Adaptive Bump Research Articles

Research on flexible skin technique for adaptive bump inlet structure

PurposeAdaptive bump inlet can adaptively change the shape of inlet bump surface according to the flight speed of aircraft, ensuring that the inlet has good inlet-engine match performance in a wide speed range. This paper aims to use a composite flexible skin reinforced by shape memory alloy (SMA) fiber as the deformable structure at bump surface to realize the adjustable bump surface of adaptive bump inlet.Design/methodology/approachAccording to the deformation and load-bearing requirements of adaptive bump, SMA is applied to the design of adaptive bump inlet due to its characteristic of super-elasticity. A kind of SMA fiber is studied. A composite flexible skin reinforced by SMA is proposed, and its mechanical properties are analyzed. On this basis, an adaptive bump inlet is designed in which the composite flexible skin reinforced by SMA is used as bump surface, and the shape of the bump surface is adjusted by way of pressuring. The design scheme and specific parameters of the adaptive bump are given.FindingsAn adaptive bump surface that meets the design requirements of the inlet is designed, which can effectively adjust the inlet throat area with a throat area change rate of 20%.Originality/valueAn adaptive bump inlet with composite flexible skin as a deformable structure at bump surface is designed, and SMA is applied as the reinforcing fiber.

Off-design performance of 2D adaptive shock control bumps

Adaptive shock control bumps can exploit the on-design drag-reducing potential of 2D bumps, while mitigating their off-design performance deterioration through geometric modifications. In this study, experiments and simulations have been employed to investigate the wave-drag reducing potential of (actuated and unconstrained) 2D adaptive shock control bumps over a wide range of shock positions. Experiments were carried out in the Imperial College supersonic wind tunnel, modelling the adaptive bump as a flexible surface placed beneath a Mach 1.4 shock wave. 2D RANS CFD simulations of the flow in a parallel channel with a solid bump complement experiments. Wave drag was demonstrated to be proportional to the ratio of inlet to exit stagnation pressure in a blow-down wind tunnel for a given shock position. The shock exhibits a hysteretic behaviour when travelling in the wind tunnel working section, governed by the wave drag reducing potential of the bump. The actuated adaptive bump tested reduces wave drag over a wider operational envelope than solid bumps as experiments revealed the presence of three preferred structural configurations, which lead to a significantly enlarged hysteresis region. Finally, tests on unconstrained bumps were shown to increase wave drag, both on- and off-design, due to the unfavourable bump shapes that result from (only) passive actuation, suggesting that some constraints are required to achieve desirable surface deformations.

Optimisation of adaptive shock control bumps with structural constraints

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 surface-pressure-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 shock-region 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.

Adaptive Control of Shock Waves with a Passively Morphing Layer for Rotating Blades

Helicopter blades are known to experience complicated unsteady flow conditions during high-speed forward flight. Transonic shock takes place along the advancing side, which decreases the performance of the blades and results in impulsive noise. Adaptive airfoils seem promising for increasing performance at considerably variable flow conditions. In this paper, a blade with a passively morphing layer is presented for transonic shock/boundary layer control at forward flight conditions. The morphing layer embedded in the upper surface of the blade can form an adaptive bump, which in turn can control transonic shock/boundary layer interaction. A fluid-structure-interaction (FSI) enabled simulator is employed to study the performance of the morphing layer at two different forward conditions. The results demonstrate that the adaptive bump formed by the morphing layer could efficiently weaken the strong normal shock over the layer by producing a λ-structural shock. Moreover, the morphing layer retreats to its undeformed state to prevent detrimental effects at weaker shock or shock-free flow. To further increase the performance of the morphing layer, a morphing layer that is inclined with respect to the spanwise direction is used to replace the layer that lies parallel to the spanwise direction. The results indicate that the inclined morphing layer performs better while the shock position takes on a less uniform distribution.

Aeroelastic Optimization of Adaptive Bumps for Yaw Control

This paper captures the aeroelastic behavior of adaptable bumps on morphing wings using trained neural networks. Parameters of the bump such as the height, size, location, and shape play a major aerodynamic and structural role. Though other issues such as wave drag minimization, boundary layer control are discussed, the primary problem addressed here is the generation of the lateral directional moment. The shape of the bump is optimized so that it produces maximum yaw moment with a minimum actuation energy spent in creating the adaptive bump. The analysis of fluid separation on the airfoil surface due to various types of bumps and its effects on the aerodynamic forces is performed using the computational fluid dynamics (CFD) software FLUENT TM . This analysis is performed at a low speed of Mach 0.3 and at a transonic speed of Mach 0.7. Structural analysis is performed using the finite element software ANSYS TM using a nonlinear beam model of the bump. In order to perform an aeroelastic analysis, the softwares FLUENT and ANSYS have to be interconnected so that the changing aerodynamic pressure with bump deformation is reflected in the structural analysis. Direct coupling of two such numerical codes, one based on CFD and the other based on finite element modeling (FEM), is computationally expensive. Hence, artificial neural networks are trained from these aerodynamic and structural analysis. Two neural networks are trained, one for the aerodynamic pressure and the other for the structural loads and strain energy. These two neural networks serve as an efficient decoupler, that facilitates an aeroelastic optimization procedure to evaluate the best bump shape for maximum drag for providing micro-yaw control while using the minimum actuation energy and minimizing the loss in the lift.

Shock control on a swept wing

Shock and boundary layer control by contour bumps and local boundary layer suction have been investigated experimentally and numerically on a transonic swept wing. Additional 2-D numerical investigations were performed for the airfoil, corresponding to the wing. The investigations were primarily stimulated by the question concerned with the influence of sweep on the bump effectiveness. This influence has been found to be rather small; the drag reduction by the bump is slightly lower for the swept wing than for the airfoil. A location of the bump in the shock region has shown its effectiveness for reducing shock strength and hence wave drag. A position of the bump downstream of the shock wave has been shown to reduce viscous drag and to postpone buffet-onset to higher lift coefficients. Furthermore, the results indicate that boundary layer suction is a powerful device for drag reduction, but the effectiveness decreases with increasing Reynolds number. Higher effectiveness of suction can be attained, when it is coupled with a contour bump. The parameters height and position (relative to the shock) of the bump, optimized in terms of drag, depend on the shock strength; an influence of the boundary layer thickness upstream of the shock on the optimal bump parameters has not been found. A possibility to control an adaptive bump, mounted on an aircraft wing, is to employ the trailing edge pressure.