Boundary stabilization of fluid flows

The latest developments in complex sensing and actuation systems for fluid flow applications coupled with the availability of high-performance embedded computational platforms, which can deliver over a hundred-gigaflop performance rates, has made it feasible to develop advanced boundary control systems for fluid flow applications.

There are a number of strategic technology areas where rigorous boundary control approaches for fluid flow can lead to dramatic improvements in performance. Modern civil engineering structures have reduced mass and stiffness making them prone to wind and ocean-wave induced oscillations. The conventional approach to vibration control is to increase structural damping by using additional mass dampers. An alternative, more effective approach would be to prevent the build-up of the forces that are responsible for the vibrations by using moving-surface boundary-layer or blowing/suction actuation to prevent the formation of vortices (vortex shedding) and reduce the drag.

The reduction of drag generated by near-wall turbulence is also a major issue for aircrafts and underwater vehicles as it represents about 50% of the total drag exerted on these vehicles. The formation of laminar separation bubbles around an aerofoil can be avoided to some extent by the use of vortex generators upstream of the separation. This approach however is not guaranteed to work under a wide range of operating conditions and generally leads to weight and costs increases. Active control approaches that use synthetic jets, acoustic excitation, micro-electro-mechanical systems (MEMS) or work by dynamically deforming the airfoil leading edge to prevent fluid phenomena such as flow separation and turbulence could bring substantial benefits in a wide range of applications related to aircrafts, engines, munitions and maritime vehicle systems. The benefits include enhanced performance, manoeuvrability, payload and range, as well as lowered overall cost. This technology alone could lead to huge reductions in human-related transportation emissions of CO2 across the globe. Given the grave climate change implications of increasing CO2 emissions and the dwindling oil reserves, the development, testing and implementation of such technologies should be amongst the top research priorities for the next decade.

The boundary control strategies developed so far can be divided into purely theoretical approaches, which are very difficult if not impossible to implement in practice, and practical but heuristic approaches that, to some extent, have been validated computationally or experimentally but are not guaranteed to work over a wide range of operating conditions and have significant performance limitations. Although experimental work has shown that, in principle, the boundary control approach works, a fully integrated turbulence control system is yet to be developed.

The project focuses on the development of theoretical and practical boundary control strategies for fluid flows using arrays of spatially localized sensors and actuators. The proposed control strategies will be evaluated using CFD simulations which will be performed on Sheffield’s high-performance computer cluster.