Computational analysis of fluid-structure interactions (FSI) represents a considerable challenge for most computational analysis codes. Simple one-way coupled problems, in which the fluid pressure deforms a structure but does not substantially affect the fluid flow characteristics, can be solved by a variety of techniques. Solutions to the more complex two-way coupled fluid-structure interactions are more elusive. These occur when pressure of the flow of fluid deforms a structure in such a way that the resulting deformation alters the flow of fluid. The two-way coupled approach solves this problem and produces accurate, time-dependent results.

Through the use of COMSOL Multiphysics, Advanced Computational and Engineering Services (ACES) has developed practical solutions to "realworld" FSI problems across a wide range of applications in the biomedical, automotive, and petrochemical industries. Examples of FSI problems in these industries include blood flow through flexible systems, characteristic acoustic signatures of valve components, structural vibration due to intermittent transient flow through compressors, and control of fluid cavitation in a flowing medium.

Figure 1. Flexible Valve in Flow of Gaseous Fluid forced at a variable pressure. Blue lines are streamlines of velocity field; black lines are pressure contours (in dB).
The multiphysics software has been used to develop a specialized multiphysics model describing closure of a valve from a transient pressure pulse. The flow of fluid results in vibration of the valve and associated generation of noise — all of which can be predicted using the multiphysics program.

The FSI solution couples the continuum equations of solid mechanics with the Navier-Stokes equations of fluid mechanics. The software solves these equations simultaneously over the same computational domain using an Arbitrary Lagrangian-Eulerian formulation (ALE). The moving mesh capabilities in the ALE formulation of the software allow a stable solution with increasing the amounts of valve deformation.

Solutions of this type can quantify the influence of "key design variables" of the system. For example, the operating stress experienced by the valve, stream lines of the fluid flow, and acoustic sound pressure levels of the operating valve (see figure). Additional results of specific interest to valve designers include the contact force on the valve at closure and the vibration response of the valve during operation.

The results of fully coupled FSI analyses have allowed ACES to resolve performance issues with new products prior to mass production, significantly reducing the time and cost of new product development and manufacture.

This work was performed by Dr. S.P. Yushanov, Dr. J.S. Crompton, Dr. J.R. Dydo, and Dr. K.C. Koppenhoefer of ACES using COMSOL Multiphysics. For more information, click here.