scholarly journals CFD Simulation of Flow Characteristics on Semi-Submersible Platforms

2020 ◽  
Vol 9 (1) ◽  
pp. 2777-2782
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Cfd Simulation ◽  
Transient Flow ◽  
Flow Characteristics ◽  
Slip Boundary Condition ◽  
Computational Domain ◽  
Hexahedral Mesh ◽  
Four Square ◽  
Lift And Drag

In this paper we present the turbulent flow around a semi-submersible platform, modelled using Ansys Fluent. The computational domain is designed as a rectangular horizontal channel with the semi-submersible platform mounted inside the channel. The top, bottom, left and right walls of the channel are treated with no slip boundary condition. The front and back walls are specified with velocity inlet and pressure outlet boundary conditions. The semi-submersible platform is designed with of two pontoons, four square columns and two bracings. The problem is modelled as three dimensional, transient, incompressible flow and turbulence is modelled using Large eddy simulation (LES) turbulence model. The computational domain is meshed to 4,72,749 hexahedral mesh cells. Parametric study is performed by varying the Reynolds number (Re) in the range of 104 ≤ Re ≤ 106 and also the shape of the columns. The investigation is carried out by plotting stream function, velocity and pressure contours. We observe vortex shedding and flow separation between the front and back columns of the semi-submersible platform. As we increase the Reynolds number the intensity of flow separation also increases. The transient flow characteristics of the lift and drag forces are evaluated by plotting the coefficients of lift and drag for different Reynolds number and column shapes

Unsteady Isothermal Flow Through a Staggered Tube Bundle Array

2012 ◽  
Author(s):  
Artit Ridluan ◽  
Surasing Arayangkun ◽  
Coochart Phayom
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Cfd Simulation ◽  
Transient Flow ◽  
Stokes Equations ◽  
Tube Bundle ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Isothermal Flow ◽  
Flow Through

Two-dimensional Unsteady simulations of isothermal flow through a staggered tube bundle array at three different Reynolds numbers 54, 72, and 90 were investigated. The Navier-Stokes equations are numerically solved. Based on the CFD simulation results, the unsteady flow patterns were developed behind the rear row of the array, while for the other rows, the steady separated and reattached flow behaviors were observed, small, short, and closed separation bubble behind the rods. At Reynolds Number of 54, the transient flow was perfectly periodic. The complicated patterns of unsteady flow could be observed at Reynolds numbers of 72 and 90. The shedding patterns of vortices from the last rods were different and no longer periodic as found at Reynolds number of 54. The degree of chaos is increased as Reynolds number progressed.

Hydrofoils with Differing Leading-Edge Protuberances: CFD and Experimental Investigations

2021 ◽  
Vol 163 (A3) ◽  
Author(s):  
R Kant ◽  
A Bhattacharyya
Keyword(s):  
Reynolds Number ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Humpback Whales ◽  
Experimental Investigations ◽  
Streamwise Vortices ◽  
Cfd Analyses ◽  
Lift And Drag ◽  
High Angles Of Attack ◽  
Base Design

Leading-edge protuberances on the pectoral fin of humpback whales have been widely adopted to the designs of foils to provide superior lifting characteristics in the post-stall regimes. The present work investigates the lift, drag and flow characteristics of finite-span rectangular hydrofoils having different configurations of two protuberances over the leading edge with NACA 634-021 as the base design section. The results obtained from CFD analyses are validated using lift and drag measurements from experiments. The influence of using a transition-sensitive turbulence model on the results is investigated. It is observed that, in general, a foil with smaller separation between protuberances has better post-stall lift characteristics whereas that with protuberances at larger separation have better pre-stall characteristics. Depending on the separation between them, streamwise vortices are generated from the leading-edge protuberances. The two protuberances can restrict the zone of separation between them at high angles of attack. The influence of Reynolds number on the lifting performance is also investigated.

scholarly journals Numerical Investigation of Turbine Blades with Leading-Edge Tubercles in Uniform Current

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2205
Author(s):  
Shuling Chen ◽  
Yan Liu ◽  
Changzhi Han ◽  
Shiqiang Yan ◽  
Zhichao Hong
Keyword(s):  
Flow Separation ◽  
Turbine Blades ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Hydrodynamic Performance ◽  
Micro Scale ◽  
Drag Forces ◽  
Uniform Current ◽  
Naca0018 Airfoil ◽  
Lift And Drag

Inspired by the tubercles on humpback whale flippers, leading-edge tubercles have been incorporated into the design of wings and turbine blades in an attempt to improve their hydrodynamic performance. Although promising improvements, especially in terms of the stall performance, have been demonstrated in the limited research that exists to date, the effectiveness of the leading-edge tubercles seems to be influenced by the base blade. This paper focuses on the introduction of sinusoidal leading-edge tubercles to a base blade developed from the classic NACA0018 airfoil, and numerically investigates the effectiveness of leading-edge tubercles on the hydrodynamics associated with the blade in uniform current with different attack angles. Both the macroscopic parameters, such as the lift and drag forces, and the micro-scale flow characteristics, including the vortex and flow separation, are analyzed. The results indicate that the leading-edge tubercles brings a significant influence on the hydrodynamic forces acting on the blade when subjected to an attack angle greater than 15°. This study also reveals the important role of the turbulence and flow separation on hydrodynamic loading on the blade and the considerable influence of the tubercles on such micro-scale flow characteristics. Although the conditions applied in this work are relatively ideal (e.g., the blade is fixed in a uniform flow and the end effect is ignored), the satisfactory agreement between the numerical and corresponding experimental data implies that the results are acceptable. This work builds a good reference for our future work on the hydrodynamic performance of tidal turbines which adopt this kind of blade for operating in both uniform and shearing currents.

Control of Flow Separation Around Bluff Obstacles by Transverse Magnetic Field

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Dipankar Chatterjee ◽  
Kanchan Chatterjee ◽  
Bittagopal Mondal
Keyword(s):  
Magnetic Field ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Field Strength ◽  
Flow Separation ◽  
Creeping Flow ◽  
Computational Domain ◽  
Number Range ◽  
Electrically Conducting ◽  
Low Reynolds

Electromagnetic fields may be used to control the flow separation during the flow of electrically conducting fluids around bluff obstacles. The steady separated flow around bluff bodies at low Reynolds numbers almost behaves as a creeping flow at a certain field strength. This phenomena, although already known, is exactly quantified through numerical simulation and the critical field strength of an externally applied magnetic field is obtained, for which the flow separation is completely suppressed. The flow of a viscous, incompressible, and electrically conducting fluid (preferably liquid metal or an electrolyte solution) at a Reynolds number range of 10–40 and at a low magnetic Reynolds number is considered in an unbounded medium subjected to uniform magnetic field strength along the transverse direction. Circular and square cross sections of the bluff obstacles are considered for simulation purposes. Fictitious confining boundaries are chosen on the lateral sides of the computational domain that makes the blockage ratio (the ratio of the cylinder size to the width of the domain) 5%. The two-dimensional numerical simulation is performed following a finite volume approach based on the semi-implicit method for pressure linked equations (SIMPLE) algorithm. The major contribution is the determination of the critical Hartmann number for the complete suppression of the flow separation around circular and square cylinders for the steady flow in the low Reynolds number laminar regime. The recirculation length and separation angle are computed to substantiate the findings. Additionally, the drag and skin friction coefficients are computed to show the aerodynamic response of the obstacles under imposed magnetic field conditions.

A Meta-Model for Aerodynamic Properties of a Reversible Profile in Cascade With Variable Stagger and Solidity

2018 ◽  
Author(s):  
Gino Angelini ◽  
Tommaso Bonanni ◽  
Alessandro Corsini ◽  
Giovanni Delibra ◽  
Lorenzo Tieghi ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Pitch Angle ◽  
Cfd Simulation ◽  
Aerodynamic Performance ◽  
Specific Work ◽  
Drag Coefficients ◽  
Stall Margin ◽  
Meta Model ◽  
Aerodynamic Properties ◽  
Lift And Drag

In this paper, a systematic CFD work is carried out with the aim to inspect the influence of different cascade parameters on the aerodynamic performance of a reversible fan blade profile. From the obtained results, we derive a meta-model for the aerodynamic properties of this profile. Through RANS simulations of different arrangements in cascades, the aerodynamic performance of airfoils are analyzed as Reynolds number, solidity, pitch angle and angle of attack are varied. The definition of a trial matrix allows the reduction of the minimum number of simulations required. The computed CFD values of lift and drag coefficients, stall margin and the zero-lift angle strongly depend on cascade configuration and differ significantly from standard panel method software predictions. In this work, X-Foil has been used as a benchmark. Particularly, the high influence of pitch angle and solidity is here highlighted, while a less marked dependence from the Reynolds number has been found. Meta-models for lift and drag coefficients have been later derived, and an analysis of variance has improved the models by reducing the number of significant factors. The application of the meta-models to a quasi-3D in-house software for fan performance prediction is also shown. The effectiveness of the derived meta-models is proven through a spanwise comparison of a reversible fan with the X-Foil based and meta-model based versions of the software and 3D fields from a standard CFD simulation. The meta-model improves the software prediction capability, leading to a very low global overestimation of the specific work of the fan.

scholarly journals Numerical analysis of high-lift configurations with oscillating flaps

2021 ◽  
Author(s):  
Johannes Ruhland ◽  
Christian Breitsamter
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Separated Flow ◽  
Navier Stokes ◽  
Rotational Axis ◽  
High Lift ◽  
Hinge Point ◽  
Reduced Frequency ◽  
Flap Deflection ◽  
The Impact

AbstractThis study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport $$k-\omega $$ k - ω turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of $$0.5 \times 10^{6}$$ 0.5 × 10 6 the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of $$20 \times 10^6$$ 20 × 10 6 , reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

scholarly journals Predicting the effect of the rib pitch on thermal performance factor of small channels plate heat exchangers fitted with Y and C shapes obstacles

2021 ◽  
Vol 3 (4) ◽  
Author(s):  
Sirine Chtourou ◽  
Hassene Djemel ◽  
Mohamed Kaffel ◽  
Mounir Baccar
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Computer Aided Design ◽  
Flow Characteristics ◽  
Plate Heat Exchanger ◽  
Geometrical Parameters ◽  
Computational Domain ◽  
Ansys Fluent ◽  
Plate Heat ◽  
Small Channels

AbstractThis study presents a numerical analysis of a laminar counter flow inside small channels plate heat exchanger fitted with Y and C shape obstacles. Using the Computational Fluid Dynamics CFD, an advanced and modern simulation technique, the influence of the geometrical parameters (such as geometry, rib pitch) on the flow characteristics, the thermal and the hydrodynamics performance of the PHE (plate heat exchanger) is investigated numerically. The main goal of this work is to increase the flow turbulence, enhance the heat transfer and the thermal efficiency by inserting new obstacles forms. The computational domain is a conjugate model which is developed by the Computer Aided Design CAD software Solidworks. The results, obtained with Ansys Fluent, show that the presence of the shaped ribs provides enhancement in heat transfer and fluid turbulence. The CFD analysis is validated with the previous study. The non-dimensional factors such as the Nusselt number Nu, the skin friction factor Cf and the thermo-hydraulic performance parameter THPP are predicted with a Reynolds number Re range of 200–800. The temperature and the velocity distribution are presented and analyzed. The Y ribs and the C ribs offer as maximum THPP values respectively about 1.44 and 2.6 times of a smooth duct.

Flow and Thermal Fields in a Pendant Droplet Moving on Lyophobic Surface

2010 ◽  
Author(s):  
Basant Singh Sikarwar ◽  
K. Muralidhar ◽  
Sameer Khandekar
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Reynolds Number ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Maximum Shear Stress ◽  
Computational Domain ◽  
Wall Shear

Clusters of liquid drops growing and moving on physically or chemically textured lyophobic surfaces are encountered in drop-wise mode of vapor condensation. As opposed to film-wise condensation, drops permit a large heat transfer coefficient and are hence attractive. However, the temporal sustainability of drop formation on a surface is a challenging task, primarily because the sliding drops eventually leach away the lyophobicity promoter layer. Assuming that there is no chemical reaction between the promoter and the condensing liquid, the wall shear stress (viscous resistance) is the prime parameter for controlling physical leaching. The dynamic shape of individual droplets, as they form and roll/slide on such surfaces, determines the effective shear interaction at the wall. Given a shear stress distribution of an individual droplet, the net effect of droplet ensemble can be determined using the time averaged population density during condensation. In this paper, we solve the Navier-Stokes and the energy equation in three-dimensions on an unstructured tetrahedral grid representing the computational domain corresponding to an isolated pendant droplet sliding on a lyophobic substrate. We correlate the droplet Reynolds number (Re = 10–500, based on droplet hydraulic diameter), contact angle and shape of droplet with wall shear stress and heat transfer coefficient. The simulations presented here are for Prandtl Number (Pr) = 5.8. We see that, both Poiseuille number (Po) and Nusselt number (Nu), increase with increasing the droplet Reynolds number. The maximum shear stress as well as heat transfer occurs at the droplet corners. For a given droplet volume, increasing contact angle decreases the transport coefficients.

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