This paper focuses on the effect of the phase offset of Leading-Edge(LE)morphing on the aerodynamic characteristics of a pitching NACA0012 airfoil.Assuming an unstretched camber and using polynomial interpolation,an explicit expression for LE nonlinear morphing is proposed and implemented for the large pitching motion of the airfoil.Flow field results and aerodynamic forces are obtained by solving the unsteady Reynolds-averaged Navier-Stokes equations for both the airfoil’s pitching motion and LE morphing.Furthermore,the index of instantaneous aerodynamic power is used to quantify the work done by the airflow in a dynamic process.According to the instantaneous aerodynamic power and energy map,which denotes the energy transfer between the airfoil’s oscillation and flow field,the airfoil is subject to stall flutter.The results show that LE morphing with an optimal phase offset of 315°reduces the energy extraction from the flow field,suppressing the stall flutter instability.This optimal phase offset is effective at different pitching axis positions of the airfoil.The results signify that LE morphing can suppress stall flutter by advancing the occurrence of the first LE vortex and increasing the nose-down moment during the upstroke period.
Climate warming and the increased demand in air travels motivate the aviation industry to urgently produce technological innovations.One of the most promising innovations is based on the smoothly continuous morphing leading-edge concept.This study proposes a two-step process for the design of a morphing leading-edge,including the optimization of the outer variable-thickness composite compliant skin and the optimization of the inner kinematic mechanism.For the compliant skin design,an optimization of the variable thickness composite skin is proposed based on a laminate continuity model,with laminate continuity constraint and other manufacturing constraints.The laminate continuity model utilizes a guiding sequence and a ply-drop sequence to describe the overall stacking sequence of plies in different thickness regions of the complaint skin.For the inner kinematic mechanism design,a coupled four-bar linkage system is proposed and optimized to produce specific trajectories at the actuation points on the stringer hats of the compliant skin,which ensures that the compliant skin can be deflected into the aerodynamically optimal profile.Finally,a morphing leading-edge is manufactured and tested.Experimental results are compared with numerical predictions,confirming the feasibility of the morphing leading-edge concept and the overall proposed design approach.
Corner stall receives noticeable attention in the aeroengine field as an important phenomenon in highly-load compressors.Non-uniform leading-edge tubercles,as an effective method to delay stall,are introduced into the compressor.In this paper,the shape of leading-edge tubercles was controlled by a third-order Fourier function.To judge corner stall,a more precise stall indicator for compressor cascade with flow control methods was defined.Besides,the total kinetic energy of the secondary flow at large incidence was adopted as a parameter for stall evaluation to save computing resources.The results of multiobjective optimization reveal that the loss coefficient exhibited negligible variation at design incidence,while the total kinetic energy of secondary flow showed a significant reduction at large incidence,resulting in a substantial increase in stall incidence.In the optimal profiling cases,the stall incidencewas delayed from 7.9°to 11.6°.The major purpose of the research is to provide proper design guidelines for nonuniformleading-edge tubercles and uncover the flow controlmechanisms of leading-edge profiling.Hence,the geometric features that meet different optimization objectives were extracted through geometric analysis near the Pareto Front and through Self-OrganizingMap(SOM)dataminingmethods in the optimization database.Besides,flow field analysis reveals the flow control mechanism of leading-edge tubercles.The convex-concave-convex structure at the 0%-70%blade height region can form two branches of leading-edge vortex pairs that are opposite in the rotation direction to the passage vortex.The two branches of leading-edge vortex pairs mixed with the leading-edge separation vortex to form two stronger mixed vortices,which can effectively suppress the development of passage vortex and delay stall incidence.