Numerical simulation of separated flow over flexible structural membranes

  • Lisa Ann Matthews

Student thesis: Doctoral ThesisPhD


This thesis describes the design of a computational Fluid-Structure Interaction algorithm for the analysis of unsteady flow of an incompressible fluid around a flexible structural membrane. An example of such a system is the interaction of a lightweight fabric building structure with the surrounding wind. These structures are highly flexible and have the potential to display aeroelastic instabilities and undergo deformations which are large compared to the membrane thickness. A numerical computational method capable of investigating this complex behaviour is developed in this work.

A boundary fitted unstructured triangular fluid mesh is used; the fully viscous Navier–Stokes equations are discretised on the moving mesh using a collocated Finite Volume method, with the SIMPLE algorithm for pressure solution. Mesh non-orthogonalities and geometric conservation are appropriately addressed. A dynamic structure approach is taken, tracking the unsteady membrane motions over time and using nodal velocities as the degrees of freedom. A new distributed elasticity model is implemented for the calculation of internal forces to improve stability. The motion of internal fluid mesh nodes is determined following a pseudo-structural approach, taking into account elastic spring forces in the mesh edges and nodal forces due to distortion of the mesh elements driven by the displacements of the fluid–structure boundary.

The method is shown to be applicable to simulations on moving meshes, and successfully predicts formation and separation of fluid boundary layers from the structure surface. Two coupled unsteady fluid-membrane structure interaction investigations are carried out; flow over an elastic membrane pinned at both ends and flow over an elastic membrane with one free end. The results highlight significant unsteady interactions between the membrane and the flow, which it is only possible to model with a coupled aeroelastic approach. Suggestions for further work, including the simple extension of the method to three dimensions, are described.

Date of Award28 Nov 2007
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorChris Williams (Supervisor) & D Greaves (Supervisor)

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