimental design and FLUENT software is carried out.FindingsEffects of fish scale pit texture on friction properties for a reciprocating pair piston surface with high velocity (impact piston) are acquired. Effects of texture characterization parameters and flow rate on the surface friction performance for impact piston are found. Effects of different characteristic parameters combination of imitating fish scale texture on friction performance for impact piston surface are obtained.Originality/valueThe model is an effective tool to study the friction and wear of reciprocating pair with high velocity. The effects of fish scale textured piston pair supply a theory lead to design the reciprocating pair with better friction performance.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2019-0398

Numerical modelling of flow field within a packed bed of granular material

Computational domain discretization is the pre-processing stage in CFD analysis and it highly contributes to reducing the level of solution error as well as increasing the numerical stability of a model. The discretization of domain representing a packed bed of granular material is a demanding task due to the topology of the model consisting of spherical granules contacting tangentially and narrow regions in the direct vicinity of the contact point. Therefore the aim of the carried out research is to define guidelines to effectively discretize the computational domain representing the packed bed of granular material and validate it using Particle Image Velocimetry (PIV). Two methods of contact point representation between granules (contact point extension, granule radius reduction) and two mesh types (tetrahedral, polyhedral) are examined within the paper. Differences between the analyzed cases are discussed and compared to experimental research results. The obtained results prove that the applied method significantly affects the calculated porosity but does not affect the flow field considerably. Polyhedral mesh turned out to be preferable as the numerical model converges within substantially lower number of iterations and the obtained results are not as affected by the numerical diffusion as in the case of tetrahedral mesh.

Numerical modeling of flow field in compound channels with non-prismatic floodplains

In this paper an attempt has been made to study flow field in compound channels with non-prismatic floodplains. A three dimensional computational fluid dynamic (CFD) model is used to calculate the velocity distribution, secondary flow circulation and boundary shear stress in non-prismatic compound channels with two different convergence angles of 3.81o and 11.31o. The ANSYS-CFX software and k-e turbulence model is used to solve Reynolds Averaged Navier-Stokes (RANS) equations. The results of the numerical modeling were then compared to the experimental data on non-prismatic compound channels with the same convergence angles. The study shows that, more or less, the k-e turbulence model is capable of predicting the velocity and boundary shear stress distributions along the flume fairly well, especially for convergence angle of 3.81o. Also by increasing relative depth, discrepancy between numerical and experimental data decreases. The results of modeling show that the k-eturbulence model is able to predict secondary flow circulations in the main channel, created by the mass exchange between the floodplains and the main channel.

Numerical modeling of flow field around the labyrinth side-weirs in the presence of guide vanes

Side weirs are hydraulic structures that are used in irrigation and drainage channels, flood control systems, and wastewater collection networks to divert the flow, isolate the sedimentation, and reduce the bed loads. Labyrinth side weirs are a type of side weirs with a higher discharge coefficient compared to the traditional side weirs. During the last decade, these weirs have been the interest of different researchers. In this study, triangular labyrinth side weirs with the groups of guide vanes were modeled numerically using OpenFOAM software. The free surface of subcritical approach flow over the labyrinth side weirs was modeled using Volume of Fluids method. The standard k-ε turbulence model was applied to calculate the flow characteristics. The results of the numerical model are compared well with those of the available experimental data. According to the results, the maximum discharge coefficient of a side weir is obtained when the vane plates are located perpendicular to the flow direction at the downstream end of the weirs across the main channel.

Numerical Modeling of Flow Field in Morning Glory Spillways and Determining Rating Curve at Different Flow Rates

Morning glory spillways with drop inlets are normally employed in dams built on narrow valleys or placed on steep slopes. In Iran, morning glory spillways have been commonly used in large Dam projects such as Sefidrood dam, Alborz dam, and Haraz dam. Physical models should be built to accurately determine hydraulic parameters of the flow and flow field in spillways. Establishment of a physical model involves extravagant costs and conditions that cannot be justified in some cases. Therefore, suitable numerical models can be proposed for such circumstances. Using FLOW3D numerical models, 3-dimensional numerical modelling of the flow was calibrated and validated by experimental information associated with morning glory spillway of Alborz dam and accuracy of numerical modelling was determined by relative error of numerical model. So it was attempted to determine flow pattern and control conditions of morning glory spillways in different modes using boundary conditions, inlet conditions and grid spacing of flow field and project rating curve of morning glory spillways. According to the results of numerical model, relative error of numerical modelling equals 6.4% for calculating discharge rate of the spillways. Numerical modelling error is 7.6% for determining depth parameter of the flow in spillway crest in comparison with experimental results.

Three-dimensional numerical modelling of flow field in shallow reservoirs

Shallow flows can play a significant role in sediment management for dam reservoirs (e.g. sedimentation in shallow reservoirs and free-flow flushing operation). When shallow flow emerges with symmetric or asymmetric patterns, the flow domain exhibits complex three-dimensional (3D) features (e.g. helical flows). This study focuses on the numerical modelling of the velocity field in shallow reservoirs with varying geometries and also varying bed conditions (i.e. flat and misshaped beds). A fully 3D numerical model using the finite-volume method was utilised to reproduce the 3D flow velocity field. The experimentally measured surface velocity in all cases and velocity profiles in one case were used to validate the model. The numerical results showed that a slight disturbance in the inflow boundary condition results in a steady asymmetric flow pattern in reservoirs with a higher defined shape factor, but does not affect the flow pattern in reservoirs with a lower defined shape factor. Nonetheless, the simulated and measured flow velocity fields are reasonably consistent in all cases. These results can be used to optimise the design of sand traps or water storage facilities, and also to optimise sediment management in existing reservoirs.

Three-dimensional numerical modelling of flow field in shallow reservoirs

Three-dimensional numerical modelling of flow field in shallow reservoirs

Numerical modelling of flow field in a recycling cyclone

This paper shows the results of numerical modelling of the flow field in a recycling cyclone. The high separation efficiency of recycling cyclone has been proved by experiments recently. However, owing to many restrictions, the information of flow field in recycling cyclone is difficult to obtain. In this paper, tangential velocity, axial velocity, radial velocity and pressure have been obtained and analysed through numerical simulation in different positions of the recycling cyclone. A good agreement has been obtained between the simulation and the experimental results. The special design of flow path in the recycling cyclone can improve the symmetry of the flow field, shorten the moving distance of the fluid, and reduce the generation of turbulence. The simulation results also confirm the applicability of computational fluid dynamics (CFD) as a promising tool to study the flow field of cyclone.

Measurements and numerical modeling of flow field and pollutant dispersion in areaway space

In residential building design, areaway can act as an open subsurface space to help improve the living environment in adjacent basement by natural ventilation. To study this particular ventilation phenomenon mainly driven by wind force, the first part of this paper presents an investigation of flow field and pollution dispersion inside areaway space based on a wind tunnel experiment. In the experiment, the measurement of mean velocity, turbulence and concentration as well as the flow visualization were carried out for a rectangular cavity-like areaway model with the width to height (w/h) ratio ranging from 0.3 to 1.0 and the influence of above-ground building has also been investigated. The experimental results reveal quite different airflow patterns characterized with unsteady vortex movement inside the areaway model, which indicates that the w/h ratio and the above-ground building are important factors for ventilating the areaway space. Furthermore, for the purpose of computational fluid dynamics (CFD) model validation, the experimental results of flow fields were compared with the simulation results. The areaway model of w/h = 1 was used for this study and the simulations were performed using large-eddy simulation (LES) and standard k-e turbulence model. The numerical results show a good agreement with the experimental results when using LES with inflow turbulence. The further investigations with regard to the characteristics of flow field and pollutant removal as well as ventilation performance were also performed by LES.