Showing papers in "Journal of Aircraft in 2016"
TL;DR: In this paper, the authors investigated the aerodynamic shape optimization of the wing with a trim constraint that is satisfied by rotating the horizontal tail, and then optimized the same wing-body configuration without the tail but with an added trim drag penalty.
Abstract: Wing shape is one of the main drivers of aircraft aerodynamic performance, so most aerodynamic shape optimization efforts have focused solely on the wing. However, the performance of the full aircraft configuration must account for the fact that the aircraft needs to be trimmed. Thus, to realize the full benefit of aerodynamic shape optimization, one should optimize the wing shape while including the full configuration and a trim constraint. To evaluate the benefit of this approach, we perform the aerodynamic shape optimization of the Common Research Model wing–body–tail configuration using gradient-based optimization with a Reynolds-averaged Navier–Stokes model that includes a discrete adjoint implementation. We investigate the aerodynamic shape optimization of the wing with a trim constraint that is satisfied by rotating the horizontal tail. We then optimize the same wing–body configuration without the tail but with an added trim drag penalty based on a surrogate model we created before the optimization...
99 citations
TL;DR: In this article, a coflow jet airfoil was used to quantify lift enhancement, drag reduction, and energy expenditure at a Mach number range from 0.03 to 0.4.
Abstract: This paper conducts a numerical and experimental investigation of a coflow jet airfoil to quantify lift enhancement, drag reduction, and energy expenditure at a Mach number range from 0.03 to 0.4. The jet momentum coefficient is held constant at 0.08, and the angle of attack varies from 0 to 30 deg. The two-dimensional flow is simulated using a Reynolds–averaged Navier–Stokes solver with a fifth-order-weighted essentially non-oscillatory scheme for the inviscid flux and a fourth-order central differencing for the viscous terms. Turbulence is simulated with the one equation Spalart–Allmaras model. The predicted coflow jet pumping power has an excellent agreement with the experiment. At a constant Mach number, the power coefficient is decreased when the angle of attack is increased from 0 to 15 deg. When the Mach number is increased from 0.03 to 0.3, the suction effect behind the airfoil leading edge is further augmented due to the compressibility effect. This results in an increased maximum lift coefficien...
95 citations
TL;DR: In this paper, a grid convergence of a noise measure and a validation metric (dierence norm between computed and wind tunnel measured near-eld signatures) is studied for the first time.
Abstract: uid dynamics solutions are gathered from nineteen participants representing three countries for the two required cases, an axisymmetric body and simple delta wing body. Structured multiblock, unstructured mixed-element, unstructured tetrahedral, overset, and Cartesian cut-cell methods are used by the participants. Participants provided signatures computed on participant generated and solution adapted grids. Signatures are also provided for a series of uniformly rened workshop provided grids. These submissions are propagated to the ground and noise measures are computed. This allows the grid convergence of a noise measure and a validation metric (dierence norm between computed and wind tunnel measured near-eld signatures) to be studied for the rst time. A statistical analysis is also presented for these measures. An optional conguration includes fuselage, wing, tail, ow-through nacelles, and blade sting. This full conguration exhibits more variation in eleven submissions than the sixty submissions provided for each required case. Recommendations are provided for potential improvements to the analysis methods and a possible subsequent workshop.
91 citations
TL;DR: In this paper, the authors investigated the effect of folding wing tips in-flight as a device to reduce dynamic gust loads, but with the introduction of a passive nonlinear hinge spring to allow wing-tip deflections only for larger load cases.
Abstract: A recent consideration in aircraft design is the use of folding wing tips with the aim of enabling higher aspect ratio aircraft with less induced drag, but also meeting airport gate limitations. This study builds on previous work investigating the effect of exploiting folding wing tips in-flight as a device to reduce dynamic gust loads, but now with the introduction of a passive nonlinear hinge spring to allow wing-tip deflections only for larger load cases. A representative civil jet aircraft aeroelastic model is used in a multibody simulation code to explore the effect of introducing such a hinged wing-tip device on the loads behavior. It was found that significant reductions in the dynamic loads were possible.
80 citations
TL;DR: In this paper, the computational time required for the functional beamforming is approximately the same as that for the conventional frequency domain beamformer and, in general, notably shorter than those of the deconvolution methods.
Abstract: Functional beamforming is a state-of-the-art nonlinear algorithm based on the conventional frequency domain beamformer. In general, it is found to provide improved array spatial resolution and dynamic range. The computational time required for the functional beamforming is approximately the same as that for the conventional frequency domain beamformer and, in general, notably shorter than those of the deconvolution methods. In this paper, several simulations are presented comparing the performance of this algorithm with other imaging methods. Moreover, this beamforming technique is applied to 115 flyover measurements performed with a 32 microphone array on landing aircraft. The simulated and experimental results show good agreement. It is found that, for both synthetic and experimental data, functional beamforming offers better quality acoustic images, with a dynamic range (i.e., the difference in decibels between the main lobe and the highest sidelobe) approximately 30 times larger and an array spatial r...
67 citations
TL;DR: In this article, an incremental nonlinear dynamic inversion technique was used to solve the problem of the nonlinear dynamics model not being control affine due to effector redundancy, dramatic nonlinearities and cross-coupling effects introduced by the use of thrust vectoring during hover and transition phases.
Abstract: A novel, tiltrotor, unmanned aerial vehicle configuration has been designed, and a preliminary dynamic model has been created for control design purposes based on a component buildup approach. This method has been preferred over a conventional stability derivative approach because it models the nonlinear aircraft dynamics in the entire flight envelope, ranging from hover to forward-flight conditions at any airflow angles. The flight control system has then been synthesized based on an incremental nonlinear dynamic inversion technique. The incremental strategy was adopted to solve the problem of the nonlinear dynamic model not being control affine due to effector redundancy, dramatic nonlinearities, and cross-coupling effects introduced by the use of thrust vectoring during hover and transition phases. Local control derivatives were calculated online from the dynamic model. Effector redundancy was managed, developing a control allocation module for distributing the control effort according to a daisy-chain...
65 citations
TL;DR: In this paper, the authors present experiments conducted in the Iowa State Icing Research Tunnel on a NACA 0012 airfoil to study the transient ice accretion process under varying icing conditions.
Abstract: Ice accretion on aircraft wings poses a performance and safety threat as aircraft encounter supercooled droplets suspended in the cloud layer. The details of the ice accretion depend on the atmospheric conditions and the flight parameters. The icing process on the wing consists of a complex interaction of water deposition, surface water transport, and freezing. The aerodynamics affect the water deposition, the heat and mass transport, and ice accumulation; meanwhile, the accumulating ice affects the aerodynamics. Until now, most experimental measurements of aircraft icing have focused on the final ice shapes formed after exposure for a set duration to icing conditions. This approach fails to capture the transient processes that form the final ice formations. Here, we present experiments conducted in the Iowa State Icing Research Tunnel on a NACA 0012 airfoil to study the transient ice accretion process under varying icing conditions. High-speed video of the icing process was acquired under controlled envi...
60 citations
TL;DR: In this article, a numerical method for the conversion of unstructured surface vorticity into directional integrated circulation has been presented, which allows for the reduction of vortivities distributions on arbitrary three-dimensional bodies into their mathematically equivalent formulations in the Prandtl lifting-line theory.
Abstract: A novel numerical method for the conversion of unstructured surface vorticity into directional integrated circulation has been presented. This method allows for the reduction of vorticity distributions on arbitrary three-dimensional bodies into their mathematically equivalent formulations in the Prandtl lifting-line theory. A discussion of its implementation into a practical numerical solver has been presented. This new solver was applied to simple wing shapes as well as complex aircraft geometries to demonstrate the applicability of such an approach to flow solvers. It was shown that the reduction to lifting-line theory was exact for simple shapes such as rectangular and elliptical wings. For complex aircraft geometries, such as leading-edge root extension and canard-equipped aircraft, it was shown that the method of integrated circulation allowed for accurate prediction of aircraft loads and the analysis of flow physics, in keeping with the Prandtl original concepts.
51 citations
TL;DR: In this paper, the feasibility of a small-scale autonomous helicopter for Mars exploration was evaluated using a 3D-model of the helicopter's rotors and a 2D-view of the terrain.
Abstract: The present study is in response to increased interest towards assessing the feasibility of a small-scale autonomous helicopter (gross weight less than 1 kg) for Martian exploration An autonomous rotorcraft may be ideally suited for such an application because of its unique advantages, which include the ability to take off/land vertically on harsh terrain, and greater speed, range, and field of view, when compared to a traditional surface rover The atmospheric conditions on Mars present a unique set of design challenges Even though the Martian gravity is only about 38% of Earth’s gravity, the Martian average atmospheric density is about 70 times lower than Earth’s atmospheric density Therefore, the rotors would be operating at extremely low Reynolds numbers, even lower than 5000 for a small-scale helicopter However, the Mach number will be significantly higher (M>04) because of the higher tip speed required (due to lower density) and because of the fact that the speed of sound on Mars is only about
46 citations
TL;DR: This paper develops a multi-information source formulation for aerospace design under uncertainty problems and presents the optimization under uncertainty of an advanced subsonic transport aircraft developed to meet the NASA N+3 goals and shows how the multi- information source approach enables practical turnaround time.
Abstract: This paper develops a multi-information source formulation for aerospace design under uncertainty problems. As a specific demonstration of the approach, it presents the optimization under uncertainty of an advanced subsonic transport aircraft developed to meet the NASA N+3 goals and shows how the multi-information source approach enables practical turnaround time for this conceptual aircraft optimization under uncertainty problem. In the conceptual design phase, there are often uncertainties about future developments of the underlying technologies. An aircraft design that is robust to uncertainty is more likely to meet performance requirements as the technologies mature in the intermediate and detailed design phases, reducing the need for expensive redesigns. In the particular example selected here to present the new approach, the multi-information source approach uses an information-reuse estimator that takes advantage of the correlation of the aircraft model in the design space to reduce the number of m...
45 citations
TL;DR: In this paper, a nonlinear lifting-line-theory algorithm for the prediction of aerodynamic coefficients and lifting-surface-pressure distribution for multiple aircraft configurations is presented, which is applied to isolated wing, high-lift systems (slat/main/flap), and multisurface configurations.
Abstract: A modern nonlinear-lifting-line-theory algorithm allowing the prediction of aerodynamic coefficients and lifting-surface-pressure distribution for multiple aircraft configurations is presented. The algorithm is applied to isolated wing, high-lift systems (slat/main/flap), and multisurface configurations, with emphasis on the treatment of high-lift geometry representations. The fuselage is not geometrically modeled, but its influence is appropriately taken into account for the aerodynamic-coefficient evaluation. The results show good agreements with wind-tunnel and/or high-fidelity numerical data for the prediction of the maximum lift coefficient and the poststall behavior in subsonic and transonic conditions. The use of sectional airfoil data obtained via solutions of the Reynolds-averaged Navier–Stokes equations with infinite-swept-wing assumptions—so-called 2.5-dimensional model—is shown to greatly improve the results over traditional two-dimensional solutions.
TL;DR: In this article, an extended unsteady vortex-lattice method is developed to study the aerodynamics of insect flapping wings while hovering and during forward flight, and a convergence analysis is carried out to derive an optimal aerodynamic mesh and a time-step size for flapping-wing models.
Abstract: An extended unsteady vortex-lattice method is developed to study the aerodynamics of insect flapping wings while hovering and during forward flight. Leading-edge suction analogy and vortex-core growth models are used as an extension, which is incorporated into a conventional unsteady vortex-lattice method in an effort to overcome the challenges that arise when simulating insect aerodynamics such as wing–wake interaction and leading-edge effects. A convergence analysis was carried out to derive an optimal aerodynamic mesh and a time-step size for flapping-wing models. A parallel computing technique was used to reduce computational time. The aerodynamics of hawkmoth (Manduca sexta) wing models was simulated, and the results were validated against previous numerical and experimental data.
TL;DR: In this article, flight test and modeling techniques were developed to accurately identify global nonlinear aerodynamic models onboard an aircraft during a single flight, with the final identified and validated models available before the aircraft landed.
Abstract: Flight test and modeling techniques were developed to accurately identify global nonlinear aerodynamic models onboard an aircraft. The techniques were developed and demonstrated during piloted flight testing of an Aermacchi MB-326M Impala jet aircraft. Advanced piloting techniques and nonlinear modeling techniques based on fuzzy logic and multivariate orthogonal function methods were implemented with efficient onboard calculations and flight operations to achieve real-time maneuver monitoring and analysis, and near-real-time global nonlinear aerodynamic modeling and prediction validation testing in flight. Results demonstrated that global nonlinear aerodynamic models for a large portion of the flight envelope were identified rapidly and accurately using piloted flight test maneuvers during a single flight, with the final identified and validated models available before the aircraft landed.
TL;DR: In this paper, the aero-elastic optimization of a subsonic transport wing box under a variety of static and dynamic aeroelastic constraints is considered, where a closed-loop flutter constraint is forced to satisfy the required flight margin.
Abstract: This paper considers the aeroelastic optimization of a subsonic transport wing box under a variety of static and dynamic aeroelastic constraints. Three types of design variables are used: structural variables (skin thickness, stiffener details), the quasi-steady deflection scheduling of a series of control surfaces distributed along the trailing edge for maneuver load alleviation and trim attainment, and the design details of a linear quadratic regulator controller (for flutter suppression), which commands oscillatory hinge moments into those same control surfaces. Optimization problems are solved where a closed-loop flutter constraint is forced to satisfy the required flight margin, and mass reduction benefits are realized by relaxing the open-loop flutter requirements.
TL;DR: In this paper, the aerodynamic behavior of the wing section of an aircraft is characterized to better understand the adverse aerodynamic effects of anti-icing fluids and ice-pellet contamination.
Abstract: The Federal Aviation Administration has worked with Transport Canada and others to develop allowance times for aircraft operating in ice-pellet precipitation based upon wind-tunnel experiments with a thin high-performance wing. These allowance times are applicable to many different airplanes. Therefore, the aim of this work is to characterize the aerodynamic behavior of the wing section in order to better understand the adverse aerodynamic effects of anti-icing fluids and ice-pellet contamination. Aerodynamic performance tests, boundary-layer surveys, and flow visualization were conducted at a Reynolds number of approximately 6.0×106 and a Mach number of 0.12. Roughness and leading-edge flow disturbances were employed to simulate the aerodynamic impact of the anti-icing fluids and contamination. In the linear portion of the lift curve, the primary aerodynamic effect is the thickening of the downstream boundary layer due to the accumulation of fluid and contamination. This causes a reduction in lift coeffi...
TL;DR: In this article, a backstepping sliding-mode control approach is proposed to develop the positioning controller for an autonomous airship in the presence of model uncertainties and external disturbances, which provides the flexibility to treat nonlinear terms and guarantee the stability of a closed-loop system.
Abstract: The problem of positioning control for an autonomous airship in the presence of model uncertainties and external disturbances is addressed in the paper. First, the “ZY-1” autonomous airship is introduced and a dynamics model of the airship is presented. Second, a backstepping sliding-mode control approach is proposed to develop the positioning controller. The backstepping controller is designed recursively by selecting some appropriate functions of state variables as pseudocontrol inputs for lower-dimension subsystems of the overall system based on a Lyapunov function, which provides the flexibility to treat nonlinear terms and guarantee the stability of a closed-loop system. Furthermore, the backstepping control combined with the sliding-mode control is proposed to assure the robustness against parametric uncertainties and external disturbances. The stability of the closed-loop controller is proven via the Lyapunov stability theorem. Finally, simulation results illustrate the effectiveness and robustness...
TL;DR: In this paper, the authors investigated maximizing net power input from a solar-photovoltaic array and/or a thermal updraft while performing constant bank angle, circular flight-path turns (that is, an orbit).
Abstract: This study investigates maximizing net power input from a solar-photovoltaic array and/or a thermal updraft while performing constant bank angle, circular flight-path turns (that is, an orbit). The process inputs are the aircraft sink polar (or, equivalently, the power required curve), the date, the time, the location, and the flight altitude. A solar insolation model is combined with a best-turn performance calculation to determine the bank angle that maximizes power input from a solar-photovoltaic array at varying sun elevation angles. In general, for low sun elevation angles, the maximum net power gain from solar input and drag output is found at higher bank angles and shows 15% (absolute) gain over the limiting case of wings-level orbits in the same conditions. For high sun elevation angles, the maximum net power is found at low bank angles. The break point between high and low sun elevation angles varies with aircraft parameters and is approximately 25 deg for the example aircraft in this paper. The ...
TL;DR: In this paper, the effect of the riblets on the aerodynamic coefficients of a complete aircraft configuration at transonic conditions is evaluated using simulations by the Reynolds-averaged Navier-Stokes equations.
Abstract: The effectiveness of the riblets, one of the most interesting drag-reduction device, is discussed in this paper. Numerical simulations by the Reynolds-averaged Navier–Stokes equations with the riblets properly taken into account are presented. Riblets are modeled as a singular roughness problem by modifying the classical Wilcox boundary condition for rough walls. The boundary condition is able to predict the flow features in the low roughness range (transitional roughness) where riblets operate. A brief discussion of the simulations performed to validate the model is first presented. Then, a complex wing–body configuration is analyzed, and the overall effect of riblets on the aerodynamic coefficients is evaluated. Calculations of a complete aircraft configuration at transonic conditions show how a proper optimized choice of the riblet height can significantly improve the drag reduction.
TL;DR: In this paper, a Mach-scale rotor system, 2.03m in diameter, was built and hover tested in three configurations: two-bladed single rotor, fourbladed one rotor, and twobladed coaxial counter-rotating rotor.
Abstract: A Mach-scale rotor system, 2.03 m in diameter, was built and hover tested in three configurations: two-bladed single rotor, four-bladed single rotor, and two-bladed coaxial counter-rotating rotor. The blades were untwisted with a VR-12 airfoil profile and a constant chord of 76.2 mm with a 3.8 mm trailing-edge tab. The hubs were rigid and had a vertical spacing of 13.8% rotor radius. Individual rotor steady and vibratory hub loads as well as lower-rotor push-rod loads were measured for several blade loadings up to 0.095. Mean loads were used to analyze rotor performance with an analytical momentum theory model as well as to validate an in-house, free-vortex wake model. Statistical analysis of the measured data revealed clear trends with a known confidence level. Because of mutual interference, the upper and lower rotors of the coaxial configuration consumed 18 and 49% more induced power than that of an isolated two-bladed rotor. The coaxial counter-rotating configuration was found to consume 6% less induc...
TL;DR: In this paper, the performance of the Froude's propulsive efficiency as a figure of merit should be separated from the power conversion efficiency in these configurations, showing that the minimization of power consumption should be used as a design criterion for aircraft using boundary layer ingestion.
Abstract: This paper presents conceptual studies to evaluate the performance of the propulsor and its associated vehicle in the configurations of wake ingestion and boundary-layer ingestion. A power conversion analysis uses the power balance method to elaborate the power-saving mechanism of wake ingestion, showing that the Froude’s propulsive efficiency as a figure of merit should be separated from the power conversion efficiency in these configurations. The body/propulsor interaction occurring in the boundary-layer ingestion configuration is qualitatively analyzed to clarify its influence on the performance of the integrated vehicle. The results suggest that the minimization of power consumption should be used as a design criterion for aircraft using boundary-layer ingestion.
TL;DR: In this article, an adaptive feed-forward controller that uses the preview information of the gust sensed by an onboard alpha probe is designed to operate the ailerons symmetrically to alleviate the wing-root bending moment induced by the gust.
Abstract: This study develops an active control technology to reduce the incremental dynamic loads of a large four-engine transport airplane flying through a gust field The mathematical model of the proposed gust-alleviation system features composite structural motions (for example, rigid-body motions, elastic vibrations, and deflections of control surfaces) and unsteady aerodynamic forces induced by the structural motions and the gusts A clear outline of the procedure is first provided to determine the aeroservoelastic equation of the system Then, an adaptive feedforward controller that uses the preview information of the gust sensed by an onboard alpha probe is designed to operate the ailerons symmetrically to alleviate the wing-root bending moment induced by the gust The rigid-body motions due to travelling gusts are also compensated for using symmetrical deflections of the elevators To solve the problems of weight drift and weight bias that are commonly encountered in adaptive control, the circular leaky l
TL;DR: In this paper, the authors investigated the aerodynamic tradeoffs of a box-wing aircraft configuration using high-fidelity aerodynamic optimization, where each study extends the previous one by progressively adding a combination of design variables and constraints.
Abstract: This study investigates the aerodynamic tradeoffs of a box-wing aircraft configuration using high-fidelity aerodynamic optimization. A total of five optimization studies are conducted, where each study extends the previous one by progressively adding a combination of design variables and constraints. Examples of design variables include wing twist and sectional shape; examples of constraints include trim and stability requirements. In all cases, the objective is to minimize inviscid drag at a prescribed lift and a Mach number of 0.78. Aerodynamic functionals are evaluated based on the discrete solution of the Euler equations, which are tightly coupled with an adjoint methodology incorporating a gradient-based optimizer. For each study, an equivalent conventional tube-and-wing baseline is similarly optimized in order to enable direct comparisons. It is found that the transonic box-wing aircraft considered here, for which the height-to-span ratio is about 0.2, produces up to 43% less induced drag than its c...
TL;DR: In this article, a comparative study of different passive control techniques was conducted on a cavity with a length of 320mm with length-to-depth and lengthto-width ratios of five and two, respectively.
Abstract: A comparative study of different passive control techniques was conducted on a cavity with a length of 320 mm with length-to-depth and length-to-width ratios of five and two, respectively. The tests were conducted at a freestream Mach number of 0.71. Both leading-edge and trailing-edge modifications were included in the studies. Results from surface pressure measurements showed that leading-edge control techniques were more effective at suppressing cavity tone amplitudes than trailing-edge modifications. A square-tooth spoiler showed the greatest reduction in tonal amplitude (8.8 dB); however, a sawtooth spoiler showed the greatest reduction in overall sound pressure level (8.13 dB). Velocity measurements inside the cavity were made using particle image velocimetry for the clean cavity and the cavity with sawtooth spoilers. The results showed a reduction in momentum exchange between the freestream flow and the cavity when spoilers were used. This is proposed to be the main reason for the reduced tonal amp...
TL;DR: In this article, an improved gradient-based algorithm is developed in a collaborative process in order to find transition trajectories and increase the convergence rate for an aerial tail sitter that uses cross-coupled thrust vectoring control.
Abstract: The main purpose of this study is to generate optimal transition trajectories for an aerial tail sitter that uses cross-coupled thrust-vectoring control. A transition maneuver is most challenging for such configurations due to coupling of the forces and moments with instability in the most critical low-speed flight phases. Based on the classical Cauchy method, an improved gradient-based algorithm is developed in a collaborative process in order to find transition trajectories and increase the convergence rate. The cost function is defined in terms of minimum time in transition from hover to cruise and minimum altitude variations from cruise to hover. In addition, physical constraints are modeled via extended penalty functions. The results, including an optimal solution for states and controls, guarantee that the estimated trajectories are feasible, taking into account all imposed constraints. It is shown that the initial cruise speed in the landing phase will greatly affect the altitude variation and tran...
TL;DR: In this paper, a relatively low-order linear dynamic model is developed for the longitudinal flight-dynamics analysis of a flexible flying-wing research drone, and results are compared to previously published results.
Abstract: A relatively low-order linear dynamic model is developed for the longitudinal flight-dynamics analysis of a flexible flying-wing research drone, and results are compared to previously published results. The model includes the dynamics of both the rigid-body and elastic degrees of freedom, and the subject vehicle is designed to flutter within its flight envelope. The vehicle of interest is a 12–lb, unmanned flying-wing aircraft with a wingspan of 10 ft. In the modeling, the rigid-body degrees of freedom are defined in terms of motion of a vehicle-fixed coordinate frame, as required for flight-dynamics analysis. As a result, the state variables corresponding to the rigid-body degrees of freedom are identical to those used in modeling a rigid vehicle, and the additional states are associated with the elastic degrees of freedom. Both body-freedom and bending–torsion flutter conditions are indicated by the model, and it is shown that the flutter speeds, frequencies, and genesis modes suggested by this low-orde...
TL;DR: In this article, the development of the unsteady wake of transport aircraft under stall conditions and its impact on the empennage are challenging to predict, and the flow physics is far from being understood.
Abstract: The development of the unsteady wake of transport aircraft under stall conditions and its impact on the empennage are challenging to predict, and the flow physics is far from being understood. In the European Strategic Wind Tunnels Improved Research Potential project, time-resolved particle image velocimetry measurements on the separated wake of the NASA Common Research Model were performed in the cryogenic European Transonic Windtunnel for flight Reynolds number conditions supplemented by aerodynamic measurements for a great variety of inflow conditions. In the time-resolved particle image velocimetry measurements, both low-speed stall (M∞=0.25, Re=11.6/17 million) and high-speed stall conditions (M∞=0.85, Re=19.8/30 million) were considered and the frequency resolution was as high as 1 kHz, enabling a sufficient characterization of the turbulent wake spectrum. For selected high- and low-speed stall conditions, hybrid Reynolds-averaged Navier–Stokes/large-eddy simulations were performed. In the present...
TL;DR: In this paper, a multiscale finite-element formulation for the second mode of zonal detached-eddy simulation is presented, which corrects the lack of stability of the standard Galerkin formulation by incorporating the effect of unresolved scales to the grid scales.
Abstract: This paper presents a multiscale finite-element formulation for the second mode of zonal detached-eddy simulation The multiscale formulation corrects the lack of stability of the standard Galerkin formulation by incorporating the effect of unresolved scales to the grid (resolved) scales The stabilization terms arise naturally and are free of user-defined stability parameters Validation of the method is accomplished via the turbulent flow over tandem cylinders The boundary-layer separation, free shear-layer rollup, vortex shedding from the upstream cylinder, and interaction with the downstream cylinder are well reproduced Good agreement with experimental measurements gives credence to the accuracy of zonal detached-eddy simulation in modeling turbulent separated flows A comprehensive study is then conducted on the performance degradation of ice-contaminated airfoils NACA 23012 airfoil with a spanwise ice ridge and Gates Learjet Corporation-305 airfoil with a leading-edge horn-shape glaze ice are sel
TL;DR: In this paper, the authors examined the effects of nozzle shapes and atmospheric conditions on the infrared susceptibility of an aircraft's propulsion system and found that relatively higher signature levels were observed on the left and right sides and below the nozzle due to increase in the aspect ratio of the nozzle outlet as well as curvature, which led to a wider distribution of the plumes along a downward slope.
Abstract: The infrared susceptibility of the propulsion system of an aircraft is significantly affected by nozzle shapes and atmospheric conditions. To examine the effects of nozzle shapes and atmospheric conditions, various nozzle shapes were selected by considering a representative low-observable unmanned aerial vehicle and its propulsion system. Then, using the density-based Navier–Stokes–Fourier computational-fluid-dynamics code, the thermal flowfield and the distribution of chemical species within a plume, which are essential for the analysis of infrared signatures, were calculated. From the analysis of plume infrared signatures for noncircular nozzles, it was found that infrared signature levels were reduced significantly in the axial direction. However, relatively higher signature levels were observed on the left and right sides and below the nozzle due to increase in the aspect ratio of the nozzle outlet as well as curvature, which led to a wider distribution of the plumes along a downward slope. Further, t...
TL;DR: In this paper, the potential of unconventional aircraft transports through numerical optimization is investigated: a box wing, a C-tip blended wing-body, and a braced wing, each transport is sized for the same regional mission and is subjected to the same optimization strategy based on the Euler equations.
Abstract: This study investigates the potential of unconventional aircraft transports through numerical optimization. Three distinct configurations are investigated: a box wing, a C-tip blended wing–body, and a braced wing. Each transport is sized for the same regional mission and is subjected to the same optimization strategy based on the Euler equations. The figure of merit is inviscid pressure drag at transonic speed; the nonlinear constraints are lift, pitching moment, and internal volume. The design variables include the section shape and twist distribution of the main lifting surfaces. It is found that the box-wing, C-tip blended-wing–body, and braced-wing configurations investigated here are, respectively, 34.1, 36.2, and 40.3% more efficient than a similarly optimized conventional tube-and-wing configuration. Each optimization revealed, in one way or another, the importance of accounting for flow nonlinearity during the early stages of unconventional aircraft design. For the blended wing–body, the C tip doe...
TL;DR: In this article, a model of energy harvesting from transient vibrations of slender wings using piezoelectric transduction is implemented in a strain-based geometrically nonlinear beam formulation, and the resulting structural dynamic equations for multifunctional beams are then coupled with a finite-state unsteady aerodynamic formulation, allowing for both energy harvesting and actuation with the nonlinear aeroelastic system.
Abstract: In this paper, modeling of energy harvesting from transient vibrations of slender wings using piezoelectric transduction is implemented in a strain-based geometrically nonlinear beam formulation. The resulting structural dynamic equations for multifunctional beams are then coupled with a finite-state unsteady aerodynamic formulation, allowing for both energy harvesting and piezoelectric actuation with the nonlinear aeroelastic system. With the development, it is possible to provide an accurate, integral aeroelastic and electromechanical solution of both energy harvesting from and active control for wing vibrations, considering the geometrical nonlinear effects of slender wings. The current paper focuses on modeling the energy harvesting subsystem and exploring its impact on the multifunctional system. Vibrations of a slender multifunctional wing excited by both aeroelastic instability and external wind gusts will be considered as the sources of energy harvesting. All simulations will be completed in the t...