07 Jun 2004
TL;DR: The loose coupling methodology is shown to be stable, convergent, and robust with full coupling of normal force, pitching moment, and chord force over a range of flight conditions.
01 May 2007
TL;DR: In this article, the aerodynamic interference effects on tiltrotor performance in cruise were investigated using comprehensive calculations, to better understand the physics and to quantify the effects on the aircraft design.
Abstract: Abstract : The aerodynamic interference effects on tiltrotor performance in cruise are investigated using comprehensive calculations, to better understand the physics and to quantify the effects on the aircraft design. Performance calculations were conducted for 146,600-lb conventional and quad tiltrotors, which are to cruise at 300 knots at 4000 ft/95 deg F condition. A parametric study was conducted to understand the effects of design parameters on the performance of the aircraft. Aerodynamic interference improves the aircraft lift-to-drag ratio of the baseline conventional tiltrotor. However, interference degrades the aircraft performance of the baseline quad tiltrotor, due mostly to the unfavorable effects from the front wing to the rear wing. A reduction of rotor tip speed increased the aircraft lift-to-drag ratio the most among the design parameters investigated.
TL;DR: In this paper, the concept of sliding meshes is introduced to account for the relative motion between the fuselage and the rotor blades, where a sliding surface forms a boundary between a CFD mesh around a fuselage, and a rotor-fixed CFD meshes which rotates to explain the movement of the rotor.
Abstract: SUMMARY The study of rotor–fuselage interactional aerodynamics is central to the design and performance analysis of helicopters. However, regardless of its significance, rotor–fuselage aerodynamics has so far been addressed by very few authors. This is mainly due to the difficulties associated with both experimental and computational techniques when such complex configurations, rich in flow physics, are considered. In view of the above, the objective of this study is to develop computational tools suitable for rotor–fuselage engineering analysis based on computational fluid dynamics (CFD). To account for the relative motion between the fuselage and the rotor blades, the concept of sliding meshes is introduced. A sliding surface forms a boundary between a CFD mesh around the fuselage and a rotor-fixed CFD mesh which rotates to account for the movement of the rotor. The sliding surface allows communication between meshes. Meshes adjacent to the sliding surface do not necessarily have matching nodes or even the same number of cell faces. This poses a problem of interpolation, which should not introduce numerical artefacts in the solution and should have minimal effects on the overall solution quality. As an additional objective, the employed sliding mesh algorithms should have small CPU overhead. The sliding mesh methods developed for this work are demonstrated for both simple and complex cases with emphasis placed on the presentation of the inner workings of the developed algorithms. Copyright q 2008 John Wiley & Sons, Ltd.
04 Jan 2010
TL;DR: The first version of the Helios platform as mentioned in this paper is based on an overset framework that employs unstructured mixed-element meshes in the near-body domain combined with high-order Cartesian meshes in o-body.
Abstract: This article describes the architecture, components, capabilities, and validation of the rst version of the Helios platform, targeted towards rotorcraft aerodynamics. Capabilities delivered in the rst version include fuselage aerodynamics with and without momentumdisk rotor models, and isolated rotor dynamics for ideal hover and forward ight coupled with aeroelasticity and trim. Helios is based on an overset framework that employs unstructured mixed-element meshes in the near-body domain combined with high-order Cartesian meshes in the o-body domain. In addition, the aerodynamics solution is coupled with structural dynamics and trim using a delta-coupling algorithm. The near-body CFD, obody CFD, CSD and trim modules are coupled using a Python infrastructure that controls the execution sequence of the solution procedure. Specic validation studies presented include the Slowed Rotor Compound fuselage, Georgia Tech rotor body, TRAM rotor in hover and UH-60A rotor in forward ight. In all cases, Helios predictions are compared with experimental data and other state-of-the-art codes to demonstrate the accuracy, eciency and scalability of the code.
TL;DR: In this article, a computational fluid dynamics (CFD) model is coupled with a computational structural dynamics (CSD) to improve prediction of helicopter rotor vibratory loads in high-speed flight.
Abstract: A computational fluid dynamics (CFD) model is coupled with a computational structural dynamics (CSD) model to improve prediction of helicopter rotor vibratory loads in high-speed flight. The two key problems of articulated rotor aeromechanics in high-speed flight-advancing blade lift phase, and underprediction of pitch link load-are satisfactorily resolved for the UH-60A rotor. The physics of aerodynamics and structural dynamics is first isolated from the coupled aeroelastic problem. The structural and aerodynamic models are validated separately using the UH-60A Airloads Program data. The key improvement provided by CFD over a lifting-line aerodynamic model is explained. The fundamental mechanisms behind rotor vibration at high speed are identified as: 1) large elastic twist deformations and 2) inboard wake interaction. The large twist deformations are driven by transonic pitching moments at the outboard stations. CFD captures 3-dimensional unsteady pitching moments at the outboard stations accurately. CFD/CSD coupling improves elastic twist deformations via accurate pitching moments and captures the vibratory lift harmonics correctly. At the outboard stations (86.5% radius out), the vibratory lift is dominated by elastic twist. At the inboard stations (67.5% and 77.5% radius), a refined wake model is necessary in addition to accurate twist. The peak-to-peak pitch link load and lower harmonic waveform are accurately captured. Discrepancies for higher harmonic torsion loads remain unresolved even with measured airloads. The predicted flap-bending moments show a phase shift of about 10 deg over the entire rotor azimuth. This error stems from 1, 2, and 3/rev lift. The 1/rev lift is unaffected by CFD/CSD coupling. The 2 and 3/rev lift are significantly improved but do not fully resolve the 2 and 3/rev bending moment error.
TL;DR: In this paper, a technique to model unsteady flow phenomenon which involve simultaneous elastic motions of the boundaries and interaction with gust fields is discussed, including the effect of the gust fields caused by a vortex wake in to the flow computations.
Abstract: A technique to model unsteady flow phenomenon which involve simultaneous elastic motions of the boundaries and interaction with gust fields is discussed. The field velocity approach is used to include the effect of the gust fields caused by a vortex wake in to the flow computations. Elastic deformations of the boundaries causes changes in grid cell volumes which requires the rigorous enforcement of the Geometric Conservation Law. Mathematical modeling required to enforce conservation when performing such unsteady flow computations is detailed. The application of the technique developed to a variety of problems from simple 2-D model problems to more complex realistic problems are detailed. The predictions obtained are validated with exact analytical results/ experimental data as appropriate. Overall, the field velocity approach together with a technique to enforce the Geometric Conservation Law is found to provide a powerful tool for unsteady flow simulation.
••04 Jan 2011
TL;DR: The capabilities and development of the Helios version 2.0, or Shasta, software for rotary wing simulations, include off-body adaptive mesh refinement and the ability to handle multiple interacting rotorcraft components such as the fuselage, rotors, flaps and stores.
Abstract: This article summarizes the capabilities and development of the Helios version 2.0, or Shasta, software for rotary wing simulations. Specific capabilities enabled by Shasta include off-body adaptive mesh refinement and the ability to handle multiple interacting rotorcraft components such as the fuselage, rotors, flaps and stores. In addition, a new run-mode to handle maneuvering flight has been added. Fundamental changes of the Helios interfaces have been introduced to streamline the integration of these capabilities. Various modifications have also been carried out in the underlying modules for near-body solution, off-body solution, domain connectivity, rotor fluid structure interface and comprehensive analysis to accommodate these interfaces and to enhance operational robustness and efficiency. Results are presented to demonstrate the mesh adaptation features of the software for the NACA0015 wing, TRAM rotor in hover and the UH-60A in forward flight.