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VortexCell2050
Fundamentals of Actively Controlled Flows with Trapped Vortices

Background

Trapping vortices is a technology used for preventing vortex shedding in flows past bluff bodies. Vortices forming near bluff bodies tend to be shed downstream. If the vortex is kept near the body at all times, it is ‘trapped’. Vortices can be trapped in special cavities in the airfoil, called vortex cells but so far, trapped vortices have been stabilised only by passive means (EKIP aircraft, Russia). Active control consists of linking sensors and actuators via a control system to stabilise the flow. Active flow control has been implemented for flows past bodies of simple shape.

Project objectives

To ensure a high lift-to-drag ratio, aircraft wings are thin and streamlined. From a structural-strength viewpoint, a thick wing would be more beneficial. With an increase in aircraft size, the balance between structural-strength and aerodynamic quality shifts in favour of a thick wing. The flow past a thick airfoil, however, is likely to separate, affecting aerodynamic qualities of the wing. The present project aims to resolve this problem by combining two advanced technologies: trapped vortices and active control. The specific objectives of the project are:

  • to develop a software tool for designing a flow past a thick airfoil with a trapped vortex, assuming that this flow is stable, apart from small-scale turbulence
  • to develop a methodology and software tools for designing a system of stabilisation of such a flow
  • to design and estimate the performance of an airfoil with a trapped vortex and a stabilisation system for the high-altitude, long endurance unmanned aircraft.
Vortex shedding in separated flow on the upper surface of a thick airfoil.
Vortex shedding in separated flow on the upper surface of a thick airfoil.

Description of the work

In the first of the three stages of the project, necessary numerical and experimental tools will be developed:

  • a specialised experimental facility for the study of cyclic boundary layers, characteristic of flows with trapped vortices
  • a wind-tunnel test-bed consisting of an airfoil with an interchangeable wall section with a vortex cell
  • a discrete vortex method code as the means of testing control algorithms
  • RANS code for general calculations
  • LES code for studying more complicated 3D effects on simple test cases
  • a vortex cell shape inverse design code incorporating a cyclic boundary layer code, and an inviscid cell design code based on various inviscid flow models.

In the second stage, these tools will be used to develop and test a vortex cell for the test-bed airfoil with a system of active control. The obtained results will be used for enhancing the tools developed during the first stage of research. The differences between the intrinsic two-dimensional nature of some of the numerical tools and real three-dimensional flows will be explored, and the limitations of two-dimensional approaches will be identified. At the third stage, an attempt will be made to design a trapped-vortex airfoil for a specific practical application, namely for a high-altitude, long endurance, unmanned aircraft. Depending on the results obtained in the second stage of the research, the airfoil will be equipped with active or passive means of flow control. The wing will be manufactured and tested in a wind tunnel.

Expected results

The project will ensure a significant advance in trapped vortex technology. In the case of complete success of the VortexCell2050 project, the main outcome will be a new technological platform: an actively controlled trapped vortex technology.

Thick airfoil with a trapped vortex. VortexCell 2050 investigates this flow control concept, which may well lead to the design of thick-winged aircraft.
Thick airfoil with a trapped vortex. VortexCell 2050 investigates this flow control concept, which may well lead to the design of thick-winged aircraft.

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