CFD-HA

Fluid Structure Interaction 

v  v Introduction

Fluid Structure Interaction is multi-physics, nonlinear and a multidisciplinary problem where solid structures interact with an internal or surrounding fluid flow.

Fluid Structure Interaction problems occur when a fluid interacts with a solid structure, exerting pressure on it which may cause deformation in the structure and in return,the deformed structure alters the flow field.The altered flow in turn exert a different kinds of force on the structure in a repeat of the process.

Fig NO:-1 Model Highlighting Elastic Deformation

v  Need of FSI:

Fluid Structure Interactions may be stable or oscillatory and is a crucial concept in medical and engineering aspects. Failing to consider which the consequence may be catastrophic.

General Fluid Structure Interaction problems deal with the flow of fluid in a pipe ( a blood vessel)or the flow of fluid over an aeroplane wing (ships rudder)

v Classification of fluid-structure interactions

Weakly coupled FSI system:

If the structure deforms or vibrates slightly in the flow field or due to the flow of fluid, the impact on the flow field is negligible because  the pressure is relatively low at low amplitudes. This FSI system is known as a weakly coupled system. For these fluid-structural interaction systems, it is assumed that the forces acting on the fluid through structural motion can be linearly superimposed on the original functional drive in the fluid..

Fig NO:-2 Weak One-Way Coupling

 Strongly coupled fluid-structural interaction system:

These fluid structural systems are called strongly coupled systems when large deformations, changes in the flow field due to large amplitudes, and vibrations of the structure  are not negligible. In such a tightly coupled fluid structural system, where large structural deformations or displacements cause large changes in the original flow field, both the changed flow field and the original flow field cannot be linearly superimposed.

  Fig NO:-3 Strong Two-Way Coupling

v TYPES OF FSI:-

There are three types of fluid-structure interactions.

1. Zero strain interactions: Such as the transport of suspended  solids in a liquid matrix.

2. Constant strain steady flow interactions: The constant force exerted on an oil-pipeline due to viscous friction between the pipeline walls and the fluid.

3. Oscillatory interactions: Where the strain induced in the solid structure causes it to move such that the source of strain is reduced, and the structure returns to its former state only for the process to repeat.

v Example of FSI:-

Check valves are simple, two-port valves in which fluid flows in one direction and out the other with no back-flow. A ball check valve is a type of check valve in which a ball is used within the valve to stop the back flow. The tiny spigots for liquid and gel dispensers, such as for hand sanitiser, also operate as ball check valves.

Ball check valves vary in design and use. For some variations, the ball is unattached in the valve, while for others the ball is aided by a spring mechanism. 

       Fig NO:-4 Ball check valve 

Using a Fluid-Solid Interaction multi physics interface, the behaviour of a spring-loaded ball check valve is studied under varying functional and reverse flow. The fluid force acting on the ball opens the valve at the opening pressure. In the case of a reversed pressure, the ball comes into contact with an O-ring, thus preventing the fluid from flowing in the reverse direction. A re-meshing technique is used to accurately resolve the fluid domain between the parts getting into contact.

v ADVANTAGES:-

Practical uses fluid film interaction.

I. FSI is responsible for countless useful effects in engineering

II. It allows fans and propellers to function.

III. Sails on marine vehicles to provide thrust.

IV. Aerofoil’s on racecars to produce down force.

Written by,

SHUBHAM K. NEWARE

Vishwakarma Institute of Technology, Pune 

v REFERENCES:-

1. Numerical Simulation of 3-D One-Way Fluid-Structure Interaction in a Tube with Twisted Tape under Laminar and Turbulent Flow Regime Laith J. Habeeb1 , Fouad A. Saleh2 , Bassim M. Maajel2

2. Fluid-structure interactions of internal pressure pipeline using the hierarchical finite element method Fakiri Hicham1 , Hadjoui Abdelhamid2 and O. Nabil Mohammed3

3. https://en.wikipedia.org/wiki/Fluid%E2%80%93structure_interaction

4. https://www.comsol.com/model/ball-check-valve-        69401.

5. https://www.flow3d.com/modeling-capabilities/fluid-structure-interaction/