Flexible flapping systems: computational investigations into fluid-structure interactions

2011 ◽  
Vol 115 (1172) ◽  
pp. 593-604 ◽  
Author(s):  
T. Fitzgerald ◽  
M. Valdez ◽  
M. Vanella ◽  
E. Balaras ◽  
B. Balachandran
Keyword(s):  
Stokes Equations ◽  
Fluid Model ◽  
Navier Stokes ◽  
Aerodynamic Load ◽  
Viscous Effects ◽  
Lattice Method ◽  
Predictive Tool ◽  
Computational Approaches ◽  
Vortex Interactions ◽  
Spatio Temporal

AbstractIn the present work, the authors examine two computational approaches that can be used to study flexible flapping systems. For illustration, a fully coupled interaction of a fluid system with a flapping profile performing harmonic flapping kinematics is studied. In one approach, the fluid model is based on the Navier-Stokes equations for viscous incompressible flow, where all spatio-temporal scales are directly resolved by means of Direct Numerical Simulations (DNS). In the other approach, the fluid model is an inviscid, potential flow model, based on the unsteady vortex lattice method (UVLM). In the UVLM model, the focus is on vortex structures and the fluid dynamics is treated as a vortex kinematics problem, whereas with the DNS model, one is able to form a more detailed picture of the flapping physics. The UVLM based approach, although coarse from a modeling standpoint, is computationally inexpensive compared to the DNS based approach. This comparative study is motivated by the hypothesis that flapping related phenomena are primarily determined by vortex interactions and viscous effects play a secondary role, which could mean that a UVLM based approach could be suitable for design purposes and/or used as a predictive tool. In most of the cases studied, the UVLM based approach produces a good approximation. Apart from aerodynamic load comparisons, features of the system dynamics generated by using the two computational approaches are also compared. The authors also discuss limitations of both approaches.

Effects of Non-Dimensional Parameters on Formation and Break Up of Cylindrical Droplets

2004 ◽  
Author(s):  
Mohammad Taeibi-Rahni ◽  
Shervin Sharafatmand
Keyword(s):  
Stokes Equations ◽  
Fluid Model ◽  
Time Dependent ◽  
Navier Stokes ◽  
Ohnesorge Number ◽  
Viscous Effects ◽  
Navier Stokes Equations ◽  
Dimensional Parameters ◽  
Break Up ◽  
Eotvos Number

The consistent behavior of non-dimensional parameters on the formation and break up of large cylindrical droplets has been studied by direct numerical simulations (DNS). A one-fluid model with a finite difference method and an advanced front tracking scheme was employed to solve unsteady, incompressible, viscous, immiscible, multi-fluid, two-dimensional Navier-Stokes equations. This time dependent study allows investigation of evolution of the droplets in different cases. For moderate values of Atwood number (AT), increasing Eotvos number (Eo) explicitly increases the deformation rate in both phenomena. Otherwise, raising the Ohnesorge number (Oh) basically amplifies the viscous effects.

scholarly journals Analysis of a Decoupled Time-Stepping Scheme for Evolutionary Micropolar Fluid Flows

2016 ◽  
Vol 2016 ◽  
pp. 1-13 ◽  
Author(s):  
S. S. Ravindran
Keyword(s):  
Micropolar Fluid ◽  
Stokes Equations ◽  
Fluid Model ◽  
Navier Stokes ◽  
Optimal Order ◽  
Step Size ◽  
Time Step ◽  
Order Error ◽  
Time Step Size ◽  
Time Stepping

Micropolar fluid model consists of Navier-Stokes equations and microrotational velocity equations describing the dynamics of flows in which microstructure of fluid is important. In this paper, we propose and analyze a decoupled time-stepping algorithm for the evolutionary micropolar flow. The proposed method requires solving only one uncoupled Navier-Stokes and one microrotation subphysics problem per time step. We derive optimal order error estimates in suitable norms without assuming any stability condition or time step size restriction.

scholarly journals Choice and Limits of a Fluid Model for the Numerical Study in Dynamic Fluid Structure Interaction Problems

2003 ◽  
Author(s):  
Jean Franc¸ois Sigrist ◽  
Christian Laine ◽  
Dominique Lemoine ◽  
Bernard Peseux
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Fluid Model ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Linear Solution ◽  
Fluid Structure ◽  
Design Engineers ◽  
Inviscid Incompressible Fluid ◽  
Basic Fluid

This paper is related to the study of a nuclear propulsion reactor prototype for the French Navy. This prototype is built on ground and is to be dimensioned toward seismic loading. The dynamic analysis takes the coupled fluid structure analysis into account. The basic fluid models used by design engineers are inviscid incompressible or compressible. The fluid can be described in a bidimensional by slice or a three-dimensional approach. A numerical study is carried out on a generic problem for the linear FSI dynamic problem. The results of this study are presented and discussed. As a conclusion, the three-dimensional inviscid incompressible fluid appears to be the best compromise between the description of physical phenomena and the cost of modeling. The geometry of the reactor is such that large displacements of the structure in the fluid can occur. Therefore, the linearity hypothesis might not be longer valid. The case of large amplitude imposed oscillating motion of a cylinder in a confined fluid is numerically studied. A CFD code is used to investigate the fluid behavior solving the NAVIER-STOKES equations. The forces induced on the cylinder by the fluid are computed and compared to the linear solution. The limit of the linear model can then be exhibited.

Fully Nonlinear Potential/RANSE Simulation of Wave Interaction With Ships and Marine Structures

2008 ◽  
Author(s):  
Pierre Ferrant ◽  
Lionel Gentaz ◽  
Bertrand Alessandrini ◽  
Romain Luquet ◽  
Charles Monroy ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Stokes Equations ◽  
Wave Interaction ◽  
Irregular Waves ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Navier Stokes Equations ◽  
Fully Nonlinear ◽  
Nonlinear Potential ◽  
6 Degrees Of Freedom

This paper documents recent advances of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations) approach, a method for simulating fully nonlinear wave-body interactions including viscous effects. The methods efficiently combines a fully nonlinear potential flow description of undisturbed wave systems with a modified set of RANS with free surface equations accounting for the interaction with a ship or marine structure. Arbitrary incident wave systems may be described, including regular, irregular waves, multidirectional waves, focused wave events, etc. The model may be fixed or moving with arbitrary speed and 6 degrees of freedom motion. The extension of the SWENSE method to 6 DOF simulations in irregular waves as well as to manoeuvring simulations in waves are discussed in this paper. Different illlustative simulations are presented and discussed. Results of the present approach compare favorably with available reference results.

scholarly journals Models for water steam condensing flows

2012 ◽  
Vol 33 (1) ◽  
pp. 67-86
Author(s):  
Włodzimierz Wróblewski ◽  
Sławomir Dykas ◽  
Tadeusz Chmielniak
Keyword(s):  
Stokes Equations ◽  
Fluid Model ◽  
Vapour Phase ◽  
Separate Flow ◽  
Navier Stokes ◽  
Governing Equations ◽  
State Equations ◽  
Water Steam ◽  
Condensing Flows ◽  
Two Fluid Model

Models for water steam condensing flows The paper presents a description of selected models dedicated to steam condensing flow modelling. The models are implemented into an in-house computational fluid dynamics code that has been successfully applied to wet steam flow calculation for many years now. All models use the same condensation model that has been validated against the majority of available experimental data. The state equations for vapour and liquid water, the physical model as well as the numerical techniques of solution to flow governing equations have been presented. For the single-fluid model, the Reynolds-averaged Navier-Stokes equations for vapour/liquid mixture are solved, whereas the two-fluid model solves separate flow governing equations for the compressible, viscous and turbulent vapour phase and for the compressible and inviscid liquid phase. All described models have been compared with relation to the flow through the Laval nozzle.

A Cartesian Explicit Solver for Complex Hydrodynamic Applications

2014 ◽  
Author(s):  
P. Bigay ◽  
A. Bardin ◽  
G. Oger ◽  
D. Le Touzé
Keyword(s):  
Level Set ◽  
Incompressible Flows ◽  
Stokes Equations ◽  
Simulation Method ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Navier Stokes Equations ◽  
Eddy Simulation ◽  
Flow Past A Cylinder ◽  
Explicit Solver

In order to efficiently address complex problems in hydrodynamics, the advances in the development of a new method are presented here. This method aims at finding a good compromise between computational efficiency, accuracy, and easy handling of complex geometries. The chosen method is an Explicit Cartesian Finite Volume method for Hydrodynamics (ECFVH) based on a compressible (hyperbolic) solver, with a ghost-cell method for geometry handling and a Level-set method for the treatment of biphase-flows. The explicit nature of the solver is obtained through a weakly-compressible approach chosen to simulate nearly-incompressible flows. The explicit cell-centered resolution allows for an efficient solving of very large simulations together with a straightforward handling of multi-physics. A characteristic flux method for solving the hyperbolic part of the Navier-Stokes equations is used. The treatment of arbitrary geometries is addressed in the hyperbolic and viscous framework. Viscous effects are computed via a finite difference computation of viscous fluxes and turbulent effects are addressed via a Large-Eddy Simulation method (LES). The Level-Set solver used to handle biphase flows is also presented. The solver is validated on 2-D test cases (flow past a cylinder, 2-D dam break) and future improvements are discussed.

Ship Roll Motion Damping Using Bilge Keels – A Detailed CFD Investigation

2015 ◽  
Author(s):  
Joshua Counsil ◽  
Kevin McTaggart ◽  
Dominic Groulx ◽  
Kiari Boulama
Keyword(s):  
Experimental Studies ◽  
The Body ◽  
Navier Stokes ◽  
Roll Motion ◽  
Empirical Methods ◽  
Viscous Effects ◽  
Vortex Interactions ◽  
Ship Roll ◽  
Semi Empirical ◽  
Bilge Keel

A study has been undertaken to test the value of unsteady Reynolds-averaged Navier-Stokes (URANS) and traditional semi-empirical methods in the face of complex ship roll phenomena, and provide insight into the selection of bilge keel span for varying roll amplitudes. The computational fluid dynamics (CFD) code STAR-CCM+ is employed and two-dimensional submerged bodies undergoing forced roll motion are analyzed. The spatial resolution and timestepping scheme are validated by comparison with published numerical and experimental studies. The model is then applied to a fully-submerged circular cylinder with bilge keels of varying span and undergoing roll motion at varying angular amplitudes. Extracted hydrodynamic coefficients indicate that in general, increasing displacement amplitude and bilge keel span yields increased added mass and increased damping. The relationship is complex and highly dependent upon vortex interactions with each other and the body. The semi-empirical methods used for comparison yield good predictions for simple vortex interactions but fail where viscous effects are strong. Hence, URANS methods are shown to be necessary for friction-dominated flows while semi-empirical methods remain useful for initial design considerations.

Viscosity Effects on the Radiation Hydrodynamics of Horizontal Cylinders

1991 ◽  
Vol 113 (4) ◽  
pp. 334-343 ◽  
Author(s):  
R. W. Yeung ◽  
C.-F. Wu
Keyword(s):  
Numerical Solutions ◽  
Stokes Equations ◽  
Small Body ◽  
Low Frequency ◽  
Body Motion ◽  
Navier Stokes ◽  
Inviscid Fluid ◽  
Viscous Effects ◽  
Navier Stokes Equations ◽  
Horizontal Cylinders

The problem of a body oscillating in a viscous fluid with a free surface is examined. The Navier-Stokes equations and boundary conditions are linearized using the assumption of small body-motion to wavelength ratio. Generation and diffusion of vorticity, but not its convection, are accounted for. Rotational and irrotational Green functions for a divergent and a vorticity source are presented, with the effects of viscosity represented by a frequency Reynolds number Rσ = g2/νσ3. Numerical solutions for a pair of coupled integral equations are obtained for flows about a submerged cylinder, circular or square. Viscosity-modified added-mass and damping coefficients are developed as functions of frequency. It is found that as Rσ approaches infinity, inviscid-fluid results can be recovered. However, viscous effects are important in the low-frequency range, particularly when Rσ is smaller than O(104).

Influence of Rotor Blade Fillets on Aerodynamic Performance of Turbine Stage

2010 ◽  
Author(s):  
Yan Shi ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Secondary Flow ◽  
Rotor Blade ◽  
Stokes Equations ◽  
Leading Edge ◽  
Navier Stokes ◽  
Aerodynamic Load ◽  
Main Stream ◽  
Shape Parameters ◽  
Turbine Stage ◽  
A Minor

In this paper, steady and unsteady flow simulations were performed to investigate the influence of rotor fillet on the performance of turbine stage, based on 3D compressible Navier-Stokes equations closed with the Spalart-Allmaras turbulence model. The profile of Aachen turbine was employed and the fillet modeled by two shape parameters was placed at the junctions between the rotor blade and the endwalls (at both tip and hub). Based on the comparisons of the efficiency and the flow rate of turbine stage among the cases with different fillet shapes, the roles of two shape parameters were evaluated. To understand the mechanism of the rotor fillet influence on the flow field, the aerodynamic load, secondary flow and loss were analyzed and compared between the cases with and without the rotor fillet. It is found that the fillet is capable of restraining the flow separation near the leading edge of the rotor blade while inducing the displacement of the flow from the endwalls towards the mid-span, which enhances the loss generated by the interaction between the secondary flow and the main stream. Consequently, associated with the distribution of the loss at the outlet of the turbine stage, the best clocking position near the endwalls for the downstream blade moves about 10%∼20% of rotor pitch in the direction of rotor rotation. Therefore, the shape of the fillet in the rotor blade should be especially controlled in the process of the rotor design and manufacture, even though it is a minor part in the turbomachine.

Sound generation by shock–vortex interactions

1999 ◽  
Vol 380 ◽  
pp. 81-116 ◽  
Author(s):  
OSAMU INOUE ◽  
YUJI HATTORI
Keyword(s):  
Shock Wave ◽  
Stokes Equations ◽  
Early Stage ◽  
Near Field ◽  
Time Integration ◽  
Flow Fields ◽  
Navier Stokes ◽  
Single Vortex ◽  
Vortex Interactions ◽  
Reflected Shock

Two-dimensional, unsteady, compressible flow fields produced by the interactions between a single vortex or a pair of vortices and a shock wave are simulated numerically. The Navier–Stokes equations are solved by a finite difference method. The sixth-order-accurate compact Padé scheme is used for spatial derivatives, together with the fourth-order-accurate Runge–Kutta scheme for time integration. The detailed mechanics of the flow fields at an early stage of the interactions and the basic nature of the near-field sound generated by the interactions are studied. The results for both a single vortex and a pair of vortices suggest that the generation and the nature of sounds are closely related to the generation of reflected shock waves. The flow field differs significantly when the pair of vortices moves in the same direction as the shock wave than when opposite to it.

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