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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Effect of wind tunnel acoustic modes on linear oscillating cascade aerodynamics

The aerodynamics of a biconvex airfoil cascade oscillating in torsion is investigated using the unsteady aerodynamic influence coefficient technique. For subsonic flow and reduced frequencies as large as 0.9, airfoil surface unsteady pressures resulting from oscillation of one of the airfoils are measured using flush-mounted high-frequency-response pressure transducers. The influence coefficient data are examined in detail and then used to predict the unsteady aerodynamics of a cascade oscillating at various interblade phase angles. These results are correlated with experimental data obtained in the traveling-wave mode of oscillation and linearized analysis predictions. It is found that the unsteady pressure disturbances created by an oscillating airfoil excite wind tunnel acoustic modes which have detrimental effects on the experimental data. Acoustic treatment is proposed to rectify this problem.

Buffum, Daniel H.↗
NASA NTRS1994

Effect of wind tunnel acoustic modes on linear oscillating cascade aerodynamics

The aerodynamics of a biconvex airfoil cascade oscillating in torsion is investigated using the unsteady aerodynamic influence coefficient technique. For subsonic flow and reduced frequencies as large as 0.9, airfoil surface unsteady pressures resulting from oscillation of one of the airfoils are measured using flush-mounted high-frequency-response pressure transducers. The influence coefficient data are examined in detail and then used to predict the unsteady aerodynamics of a cascade oscillating at various interblade phase angles. These results are correlated with experimental data obtained in the traveling-wave mode of oscillation and linearized analysis predictions. It is found that the unsteady pressure disturbances created by an oscillating airfoil excite wind tunnel acoustic modes, which have detrimental effects on the experimental results. Acoustic treatment is proposed to rectify this problem.

Buffum, D. H.↗
NASA NTRS1998

Process Developed for Forming Urethane Ice Models

A new process for forming ice shapes on an aircraft wing was developed at the NASA Lewis Research Center. The innovative concept was formed by Lewis' Icing Research Tunnel (IRT) team, and the hardware was manufactured by Lewis' Manufacturing Engineering Division. This work was completed to increase our understanding of the stability and control of aircraft during icing conditions. This project will also enhance our evaluation of true aerodynamic wind tunnel effects on aircraft. In addition, it can be used as a design tool for evaluating ice protection systems.

Vannuyen, Thomas↗
NASA NTRS2006

Techniques for Connecting Superconducting Thin Films

Several improved techniques for connecting superconducting thin films on substrates have been developed. The techniques afford some versatility for tailoring the electronic and mechanical characteristics of junctions between superconductors in experimental electronic devices. The techniques are particularly useful for making superconducting or alternatively normally conductive junctions (e.g., Josephson junctions) between patterned superconducting thin films in order to exploit electron quantum-tunneling effects. The techniques are applicable to both low-Tc and high-Tc superconductors (where Tc represents the superconducting- transition temperature of a given material), offering different advantages for each. Most low-Tc superconductors are metallic, and heretofore, connections among them have been made by spot welding. Most high-Tc superconductors are nonmetallic and cannot be spot welded. These techniques offer alternatives to spot welding of most low-Tc superconductors and additional solutions to problems of connecting most high-Tc superconductors.

Mester, John↗
NASA NTRS2012

Localized, Non-Harmonic Active Flap Motions for Low Frequency In-Plane Rotor Noise Reduction

A first-of-its-kind demonstration of the use of localized, non-harmonic active flap motions, for suppressing low frequency, in-plane rotor noise, is reported in this paper. Operational feasibility is verified via testing of the full-scale AATD/Sikorsky/UTRC active flap demonstration rotor in the NFAC's 40- by 80-Foot anechoic wind tunnel. Effectiveness of using localized, non-harmonic active flap motions are compared to conventional four-per-rev harmonic flap motions, and also active flap motions derived from closed-loop acoustics implementations. All three approaches resulted in approximately the same noise reductions over an in-plane three-by-three microphone array installed forward and near in-plane of the rotor in the nearfield. It is also reported that using an active flap in this localized, non-harmonic manner, resulted in no more that 2% rotor performance penalty, but had the tendency to incur higher hub vibration levels.

FLAPS(CONTROL SURFACES)↗
NASA NTRS2020

Computational Simulations of a Mach 0.745 Transonic Truss-Braced Wing Design

A joint effort between the NASA Ames and Langley Research Centers was undertaken to analyze the Mach 0.745 variant of the Boeing Transonic Truss-Braced Wing (TTBW) Design. Two different flow solvers, LAVA and USM3D, were used to predict the TTBW flight performance. Sensitivity studies related to mesh resolution and numerical schemes were conducted to define best practices for this type of geometry and flow regime. Validation efforts compared the numerical simulation results of various modeling methods against experimental data taken from the NASA Ames 11-foot Unitary Wind Tunnel experimental data. The fidelity of the computational representation of the wind tunnel experiment, such as utilizing a porous wall boundary condition to model the ventilated test section, was varied to examine how different tunnel effects influence CFD predictions. LAVA and USM3D results both show an approximate 0.5 angle of attack shift from experimental lift curve data. This drove an investigation that revealed that the trailing edge of the experimental model was rounded in comparison to the CAD model, due to manufacturing tolerances, which had not been accounted for in the initial simulations of the experiment. Simulating the TTBW with an approximation of this rounded trailing-edge reduces error by approximately 60%. An accurate representation of the tested TTBW geometry, ideally including any wing twists and deflections experienced during the test under various loading conditions, will be necessary for proper validation of the CFD.

Maldonado, Daniel↗
NASA NTRS2020

Computational Simulations of a Mach 0.745 Transonic Truss-Braced Wing Design

A joint effort between the NASA Ames and Langley Research Centers was undertaken to analyze the Mach 0.745 variant of the Boeing Transonic Truss-Braced Wing (TTBW) Design. Two different flow solvers, LAVA and USM3D, were used to predict the TTBW flight performance. Sensitivity studies related to mesh resolution and numerical schemes were conducted to define best practices for this type of geometry and flow regime. Validation efforts compared the numerical simulation results of various modeling methods against experimental data taken from the NASA Ames 11-foot Unitary Wind Tunnel experimental data. The fidelity of the computational representation of the wind tunnel experiment, such as utilizing a porous wall boundary condition to model the ventilated test section, was varied to examine how different tunnel effects influence CFD predictions. LAVA and USM3D results both show an approximate 0.5o angle of attack shift from experimental lift curve data. This drove an investigation that revealed that the trailing edge of the experimental model was rounded in comparison to the CAD model, due to manufacturing tolerances, which had not been accounted for in the initial simulations of the experiment. Simulating the TTBW with an approximation of this rounded trailing-edge reduces error by approximately 60%. An accurate representation of the tested TTBW geometry, ideally including any wing twists and deflections experienced during the test under various loading conditions, will be necessary for more thorough validation of the CFD.

Maldonado, Daniel↗
NASA NTRS1962

Tables of Interference Factors for Use in Wind-tunnel and Ground-effect Calculations for VTOL-STOL Aircraft. Part III- Wind Tunnels Having Width-height Ratio of 1.0

Tables of interference factors for use in wind-tunnel and ground-effect calculations for VTOL-STOL aircraft are presented for wind tunnels having a width-height ratio of 1.0. These tables were machine-calculated and are intended for use with the procedures of NASA Technical Report R-124. These tables are presented without comment.

STOL aircraft↗
NASA NTRS1962

Tables of Interference Factors for Use in Wind-tunnel and Ground-effect Calculations for VTOL-STOL Aircraft. Part I - Wind Tunnels Having Width-height Ratio of 2.0

Tables of interference factors for use in wind-tunnel and ground-effect calculations for VTOL-STOL aircraft are presented for wind tunnels having a width-height ratio of 2.0. These tables were machine-calculated and are intended for use with the procedures of NASA Technical Report R-124. These tables are presented without comment.

Interference factor table↗
NASA NTRS1990

A numerical study of the effects of wind tunnel wall proximity on an airfoil model

A procedure was developed for modeling wind tunnel flows using computational fluid dynamics. Using this method, a numerical study was undertaken to explore the effects of solid wind tunnel wall proximity and Reynolds number on a two-dimensional airfoil model at low speed. Wind tunnel walls are located at varying wind tunnel height to airfoil chord ratios and the results are compared with freestream flow in the absence of wind tunnel walls. Discrepancies between the constrained and unconstrained flows can be attributed to the presence of the walls. Results are for a Mach Number of 0.25 at angles of attack through stall. A typical wind tunnel Reynolds number of 1,200,000 and full-scale flight Reynolds number of 6,000,000 were investigated. At this low Mach number, wind tunnel wall corrections to Mach number and angle of attack are supported. Reynolds number effects are seen to be a consideration in wind tunnel testing and wall interference correction methods. An unstructured grid Navier-Stokes code is used with a Baldwin-Lomax turbulence model. The numerical method is described since unstructured flow solvers present several difficulties and fundamental differences from structured grid codes, especially in the area of turbulence modeling and grid generation.

Potsdam, Mark↗
NASA NTRS1972

Wind-tunnel Investigation of Effects of Rear Upper Surface Modification on a NASA Supercritical Airfoil

Wind tunnel tests were conducted at Mach numbers from 0.60 to 0.81 to examine the effects on supercritical airfoil of modifying the rear upper surface to reduce the magnitude of an intermediate off design second velocity peak. The modification was accomplished by increasing the upper surface curvature around the 50 percent chord station and reducing the curvature over approximately the rearmost 30 percent of the airfoil while maintaining the same trailing edge thickness.

Harris, C. D.↗
NASA NTRS1962

Tables of Interference Factors for Use in Wind-tunnel and Ground-effect Calculations for VTOL-STOL Aircraft. Part IV- Wind Tunnels Having Width-height Ratio of 0.5

Tables of interference factors for use in wind-tunnel and ground-effect calculations for VTOL-STOL aircraft are presented for wind tunnels having a width-height ratio of 0.5. These tables were machine-calculated and are intended for use with the procedures of NASA Technical Report R-124. These tables are presented without comment.

Wind tunnel↗
NASA NTRS1979

Analytical study of the effects of wind tunnel turbulence on turbofan rotor noise

The influence of tunnel turbulence on turbofan rotor noise was carried out to evaluate the effectiveness of the NASA Ames 40 by 80 foot tunnel in simulating flight levels of fan noise. A previously developed theory for predicting rotor/turbulence interaction noise was refined and extended to include first-order effects of inlet turbulence anisotropy. This theory was then verified by carrying out extensive data/theory comparisons. The resulting model computer program was then employed to carry out a parametric study of the effects of fan size, blade number, and operating line on rotor/turbulence noise for outdoor test stand. NASA Ames wind tunnel, and flight inlet turbulence conditions. A major result of this study is that although wind tunnel rotor/turbulence noise levels are not as low as flight levels they are substantially lower than the outdoor test stand levels and do not mask other sources of fan noise.

Gliebe, P. R.↗
NASA NTRS1941

Wind-tunnel investigation of effect of interference on lateral-stability characteristics of four NACA 23012 wings, an elliptical and a circular fuselage and vertical fins

Report presents the results of a wind-tunnel investigation of the effect of wing-fuselage interference on lateral-stability characteristics made in the NACA 7 by 10-foot wind tunnel on four fuselages and two fins, representing high-wing, low-wing, and midwing monoplanes. The fuselages are of circular and elliptical cross section. The wings have rounded tips and, in plan form, one is rectangular and the three are tapered 3:1 with various amounts of sweep. The rate of change in the coefficients of rolling moment, yawing moment, and lateral force with angle of yaw is given in a form to show the increment caused by wing-fuselage interference for the model with no fin and the effect of wing-fuselage interference on fin effectiveness. Results for the fuselage-fin combination and the wing tested alone are also given.

House, Rufus O↗
NASA NTRS1981

A theory for predicting boundary impedance and resonance frequencies of slotted-wall wind tunnels, including plenum effects

Wave-induced resonance associated with the geometry of wind-tunnel test sections can occur. A theory that uses acoustic impedance concepts to predict resonance modes in a two dimensional, slotted wall wind tunnel with a plenum chamber is described. The equation derived is consistent with known results for limiting conditions. The computed resonance modes compare well with appropriate experimental data. When the theory is applied to perforated wall test sections, it predicts the experimentally observed closely spaced modes that occur when the wavelength is not long compared with he plenum depth.

Barger, R. L.↗
NASA NTRS1971

Wind-tunnel investigation of effects of trailing-edge geometry on a NASA supercritical airfoil section

Wind-tunnel tests have been conducted at Mach numbers from 0.60 to 0.81 to determine the effects of trailing-edge geometry on the aerodynamic characteristics of a NASA supercritical airfoil shape. Variations in trailing-edge thicknesses from 0 to 1.5 percent of the chord and a cavity in the trailing edge were investigated with airfoils with maximum thicknesses of 10 and 11 percent of the chord.

Harris, C. D.↗