Fluid-structure-interaction of adaptive shock control bumps

Abstract

Improving aircraft aerodynamic efficiency is key to achieve the desired performance enhancements, in the light of ambitious environmental targets. Flow control measures are required to mitigate the detrimental effects of normal shock waves, which occur on the wings of modern commercial aircraft and generate wave drag. A review of the relevant literature has identified the potential of Shock Control Bumps (SCBs) for reducing overall drag, although only for a narrow operating envelope. Recent work has shown that, through geometric modifications, adaptive SCBs could be effective over a wider range of flow conditions. However, further research is required to fully assess their aero-structural behaviour.

In the present study, an investigation of the Fluid-Structure-Interaction of adaptive SCBs has been conducted to characterise their unsteady behaviour and assess their potential for reducing drag. The adaptive SCB was modelled as a thin aluminium alloy flexible plate, deployed by means of different actuation mechanisms, and was tested at Mach 1.4 in the Imperial College supersonic wind tunnel for a range of flow conditions. Point-tracking photogrammetry and Pressure Sensitive Paint (PSP) were successfully applied to the challenging setup of a deforming flexible surface in transonic flow, to obtain reliable full-field deformation and surface pressure measurements during experiments. The accuracy of these techniques and their sensitivity to testing conditions have been estimated.

RANS CFD simulations of the flow above a rigid SCB, performed in OpenFOAM, complement experiments. Computed stagnation pressure profiles downstream of the rigid SCB aided the development of a methodology to evaluate the drag reduction potential of adaptive SCBs from experiments in a blow-down supersonic wind tunnel. In addition, stability of the shock travelling in the wind tunnel working section was shown to be related to the drag generated by the bump for various flow conditions.

The performance of two- and three-dimensional adaptive SCBs has been assessed and compared with the baseline case of a solid flat plate. Carefully designed adaptive SCBs were found to successfully bifurcate the strong normal shock that is expected on next generation transonic wings, and, through passive geometric modifications, maintain good properties over a range of flow conditions. This study has showed the promising potential of adaptive SCBs for mitigating the off-design performance penalty typical of rigid SCBs, without compromising the on-design drag saving capabilities. Some recommendations for further work are suggested.