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Showing papers on "Vortex lattice method published in 2005"


Journal ArticleDOI
TL;DR: In this paper, coupled time-domain computational-fluid-dynamics (CFD) and computationalstructural-Dynamics simulations for flutter analysis of a real aircraft in the transonic regime are presented.
Abstract: This paper demonstrates coupled time-domain computational-fluid-dynamics (CFD) and computationalstructural-dynamics simulations for flutter analysis of a real aircraft in the transonic regime. It is shown that a major consideration for a certain class of structural models is the transformation method, which is used to pass information between the fluid and structural grids. The aircraft used for the calculations is the BAE Systems Hawk. A structural model, which has been developed by BAE Systems for simplified linear flutter calculations, only has a requirement for O(10) degrees of freedom. There is a significant mismatch between this and the surface grid on which loads and deflections are defined in the CFD calculation. This paper extends the constant volume tetrahedron tranformation, previously demonstrated for wing-only aeroelastic calculations, to multicomponent, or full aircraft, cases and demonstrates this for the Hawk. A comparison is made with the predictions of a linear flutter code.

40 citations


Journal ArticleDOI
TL;DR: In this article, a vortex lattice method is used to evaluate the performance and the time-dependent pressure distribution on the blade surface in a non-uniform flow, while efficient optimization algorithms are used to modify the blade sections.
Abstract: A new method for designing propeller blade sections is presented. A vortex lattice method is used to evaluate the performance and the time-dependent pressure distribution on the blade surface in a non-uniform flow, while efficient optimization algorithms are used to modify the blade sections. Two different designs were carried out in this study. The first was a design to realize a target pressure distribution in a rotating three-dimensional flow. A two-dimensional wing theory was used to obtain the target pressure distribution. The predicted increase in efficiency and the reduction in the cavity volume were confirmed by model experiments. The second was a design to maximize the propeller efficiency. By this method, the propeller efficiency was improved by 1.2% under the constrains of constant thrust and a prescribed margin for face cavitation.

27 citations


Proceedings ArticleDOI
Ernest Brock Keen1
06 Jun 2005
TL;DR: In this article, an aerodynamic analysis methodology for upper surface blowing aerodynamics is presented, which is useful for aerodynamic estimation in the conceptual and preliminary design phases of USB or Distributed Propulsion aircraft concepts.
Abstract: An aerodynamic analysis methodology for Upper Surface Blowing aerodynamics is presented. This methodology is useful for aerodynamic estimation in the conceptual and preliminary design phases of USB or USB/Distributed Propulsion aircraft concepts. Analytical flow models together with an examination of some two-dimensional experimental data is used to establish the method. The method was then extended to treat fully 3-D wings. Comparisons of the method with experimental data from wind tunnel and flight-testing of USB designs demonstrates its usefulness. Finally, a brief comparison was done with an existing Vortex Lattice Method for USB wings, and the current method demonstrated good agreement.

23 citations


01 Jan 2005
TL;DR: In this article, the authors describe the methodology and computational design strategies used to develop a series of fixed wing micro air vehicles (MAVs) at the Ghent University, which are used to find an optimal MAV-platform that is bound to geometrical constraints but superior in its performance.
Abstract: The paper describes the methodology and computational design strategies used to develop a series of fixed wing micro air vehicles (MAVs) at the Ghent University. The emphasis of the research is to find an optimal MAV-platform that is bound to geometrical constraints but superior in its performance. This requires a multidisciplinary design optimisation but the challenges are mainly of aerodynamic nature. Key areas are endurance, stability, controllability, manoeuvrability and component integration. The highly three-dimensional low Reynolds number flow, the lack of experimental databases and analytical or empirical models of MAV-aerodynamics required fundamental research of the phenomena. This includes the use of a vortex lattice method, three-dimensional CFD-computations and a numerical propeller optimisation method to derive the forces and their derivatives of the MAV and propeller for performance and stability-related optimisation studies. The design method leads to a simple, stable and robust flying wing MAV-platform that has the agility of a fighter airplane. A prototype, the UGMAV25, was constructed and flight tests were performed. The capabilities of the MAV were tested in a series of successful flight manoeuvres. The UGMAV15, a MAV with a span of 15cm, is also developed to test flight-qualities and endurance at this small scale. With the current battery technology, a flight-time of at least one hour is expected.

20 citations


Journal ArticleDOI
TL;DR: In this article, the half-span of the hitchhiker aircraft by the half span of the mother ship was analyzed. But the authors focused on the non-dimensional half-spans of the two-dimensional plane and the hitch-hiker.
Abstract: Nomenclature bH = nondimensionalized half-span of the hitchhiker aircraft by the half-span of the hitchhiker aircraft, Eq. (1) bM = half-span of the mothership divided by the half-span of the hitchhiker aircraft dt = time step, s dy = distance between the mothership and the hitchhiker divided by the half-span of the hitchhiker aircraft dz = relative height between the mothership and the hitchhiker divided by the half-span of the hitchhiker aircraft N = total number of elements representing each wing (u, v) H j = induced velocity at a wake vortex j on the hitchhiker aircraft by other vortices on the hitchhiker aircraft (u, v) M j = induced velocity at a wake vortex j on the hitchhiker aircraft by vortices from the mothership aircraft (u, v) H j = induced velocity at a wake vortex j on the mothership aircraft by vortices on the hitchhiker aircraft (u, v) M j = induced velocity at a wake vortex j on the mothership aircraft from other vortices on the mothership aircraft x = downstreamwise distance from a wing’s trailing edge H 0 = maximum circulation on the hitchhiker for an elliptic load distribution M 0 = maximum circulation on the mothership for an elliptic load distribution δ = smoothing factor, 0.1

13 citations


01 Aug 2005
TL;DR: In this paper, the analysis tools are embedded in a parametric modelling environment to predict aerodynamic loads on speciflc structural parts, like the fln, during dynamic manoeuvres.
Abstract: This paper addresses the development of analysis tools for ∞ight loads predic- tion in the pre-design stage. The analysis tools are embedded in a parametric modelling environment. Emphasis will be on prediction of aerodynamic loads on speciflc structural parts, like the fln, during dynamic manoeuvres. Principal requirement is that these loads can be computed with low efiort, but with su-cient accuracy. In the frame of this work, an available transport aircraft model has been taken as reference. The aerodynamic loads on the fln are computed using the Vortex Lattice Method (VLM), allowing for comparison with the original aerodynamics data base. For this structural com- ponent of the aircraft, a dense panel grid is chosen. In order to account for aerodynamic cross interferences, the remainder of the aircraft geometry is also taken into account, but with a considerably coarser grid. From the comparison with the original database, correction factors and uncertainty bounds are estimated. Next, the geometry of the fln is modifled. Based on aerodynamic loads com- puted with the VLM, the impact on (lateral) manoeuvre loads is analyzed. Hereby the estimated uncertainty levels from the flrst step are used to predict sensitivities for consid- eration in structural sizing.

11 citations


Proceedings ArticleDOI
TL;DR: In this paper, a finite volume method based Euler solver (GBFLOW) is applied to predict the flow field around the open or ducted propellers, coupled with MPUF-3A in order to determine the interaction of the propeller with the inflow (i.e. the effective wake) or with the duct.
Abstract: Recently developed methods at UT Austin for the analysis of open or ducted propellers are presented, and then coupled with a constrained nonlinear optimization method to design blades of open or ducted propellers for maximum efficiency satisfying the minimum pressure constraint for fully wetted case, or the specified maximum allowable cavity area for cavitating case. A vortex lattice method (named MPUF3A) is applied to analyze the unsteady cavitating performance of open or ducted propellers subject to non-axisymmetric inflows. A finite volume method based Euler solver (named GBFLOW) is applied to predict the flow field around the open or ducted propellers, coupled with MPUF-3A in order to determine the interaction of the propeller with the inflow (i.e. the effective wake) or with the duct. The blade design of open or ducted propeller is performed by using a constrained nonlinear optimization method (named CAVOPT-BASE), which uses a database of computed performance for a set of blade geometries constructed from a base-propeller. The performance is evaluated using MPUF-3A and GBFLOW. CAVOPT-BASE approximates the database using the least square method or the linear interpolation method, and generates the coefficients of polynomials based on the design parameters, such as pitch, chord, and camber. CAVOPT-BASE finally determines the optimum blade design parameters, so that the propeller produces the desired thrust for the given constraints on the pressure coefficient or the allowed amount of cavitation.

10 citations


Journal Article
TL;DR: In this article, a submerged vortex lattice method for calculation of the flow around a 3-D hydrofoil is presented, where the normal dipoles are posted on a second surface submerged under the wing surface and on a tail vortex surface.
Abstract: A submerged vortex lattice method for calculation of the flow around a 3-D hydrofoil is presented.The normal dipoles are posted on a second surface submerged under the wing surface and on a tail vortex surface.The control points are posted on the wing surface.The nonlinear free surface boundary condition is considered and the hydrodynamics forces of the hydrofoil near the free surface are calculated by the submerged vortex lattice method.The computational results show that the present method is correct and available.This method can be used for the hydrodynamic computation of the varied hydrofoils and stabilizing fins.

8 citations


Journal ArticleDOI
TL;DR: In this paper, the critical speed of antisymmetric flutter has an abnormally strong dependence on stabilizer deflections and angle of attack on a T-shaped empennage.
Abstract: It was found using wind-tunnel tests of airplanes with T empennage that the critical speed of antisymmetric flutter (based on composition of bending and torsional oscillations of the vertical tail) has an abnormally strong dependence on stabilizer deflections and angle of attack. This specific kind of antisymmetric flutter is characterized by relatively large amplitudes of oscillations of the stabilizer in its plane. Additional work of the induced drag forces on the in-plane component of oscillations might explain the nature of this kind of flutter. The numerical method for flutter analysis is described, which takes into account the effect of angles of attack and sideslip and aerodynamic control angles on flutter critical parameters. The method is based on a modification of the vortex lattice method and allows for induced drag when computing generalized aerodynamic forces. Numerical results for the flutter critical speed compare well with test data for a dynamically similar model of the civil airplane T-shaped empennage.

7 citations


10 Mar 2005
TL;DR: In this article, a non-linear vortex lattice method was used to optimize the mutual distance between the hydrofoils of a 40-knot, 40m catamaran with a hydrofoil system developed for modern high speed catamarans.
Abstract: Extensive experimental investigations of hydrofoil-assisted catamarans have identified the main hydrodynamic parameters affecting the performance of these vessels. Design principles of existing vessels are discussed in the light of these hydrodynamic findings. The experience gained from experimental testing has provided the basis for the development of a non-linear vortex lattice method for design purposes. The method is validated by comparison with experimental results and applied to the problem of optimizing a 40-knot, 40m hydrofoil-assisted catamaran with a hydrofoil system developed for modern high-speed catamarans. It is shown that the method can be successfully applied to optimization problems of these vessels as it successfully captures the complex hull-foil interactions. Results of the numerical investigation performed, indicate that optimizing the mutual distance between the hydrofoils can significantly improve the lift to drag ratio of such a vessel.

4 citations


Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this article, an experimental effort was undertaken to assess the effectiveness and efficiency of three winglets mounted chordwise to the tip of a rectangular wing (NACA 0018) and the results showed that the winglets placed at 60, 45 and 30 degrees, respectively, produced nominal 4% higher lift and 46% lower drag.
Abstract: An experimental effort was undertaken to assess the effectiveness and efficiency of three winglets mounted chordwise to the tip of a rectangular wing (NACA 0018 section). The winglets, with an aspect ratio of 3.6, were mounted on a half-span wing having an aspect ratio of 3.1. Twenty configurations of varying dihedral arrangements were analyzed with a vortex lattice method and tested in a low-speed wind tunnel at a Reynolds number of 600,000. In general, the arrangements involving high dihedral angles had lower performance increments, due to lower lift and higher interference drag. More specifically, the results showed that the winglets placed at 60, 45, and 30 degrees, respectively, produced nominal 4% higher lift and 46% lower drag. The most dramatic findings from this study show that positioning the winglet dihedral angles had the result of adjusting the point of maximum L/D and the magnitude of the pitching moment coefficient. These observations suggest that multiple winglet dihedral changes affect the lift, drag, and pitching moment in such a way that they are feasible for use as actively-controlled surfaces to improve the performance of aircraft at various flight conditions and to “tune” the longitudinal stability characteristics of the wing.Copyright © 2005 by ASME

Journal Article
TL;DR: In this article, a computer simulation system of the hydrodynamic performance of the propeller-rudder-rummer bubble combination was built, in which vortex lattice method and Hess-Smith boundary element method were used.
Abstract: Computer simulation system of the hydrodynamic performance of the propeller-rudder-rudder bubble combination was built.The hydrodynamic performance computation method of the propeller-rudder-rudder bubble combination was studied,in which the hydrodynamic performance of the propeller was calculated with vortex lattice method,while the influence of the hub to the hydrodynamic performance of the propeller was calculated with Hess-Smith boundary element method.For thinking about the influence of the rudder and rudder bubble,the velocities induced by the rudder and rudder bubble was regarded as correction of the velocity of the incoming flow of the propeller and hub.Computer simulation system was used to design and simulate four kinds of propeller-rudder-rudder bubble combination,then the comparison with the computation result of the original propeller-rudder design was carried out.It is shown that the designed rudder bubbles can increase the efficiency of propeller obviously,in which the dissymmetric rudder bubbleachieves energy-saving effect 5.1% and increases the power reserve of main engine up to 5% in real boat test.

01 Jan 2005
TL;DR: In this article, a new residual unsteady aerodynamic model suitable for the simulation of maneuvering aircraft is presented, which is based on accurate steady aerodynamic loads from a database in combination with a time stepping lifting-surface method.
Abstract: In this paper a new residual unsteady aerodynamic model suitable for the simulation of maneuvering aircraft is presented. Rather than obtaining the time domain unsteady aerodynamic loading from a rational function approximation of frequency domain loads, the model is based on accurate steady aerodynamic loads from a database in combination with a time stepping lifting-surface method. The time stepping method provides circulatory load correction factors for the steady database loads and unsteady non-circulatory load increments. It is based on a solution by vortex rings and allows for the accurate modelling of the wake shape. As a test case, a typical modern transport aircraft wing is analyzed. Steady calculations performed with the lifting-surface method are in excellent agreement with a commercial vortex lattice method. The effect of wing thickness is quantified by comparison with surface panel and Euler CFD computations. Unsteady calculations performed with the lifting-surface method are compared to an analytical approximation for a finite aspect ratio wing in heaving motion and show good agreement. The residual unsteady aerodynamic model is tested for the heaving motion of the transport aircraft wing and compared to unsteady Euler CFD reference results. The new method shows good agreement for total wing lift and pitching moment but over-predicts the unsteady effect for local lift and pitching moment.

Journal Article
TL;DR: In this article, the authors evaluated the security of an underwater towed system which is deployed or retracted from the up stabilizer of a submarine by calculating the near wake flow field of the propeller and hull.
Abstract: In order to evaluate the security of an underwater towed system which is deployed or retracted from the up stabilizer of a submarine, the near wake flow field of the propeller and hull was calculated. The vortex lattice method is used for the propeller based on the lifting surface theory, and the panel method is used for the hull, and also the interaction of the two parts is taken into account. A dynamic model of the towed system was established in the non-uniform wake flow field, and the shape of the towed system was investigated by finite difference method. The results of the calculation show that the security is enough for deploying and retracting cable.