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At least 271 records · Page 15

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NASA NTRS2014

High-Lift OVERFLOW Analysis of the DLR-F11 Wind Tunnel Model

In response to the 2nd AIAA CFD High Lift Prediction Workshop, the DLR-F11 wind tunnel model is analyzed using the Reynolds-averaged Navier-Stokes flow solver OVERFLOW. A series of overset grids for a bracket-off landing configuration is constructed and analyzed as part of a general grid refinement study. This high Reynolds number (15.1 million) analysis is done at multiple angles-of-attack to evaluate grid resolution effects at operational lift levels as well as near stall. A quadratic constitutive relation recently added to OVERFLOW for improved solution accuracy is utilized for side-of-body separation issues at low angles-of-attack and outboard wing separation at stall angles. The outboard wing separation occurs when the slat brackets are added to the landing configuration and is a source of discrepancy between the predictions and experimental data. A detailed flow field analysis is performed at low Reynolds number (1.35 million) after pressure tube bundles are added to the bracket-on medium grid system with the intent of better understanding bracket/bundle wake interaction with the wing's boundary layer. Localized grid refinement behind each slat bracket and pressure tube bundle coupled with a time accurate analysis are exercised in an attempt to improve stall prediction capability. The results are inconclusive and suggest the simulation is missing a key element such as boundary layer transition. The computed lift curve is under-predicted through the linear range and over-predicted near stall, and the solution from the most complete configuration analyzed shows outboard wing separation occurring behind slat bracket 6 where the experiment shows it behind bracket 5. These results are consistent with most other participants of this workshop.

High-lift↗

NASA NTRS1982

Application of Zimmerman flutter-margin criterion to a wind tunnel model

The Zimmerman flutter margin criterion was studied by applying it to data obtained from a wind tunnel model. The sensitivity of the flutter margin parameter was explored with a parametric trend study and by calculation of the derivatives with respect to the input frequency and damping parameters. The criterion is simple in concept and application, and it serves as a good flutter onset predictor because it gives a nearly linear variation with dynamic pressure. However, accurate values of both frequency and damping of both modes involved in flutter are required for reliable flutter onset prediction. The simplified version using only frequencies gave a highly nonconservative flutter onset in one case and should not be used in general.

Bennett, R. M.↗

NASA NTRS1990

Digital-flutter-suppression-system investigations for the active flexible wing wind-tunnel model

Active flutter suppression control laws were designed, implemented, and tested on an aeroelastically-scaled wind tunnel model in the NASA Langley Transonic Dynamics Tunnel. One of the control laws was successful in stabilizing the model while the dynamic pressure was increased to 24 percent greater than the measured open-loop flutter boundary. Other accomplishments included the design, implementation, and successful operation of a one-of-a-kind digital controller, the design and use of two simulation methods to support the project, and the development and successful use of a methodology for on-line controller performance evaluation.

Perry, Boyd, III↗

NASA NTRS1999

Multi-Body Analysis of the 1/5 Scale Wind Tunnel Model of the V-22 Tiltrotor

The paper presents a multi-body analysis of the 1/5 scale wind tunnel model of the V-22 tiltrotor, the Wing and Rotor Aeroelastic Testing System (WRATS), currently tested at NASA Langley Research Center. An original multi-body formulation has been developed at the Dipartimento di Ingegneria Aerospaziale of the Politecnico di Milano, Italy. It is based on the direct writing of the equilibrium equations of independent rigid bodies, connected by kinematic constraints that result in the addition of algebraic constraint equations, and by dynamic constraints, that directly contribute to the equilibrium equations. The formulation has been extended to the simultaneous solution of interdisciplinary problems by modeling electric and hydraulic networks, for aeroservoelastic problems. The code has been tailored to the modeling of rotorcrafts while preserving a complete generality. A family of aerodynamic elements has been introduced to model high aspect aerodynamic surfaces, based on the strip theory, with quasi-steady aerodynamic coefficients, compressibility, post-stall interpolation of experimental data, dynamic stall modeling, and radial flow drag. Different models for the induced velocity of the rotor can be used, from uniform velocity to dynamic in flow. A complete dynamic and aeroelastic analysis of the model of the V-22 tiltrotor has been performed, to assess the validity of the formulation and to exploit the unique features of multi-body analysis with respect to conventional comprehensive rotorcraft codes; These are the ability to model the exact kinematics of mechanical systems, and the possibility to simulate unusual maneuvers and unusual flight conditions, that are particular to the tiltrotor, e.g. the conversion maneuver. A complete modal validation of the analytical model has been performed, to assess the ability to reproduce the correct dynamics of the system with a relatively coarse beam model of the semispan wing, pylon and rotor. Particular care has been used to model the kinematics of the gimbal joint, that characterizes the rotor hub, and of the control system, consisting in the entire swashplate mechanism. The kinematics of the fixed and the rotating plates have been modeled, with variable length control links used to input the controls, the rotating flexible links, the pitch horns and the pitch bearings. The investigations took advantage of concurring wind tunnel test runs, that were performed in August 1998, and allowed the acquisition of data specific to the multi-body analysis.

Ghiringhelli, G. L.↗

NASA NTRS1978

Stable boundary layer wind shear model for aircraft flight hazard definition

It is pointed out that wind shear, particularly at the lower altitudes in the terminal area, has been identified as being hazardous to aircraft operations. Accurate and reliable wind profiles are required for use in fast time and manned flight simulation studies aimed at fully defining and understanding the wind shear hazard. A description is presented of wind speed profiles for neutral and stable atmospheric conditions developed for the simulation studies to improve the safety and reliability of operations in the terminal area. The wind shear is mathematically modeled and the mathematical scenarios are presented in a format for direct application to wind shear hazard/flight simulation studies.

Frost, W.↗

NASA NTRS1990

Numerically Controlled Machining Of Wind-Tunnel Models

New procedure for dynamic models and parts for wind-tunnel tests or radio-controlled flight tests constructed. Involves use of single-phase numerical control (NC) technique to produce highly-accurate, symmetrical models in less time.

Kovtun, John B.↗

NASA NTRS1984

Cryogenic wind-tunnel model technology development activities at the NASA Langley Research Center

This paper summarizes the current cryogenic wind-tunnel model technology development activities at the NASA Langley Research Center. These research and development activities are being conducted in support of the design and fabrication of models for the new National Transonic Facility (NTF). The scope and current status of major research and development work is described and where available, data are presented from various investigations conducted to date. In addition, design and fabrication experience for existing developmental models to be tested in the NTF is discussed.

Young, C. P., Jr.↗

NASA NTRS1986

Thermal sensing of cryogenic wind tunnel model surfaces Evaluation of silicon diodes

Different sensors and installation techniques for surface temperature measurement of cryogenic wind tunnel models were investigated. Silicon diodes were selected for further consideration because of their good inherent accuracy. Their average absolute temperature deviation in comparison tests with standard platinum resistance thermometers was found to be 0.2 K in the range from 125 to 273 K. Subsurface temperature measurement was selected as the installation technique in order to minimize aerodynamic interference. Temperature distortion caused by an embedded silicon diode was studied numerically.

Daryabeigi, K.↗

NASA NTRS1986

Thermal sensing of cryogenic wind tunnel model surfaces - Evaluation of silicon diodes

Daryabeigi, Kamran↗

NASA NTRS1990

Digital-flutter-suppression-system investigations for the active flexible wing wind-tunnel model

Active flutter suppression control laws were designed, implemented, and tested on an aeroelastically-scaled wind-tunnel model in the NASA Langley Transonic Dynamics Tunnel. One of the control laws was successful in stabilizing the model while the dynamic pressure was increased to 24 percent greater than the measured open-loop flutter boundary. Other accomplishments included the design, implementation, and successful operation of a one-of-a-kind digital controller, the design and use of two simulation methods to support the project, and the development and successful use of a methodology for online controller performance evaluation.

Perry, Boyd, III↗

NASA NTRS1990

Design, implementation, simulation, and testing of digital flutter suppression systems for the active flexible wing wind-tunnel model

Active flutter suppression control laws were designed, implemented, and tested on an aeroelastically-scaled wind-tunnel model in the NASA Langley Transonic Dynamics Tunnel. One of the control laws was successful in stabilizing the model while the dynamic pressure was increased to 24 percent greater than the measured open-loop flutter boundary. Other accomplishments included the design, implementation, and successful operation of a one-of-a-kind digital controller, the design and use of two simulation methods to support the projet, and the development and successful use of a methodology for online controller performance evaluation.

Perry, Boyd, III↗

NASA NTRS1994

Holographic testing of composite propfans for a cruise missile wind tunnel model

Each of the approximately 90 composite propfan blades constructed for a 55 percent scale cruise missile wind tunnel model were holographically tested to obtain natural frequencies and mode shapes. These data were used not only for quality assurance, but also to select sets of similar blades for each blade row. Presented along with the natural frequency data is a description of a computer-based image processing system developed to supplement the photographic based system for holographic image analysis and storage. The new system is quicker and cheaper, the holograms are indexed better, and several engineers can access the data simultaneously. The only negative effect is a slight reduction in image resolution, which does not influence the end use.

Miller, Christopher J.↗

NASA NTRS1974

Experimental and theoretical investigation of a slotted noise shield model for wind tunnel walls

Tests at Mach 6 and 8 have been conducted on a model of a wind tunnel sound radiation shield which consists of interchangeable circular and wedge-shaped longitudinal rods with gaps between the rods for boundary layer removal. In view of the large effective sweep angle of the circular rods with respect to the local flow, the boundary layer behavior was surprisingly well represented by swept cylinder theory. Laminar flow was maintained up to a maximum local unit Reynolds number of 8 million per foot which would presumably be independent of model length for a given rod diameter by analogy with results on swept cylinders. Reduction in wind-tunnel sound levels within the shielded region of the circular rod model were about 90% of the maximum possible reduction for an ideal shield.

Harvey, W. D.↗

NASA NTRS1970

Performance of a fixed geometry wind tunnel model of an auxiliary inlet ejector with a clamshell flow diverter from Mach 0 to 1.2

Fixed geometry wind tunnel model of auxiliary inlet ejector with clamshell flow diverter from Mach 0 to 1.2

Johns, A. L.↗

NASA NTRS1989

Techniques for extreme attitude suspension of a wind tunnel model in a magnetic suspension and balance system

Although small scale magnetic suspension and balance systems (MSBSs) for wind tunnel use have been in existence for many years, they have not found general application in the production testing of flight vehicles. One reason for this is thought to lie in the relatively limited range of attitudes over which a wind tunnel model may be suspended. Modifications to a small MSBS to permit the suspension and control of axisymmetric models over angles of attack from less than zero to over ninety degrees are reported. Previous work has shown that existing arrangement of ten electromagnets was unable to generate one of the force components needed for control at extreme attitudes. Examination of possible solutions resulted in a simple alteration to rectify this deficiency. To generate the feedback signals to control the suspended model, an optical position sensing system using collimated laser beams and photodiode arrays was installed and tested. An analytical basis was developed for distributing the demands for force and moment needed for model stabilization amonge the electromagnets over the full attitude range. This was implemented by an MSBS control program able to continually adjust the distribution for the instantaneous incidence in accordance with prescheduled data. Results presented demonstrate rotations of models from zero to ninety degrees at rates up to ninety degrees per second, with pitching rates rising to several hundred degrees per second in response to step-change demands. A study of a design for a large MSBS suggests that such a system could be given the capability to control a model in six degrees of freedom over an unlimited angle of attack range.

Parker, David Huw↗

NASA NTRSDate not supplied

Topology Optimization of Low-Speed Aeroelastic Wind Tunnel Models

The goal of this work is to utilize topology optimization methods to obtain low-speed flexible wind tunnel models with simple jig outer mold lines, but highly-tuned aeroelastic flutter behavior. The wing is conceptually constructed with commonly-available 3D printed materials, of which the optimizer may select one of two at every location in the wing; a stiffer material meant to bear the loads, and a softer rubber-like material for space filling, and to form the outer mold line, where needed. Results are shown for three topological parameterizations: 2D topologies with a fixed nondesignable plate through the camber line, 2D parameterizations without the plate, and 3D parameterizations where the topology can vary though the depth of the wing, at a given planform location.

Aeroelasticity↗

NASA NTRS1972

The steady-state flow quality of an open return wind tunnel model.

The structural cost of open return wind tunnels is significantly less than that of the more conventional closed return wind tunnels. However, because of the effects of external winds, the flow quality of open return wind tunnels is an area of concern at the low speeds required for V/STOL testing. The development of a configuration which has good flow quality at low as well as at high test speeds is described. The flow quality required at the low test speeds of interest for V/STOL aircraft is discussed and alternatives to the traditional manner of specifying the flow quality requirements in terms of dynamic pressure and angle of attack are suggested.

Mort, K. W.↗

NASA NTRS1998

Parameter Estimation of Actuators for Benchmark Active Control Technology (BACT) Wind Tunnel Model with Analysis of Wear and Aerodynamic Loading Effects

This report describes the development of transfer function models for the trailing-edge and upper and lower spoiler actuators of the Benchmark Active Control Technology (BACT) wind tunnel model for application to control system analysis and design. A simple nonlinear least-squares parameter estimation approach is applied to determine transfer function parameters from frequency response data. Unconstrained quasi-Newton minimization of weighted frequency response error was employed to estimate the transfer function parameters. An analysis of the behavior of the actuators over time to assess the effects of wear and aerodynamic load by using the transfer function models is also presented. The frequency responses indicate consistent actuator behavior throughout the wind tunnel test and only slight degradation in effectiveness due to aerodynamic hinge loading. The resulting actuator models have been used in design, analysis, and simulation of controllers for the BACT to successfully suppress flutter over a wide range of conditions.

Waszak, Martin R.↗