Research in Mechanical Engineering

FLOW-STRUCTURE INTERACTION

Staff Involved: A.D. Lucey

Project Description(s):

Excitation of waves on a flexible wall in a fluid flow

Perhaps the simplest problem that could be envisaged in flow-structure interaction is that of a flat elastic plate undergoing small amplitude oscillatory line-excitation in the presence of a uniform flow. In the last decade this system has been shown to evince remarkably complex wave responses; both convective and absolute instabilities can be found as can negative- and positive-energy waves while energy fluxes may be conventional or anomalous. In the latter, wave energy flows towards the driver. Thus, over a range of excitation frequencies, the line-driver actually absorbs energy. Work is currently being conducted using numerical simulation to study systems of finite length for which wave reflection is an important feature and using other types of flexible boundary. Further work has begun to tackle nonlinear aspects of the problem and that of flexible panels with spatially varying stiffness. Collaboration on theoretical aspects of these problems exists with researchers at Manchester and Cambridge Universities in the U.K. and at I.I.T Delhi in India.

For a recent review of this subject area see: Lucey & Peake 2002, "Wave excitation on flexible walls in the presence of a mean flow", IUTAM: Flow through collapsible tubes and past other highly compliant boundaries. Springer-Verlag, Chapter 6.

Drag-reduction using compliant coatings

A mature research programme in collaboration with Warwick and Cardiff Universities has demonstrated that compliant (typically comprising rubber-like materials) coatings are capable of attenuating Tollmien-Schlichting waves in the linear phase of laminar-to-turbulent boundary later transition, thereby postponing transition and yielding skin-friction drag reduction for marine vehicles. In fact, it has recently been shown that the possibility of indefinite postponement exists. Work here at Curtin concentrates on the modelling of hydroelastic instabilities in such flow-structure systems. These 'wall instabilities' need to be designed out of any practicable compliant coating. Our computational techniques involve vortex-element, boundary-element and finite-difference methods to create fully coupled wall-flow simulations. Further to their benefit in the laminar region of the boundary layer, it has been shown experimentally that compliant-coatings are able to reduce turbulent skin-friction. Numerical simulation offers a means to understand this interaction.

For a recent review of this subject area see: Carpenter, P.W., Davies, C. & LUCEY, A.D. 2000. Hydrodynamics and complaint walls: Does the dolphin have a secret? Current Science 79(3), pp. 758-765.

Nonlinear deformation of fabric surfaces

Research is currently being conducted on the interaction of the fabric roof of a convertible car with the wind-loads associated with the car's forward speed. A key feature of the problem is nonlinearity in the tension induced in the fabric as it is deformed by the airflow. In turn, the boundary conditions of the flow field are dependent upon the deformed geometry of the fabric. In this work a commercial finite-volume CFD code is being used, coupled to an in-house structural solver. A simpler in-house modified inviscid flow-solver has also been used as an alternative to running the computationally expensive CFD at each step of the flow-structure iteration. The techniques developed in this work have general applicability; for example, they could be used in sail design.

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