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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Three dimensional flow simulation with application to aeroelastic analysis

The three-dimensional flowfield about realistic launch vehicle configurations is simulated using the Reynolds-averaged Navier-Stokes equations. Turbulent mixing is accounted for by means of the two-layer Baldwin and Lomax (1978) algebraic eddy viscosity model. The Beam and Warming (1976) implicit approximate factorization algorithm is used for the solution of the finite difference equations. Applications include the study of the flowfield about a hemisphere-cylinder configuration both in the subsonic and supersonic flight regimes, and about two hammerhead payload configurations at transonic speeds. A method is also described which permits incorporating this flow solver into a complete algorithm to perform time-domain aeroelastic stability analyses. The vehicle is modeled as a free-free beam and modal superposition techniques are used for the structural-dynamic formulation. Aeroelastic analyses were performed for the hammerhead configurations.

Azevedo, Joao Luiz F.↗
NASA NTRS1988

Aeroelastic response of metallic and composite propfan models in yawed flow

An analytical investigation of aeroelastic response of metallic and composite propfan models in yawed flow was performed. The analytical model is based on the normal modes of a rotating blade and the three-dimensional unsteady lifting surface aerodynamic theory including blade mistuning. The calculated blade stresses or strains are compared with published wind tunnel data on two metallic and three composite propfan wind tunnel models. The comparison shows a good agreement between theory and experiment. Additional parametric results indicate that blade response is very sensitive to the blade stiffness and also to blade frequency and mode shape mistuning. From these findings, it is concluded that both frequency and mode shape mistuning should be included in aeroelastic response analysis. Furthermore, both calculated and measured strains show that combined blade frequency and mode shape mistuning has beneficial effects on response due to yawed flow.

Kaza, Krishna Rao↗
NASA NTRS1988

Aeroelastic optimization of a helicopter rotor

Structural optimization of a hingeless rotor is investigated to reduce oscillatory hub loads while maintaining aeroelastic stability in forward flight. Design variables include spanwise distribution of nonstructural mass, chordwise location of blade center of gravity and blade bending stiffnesses (flap, lag and torsion). A comprehensive aeroelastic analysis of rotors, based on a finite element method in space and time, is linked with optimization algorithms to perform optimization of rotor blades. Sensitivity derivatives of blade response, hub loads, and eigenvalues with respect to the design variables are derived using a direct analytical approach, and constitute an integral part of the basic blade response and stability analyses. This approach reduces the computation time substantially; an 80 percent reduction of CPU time to achieve an optimum solution, as compared to the widely adopted finite difference approach. Through stiffness and nonstructural mass distributions, a 60-90 percent reduction in all six 4/rev hub loads is achieved for a four-bladed soft-inplane rotor.

Lim, Joon W.↗
NASA NTRS1989

Analytic simulation of higher harmonic control using a new aeroelastic model

This paper describes a higher harmonic control (HHC) study of a four bladed hingeless rotor using a coupled flap-lag-torsional aeroelastic stability and response analysis which incorporates finite-state, time-domain aerodynamics. The rotor trim condition is determined using a coupled trim-aeroelastic analysis. Deterministic and cautious controllers based on local and global HHC models are implemented with different combinations of input parameters identified using a Kalman filter. The effects of unsteady versus quasisteady aerodynamic modeling on HHC simulations are investigated, including the effectiveness of the local and global HHC models and the advantages of different identification schemes.

Friedmann, P. P.↗
NASA NTRS1990

Airloads, wakes, and aeroelasticity

Fundamental considerations regarding the theory of modeling of rotary wing airloads, wakes, and aeroelasticity are presented. The topics covered are: airloads and wakes, including lifting-line theory, wake models and nonuniform inflow, free wake geometry, and blade-vortex interaction; aerodynamic and wake models for aeroelasticity, including two-dimensional unsteady aerodynamics and dynamic inflow; and airloads and structural dynamics, including comprehensive airload prediction programs. Results of calculations and correlations are presented.

Johnson, Wayne↗
NASA NTRS1990

Aeroelastic optimization of a helicopter rotor using an efficient sensitivity analysis

To reduce oscillatory hub loads in forward flight, a structural optimization analysis of a hingeless helicopter rotor has been developed and applied. The aeroelastic analysis of the rotor is based on a finite element method in space and time, and linked with automated optimization algorithms. For the optimization analysis two types of structural representation are used: a generic stiffness-distribution and a single-cell thin-walled beam. For the first type, the design variables are nonstructural mass and its placement, chordwise center of gravity offset from the elastic axis, and stiffness. For the second type, width, height and thickness of spar are used as design variables. For the behavior constraints, frequency placement, autorotational inertia and aeroelastic stability of the blade are included. The required sensitivity derivatives are obtained using a direct analytical approach. An optimum oscillatory hub load shows a 25-77 percent reduction for the generic blade, and 30-50 percent reduction for the box-beam.

Lim, Joon W.↗
NASA NTRS1990

Aeroelastic problems in turbomachines

A review of the field of turbomachinery aeroelasticity is presented. Developments over the past decade are emphasized, and an assessment of possible future directions of research is offered. The paper reviews the areas of unsteady cascade flows, structural modeling, and flutter prediction methods. Representative results for unsteady flow calculations and flutter boundary predictions in subsonic, transonic, and supersonic flows are discussed, including recent calculations based on the methods of computational fluid mechanics. Results from current attempts to correlate experimental data with theoretical predictions are discussed briefly. It is recommended that future research include investigations of novel approaches to flutter calculations that can take full advantage of parallel processing supercomputers. The feasibility of using mistuning and aeroelastic tailoring as passive flutter suppression techniques should also be pursued.

Bendiksen, Oddvar O.↗
NASA NTRS1990

Experimental aeroelasticity - History, status and future in brief

The National Aeronautics and Space Administration (NASA) conducts wind-tunnel experiments to determine and understand the aerolastic characteristics of new and advanced flight vehicles, including fixed-wing, rotary-wing, and space-launch configurations. Review and assessments are made of the state-of-the-art in experimental aeroelasticity regarding available facilities, measurement techniques, and other means and devices useful in testing. In addition, some past experimental programs are described which assisted in the development of new technology, validated new analysis codes, or provided needed information for clearing flight envelopes of unwanted aeroelastic response. Finally, needs and requirements for advances and improvements in testing capabilities for future experimental research and development programs are described.

Ricketts, Rodney H.↗
NASA NTRS1989

Unsteady aerodynamics methods for transonic aeroelastic analysis

The paper describes the current status of methods development for transonic aeroelastic analysis within the Unsteady Aerodynamics Branch at NASA Langley. The paper first highlights the development of an approximate factorization (AF) algorithm for solution of the unsteady transonic small-distribution (TSD) equation. The AF algorithm has been used as the basis for a three-dimensional TSD code for complete aircraft applications. The paper also describes the development of solution algorithms for the unsteady Euler equations based on the use of unstructured meshes. These Euler methods contain a dynamic mesh algorithm, which is a general procedure to move or deform the mesh so that it continuously conforms to the instantaneous shape of the aeroelastically deformed vehicle.

Batina, John T.↗
NASA NTRS1989

Theoretical and experimental investigation of the aeroelastic stability of an advanced bearingless rotor in hover and forward flight

The aeroelastic stability of a shaft-fixed, 1/8th Froude scaled bearingless rotor was investigated in a series of wind tunnel experiments simulating a wide range of operating conditions. A finite element formulation was used to perform a parallel theoretical analysis, with the goal of determining whether a bearingless rotor system could be made aeroelastically stable without the incorporation of auxilliary dampers. A quick estimate of lag mode damping was provided by a refined moving-block analysis implemented in real time which predicted similar damping values. Model rotor and blade properties were also determined, and these properties were used as inputs for a newly refined bearingless rotor analysis. Predicted results were compared with experimental results in hover and forward flight. Results indicated that soft pitch link stiffness increases pitch-lag coupling and stabilizes lag mode stability in hover and at low advance ratios, but destabilizes at higher advance ratios.

Wang, James M.↗
NASA NTRS1991

Calculation Of Aeroelastic Transients Using Euler Equations

Method for calculation of transient aeroelastic effects on airplane wings based on Euler equations of flow. Conforming grids facilitate calculations of flows about changing shapes. Capability to compute aeroelastic effects reduces cost of developing aircraft.

Guruswamy, Guru P.↗
NASA NTRS1991

Efficient computation of aerodynamic influence coefficients for aeroelastic analysis on a transputer network

Aeroelastic analysis is multi-disciplinary and computationally expensive. Hence, it can greatly benefit from parallel processing. As part of an effort to develop an aeroelastic capability on a distributed memory transputer network, a parallel algorithm for the computation of aerodynamic influence coefficients is implemented on a network of 32 transputers. The aerodynamic influence coefficients are calculated using a 3-D unsteady aerodynamic model and a parallel discretization. Efficiencies up to 85 percent were demonstrated using 32 processors. The effect of subtask ordering, problem size, and network topology are presented. A comparison to results on a shared memory computer indicates that higher speedup is achieved on the distributed memory system.

Janetzke, David C.↗
NASA NTRS1991

ASTROP2 users manual: A program for aeroelastic stability analysis of propfans

A user's manual is presented for the aeroelastic stability and response of propulsion systems computer program called ASTROP2. The ASTROP2 code preforms aeroelastic stability analysis of rotating propfan blades. This analysis uses a two-dimensional, unsteady cascade aerodynamics model and a three-dimensional, normal-mode structural model. Analytical stability results from this code are compared with published experimental results of a rotating composite advanced turboprop model and of nonrotating metallic wing model.

Narayanan, G. V.↗
NASA NTRS1991

Model order reduction applied to a hot-bench simulation of an aeroelastic wind-tunnel model

Simulations of an aeroelastically scaled wind-tunnel model were developed for hot-bench testing of a digital controller. The digital controller provided active flutter-suppression, rolling-maneuver-load alleviation, and plant estimation. To achieve an acceptable time scale for the hot-bench application, the mathematical model of the wind-tunnel model was reduced from 220 states to approximately 130 states while assuring that the required accuracy was preserved for all combinations of 10 inputs and 56 outputs. The reduction was achieved by focussing on a linear, aeroelastic submodel of the full mathematical model and by applying a method based on the internally balanced realization of a dynamic system. The error-bound properties of the internally balanced realization significantly contribute to its utility in the model reduction process. The reduction method and the results achieved are described.

Buttrill, Carey S.↗
NASA NTRS1991

The benchmark aeroelastic models program: Description and highlights of initial results

An experimental effort was implemented in aeroelasticity called the Benchmark Models Program. The primary purpose of this program is to provide the necessary data to evaluate computational fluid dynamic codes for aeroelastic analysis. It also focuses on increasing the understanding of the physics of unsteady flows and providing data for empirical design. An overview is given of this program and some results obtained in the initial tests are highlighted. The tests that were completed include measurement of unsteady pressures during flutter of rigid wing with a NACA 0012 airfoil section and dynamic response measurements of a flexible rectangular wing with a thick circular arc airfoil undergoing shock boundary layer oscillations.

Bennett, Robert M.↗
NASA NTRS1992

A historical overview of tiltrotor aeroelastic research at Langley Research Center

The Bell/Boeing V-22 Osprey which is being developed for the U.S. Military is a tiltrotor aircraft combining the versatility of a helicopter with the range and speed of a turboprop airplane. The V-22 represents a tiltrotor lineage which goes back over forty years, during which time contributions to the technology base needed for its development were made by both government and industry. NASA Langley Research Center has made substantial contributions to tiltrotor technology in several areas, in particular in the area of aeroelasticity. The purpose of this talk is to present a summary of the tiltrotor aeroelastic research conducted at Langley which has contributed to that technology.

Kvaternik, Raymond G.↗
NASA NTRS1992

Sensitivity analysis of dynamic aeroelastic responses

This paper summarizes ongoing research on the sensitivity analysis of dynamic aeroelastic response of wings. Two approaches are being used to express the unsteady aerodynamic loads: (1) the frequency-domain approach, and (2) the state-space approach. The frequency-domain approach is demonstrated on a three-dimensional box wing and the state-space domain approach is demonstrated on a simple two-dimensional sectional model. Three different methods are used to find the sensitivities: (1) a purely finite difference approach, (2) a semi-analytical approach in which an analytical expression is used for calculating the sensitivity of an eigenvalue of the complex valued aeroelastic matrix, however, the derivatives of the components of the matrix are obtained using finite difference, and (3) a semi-analytic approach that differs from (2) in the sense that the sensitivity of the aerodynamic matrix is now obtained analytically. A good agreement is seen between the three sets of results. For the two-dimensional sectional model the results for the sensitivities of the flutter speed with respect to the various parameters are obtained.

Kapania, Rakesh K.↗
NASA NTRS1992

The benchmark aeroelastic models program: Description and highlights of initial results

An experimental effort was implemented in aeroelasticity called the Benchmark Models Program. The primary purpose of this program is to provide the necessary data to evaluate computational fluid dynamic codes for aeroelastic analysis. It also focuses on increasing the understanding of the physics of unsteady flows and providing data for empirical design. An overview is given of this program and some results obtained in the initial tests are highlighted. The tests that were completed include measurement of unsteady pressures during flutter of a rigid wing with an NACA 0012 airfoil section and dynamic response measurements of a flexible rectangular wing with a thick circular arc airfoil undergoing shock boundary layer oscillations.

Bennett, Robert M.↗