Tip Store Research Articles

Preliminary investigation on experimental modal analysis of high aspect ratio rectangular wing model

Procedure of conducting an experimental modal analysis (EMA) of roving hammer test for high aspect ratio (HAR) wing containing geometric nonlinearities is presented along with consideration of various tip store sizes. Two sets of test setups of vertical and horizontal arrangements have been considered, which respectively demonstrates the undeformed and deformed cases. Modal properties in terms of natural frequency and mode shape were experimentally measured using the LMS Test.Lab package and the results were then compared between the undeformed and its corresponding deformed configuration. From the finding, it confirms that the chordwise and torsional modes of the undeformed configurations has respectively turned into chordwise-torsion and torsion-chordwise modes as they are in deformed configuration. Meanwhile, the impact related to bending modes is insignificant. Hence, this may result in inaccurate prediction if conventional aeroelastic solution is employed for HAR wing configuration. Â

Safe Flutter Tests Using Parametric Flutter Margins

The recently developed numerical parametric flutter margin method is applied to perform safe flutter tests in which the flutter-onset conditions of a nominal configuration are positively identified, while the system is stabilized by an added concentrated mass. A known excitation force is applied to the added mass, and the collocated normal acceleration response is measured. Fourier transforms of the two signals are used for calculating flutter margins that change sign at flutter-onset conditions of the nominal system. The stability of the modified model at these conditions facilitates safe, flutter-free, testing conditions with a robustly measured response. The method is applied in wind-tunnel flutter tests of a clamped wing with a tip store, to which a stabilizing mass is added at a forward location. The added mass is connected through a thin cord and a pulley to a weight outside the tunnel. The excitation is performed by cutting the cord, and the mass acceleration is extrapolated from other accelerometers on the wing. The process is repeated at several airspeeds to compute frequency response functions and pinpoint the flutter-onset velocity of the nominal system. The resulting flutter boundaries are within a few percent of those measured by direct-flutter tests.

Quantification of dimethylsulfoniopropionate (DMSP) in Acropora spp. of reef-building coral using mass spectrometry with deuterated internal standard.

Dimethylsulfoniopropionate (DMSP) in scleractinian coral is usually analysed indirectly as dimethylsulfide (DMS) using gas chromatography (GC) with a sulfur-specific detector. We developed a headspace GC method for mass spectral analysis of DMSP in branching coral where hexa-deuterated DMSP (d 6 -DMSP) was added to samples and standards to optimise the analytical precision and quantitative accuracy. Using this indirect HS-GC-MS method, we show that common coral sample handling techniques did not alter DMSP concentrations in Acropora aspera and that endogenous DMS was insignificant compared to the store of DMSP in A. aspera. Field application of the indirect HS-GC-MS method in all seasons over a 5-year period at Heron Island in the southern Great Barrier Reef indicated that healthy colonies of A. aspera ordinarily seasonally conserve their branch tip store of DMSP; however, this store increased to a higher concentration under extended thermal stress conditions driven by a strong El Niño Southern Oscillation event. A liquid chromatography mass spectral method (LC-MS) was subsequently developed for direct analysis of DMSP in branching coral, also utilising the d 6 -DMSP internal standard. The quantitative comparison of DMSP in four species of Acropora coral by indirect HS-GC-MS and direct LC-MS analyses gave equivalent concentrations in A. aspera only; in the other three species, HS-GC-MS gave consistently higher concentrations, indicating that indirect analysis of DMSP may lead to artificially high values for some coral species. Graphical Abstract Dimethylsulfoniopropionate (DMSP) was quantified in Acropora spp. of branching coral using deuterated stable isotope dilution mass spectrometry.

Nonlinear Aeroelastic Formulation and Postflutter Analysis of Flexible High-Aspect-Ratio Wings

The nonlinear aeroelastic modeling and the post-flutter behavior of high-altitude long-endurance wings are discussed. A parametric structural model of wings based on an exact kinematic approach is formulated and coupled with an incompressible unsteady aerodynamic model that is obtained via an indicial formulation accounting for viscous effects, including dynamic stall and flow separation. To this end, a modified Beddoes-Leishman model is employed, and the equations of motion, together with the equations governing the aerodynamic states, are obtained via a total Lagrangian formulation. The critical and post-critical dynamic aeroelastic response is evaluated, and the limit cycles occurring in the post-flutter condition past the Hopf bifurcation are studied. Together, with comparisons from the available data of an experimental wing model with tip store, the effects of the unsteady loads and dynamic stall are evaluated and compared with predictions obtained from a model using a classical quasi-steady aerodynamic formulation. Aeroelastic simulations are concurrently performed within a finite element solution platform. Space and time integrations are conducted using a numerical scheme that directly discretizes the partial differential equations, which are associated with the equations of motion of the flexible wing, and the ordinary differential equations, which are associated with the added lag-state formulation pertinent to the unsteady aerodynamic loads, in a hybrid solution form. The aim is the study of the aeroelastic behavior of these highly nonlinear wings for an improved understanding of the nonlinear phenomena occurring particularly in the neighborhood of the flutter boundary and in the post-critical regime when the unsteady aerodynamic effects and dynamic stall contribute more significantly to the wing dynamic behavior.

Resonant Frequency Determination of a Multistore High-Altitude/Long-Endurance Wing

It is desirable to predict the resonant frequencies and mode shapes of extremely high-aspect ratio wings for high-altitude/long-endurance applications. Such results give insight into structural response and serve as a precursor to flutter and gust response calculations. The influence of rigid body modes has been shown to be significant for the aeroelastic response of these aircraft, but this effect is frequently not captured in a laboratory setting. Additionally, resonant frequencies can be difficult to predict when multiple discrete masses such as engines or mission pods are distributed along the span. In this work, the resonant frequencies of a high-altitude/long-endurance wing mounted on a spring of variable stiffness with both root and tip stores are determined analytically from classical beam theory. The model is then extended through a component-mode synthesis to incorporate multiple spanwise masses of any discrete distribution. Computational results are compared with an experiment, and good agreement is shown.

Transport Wing Flutter Model Transonic Limit Cycle Oscillation Test

The model for aeroelastic validation research involving computation semispan wind-tunnel model, a transport wing-fuselage flutter model, was tested in NASA Langley's Transonic Dynamics Tunnel with the goal of obtaining experimental limit cycle oscillation behavior data at transonic separation onset conditions. This research model is notable for its inexpensive construction and instrumentation installation procedures. Unsteady pressures and wing responses were obtained for three wing-tip configurations: clean, tip store, and winglet. Traditional flutter boundaries were measured over the range of M = 0.6-0.9, and maps of limit cycle oscillation behavior were made in the range of M = 0.85-0.95. The effects of dynamic pressure and angle of attack were measured. Testing in both R134a heavy gas and air provided unique data on the Reynolds number, transition effects, and the effect of speed of sound on limit cycle oscillation behavior. This report gives an overview of the test results, including experimental flutter boundaries, and the conditions involving shock-induced transonic flow separation onset at low wing angles, including maps of limit cycle oscillation behavior.

Comparison of Theoretical Structural Models with Experiment for a High-Aspect-Ratio Aeroelastic Wing

M ATERIALS of various densities and stiffnesses typically constitute the experimental slender wing structures designed for flutter and limit cycle oscillation experiments of high-altitude long-endurance (HALE) aircraft. Recent research performed atDuke University includes a study inter alia of the effects of structural nonuniformity on the natural frequencies and mode shapes of very flexible beams, which are frequently used in geometrically nonlinear structural analyses of HALE wings [1–5]. Jaworski and Dowell [6] demonstrated that such beamlike structures with spanwise discontinuities could be represented modally as a uniform beam for sufficiently small spanwise discontinuities. However, determining the set of natural frequencies requires knowledge of any such discontinuities or variations. This work addresses the effects of these nonuniformities on the four lowest natural frequencies of a cantilevered HALE-type wing. Here, the experimental wing model used by Tang and Dowell [2–4] is analyzed using the commercial finite element program ANSYS. As shown in Fig. 1, the HALE wing is composed of a steel spar with multiple steps, periodically-spaced aluminum ribs, balsa wood fairings to fill the space between ribs, and a tip store. Specifically, the effects examined herein are the step depth for the particular step distribution used by Tang and Dowell [2–4]; the addition of periodically-spaced ribs; the presence of balsa wood fairings with varying levels of rigid connection to the central spar; and the addition of a tip store.

Computational Aeroelastic Analysis of Store-Induced Limit-Cycle Oscillation

Limit-cycle oscillation was simulated for a rectangular wing referred to as the Goland + wing. It was found that the aerodynamic nonlinearity responsible for limit-cycle oscillation in the Goland + wing was shock motion and the periodic appearance/disappearance of shocks. The Goland + structural model was such that in the transonic flutter dip region, the primary bending and twisting modes were in phase and coupled to produce a single-degree-of-freedom, torsional flutter mode about a point located ahead of the leading edge of the wing. It was determined that the combination of strong trailing-edge and lambda shocks which periodically appear/disappear, limited the energy flow into the structure. This mechanism quenched the growth of the flutter, resulting in a steady limit-cycle oscillation. Underwing and tip stores were added to the Goland + wing to determine how they affected limit-cycle oscillation. It was found that the aerodynamic forces on the store transferred additional energy into the structure increasing the amplitude of the limit-cycle oscillation. However, it was also found that the underwing store interfered with the airflow on the bottom of the wing, which limited the amplitude of the limit-cycle oscillation.

Parametric Studies of Transonic Aeroelastic Effects of an Aircraft Wing/Tip Store

This research investigates the effect of store parameters variation on store-induced flutter and limit-cycle oscillation phenomena of an aircraft wing in the transonic regime. The primary store parameters were its mass and the chordwise location of its center of gravity. The effect of including store aerodynamics on the wing/tip store configuration was also investigated. The tip store center of gravity (c.g.) was varied and positioned at three different locations: 32.5, 40, and 50%, with respect to aerodynamic tip chord. Automated Structural Optimization System and Computational Aeroelasticity Program‐Transonic Small Disturbance were used in the linear and nonlinear region to perform this research. Studies showed that flutter speed increases as the store c.g. was moved forward toward the leading edge. This gives an indication that store c.g. must be placed as far forward as possible with respect to the elastic axis to delay the occurrence of flutter, while satisfying other design constraints. It was observed that the increase in tip store mass significantly reduced the flight operating speed range of the aircraft. The effect of inclusion of store aerodynamics for different wing/store configurations was found to be insignificant compared to their corresponding mass-only models in the transonic regime. The limit-cycle oscillation (LCO) onset speed was found to be sensitive to both store mass and store c.g. parameters and varied significantly for different store mass configurations. The LCO onset speed decreased significantly with increase in store mass and aft movement of store c.g.

Numerical Analysis of Store-Induced Limit-Cycle Oscillation

Store-induced limit-cycle oscillation of a rectangular wing with tip store in transonic flow is simulated using a variety of mathematical models for the flowfield: transonic small-disturbance theory (with and without inclusion of store aerodynamics) and transonic small-disturbance theory with interactive boundary layer (without inclusion of store aerodynamics). For the conditions investigated, assuming inviscid flow, limit-cycle oscillations are observed to occur as a result of a weakly subcritical Hopf bifurcation and are obtained at speeds lower than those predicted 1) nonlinearly for clean-wing flutter and 2) linearly for wing/store flutter. The ability of transonic small-disturbance theory to predict the occurrence and strength of this type of limit-cycle oscillation is compared for the different models. Differences in unmatched and matched aeroelastic analysis are described. Solutions computed for the clean rectangular wing are compared to those computed with the Euler equations for a case of static aeroelastic behavior and for a case of forced, rigid-wing oscillation at Mach 0.92.

Optimal Dynamic Response Control of Adaptive Thin-Walled Cantilevers Carrying Heavy Stores and Exposed to Blast Pulses

The optimal dynamic response control of adaptive thin-walled beam cantilevers carrying externally mounted stores and exposed to blast pulses is investigated. The structure under consideration is modeled as a thin-walled beam of closed cross-section contour, encompassing a number of non-classical features such as transverse shear, secondary warping, and anisotropy of the constituent materials. The structure can carry along its span heavy concentrated masses and/or tip stores. The vibration control is achieved via the use of actuating and sensing capabilities provided by piezoelectric devices which are bonded or embedded into the host structure. The cases of piezoactuators spread over the entire span of the structure, or in the form of a patch are considered, and issues related to the influence of patch location and size upon the vibration control efficiency are highlighted. Other issues related to the minimization of the required input power and of that generated by the inclusion/discard in the quadratic performance index of time-dependent external excitations are also addressed.

Static and Dynamic Aeroelasticity of Advanced Aircraft Wings Carrying External Stores

A study of the static and dynamic aeroelasticity of aircraft wings carrying external stores is presented. The wing structure is modeled as a laminated composite plate exhibiting flexibility in transverse shear and including warping restraint effects. The relevant equations of motion and boundary conditions are obtained via Hamilton's variational principle and application of generalized function theory. To achieve a realistic representation of the store influence on static and dynamic behavior of the system, static weights, as well as dynamic inertias of the stores, are considered. For the problem at hand, three-dimensional strip theory aerodynamics is employed. The obtained eigenvalue/boundary value problems are being solved by application of the extended Galerkin method. The solution procedure is used to investigate the implications of external stores on static aeroelastic response, divergence, free vibration, and flutter. Comparisons with the very few results highlighting the effects of underwing and tip stores on flutter instability are carried out, and excellent agreements with the present predictions are reported.

Effects of externally mounted stores on aeroelasticity of advanced swept cantilevered aircraft wings

In this paper, the static aeroelastic response and flutter instability of straight/swept aircraft wings carrying external stores along their span and at their tip are investigated. In this context, a comprehensive structural model for the aircraft wing is used which incorporates flexibility in transverse shear, anisotropy, and warping effects. The relevant equations of motion as well as the appropriate boundary conditions are obtained via Hamilton's Variational Principle and application of generalized function theory in order to exactly consider the spanwise location and properties of the attached stores. To achieve a realistic representation of the store influence upon static and dynamic aeroelastic behavior of the system, static weights and dynamic inertias of the attached stores have been modelled. The obtained eigenvalue/boundary value problems are being solved by application of the Extended Galerkin Method. Comparisons with the very few results highlighting the effects of underwing and tip stores on flutter instability are carried out and excellent agreements with the present predictions are reported.

Application of XTRAN3S and CAP-TSD to fighter aircraft

Two unsteady transonic small-disturbance (TSD) codes, XTRAN3S and CAP-TSD, were used to perform aeroelastic analyses of four fighter aircraft configurations. The XTRAN3S code was used for a wing-alone analysis of the F-15 and F/A-18 aircraft, whereas the CAP-TSD code, with its more flexible geometric modeling capability, was used to analyze a canard, wing, and tail arrangement of the F-15 S/MTD and a wing, launcher, and tip missile arrangement of the F/A-18. Static and dynamic aeroelastic calculations were performed using both the linear and nonlinear forms of the small-disturbance equation. Comparisons are made between the F-15 and F/A-18 wing-alone flutter results and those from a linear flutter analysis computed using doublet lattice aerodynamics. These comparisons show good agreement for the linear aerodynamic TSD solutions but significant changes in the flutter speed for the nonlinear aerodynamic TSD solutions. Comparisons were also made for the canard/wing/tail and the wing/launcher/tip missile configurations with the corresponding wing-alone configurations to assess the effects of multiple lifting surfaces and tip stores on flutter.

Transonic aeroelasticity of wings with tip stores

The presence of tip stores influences both aerodynamic and aeroelastic performances of wings. Such effects are more pronounced in the transonic regime. In this study, transonic aeroelasticity of wings with tip stores is studied for the first time by a theoretical method using the unsteady-small disturbance transonic aerodynamic equations coupled with modal structural equations of motion. The aerodynamic and structural equations of motion are simultaneously integrated by a time-accurate numerical scheme. To validate the tip store simulation, aeroelastic computations are made for a typical rectangular wing with a tip store and results are correlated with available wind tunnel data for the corresponding wing without a tip store at various flight conditions. Aeroelastic computations are also made for a typical fighter wing with a tip store. Present computations show that it is important to account for the aerodynamics of the tip store, particularly in the transonic regime where the tip store can make the wing aeroelastically unstable.

Optimization of wing tip store modeling

I N present three-dimensional flutter investigations of aircraft with external stores, the stores are often approximated by flat plates to reduce the cost and complexity of the analyses. In this Synoptic, the doublet lattice and kernel function methods are utilized to investigate the validity of this flatplate approximation in comparison to store models of other geometries for an F-5 wing with tip-mounted launcher/store combination. Various cross sections are found that show improved results with only a moderate increase in model complexity and thus computer cost.

Unsteady transonics of a wing with tip store

The presence of tip stores influences both the aerodynamic and the aeroelastic performance of wings. Such effects are more pronounced in the transonic regime. In this study, a theoretical method is developed, for the first time, to compute unsteady transonics of oscillating wings with tip stores. The method is based on the small-disturbance, aerodynamic equations of motion from the potential-flow theory. To validate the method, subsonic and transonic aerodynamic computations are made for a lower-aspect-ratio wing, and they are compared with the available experimental data. Comparisons are favorable. The strong effects of the tip store on the transonic aerodynamics of the wing are also illustrated. The method developed in this steady can be used for transonic, aeroelastic computations of wings with tip stores.