Interaction Between IL and CF VIV: On the Importance of Orbital Direction

2017 ◽  
Author(s):  
K. H. Aronsen ◽  
Z. Y. Huang ◽  
K. B. Skaugset ◽  
C. M. Larsen
Keyword(s):  
Vortex Shedding ◽  
Particle Image ◽  
Hydrodynamic Force ◽  
Three Dimensional ◽  
Higher Harmonics ◽  
Eddy Simulation ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Vortex Shedding Modes ◽  
Good Agreement

This paper discusses results from an experiment where forces on a rigid cylinder are measured during prescribed oscillations both in-line with and transverse to a constant flow. Two “figure of eight” oscillation patterns with identical shape but opposite orbital direction, relative to the flow, have been tested at a Reynolds number of 24000. Results show that the hydrodynamic force acting on the cylinder is significantly different for the two orbital directions. The force in phase with velocity, which represents the energy transfer between the fluid and the cylinder, has opposite sign and different magnitude for the two orbital directions. Flow visualization by particle image velocimetry (PIV) reveals that the two orbits leads to different vortex shedding modes. Hydrodynamic forces at multiples of the oscillation frequency, known as higher harmonics, are seen for both orbital directions. Comparison with pure in-line and pure transverse oscillations indicates that the higher harmonics are related to oscillations in in-line direction. A three-dimensional Large Eddy Simulation numerical simulation with equivalent experiment parameters has been conducted. It is very encouraging to see a good agreement between numerical results and observations with respect to global forces, vortex shedding modes and hydrodynamic co-efficients.

Investigation of the Flow Around Two Interacting Ship-Like Sections

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Tufan Arslan ◽  
Bjørnar Pettersen ◽  
Helge I. Andersson
Keyword(s):  
Vortex Shedding ◽  
Particle Image ◽  
Three Dimensional ◽  
Cross Flow ◽  
Eddy Simulation ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Close Proximity ◽  
Computational Fluid Dynamics Cfd ◽  
Cross Current

This paper reports calculations of three-dimensional (3D) unsteady cross flow over two ship sections in close proximity and compares the results with measurements. The ship sections have different breadth and draft conditions which represent typical situations in a ship-to-ship marine operation in a cross current. The behavior of the vortex-shedding around the two different ship hull sections is investigated numerically by computational fluid dynamics (CFD) methods. For the two sections, simulations are done for Reynolds number Re = 68,000, Froude number Fr = 0.25, and Re = 6800, Fr = 0.025 by using the dynamic Smagorinsky large eddy simulation (LES) turbulence model. The simulations are performed by using the software ansysfluent and the numerical results are compared with particle image velocimetry (PIV) results taken from the literature. The hydrodynamic forces acting on the two ship sections are predicted by numerical simulations and interaction effects between the two ships are evaluated.

Large Eddy Simulation (LES) and Time-Resolved Particle Image Velocimetry (TR-PIV) in the Wake of a Cavitating Hydrofoil

2005 ◽  
Author(s):  
Martin Wosnik ◽  
Qiao Qin ◽  
Damien T. Kawakami ◽  
Roger E. A. Arndt
Keyword(s):  
Particle Image Velocimetry ◽  
Large Eddy Simulation ◽  
High Speed ◽  
Particle Image ◽  
Three Dimensional ◽  
Pair Type ◽  
Time Resolved ◽  
Eddy Simulation ◽  
Image Velocimetry ◽  
Large Eddy

A Large Eddy Simulation (LES) approach for cavitating flow, based on a virtual single-phase, fully compressible cavitation model which includes the effects of incondensable gas, has been shown to be capable of capturing the complex dynamical features of highly unsteady cavitating flows of two-dimensional hydrofoils. Here the LES results are compared to Time-Resolved Particle Image Velocimetry (TR-PIV) in the wake of a cavitating NACA 0015 hydrofoil, with particular attention to the predicted vortex shedding mechanisms. Despite some difficulty with obtaining vector fields from vortical clouds of vaporous-gaseous bubbles with cross-correlation techniques, the initial results seem promising in that they confirm the existence of a primary vortex pair (type A-B). In addition to TR-PIV, the cavitation cloud shedding was also documented with phase-locked, time-resolved photography and high speed volume-illuminated video, both with simultaneous imaging of side and plan views of the foil. All three experimental techniques confirm the need for fully three-dimensional simulations to properly describe the unsteady, three-dimensional cavitation cloud shedding mechanism.

Wake-Airfoil Interaction as Broadband Noise Source: A Large-Eddy Simulation Study

2005 ◽  
Vol 4 (1-2) ◽  
pp. 93-115 ◽  
Author(s):  
Jérôme Boudet ◽  
Nathalie Grosjean ◽  
Marc C. Jacob
Keyword(s):  
Large Eddy Simulation ◽  
Particle Image ◽  
Broadband Noise ◽  
Far Field ◽  
Acoustic Analogy ◽  
Eddy Simulation ◽  
Naca0012 Airfoil ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Proper Orthogonal

A large-eddy simulation is carried out on a rod-airfoil configuration and compared to an accompanying experiment as well as to a RANS computation. A NACA0012 airfoil (chord c = 0.1 m) is located one chord downstream of a circular rod (diameter d = c/10, Red = 48 000). The computed interaction of the resulting sub-critical vortex street with the airfoil is assessed using averaged quantities, aerodynamic spectra and proper orthogonal decomposition (POD) of the instantaneous flow fields. Snapshots of the flow field are compared to particle image velocimetry (PIV) data. The acoustic far field is predicted using the Ffowcs Williams & Hawkings acoustic analogy, and compared to the experimental far field spectra. The large-eddy simulation is shown to accurately represent the deterministic pattern of the vortex shedding that is described by POD modes 1 & 2 and the resulting tonal noise also compares favourably to measurements. Furthermore higher order POD modes that are found in the PIV data are well predicted by the computation. The broadband content of the aerodynamic and the acoustic fields is consequently well predicted over a large range of frequencies ([0 kHz; 10 kHz]).

A Method of Measuring Turbulent Flow Structures With Particle Image Velocimetry and Incorporating Into Boundary Conditions of Large Eddy Simulations

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Puxuan Li ◽  
Steve J. Eckels ◽  
Garrett W. Mann ◽  
Ning Zhang
Keyword(s):  
Particle Image Velocimetry ◽  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Particle Image ◽  
Advantages And Disadvantages ◽  
Eddy Simulation ◽  
Piv Measurement ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Inlet Conditions

The setup of inlet conditions for a large eddy simulation (LES) is a complex and important problem. Normally, there are two methods to generate the inlet conditions for LES, i.e., synthesized turbulence methods and precursor simulation methods. This study presents a new method for determining inlet boundary conditions of LES using particle image velocimetry (PIV). LES shows sensitivity to inlet boundary conditions in the developing region, and this effect can even extend into the fully developed region of the flow. Two kinds of boundary conditions generated from PIV data, i.e., steady spatial distributed inlet (SSDI) and unsteady spatial distributed inlet (USDI), are studied. PIV provides valuable field measurement, but special care is needed to estimate turbulent kinetic energy and turbulent dissipation rate for SSDI. Correlation coefficients are used to analyze the autocorrelation of the PIV data. Different boundary conditions have different influences on LES, and their advantages and disadvantages for turbulence prediction and static pressure prediction are discussed in the paper. Two kinds of LES with different subgrid turbulence models are evaluated: namely dynamic Smagorinsky–Lilly model (Lilly model) and wall modeled large eddy simulation (WMLES model). The performances of these models for flow prediction in a square duct are presented. Furthermore, the LES results are compared with PIV measurement results and Reynolds-stress model (RSM) results at a downstream location for validation.

scholarly journals ICCM2015: A Comparison of RANS and LES Computational Methods in Analyzing Ventilation Flow Through a Room Fitted with a Two-Sided Windcatcher

2017 ◽  
Vol 14 (03) ◽  
pp. 1750021 ◽  
Author(s):  
A. Niktash ◽  
B. P. Huynh
Keyword(s):  
Natural Ventilation ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Interior Space ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
Cfd Method ◽  
Good Agreement

A windcatcher is a structure for providing natural ventilation using wind power; it is usually fitted on the roof of a building to exhaust the inside stale air to the outside and supplies the outside fresh air into the building interior space working by pressure difference between outside and inside of the building. In this paper, the behavior of free wind flow through a three-dimensional room fitted with a centered position two-canal bottom shape windcatcher model is investigated numerically, using a commercial computational fluid dynamics (CFD) software package and LES (Large Eddy Simulation) CFD method. The results have been compared with the obtained results for the same model but using RANS (Reynolds Averaged Navier–Stokes) CFD method. The model with its surrounded space has been considered in both method. It is found that the achieved results for the model from LES method are in good agreement with RANS method’s results for the same model.

NUMERICAL ANALYSIS OF BULK DRAG COEFFICIENT IN DENSE VEGETATION BY IMMERSED BOUNDARY METHOD

2011 ◽  
Vol 1 (32) ◽  
pp. 48 ◽  
Author(s):  
Tomohiro Suzuki ◽  
Taro Arikawa
Keyword(s):  
Drag Coefficient ◽  
Immersed Boundary Method ◽  
Three Dimensional ◽  
Vertical Cylinder ◽  
Immersed Boundary ◽  
Dense Vegetation ◽  
Eddy Simulation ◽  
Boundary Method ◽  
Large Eddy ◽  
Good Agreement

In this paper, bulk drag coefficient in rigid dense vegetation is investigated mainly by using a three dimensional numerical simulation model CADMAS-SURF/3D by incorporating Immersed Boundary Method to calculate flow around the vertical cylinder in the Cartesian grid. Large Eddy Simulation is also incorporated as a turbulence model. Firstly, validation of the developed model is conducted with a single cylinder in the flow field based on literature. All the results obtained here (Re=300, 3,900 and 8,000) show good agreement with the reference data in literature. After the validation, multiple cylinders are allotted in three different densities (S/D=2.8, 2.0, 1.4) in a numerical wave tank and numerical simulations are conducted to investigate bulk drag coefficient. The result shows that the ratio of bulk drag coefficient to drag coefficient, which represents a reduction, is not just a function of density but a function of parameter 2a/S, in which 2a is stroke of the motion and S is cylinder distance. 2a is less than S, the effect of the density is neglected because the wake does not reach the other cylinders even when the density is high. On the contrary, it might affect the ratio of bulk drag coefficient to drag coefficient when the stroke of the motion is larger than the cylinder distance even when the density is low. In general, the ratio of bulk drag coefficient to drag coefficient decreases when 2a/S increases.

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