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...

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.

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.

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...

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...

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...

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

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.

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...

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.

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...

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...

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

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...

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 ...

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...

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...

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...

Abstract: This paper reports on a numerical investigation of the use of trailing-edge circulation control as a roll effector on a generic unmanned combat aerial vehicle: the DLR-F19 stability and control configuration. The Coanda effect induced by fluidic injections at the trailing edge of a wing is used to increase circulation and generate lift. Reynolds-averaged Navier–Stokes predictions are validated against wind-tunnel experiments conducted at the Georgia Institute of Technology and NASA’s basic aerodynamic research tunnel on an airfoil employing trailing-edge circulation control. Two turbulence models are used: the Wilcox k-ω model and Menter’s shear-stress transport, showing that the Wilcox k-ω model provides the best comparisons with the experimental data. Baseline data for the stability and control configuration with conventional control surfaces from wind-tunnel experiments done at the low speed wind-tunnel owned by the German- Dutch Wind Tunnels foundation (DNW-NWB) are used to ensure the correct flow fea...

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.

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.

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

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...

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.

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...

Abstract: This paper examines the effects of corotating blade-type vortex generators on transonic sweptback wings using computational fluid dynamics studies. Infinite-span (two-dimensional) swept wings are first considered to understand the basic physics of vortex generators. Sweep angles are given virtually to the wings by changing the freestream direction. Vortex generators are placed on the wings, and the visualized interactions of their tip vortices with the boundary layer reveal the relationship between the effect of the vortex generators and the wing sweep angle. The physics of vortex-generator tip vortices are then described to explain how vortex generators on swept wings efficiently suppress shock-induced separation by mixing boundary layers. It is also shown that the vortex-generator angle of incidence to the local flow can slightly improve the effect of the vortex generators but that wing sweep angle has a greater influence on their effect. Based on the discussion of infinite-span wings, the computational...

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...

Abstract: There has been a recent interest to explore the shape and kinematics parameters of distinct pterosaurs from their fossil records. Clearly, far more evidence is needed to understand the nuances of dinosaurs flight. A multiobjective aerodynamic optimization problem of the wing kinematics and planform of a pterosaur replica ornithopter designed by Aerovironment is performed. Objective functions include minimization of the required cycle-averaged aerodynamic power and maximization of the propulsive efficiency. It is found that inclusion of the inertial power requirements is necessary for a physical and proper formulation of the optimization problem. Furthermore, the mere addition of the inertial power requirements is not enough to obtain reasonable results. Rather, one has to consider a partial (or even zero) elastic energy storage. The minimum power kinematic parameters closely match those of the previously designed pterosaur replica. Nevertheless, the obtained efficiency for such a design (minimum power) is...

Abstract: The wing tip device in this study was to mimic the wing tips of a soaring bird, featuring three smoothly blended elements. Each such multi-element winglet was integrated into a complete wing–tail–body aircraft configuration. The geometry of each of the three elements in the multi-element winglet was defined using 11 parameters, totaling 33 parameters for a complete multi-element winglet geometry. This design methodology used a three-dimensional geometry generation algorithm based on locally analytical smoothly connected surface patches, allowing for the creation of vastly diverse three-dimensional geometries with a minimal number of specified design parameters. A three-dimensional, compressible, turbulent flow, steady-state analysis was performed using a Reynolds-averaged Navier–Stokes solver on each configuration to obtain the objective function values. Each configuration was analyzed at a freestream Mach number of 0.25 and at an angle of attack of 11 deg to mimic the takeoff conditions of a passenger ai...