CFD Investigation of the Effect of Current Turbulence on the Hydrodynamic Forces on a Cylinder

2005 ◽  
Author(s):  
Hyung Taek Ahn ◽  
Yannis Kallinderis
Keyword(s):  
Turbulence Model ◽  
Reynolds Numbers ◽  
Offshore Structures ◽  
Hydrodynamic Forces ◽  
Current Profile ◽  
Time Step ◽  
Lack Of Information ◽  
Turbulent Inflow ◽  
Inflow Condition ◽  
High Reynolds

Practical cases of flow-structure interactions involve ocean currents with turbulence. Ocean turbulence effects on offshore structures are of high interest due to the lack of information about its role regarding the hydrodynamic forces and fatigue load on structures. Current turbulence profiles are employed for various Reynolds numbers that are based on an isotropic geophysical turbulence model. These turbulence profiles are specified as the inflow condition for the numerical simulations over a circular cylinder. The present work consists of three parts: (i) determination of appropriate mesh and time step resolution to accommodate the turbulence, (ii) investigation of the effect of current profile turbulence on the amplitude and frequencies of the hydrodynamic forces acting on a cylinder, and (iii) study of the sensitivity of the hydrodynamic load exerted on the cylinder for a range of Reynolds numbers with a turbulent inflow profile. Spalart-Allmaras one-equation turbulence model is used for high Reynolds number simulations.

scholarly journals Binary Neutron Star Merger Simulations with a Calibrated Turbulence Model

Symmetry ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1249 ◽  
Author(s):  
David Radice
Keyword(s):  
Neutron Star ◽  
Turbulence Model ◽  
Reynolds Numbers ◽  
Mhd Turbulence ◽  
Binary Neutron Star ◽  
Eddy Simulation ◽  
Moderate Resolution ◽  
Scale Turbulence ◽  
High Reynolds ◽  
The Impact

Magnetohydrodynamic (MHD) turbulence in neutron star (NS) merger remnants can impact their evolution and multi-messenger signatures, complicating the interpretation of present and future observations. Due to the high Reynolds numbers and the large computational costs of numerical relativity simulations, resolving all the relevant scales of the turbulence will be impossible for the foreseeable future. Here, we adopt a method to include subgrid-scale turbulence in moderate resolution simulations by extending the large-eddy simulation (LES) method to general relativity (GR). We calibrate our subgrid turbulence model with results from very-high-resolution GRMHD simulations, and we use it to perform NS merger simulations and study the impact of turbulence. We find that turbulence has a quantitative, but not qualitative, impact on the evolution of NS merger remnants, on their gravitational wave signatures, and on the outflows generated in binary NS mergers. Our approach provides a viable path to quantify uncertainties due to turbulence in NS mergers.

Numerical Wave Tank Including a Fixed Vertical Cylinder Subjected to Waves, Towards the Investigation of Floating Offshore Wind Turbine Hydrodynamics

2020 ◽  
Author(s):  
Constance Clément ◽  
Pauline Bozonnet ◽  
Guillaume Vinay ◽  
Adria Borras Nadal ◽  
Philippe Pagnier ◽  
...  
Keyword(s):  
Turbulence Model ◽  
Wave Generation ◽  
Hydrodynamic Forces ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Numerical Wave Tank ◽  
Time Step ◽  
Cfd Simulations ◽  
Wave Tank ◽  
Numerical Wave

Abstract Specific engineering tools are used to design Floating Offshore Wind Turbines (FOWT). These so-called aero-hydro-servo-elastic solvers simulate the coupled behaviour of the turbine subjected to wind with the floater motion due to waves, including elasticity of the whole structure. The implemented hydrodynamic forces rely on a strong Oil&Gas background and include potential flow theory and empirical laws, such as Morison forces. The undergoing study aims at re-evaluating the validity range of such theories, when applied to FOWT. To do so, CFD simulations will be run to model wave propagation and interaction with a FOWT floater. Hydrodynamic forces will be extracted from the CFD simulations and compared to current hydrodynamic theories. A fixed cylinder in regular second order deep water waves (steepness of 0.9) is simulated and results are validated against experiments [1]. This basic first case implemented with Open-FOAM using waves2Foam library allows to master regular wave generation and interaction with a rather simple structure, running multiple simulations. Convergence (mesh refinement, time step) and parameterization (numerical schemes, turbulence models) studies are carried out to ensure controlled wave generation. An accurate Numerical Wave Tank (NWT) is finally obtained. However, the resolution of air/water interface with Volume Of Fluid (VOF) MULES method seems to be responsible for extreme air velocities on crests resulting in wave damping. This phenomena is solved by decreasing time step. Hydrodynamic forces on the cylinder match experiments with an error below 3%. As the flow is turbulent (Re = 105), a turbulence model is included in the simulation giving results rather close to the ones obtained without turbulence model.

Examination of Hydrodynamic Forces Acting on a Group of Circular Cylinders at High Reynolds Numbers

2016 ◽  
Author(s):  
Linwei Shen ◽  
Rajeev Kumar Jaiman ◽  
Peter Francis Bernad Adaikalaraj ◽  
Vaibhav Joshi ◽  
Jungao Wang ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Hydrodynamic Forces ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Incoming Flow ◽  
Drag Coefficients ◽  
Numerical Result ◽  
High Reynolds ◽  
Engineering Practices

A group of circular cylinders exists in many engineering practices, such as offshore drilling riser system. Due to the interference between the riser main tube and auxiliary lines, the hydrodynamic forces acting on the riser system is much different from those on a single circular cylinder. It is very rare in the publication and still not certain in the determination of the forces in the drilling riser design of the industry. Particularly, it is unclear of the hydrodynamic forces when the Reynolds number is very high which is quite common in the real ocean fields. In this paper, the stationary riser system consisting of a group of six circular cylinders with unequal diameters is considered. The hydrodynamic forces acting on the main cylinder in the Reynolds number ranging from 105 to 2×106 are numerically calculated by solving the Reynolds averaged Navier-Stokes (RANS) equations. The Spalart-Allmaras RANS model is employed to account for the turbulence effect. It is found that drag coefficients are close to 1 when the incoming flow is symmetrical with respect to the configuration of the cylinders and are dramatically reduced when the incoming flow is asymmetrical. No “drag crisis”, which is a well-known phenomenon in a single cylinder case, is found in this particular range of Reynolds numbers. A detailed analysis, including the flow field and pressure distribution around the main tube, is also presented in the present work. The numerical result of the hydrodynamic forces on the main line is very helpful for the engineers to determine the drag coefficients in the practice of drilling riser system design, under the guidance of API-RP-16Q.

Efficient Computation and Modeling of Viscous Flow Effects in ComFLOW

2013 ◽  
Author(s):  
Henri J. L. van der Heiden ◽  
Peter van der Plas ◽  
Arthur E. P. Veldman ◽  
Roel W. C. P. Verstappen ◽  
Roel Luppes
Keyword(s):  
Reynolds Number ◽  
Viscous Flow ◽  
Turbulence Model ◽  
Cfd Simulation ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Second Order ◽  
Efficient Computation ◽  
Flow Effects ◽  
High Reynolds

In offshore applications, details of viscous flow effects can become relevant when predicting e.g. drag forces on the columns of oil drilling rigs, or the flow around a semisubmersible in figure 1. This motivates a novel approach for efficiently simulating viscous flow effects at high Reynolds numbers with the CFD simulation tool ComFLOW. In ComFLOW, the Navier–Stokes equations can be solved for one-phase and for two-phase flow. The equations are discretized second-order in space, and second-order in time. An Improved Volume-of-Fluid (IVOF) algorithm is used for free-surface advection and reconstruction [1, 2]. Modeling viscous flow effects in high Reynolds number flows requires a turbulence model that provides accurate results on coarse grids. We pursue to achieve a high local grid resolution in a computationally efficient manner. Both approaches are tested for flows around a square cylinder: grid refinement at Reynolds numbers 10 and 100, and the turbulence model at Reynolds number 22,000.

scholarly journals Numerical Study on the Aerodynamic Characteristics of the NACA 0018 Airfoil at Low Reynolds Number for Darrieus Wind Turbines Using the Transition SST Model

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 477
Author(s):  
Krzysztof Rogowski ◽  
Grzegorz Królak ◽  
Galih Bangga
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Wind Turbines ◽  
Numerical Study ◽  
Experimental Studies ◽  
Turbulence Models ◽  
Vertical Axis ◽  
Reynolds Numbers ◽  
Time Step ◽  
Sst Turbulence Model

A symmetrical NACA 0018 airfoil is often used in such applications as small-to-medium scale vertical-axis wind turbines and aerial vehicles. A review of the literature indicates a large gap in experimental studies of this airfoil at low and moderate Reynolds numbers in the previous century. This gap has limited the potential development of classical turbulence models, which in this range of Reynolds numbers predict the lift coefficients with insufficiently accurate results in comparison to contemporary experimental studies. Therefore, this paper validates the aerodynamic performance of the NACA 0018 airfoil and the characteristics of the laminar separation bubble formed on its suction side using the standard uncalibrated four-equation Transition SST turbulence model and the unsteady Reynolds-averaged Navier-Stokes (URANS) equations. A numerical study was conducted for the chord Reynolds number of 160,000, angles of attack between 0 and 11 degrees, as well as for the free-stream turbulence intensity of 0.05%. The calculated lift and drag coefficients, aerodynamic derivatives, as well as the location and length of the laminar bubble quite well agree with the results of experimental measurements taken from the literature for validation. A sensitivity study of the numerical model was performed in this paper to examine the effects of the time-step size, geometrical parameters and mesh distribution around the airfoil on the simulation results. The airfoil data sets obtained in this work using the Transition SST and the k-ω SST turbulence models were used in the improved double multiple streamtube (IDMS) to calculate aerodynamic blade loads of a vertical-axis wind turbine. The characteristics of the normal component of the aerodynamic blade load obtained by the Transition SST approach are much better suited to the experimental data compared to the k-ω SST turbulence model.

Numerical Simulations of Flow Around Wall-Mounted Square and Trapezoidal Structures at High Reynolds Numbers

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Martin Andersen ◽  
Guang Yin ◽  
Muk Chen Ong
Keyword(s):  
Turbulence Model ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Freestream Velocity ◽  
High Reynolds Numbers ◽  
Sst Turbulence Model ◽  
Layer Flow ◽  
High Reynolds ◽  
Two Sides ◽  
Good Agreement

Abstract In the present study, flow around symmetric trapezoidal wall-mounted structures with different slope angles of the two sides subjected to a boundary layer flow at Reynolds numbers of 1.19 × 105 and 1 × 106 (based on the height of the structures and the freestream velocity) is investigated using two-dimensional (2D) Reynolds-averaged Navier–Stokes (RANS) equations combined with the k − ω shear stress transport (SST) turbulence model. It is found that the drag coefficient of the wall-mounted square structures using the k − ω SST turbulence model is in good agreement with the available published experimental data. The effects of slope angles of the two sides on the hydrodynamic quantities and the flow fields around the structures have been investigated.

Numerical Prediction of the Hydrodynamic Loads and Vortex-Induced Vibrations of Offshore Structures

2000 ◽  
Vol 122 (4) ◽  
pp. 289-293 ◽  
Author(s):  
Karl W. Schulz ◽  
Yannis Kallinderis
Keyword(s):  
Reynolds Number ◽  
Stokes Flow ◽  
Structural Response ◽  
Reynolds Numbers ◽  
Offshore Structures ◽  
Navier Stokes ◽  
High Reynolds Numbers ◽  
Vortex Induced Vibrations ◽  
Flow Algorithm ◽  
High Reynolds

An incompressible Navier-Stokes flow algorithm is coupled with an elastic body structural response to numerically investigate the hydrodynamics of several relevant offshore applications. These applications include the effects of surface roughness on a bare cylinder and the study of vortex-induced vibrations (VIV) for a cylinder at high Reynolds numbers. The Reynolds number for the roughness cases was Re=4×106, while the Reynolds number for the VIV cases ranged from 2.25×105⩽Re⩽4.75×105. Additional VIV cases were also performed for two common suppression devices: strakes and fairings. The results from both the roughness and bare cylinder VIV applications were compared to experimental data in order to further validate the numerical scheme and illustrate the effectiveness of applying Navier-Stokes technologies to offshore applications. [S0892-7219(00)00604-X]

Hybrid RANS-LES Formulations for Wake Interference Physics in Tandem Cylinders and Multi-Column Floaters

2015 ◽  
Author(s):  
Harish Gopalan ◽  
Peifeng Ma ◽  
Haihua Xu ◽  
Ankit Choudhary ◽  
Anis Hussain ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Hydrodynamic Forces ◽  
Hybrid Models ◽  
Bluff Bodies ◽  
Tandem Cylinders ◽  
High Reynolds Numbers ◽  
Spacing Ratio ◽  
Non Linear ◽  
High Reynolds

Accurate prediction of hydrodynamic forces on tandem bluff bodies at high Reynolds numbers is of interest in many fields of offshore engineering. The most commonly used turbulence modeling strategy for studying these flows is unsteady Reynolds-averaged Navier-Stokes methods (URANS) due to its speed. However, the accuracy of URANS results are problem dependent and usually poor for bluff bodies flow separation predictions. To overcome this deficiency, two different modeling methods have been considered: (i) large eddy simulation (LES) and (ii) non-linear URANS. LES are accurate and computationally feasible for low to moderate Reynolds number flows. However, the cost of LES makes it infeasible at high Reynolds numbers. On the other hand, non-linear URANS methods are fast like URANS, and its accuracy is comparable to LES for certain flows. It is usually not known in advance if the simulations using non-linear methods are accurate. Hybrid models have been proposed in the literature as an alternative to existing methods. They employ a URANS model in the near-body region and LES in the near and far wake regions. Simulations performed using hybrid models are computationally cheaper than LES and more accurate than URANS. Most hybrid models developed in the literature employ linear URANS models. The use of non-linear URANS models in the hybrid context has not received significant attention. In this study, we propose the use of a hybrid model based on a non-linear URANS model. Flow past tandem cylinders, with different spacing ratio, at sub-critical Reynolds number regime, is chosen as the test case. Simulations are also performed using URANS and linear hybrid models for comparison. It is shown that the non-linear hybrid models provides the best agreement to measurement data in the literature. Non-linear URANS models will be shown to provide acceptable prediction of hydrodynamic forces. The models are finally used to predict the current load on a generic multi-column floater.

TRANSONIC CROSS FLOW (M∞ = 0.8) OVER A CIRCULAR CYLINDER AT HIGH REYNOLDS NUMBERS

2012 ◽  
Vol 43 (5) ◽  
pp. 589-613
Author(s):  
Vyacheslav Antonovich Bashkin ◽  
Ivan Vladimirovich Egorov ◽  
Ivan Valeryevich Ezhov ◽  
Sergey Vladimirovich Utyuzhnikov
Keyword(s):  
Circular Cylinder ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
High Reynolds Numbers ◽  
High Reynolds
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