Small and micro unmanned aircraft are the focus of scientific interest due to their wide range of applications.They often operate in a highly unstable flight environment where the application of new morphing wing tech...Small and micro unmanned aircraft are the focus of scientific interest due to their wide range of applications.They often operate in a highly unstable flight environment where the application of new morphing wing technologies offers the opportunity to improve flight characteristics.The investigated concept comprises port and starboard adjustable wings,and an adaptive elastoflexible membrane serves as the lifting surface.The focus is on the benefits of the deforming membrane during the impact of a one-minus-cosine type gust.At a low Reynolds number of Re=264000,the morphing wing model is investigated numerically by unsteady fluid-structure interaction simulations.First,the numerical results are validated by experimental data from force and moment,flow field,and deformation measurements.Second,with the rigid wing as the baseline,the flexible case is investigated,focusing on the advantages of the elastic membrane.For all configurations studied,the maximum amplitude of the lift coefficient under gust load shows good agreement between the experimental and numerical results.During the decay of the gust,they differ more the higher the aspect ratio of the wing.When considering the flow field,the main differences are due to the separation behavior on the upper side of the wing.The flow reattaches earlier in the experiments than in the simulations,which explains the higher lift values observed in the former.Only at one intermediate configuration does the lift amplitude of the rigid configuration exceeds that of the flexible by about 12%,with the elastic membrane resulting in a smaller and more uniform peak load,which is also evident in the wing loading and hence in the root bending moment.展开更多
Herein, the dynamics and flow fields of an inverted flag are studied using hydrogen bubble flow visualization and particle image velocimetry technologies at different height-to-length ratios and flow velocities in a w...Herein, the dynamics and flow fields of an inverted flag are studied using hydrogen bubble flow visualization and particle image velocimetry technologies at different height-to-length ratios and flow velocities in a water tunnel. Results show that the heightto-length ratio of the inverted flag at which the critical flow velocity remains nearly constant is approximately 1.4. Moreover, a nonperiodic flapping phenomenon is observed under various height-to-length ratios. This phenomenon may be attributed to the existence of multiple equilibrium solutions to the self-excited vibration system, thus engendering chaos in the system comprising an inverted flag and surrounding fluid. Other indications that the system has entered chaos include multiple frequencies, nonoverlapping phase diagram, and positive Lyapunov exponent. Further discussion of the flow fields around the inverted flag reveals that the large-amplitude oscillation is due to the flow separation, while the flapping instability is a static divergence instability. In the large flapping mode, the starting leading-edge vortex(LEV) is wrapped by Kelvin-Helmholtz instabilities,which are arranged at almost uniform spacing along a circular path. In addition, the variation in position, circulation, and radius of the starting LEV are discussed in detail.展开更多
The morphing wing concept aims to constantly adapt the aerodynamics to different flight stages.The wing is able to adapt to different flight conditions by an adjustable Aspect Ratio(AR)and sweep.A high AR configuratio...The morphing wing concept aims to constantly adapt the aerodynamics to different flight stages.The wing is able to adapt to different flight conditions by an adjustable Aspect Ratio(AR)and sweep.A high AR configuration provides high aerodynamic efficiency,while a low AR configuration,with highly swept wings offers a good maneuverability.Additionally,the flexible membrane allows the wing surface to stretch and contract in-plane as well as the airfoil to adapt to different aerodynamic loads.In the context of this work,the aerodynamic characteristics of a full model with form-adaptive elasto-flexible membrane wings are investigated experimentally.The focus is on the high-lift regime and on the analysis of the aerodynamic coefficients as well as their sensitivities.Especially,the lateral aerodynamic derivatives at asymmetric wing positions are of interest.展开更多
基金funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)(No.BR 1511/12-1)。
文摘Small and micro unmanned aircraft are the focus of scientific interest due to their wide range of applications.They often operate in a highly unstable flight environment where the application of new morphing wing technologies offers the opportunity to improve flight characteristics.The investigated concept comprises port and starboard adjustable wings,and an adaptive elastoflexible membrane serves as the lifting surface.The focus is on the benefits of the deforming membrane during the impact of a one-minus-cosine type gust.At a low Reynolds number of Re=264000,the morphing wing model is investigated numerically by unsteady fluid-structure interaction simulations.First,the numerical results are validated by experimental data from force and moment,flow field,and deformation measurements.Second,with the rigid wing as the baseline,the flexible case is investigated,focusing on the advantages of the elastic membrane.For all configurations studied,the maximum amplitude of the lift coefficient under gust load shows good agreement between the experimental and numerical results.During the decay of the gust,they differ more the higher the aspect ratio of the wing.When considering the flow field,the main differences are due to the separation behavior on the upper side of the wing.The flow reattaches earlier in the experiments than in the simulations,which explains the higher lift values observed in the former.Only at one intermediate configuration does the lift amplitude of the rigid configuration exceeds that of the flexible by about 12%,with the elastic membrane resulting in a smaller and more uniform peak load,which is also evident in the wing loading and hence in the root bending moment.
基金supported by the National Natural Science Foundation of China(Grant Nos.11721202,and 11761131009)
文摘Herein, the dynamics and flow fields of an inverted flag are studied using hydrogen bubble flow visualization and particle image velocimetry technologies at different height-to-length ratios and flow velocities in a water tunnel. Results show that the heightto-length ratio of the inverted flag at which the critical flow velocity remains nearly constant is approximately 1.4. Moreover, a nonperiodic flapping phenomenon is observed under various height-to-length ratios. This phenomenon may be attributed to the existence of multiple equilibrium solutions to the self-excited vibration system, thus engendering chaos in the system comprising an inverted flag and surrounding fluid. Other indications that the system has entered chaos include multiple frequencies, nonoverlapping phase diagram, and positive Lyapunov exponent. Further discussion of the flow fields around the inverted flag reveals that the large-amplitude oscillation is due to the flow separation, while the flapping instability is a static divergence instability. In the large flapping mode, the starting leading-edge vortex(LEV) is wrapped by Kelvin-Helmholtz instabilities,which are arranged at almost uniform spacing along a circular path. In addition, the variation in position, circulation, and radius of the starting LEV are discussed in detail.
基金The research project is funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)–BR 1511/12-1.Furthermore,the authors thank the team from the Xi’an Jiaotong University for the invitation and the organization of the Smart Aircraft 2019 Conference.
文摘The morphing wing concept aims to constantly adapt the aerodynamics to different flight stages.The wing is able to adapt to different flight conditions by an adjustable Aspect Ratio(AR)and sweep.A high AR configuration provides high aerodynamic efficiency,while a low AR configuration,with highly swept wings offers a good maneuverability.Additionally,the flexible membrane allows the wing surface to stretch and contract in-plane as well as the airfoil to adapt to different aerodynamic loads.In the context of this work,the aerodynamic characteristics of a full model with form-adaptive elasto-flexible membrane wings are investigated experimentally.The focus is on the high-lift regime and on the analysis of the aerodynamic coefficients as well as their sensitivities.Especially,the lateral aerodynamic derivatives at asymmetric wing positions are of interest.
