Aerodynamic Analysis of the Joiined-wing Configuration of a High-altitude, Long-endurance (hale) Aircraft PDF Download
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Languages : en
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The three-dimensional, unsteady, flow is simulated over the joined-wing section of a HALE (High-Altitude Long Endurance) aircraft based on the Sensorcraft configuration. This is the first step in the high-fidelity, nonlinear aeroelastic analysis of the HALE aircraft. These vehicles operate in a high-altitude, low-density, low-Reynolds number (Re) environment. Also, the sensor Equipment housed within the wings requires the sections to be thick. In order to produce the necessary lift, the wings of these aircraft are made extremely long compared to the average chord of the wing section, leading to aspect ratios typically around 25. The fluid loads experienced by the structure result in these high-aspect ratio wings undergoing large deflections. These can cause appreciable change in the geometry, and hence, in the corresponding flow, and necessitate an aeroelastic analysis. The flow solution is obtained by solving the Reynolds-Averaged Navier-Stokes (RANS) governing equations, using the Spalart-Allmaras turbulence model, or by using Detached Eddy Simulation (DES). The flow solver, COBALT60 is a finite-volume, cell-centered, second-order accurate in space and time, unstructured-grid flow solver. With successful completion of the validation cases, simulations were performed at the lower and upper limits (M = 0.4-0.6, [alpha] = 0-12ʻ) of the operating regime of the Sensorcraft. Inviscid simulations were also considered as a computationally efficient alternative to viscous simulations for the computation of the surface pressure loads to be applied on the structure, particularly at low angle of attack ([alpha] = 0ʻ). This is verified by performing inviscid simulations, and comparing the resulting pressure with the corresponding viscous results at the Mach number of 0.6. The surface pressure comparison is satisfactory for this low angle of attack (? = 0ʻ), whereas at? = 12ʻ, the presence of flow separation in the joint region, and a mild oblique shock at the trailing edge of the aft wing in the joint region results in significant viscous effects. A procedure has been set up for the preliminary process of load transfer to the joined-wing structure. The study serves as the foundation to provide an integrated aerodynamic and structural analyses software using a Multi-Disciplinary Computing Environment (MDICE) to predict the aeroelastic behavior of lifting bodies.
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Languages : en
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Book Description
The three-dimensional, unsteady, flow is simulated over the joined-wing section of a HALE (High-Altitude Long Endurance) aircraft based on the Sensorcraft configuration. This is the first step in the high-fidelity, nonlinear aeroelastic analysis of the HALE aircraft. These vehicles operate in a high-altitude, low-density, low-Reynolds number (Re) environment. Also, the sensor Equipment housed within the wings requires the sections to be thick. In order to produce the necessary lift, the wings of these aircraft are made extremely long compared to the average chord of the wing section, leading to aspect ratios typically around 25. The fluid loads experienced by the structure result in these high-aspect ratio wings undergoing large deflections. These can cause appreciable change in the geometry, and hence, in the corresponding flow, and necessitate an aeroelastic analysis. The flow solution is obtained by solving the Reynolds-Averaged Navier-Stokes (RANS) governing equations, using the Spalart-Allmaras turbulence model, or by using Detached Eddy Simulation (DES). The flow solver, COBALT60 is a finite-volume, cell-centered, second-order accurate in space and time, unstructured-grid flow solver. With successful completion of the validation cases, simulations were performed at the lower and upper limits (M = 0.4-0.6, [alpha] = 0-12ʻ) of the operating regime of the Sensorcraft. Inviscid simulations were also considered as a computationally efficient alternative to viscous simulations for the computation of the surface pressure loads to be applied on the structure, particularly at low angle of attack ([alpha] = 0ʻ). This is verified by performing inviscid simulations, and comparing the resulting pressure with the corresponding viscous results at the Mach number of 0.6. The surface pressure comparison is satisfactory for this low angle of attack (? = 0ʻ), whereas at? = 12ʻ, the presence of flow separation in the joint region, and a mild oblique shock at the trailing edge of the aft wing in the joint region results in significant viscous effects. A procedure has been set up for the preliminary process of load transfer to the joined-wing structure. The study serves as the foundation to provide an integrated aerodynamic and structural analyses software using a Multi-Disciplinary Computing Environment (MDICE) to predict the aeroelastic behavior of lifting bodies.
![Structural Modeling and Optimization of a Joined-wing Configuration of a High-altiude [i.e. Altitude] Long-endurance (HALE) Aircraft PDF](https://books.google.com/books/content/images/frontcover/vld6AQAACAAJ?fife=w80-h100)
Author: Valentina B. Kaloyanova
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Languages : en
Pages : 207
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Recent research trends have indicated an interest in High-Altitude, Long-Endurance (HALE) aircraft as a low-cost alternative to certain space missions, such as telecommunication relay, environmental sensing and military reconnaissance. HALE missions require a light vehicle flying at low speed in the stratosphere at altitudes of 60,000-80,000 ft, with a continuous loiter time of up to several days. To provide high lift and low drag at these high altitudes, where the air density is low, the wing area should be increased, i.e., high-aspect-ratio wings are necessary. Due to its large span and lightweight, the wing structure is very flexible. To reduce the structural deformation, and increase the total lift in a long-spanned wing, a sensorcraft model with a joined-wing configuration, proposed by AFRL, is employed. The joined-wing encompasses a forward wing, which is swept back with a positive dihedral angle, and connected with an aft wing, which is swept forward. The joined-wing design combines structural strength, high aerodynamic performance and efficiency. The results of the simulation of the complex, three-dimensional flow past the joined-wing of a HALE aircraft are used as an input for the structural analysis. The Reynolds-Averaged Navier-Stokes (RANS)-based flow solver, COBALT, provided detailed flow results for altitudes 30,000 ft and 60,000 ft for the cases with M=0.4 and [alpha] = 0°, M = 0.6 and [alpha] = 0°, and M = 0.6 and [alpha] = 12°. The surface static pressure from the flow analyses comprises the load transferred to the structural models developed in this study. To date in the existing studies, only simplified structural models have been examined. In the present work, a semi-monocoque structural model is developed. All stringers, skin panels, ribs and spars are represented by appropriate elements in a finite-element model. Also, the model accounts for the fuel weight and sensorcraft antennae housed within the wings. Linear and nonlinear static analyses under the aerodynamic load are performed. Design optimization is performed to achieve a fully stressed design. The shell elements thickness and stringers cross-sectional area are properly resized to obtain a structure that meets the allowable stress in each element and is minimum weight. In addition to the stress constraints, deflection constraints are also imposed in the design optimization. As the joined-wing structure is prone to buckling, after the design optimization is complete linear and nonlinear bucking analyses are performed to study the global joined-wing structural instability, the load magnitude at which it is expected to occur, and the buckling mode. As this design and analysis study is aimed towards developing a realistic structural representation of the innovative joined-wing configuration, in addition to the global, or upper-level optimization, a local level design optimization is performed as well. At the lower (local) level detailed models of wing structural panels are used to compute more complex failure modes and to design details not included in the upper (global) level model. Proper coordination between local skin-stringer panel models and the global joined-wing model prevents inconsistency between the global and local level models.
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Languages : en
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The current research focuses on studying the modal response of a joined wing aircraft based on the Sensorcraft configuration. Sensorcraft, a class of High-Altitude, Long-Endurance (HALE) aircraft, is an Unmanned Air Vehicle (UAV), and is being studied by the AFRL for applications involving telecommunication relay, environmental sensing and military reconnaissance. The Sensorcraft is designed to operate at high altitudes (60,000 ft) with low speed and for long durations of time (60 to 80 hours). At these operating conditions, the density, and hence, the Reynolds number, is low. These conditions require the Sensorcraft to operate with high lift and low drag with high-aspect ratio wings. Moreover, the vehicle must be lightweight and strong, and offer high aerodynamic performance and efficiency. The AFRL has identified a diamond shape joined wing configuration for Sensorcraft due to the primary structural advantage of strength as each wing braces the other against lift loads. The University of Cincinnati (UC), along with its partners, AFRL and Ohio State University are working together to study the complete nonlinear aeroelastic behavior of the joined-wing model. At UC, four different structural modeling approaches were adopted for analysis. The current research focuses on the analysis of an in-house Sensorcraft joined wing model developed by the AFRL. This model is an equivalent representation of the actual 3-D joined wing model. The wing is idealized as a box structure consisting of shells, rods, beams, shear panels and concentrated masses. This box wing structure has the advantage of being computationally inexpensive over the full 3-D model, and has been optimized to minimize the deflections of the antennae equipment in the control surface of the wing. The fluid loads applied on the box-wing structure are obtained from a concurrent aerodynamic analysis for different mach numbers and angles of attack performed at UC. A modal representation is obtained for different operating boundary conditions as the first step in the overall aeroelastic analysis of the joined wing. AFRL has obtained the modal representation for the Sensorcraft model using NASTRAN, and as part of the DAGSI project requirement, the structural analyses at UC are performed using ANSYS. The results are compared with those from NASTRAN and the correctness of the methodology is verified. Prior to the NASTRAN box-wing model translation into ANSYS, a number of validation tests are performed to test the consistency between the functionalities of the ANSYS elements and NASTRAN elements. Once the results of the validation test cases are found to be satisfactory, the actual analysis of the joined wing is performed for clamped, rigid and symmetry boundary conditions at the wing roots. The frequencies were found to be different between the two codes for each of these boundary conditions. In order to trace the issue causing the differences in the results, a number of simpler joined wing models are analyzed. Finally, the problem is traced down to differences in the formulation between the constraint equations in ANSYS and RBE1 elements in NASTRAN. Due to the assumption of small deflections, linear static analysis is performed and considered sufficient for predicting the displacement response. However, a nonlinear analysis is also performed to validate the assumptions of linearity that have been used in the modeling of the wing. The tip deflection from linear is estimated to be 5.3 % of the span of the wing. For higher angles of attack, the pressure difference between the upper and lower surfaces of the wing is higher, and consequently the lift forces are greater in magnitude. This could cause larger deformation in the main wing that could potentially lead to buckling of the aft wing. Hence, an eigenvalue buckling analysis is performed which show that the wing is stable and not prone to buckling for the loads employed for the linear static analysis. A procedure is also established to determine the structural response under time varying aerodynamic loads from the CFD analysis. This analysis serves as a starting point for future complete aeroelastic analysis of the joined wing.
Author: Rangarajan Sivaji
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Languages : en
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Author: Soujanya Marisarla
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Languages : en
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Author: Vanessa L. Bond
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Category : Pitching (Aerodynamics)
Languages : en
Pages : 410
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Author: Grigorios Dimitriadis
Publisher: John Wiley & Sons
ISBN: 1118756460
Category : Technology & Engineering
Languages : en
Pages : 944
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Book Description
Introduction to Nonlinear Aeroelasticity Introduces the latest developments and technologies in the area of nonlinear aeroelasticity Nonlinear aeroelasticity has become an increasingly popular research area in recent years. There have been many driving forces behind this development, increasingly flexible structures, nonlinear control laws, materials with nonlinear characteristics and so on. Introduction to Nonlinear Aeroelasticity covers the theoretical basics in nonlinear aeroelasticity and applies the theory to practical problems. As nonlinear aeroelasticity is a combined topic, necessitating expertise from different areas, the book introduces methodologies from a variety of disciplines such as nonlinear dynamics, bifurcation analysis, unsteady aerodynamics, non-smooth systems and others. The emphasis throughout is on the practical application of the theories and methods, so as to enable the reader to apply their newly acquired knowledge Key features: Covers the major topics in nonlinear aeroelasticity, from the galloping of cables to supersonic panel flutter Discusses nonlinear dynamics, bifurcation analysis, numerical continuation, unsteady aerodynamics and non-smooth systems Considers the practical application of the theories and methods Covers nonlinear dynamics, bifurcation analysis and numerical methods Accompanied by a website hosting Matlab code Introduction to Nonlinear Aeroelasticity is a comprehensive reference for researchers and workers in industry and is also a useful introduction to the subject for graduate and undergraduate students across engineering disciplines.
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Languages : en
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Author: Clarence D. Cone (Jr.)
Publisher:
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Category : Airplanes
Languages : en
Pages : 40
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"The basic aerodynamic relations needed for the design of wings with cambered span having a minimum induced drag at specified flight conditions are developed for wings of arbitrary spanwise camber. Procedures are also developed for determining the physical wing form required to obtain the maximum value of lift-drag ratio at cruise, when the wing spanwise camber-line and section profiles are specified, by optimizing the wing chord and twist distributions with respect to both profile and induced drags. The application of the design procedure is illustrated by determining the physical wing form for a circular-arc spanwise camber line. The efficiency of this cambered wing is compared with that of an equal-span, flat wing of elliptical planform which satisfies the same set of fright operating conditions as does the cambered wing. The wing pitching- moment equations for optimally loaded cambered-span wings at design flight conditions are also developed for use in trim analyses on complete aircraft designs."--Page 1.
Author: S. Sivasundaram
Publisher:
ISBN:
Category : Mathematics
Languages : en
Pages : 778
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"The Fifth International Conference on Mathematical Problems in Engineering and Aerospace Sciences was held at the West University of Timisoara on June 2-4, 2004"--Preface.
