Adaptive shock control bumps (SCB) aim to retain the performance of static SCV and improve off-design performance caused by variations in shock position due to flowfield unsteadiness and changes in aircraft cruise conditions. An adaptive SCB requires the flexibility to deform and the stiffness to withstand the complex pressure field that is present on the upper surface of a transonic aircraft wing. This study uses a quasi-steady aerostructural solver to design adaptive SCB. Both flexible and actuated plates have been tested in a Mach 1.4 blowdown wind tunnel. The shock structure has been captured over both plates (t = 0.4mm) using high speed Schlieren Imaging. Experimental results show that the flexible and actuated plates both have a stabilising effect on the shock, reducing the amplitude of unsteady shock motion from 30 mm to 20 mm and 10 mm respectively. In addition, the actuated plate enabled the shock's mean stream wise position to be varied by up to 26 mm for an actuator displacement of just 3 mm. The shock holding characteristics were attributed to how changes in surface curvature caused by the cavity pressure and actuation affected the external flow structure and shock structure. The cavity pressure beneath a flexible plate is shown to be a significant design variable with the plate geometry moving from a depression to a protrusion with just 0.1 bar variation.
This paper presents the results from a study to design an adaptive shock control bump for a transonic aerofoil. An optimisation framework comprising aerodynamic and structural computational tools has been used to assess the performance of candidate adaptive bump geometries based on a novel surfacepressure-based performance metric. The geometry of the resultant design is a unique feature of its adaptivity; being strongly influenced by the (passive) aerodynamic pressure forces on the flexible surface as well as the (active) displacement constraints. This optimal geometry bifurcates the shock-wave and carefully manages the recovering post-shock flow to maximise pressure-smearing in the shockregion with only a small penalty in L/D for the aerofoil. Short adaptive bumps (with small imposed displacements) generally perform better than taller ones, and maintain their performance advantage for a wide range of bump positions, suggesting good robustness to variations in shock position, which are an inevitable feature of a real-world flight application. Such devices may offer advantages over conventional (fixed geometry) shock control bumps, where optimal performance is achieved with taller devices, at the expense of poor robustness to variations in shock position.
Aeroelastic phenomena of stall flutter are the result of the negative aerodynamic damping associated with separated flow. From this basis, an investigation has been conducted to estimate the aerodynamic damping from a time-marching aeroelastic computation. An initial investigation is conducted on the NACA 0012 aerofoil section, before transition to 3D propellers and full aeroelastic calculations. Estimates of aerodynamic damping are presented, with a comparison made between URANS and SAS. Use of a suitable turbulence closure to allow for shedding of flow structures during stall is seen as critical in predicting negative damping estimations. From this investigation, it has been found that the SAS method is able to capture this for both the aerofoil and 3D test cases.
This paper describes a numerical investigation into the optimal design of adaptive shock control bumps (SCB) for transonic wings. A multi-disciplinary approach to optimization is utilized, combining structural and aerodynamic analysis to ensure that optimal adaptive SCB do not exceed material constraints whilst maintaining aerodynamic qualities. It is found that adaptive SCB can perform to within 95% of the non-structurally constrained bumps but over a much wider flight envelope. Two dimensional single crest bumps have been shown to match the performance of table top bumps originating from three dimensional SCB. Total pressure recovery has been successfully used as a performance metric and will provide valuable comparisons to wind tunnel experiments with a prototype adaptive SCB.
Shock control bumps (SCB) are a transonic flow control device that aim to reduce the overall drag due to a normal shock on a typical passenger jet at cruise. The concept of adaptive SCB which can be deployed for best use are investigated through an aero-structural design tool that produces optimal geometries. The optimizer uses a surface based performance metric to highlight the importance of the flow quality around the SCB as well as including a structural element that is required to provide the necessary flexibility to deform. The performance metric produces the target pressure distribution and successfully smears the shock. It is found that the structural constraint does not inhibit bump height and global airfoil performance is not significantly a↵ected, L/D varies < 0.6%. The aerodynamic pressure loading can be utilised to produce a new family of SCB geometries that are unachievable with mechanical actuation alone. The study shows that adaptive SCB that exploit the naturally occurring pressure field around an airfoil in a passive way are a feasible technology to mitigate the poor o↵-design performance of static SCB.
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