Ivan Wang

Aeroelastic Model of Multisegmented Folding Wings: Theory and Experiment

Morphing-wing research has garnered much attention in the aerospace community over the last decade, and the folding wing is a promising concept that can improve aircraft performance over multiple types of missions. Several high-fidelity analyses of folding-wing aeroelastic stability have been published, but most analyses are specifi ct o certain wing planforms or a fixed number of wing segments. This paper presents a general aeroelastic model that predicts the flutter speed and flutter frequency of a folding wing with simplified geometry but with an arbitrary numberof wingsegments. Thebeam-theory structuralmodelandthe strip-theoryunsteadyaerodynamic modelare coupled using Lagrange’s equations. Three experimental models are constructed, and flutter tests are performed over a wide range of fold angles. The theoretical predictions for flutter speeds are within 10% of experimentally measured values for most configurations. In general, the results show that the essential physics of the problem is captured by the present first-principles model. Furthermore, data show that increasing the fold angle causes up to 30% increase in flutter speed, which has applications in extending the flutter boundaries of morphing aircraft.

Structural Dynamics Model of Multisegmented Folding Wings: Theory and Experiment

Morphing wing research has garnered much attention in the aerospace community over the last decade, and the folding wing is a promising concept that can improve aircraft performance over multiple types of missions. Several high-fidelity analyses of folding wing structural dynamics have been published, but most analyses are specifi ct o certain wing planforms or a fixed number of wing segments. This paper presents a general structural dynamics modelthatpredictsthenaturalfrequencies ofafoldingwingwithsimplifiedgeometry butwithanarbitrary number of wing segments. The model is derived using beam theory and component modal analysis: the energy expressions and constraint equations are derived from kinematics, and the equations of motion are derived using Lagrange’s equations with Lagrange multipliers. Three experimental models are constructed, and the natural frequencies are measured over a wide range of fold angles. The agreement between theory and experiment is within 10% for most data points. The results agree well with trends from existing work, and the model can be used to study the structural dynamics behavior of folding wings as well as similar multibody systems.

Stability of Rectangular Plates in Subsonic Flow with Various Boundary Conditions

The aeroelastic stability of rectangular plates in subsonic flow is well documented in literature. For example, the stability of a cantilever plate with a clamped edge parallel to the flow is well understood due to the similarity of this system to an aircraft wing. However, an ongoing push for lighter aerospace structures and novel designs requires advancing the understanding of the aeroelastic stability of plates with nonconventional boundary condition combinations. This paper summarizes the aeroelastic theory and experimental results on the flutter and/or divergence mechanisms of a rectangular plate with different sets of structural boundary conditions. The theory combines a linear plate structural model with a three-dimensional vortex lattice aerodynamic mode to create a high-fidelity frequency domain aeroelastic model. The paper also discusses the development of a modular experimental test bed to test the different boundary conditions. A pair of well-understood boundary condition configurations acts a...

Aeroelastic Behavior of Noise-Reducing Membranes for Aircraft Lifting Surfaces Part I: Theory

xed, trailing edge free. This paper presents a theoretical study of the aeroelastic behavior of elastic plates with this boundary condition. Specically the paper discusses a vortex lattice aerodynamic model coupled with a classical plate/membrane model. The model is used to predict the linear utter boundary and utter characteristics of the panel while the support structure size, streamwise length, and normal direction tension are varied. The stability boundary is determined to be relatively insensitive to the support structure size, but varies non-simply with both the streamwise chord and the tension in the normal direction. Additionally the results are compared to previous aeroelastic simulations which suggested a higher mode utter which is not encountered in the current simulations. Experimental validation of the structural and aeroelastic models is presented in the companion paper.

Flutter of Rectangular Plates in Three Dimensional Incompressible Flow With Various Boundary Conditions: Theory and Experiment

The aeroelastic stability of rectangular plates are well-documented in literature for certain sets of boundary conditions. Specifically, wing flutter, panel flutter, and divergence of a plate that is clamped on all sides are well-understood. However, the ongoing push for lighter structures and novel designs have led to a need to understand the aeroelastic behavior of elastic plates for other boundary conditions. One example is NASA’s continuous mold-line link project for reducing the noise generated by commercial transport aircraft during landing; in order to reduce the noise generated by vortex shedding from the trailing edge flap during landing, the project proposes to connect the gap between the trailing edge flap and the rest of the wing with a flexible plate. This paper summarizes the aeroelastic theory, numerical results, and experimental results of a study on the flutter and/or divergence mechanisms of a rectangular plate for different sets of structural boundary conditions. The theory combines a three-dimensional vortex lattice aerodynamic model with a plate structural model to create a high-fidelity frequency domain aeroelastic model. A modular experimental test bed is designed for this study in order to test the different boundary conditions. The test bed is also designed to test different plate thicknesses and sizes with only a small number of modifications. The well-understood boundary conditions are used as test cases to validate the analysis results, and then results of additional configurations that have not been extensively explored are presented. The results of this paper can be used to support the design efforts of projects involving plates or plate-membranes. In addition, the paper adds to the fundamental understanding of plate aeroelasticity and provides a wealth of experimental data for comparison and future validation.Copyright

A Structural Dynamics Model of a Multi-Segmented Folding Wing: Theory and Experiment

This paper presents a general structural dynamics model based on beam theory that predicts the natural frequencies of a folding wing with an arbitrary number of wing segments. The structural model is derived from a modal analysis using work-energy principles - the energy expressions and constraint equations are derived from a kinematics analysis, and the equations of motion are derived using Lagrange’s equations with Lagrange multipliers. The theoretical results are compared to experimental data for three dierent congurations: a 2-segment model, a 3-segment model, and a 4-segment model. The theoretical model accurately predicts the general behavior of natural frequencies versus fold angle for all three congurations, and the computed values are within 10% of the measured values for the majority of the modes.

Aeroelastic Analysis of a Folding Wing: Comparison of Simple and Higher Fidelity Models for a Wide Range of Fold Angles

The goal of folding wing research is to enable wing shape changes during flight in order to optimize aircraft performance over a multitude of mission segments. However, the additional mechanisms needed to implement the morphing capability tends to increase the weight, reduce the stiffness in comparison, and make it more susceptible to aeroelastic effects. In addition, the drastic geometric changes in itself affect the dynamics and aeroelastic behavior of the wing. This paper explores the effect of large geometric changes on the natural frequencies and modes, and subsequent effects on the flutter onset. The structural dynamics analysis compares beam theory results versus ANSYS finite element results, and the aeroelastic analysis compares results from using Theodorsen unsteady strip theory versus those obtained using unsteady vortex lattice method. This paper shows that the flutter onset of folding wings can be predicted using simplified beam dynamics and strip theory aerodynamics, as well as ANSYS structural analysis coupled with unsteady vortex lattice aerodynamics. However, when natural frequencies begin to migrate due to large changes in geometry, special care needs to be taken when studying the aeroelastic behavior.

Microscale ethanol vapor ejector and injector

Two non-rotating pumping components, a jet ejector and injector, were designed and tested. Two jet ejectors were designed and tested to induce a suction draft using a supersonic micronozzle. Three-dimensional axisymmetric nozzles were microfabricated to produce throat diameters of 187 μm and 733 μm with design expansion ratios near 2.5:1. The motive nozzles achieved design mass flow efficiencies above 95% compared to isentropic calculations. Ethanol vapor was used to motivate and entrain ambient air. Experimental data indicate that the ejector can produce a sufficient suction draft to satisfy both microengine mass flow and power off-take requirements to enable its substitution for high speed microscale pumping turbomachinery. An ethanol vapor driven injector component was designed and tested to pressurize feed liquid ethanol. The injector was supplied with 2.70 atmosphere ethanol vapor and pumped liquid ethanol up to a total pressure of 3.02 atmospheres. Dynamic pressure at the exit of the injector was computed by measuring the displacement of a cantilevered beam placed over the outlet stream. The injector employed a three-dimensional axisymmetric nozzle with a throat diameter of 733 μm and a three-dimensional converging axisymmetric nozzle. The experimental data indicate that the injector can pump feed liquid into a pressurized boiler, enabling small scale liquid pumping without any moving parts. Microscale injectors could enable microscale engines and rockets to satisfy pumping and feedheating requirements without high speed microscale turbomachinery.

Experimental investigation and modeling of scale effects in jet ejectors

Three microscale jet ejectors were designed and tested to induce a suction draft using a supersonic micronozzle. Each axisymmetric nozzle was fabricated using three-dimensional electro-discharge machining to create throat diameters of 64, 187 and 733 µm with design expansion ratios of 2.5:1 and design ejector area ratios of 8. The experimental data using nitrogen gas for the motive fluid indicate that the ejector can produce a sufficient suction draft to enable its substitution for high-speed turbomachinery in micro engine applications. A pumping power density of 308 kW L−1 is observed experimentally, which agrees well with a theoretical model including losses associated with the suction flow inlet and viscous effects in the motive nozzle and mixing regions. The present theoretical model further predicts a maximum achievable power density of 1 MW L−1 for microscale ejectors with a throat diameter of 10 µm and throat Reynolds number of 1300.