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NASA NTRS2018

Investigation of Turbulence Generated by Upwind Blockages at the Inlet of a 1/50th-Scale Model of the 80- by 120-Foot Wind Tunnel

A 1/50th scale model of the 80- by 120-Foot Wind Tunnel (hereafter referred to as the 80x120) was utilized to determine the magnitude of turbulence caused by buildings located upstream of the wind tunnel inlet. The 1/50th scale models of existing and proposed buildings were constructed to act as blockage for the test. Various inlet locations were sampled for turbulence intensity levels under a variety of blockage conditions including simple three-dimensional rectangular bodies creating quasi two-dimensional physics along the tunnel centerline, existing building structures in the vicinity of the full-scale wind tunnel inlet flow field, and proposed building structures that may someday be constructed at NASA Ames Research Center upwind of the inlet. Therefore, the testing performed and reported in this report can be considered representative of quiescent atmospheric conditions that exist when operating the full-scale 80x120 at night. At quiescent atmospheric conditions there is a measurable increase in turbulence intensity produced by upstream blockages. The blockages examined produced an average turbulence intensity level between 2% and 5% when measured at the inlet. Previous research has shown that the flow control of the 80x120 is capable of reducing this turbulence to less than 0.5% when measured in the test section. Additional research will need to be conducted to determine the influence of atmospheric wind on relative turbulence intensity at the inlet. These results show that for future buildings lying more than 1,000 ft upstream of the full-scale 80x120 inlet, these new buildings will have a negligible effect on the flow quality of the air entering the 80x120 test section under strictly quiescent atmospheric conditions. The Googleplex buildings modeled and tested in this experiment are located approximately 2,450 ft upstream and, as seen in this test campaign, have a negligible influence on the turbulence levels measured at the inlet under quiescent atmospheric conditions.

80- by 120-Foot Wind Tunnel↗

NASA NTRS1982

Adaptive-wall wind-tunnel research at NASA-Ames Research Center

Adaptive wall wind tunnel research is summarized. Small scale two and three dimensional wind tunnel experiments and numerical experiments with a three dimensional adaptive wall simulator are included. A NACA 0012 airfoil was tested in a 25 by 13 cm slotted wall test section. Airflow through the test section walls was controlled by adjusting the pressures in segmented plenums. Interference free conditions were successfully attained in subsonic and transonic flows. For the three dimensional experiment, the 25 by 13 cm wind tunnel was modified to permit cross stream wall adjustments. The test model was a semispan wing mounted to one sidewall. Wall interference was substantially reduced at several angles of attack at Mach 0.60. A wing on wall configuration was also modeled in the numerical experiments. These flow simulations showed that free air conditions can be approximated by adjusting boundary conditions at only the floor and ceiling of the test section. No sidewall control was necessary. Typical results from these experiments are discussed.

Schairer, E. T.↗

NASA NTRS2003

Wind Tunnel Database Development using Modern Experiment Design and Multivariate Orthogonal Functions

A wind tunnel experiment for characterizing the aerodynamic and propulsion forces and moments acting on a research model airplane is described. The model airplane called the Free-flying Airplane for Sub-scale Experimental Research (FASER), is a modified off-the-shelf radio-controlled model airplane, with 7 ft wingspan, a tractor propeller driven by an electric motor, and aerobatic capability. FASER was tested in the NASA Langley 12-foot Low-Speed Wind Tunnel, using a combination of traditional sweeps and modern experiment design. Power level was included as an independent variable in the wind tunnel test, to allow characterization of power effects on aerodynamic forces and moments. A modeling technique that employs multivariate orthogonal functions was used to develop accurate analytic models for the aerodynamic and propulsion force and moment coefficient dependencies from the wind tunnel data. Efficient methods for generating orthogonal modeling functions, expanding the orthogonal modeling functions in terms of ordinary polynomial functions, and analytical orthogonal blocking were developed and discussed. The resulting models comprise a set of smooth, differentiable functions for the non-dimensional aerodynamic force and moment coefficients in terms of ordinary polynomials in the independent variables, suitable for nonlinear aircraft simulation.

Morelli, Eugene A.↗

NASA NTRS1974

Noise reduction in transonic wind tunnels

The phenomena of background noise generation in transonic wind tunnels are analyzed. In unsteady aerodynamic tests, background disturbances create problems because the instrumentation senses them in addition to the fluctuations generated by the aerodynamic flow over wind-tunnel models. Calibrations of 25 facilities show that the amplitudes of the background fluctuations are excessive. In porous-wall facilities, one noise source consists of porous-wall edgetones that are generated by the passage of air over the holes. A flow model is developed that yields the frequencies of these oscillations. Test section boundary layers and hole configurations govern the occurrence of these fluctuations. In slotted-wall facilities, a noise source is the slotted-wall shearing caused by the air flowing along the openings. In both types of wind tunnels, other flow mechanisms also cause disturbances, and these phenomena are described. Noise-reduction methods are outlined which will provide valid unsteady aerodynamic results.

Mccanless, G. F., Jr.↗

NASA NTRS1986

Performance of the high speed anechoic wind tunnel at Lyon University

The characteristics of the feed duct, the wind tunnel, and the experiments run in the convergent-divergent anechoic wind tunnel at Lyon University are described. The wind tunnel was designed to eliminate noise from the entrance of air or from flow interactions with the tunnel walls so that noise caused by the flow-test structure interactions can be studied. The channel contains 1 x 1 x 0.2 m glass and metal foil baffles spaced 0.2 m apart. The flow is forced by a 350 kW fan in the primary circuit, and a 110 kW blower in the secondary circuit. The primary circuit features a factor of four throat reductions, followed by a 1.6 reduction before the test section. Upstream and downstream sensors permit monitoring of the anechoic effectiveness of the channel. Other sensors allow modeling of the flow structures in the tunnel. The tunnel was used to examine turbulent boundary layers in flows up to 140 m/sec, tubulence-excited vibrations in walls, and the effects of laminar and turbulent flows on the appearance and locations of noise sources.

Sunyach, M.↗

NASA NTRS1980

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

An analytical study of the effects of wind tunnel turbulence on turbofan rotor noise was carried out to evaluate the effectiveness of the NASA Ames 40 by 80-foot wind tunnel in simulating flight levels of fan noise. A previously developed theory for predicting rotor/turbulence interaction noise, refined and extended to include first-order effects of inlet turbulence anisotropy, was employed to carry out a parametric study of the effects of fan size, blade number, and operating line 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 NTRS1999

Analysis of Wind Tunnel Oscillatory Data of the X-31A Aircraft

Wind tunnel oscillatory tests in pitch, roll, and yaw were performed on a 19%-scale model of the X-31A aircraft. These tests were used to study the aerodynamic characteristics of the X-31A in response to harmonic oscillations at six frequencies. In-phase and out-of-phase components of the aerodynamic coefficients were obtained over a range of angles of attack from 0 to 90 deg. To account for the effect of frequency on the data, mathematical models with unsteady terms were formulated by use of two different indicial functions. Data from a reduced set of frequencies were used to estimate model parameters, including steady-state static and dynamic stability derivatives. Both models showed good prediction capability and the ability to accurately fit the measured data. Estimated static stability derivatives compared well with those obtained from static wind tunnel tests. The roll and yaw rate derivative estimates were compared with rotary-balanced wind tunnel data and theoretical predictions. The estimates and theoretical predictions were in agreement at small angles of attack. The rotary-balance data showed, in general, acceptable agreement with the steady-state derivative estimates.

Smith, Mark S.↗

NASA NTRS2012

Validation of US3D for Capsule Aerodynamics using 05-CA Wind Tunnel Test Data

Several comparisons of computational fluid dynamics to wind tunnel test data are shown for the purpose of code validation. The wind tunnel test, 05-CA, uses a 7.66% model of NASA's Multi-Purpose Crew Vehicle in the 11-foot test section of the Ames Unitary Plan Wind tunnel. A variety of freestream conditions over four Mach numbers and three angles of attack are considered. Test data comparisons include time-averaged integrated forces and moments, time-averaged static pressure ports on the surface, and Strouhal Number. The applicability of the US3D code to subsonic and transonic flow over a bluff body is assessed on a comprehensive data set. With close comparison, this work validates US3D for highly separated flows similar to those examined here.

Schwing, Alan↗

NASA NTRS1993

Development of a quiet supersonic wind tunnel with a cryogenic adaptive nozzle

The main objective of this work is to develop an interim Quiet (low-disturbance) supersonic wind tunnel for the NASA-Ames Fluid Mechanics Laboratory (FML). The main emphasis is to bring on-line a full-scale Mach 1.6 tunnel as rapidly as possible to impact the NASA High Speed Research Program (HSRP). The development of a cryogenic adaptive nozzle and other sophisticated features of the tunnel will now happen later, after the full scale wind tunnel is in operation. The work under this contract for the period of this report can be summarized as follows: provide aerodynamic design requirements for the NASA-Ames Fluid Mechanics Laboratory (FML) Laminar Flow Supersonic Wind Tunnel (LFSWT); research design parameters for a unique Mach 1.6 drive system for the LFSWT using an 1/8th-scale Proof-of-Concept (PoC) supersonic wind tunnel; carry out boundary layer transition studies in PoC to aid the design of critical components of the LFSWT; appraise the State of the Art in quiet supersonic wind tunnel design; and help develop a supersonic research capability within the FML particularly in the areas of high speed transition measurements and schlieren techniques. The body of this annual report summarizes the work of the Principal Investigator.

Wolf, Stephen W. D.↗

NASA NTRS1973

Comparison of aircraft noise measured in flight test and in the NASA Ames 40- by 80-foot wind tunnel.

A method to determine free-field aircraft noise spectra from wind-tunnel measurements has been developed. The crux of the method is the correction for reverberations. Calibrated loud speakers are used to simulate model sound sources in the wind tunnel. Corrections based on the difference between the direct and reverberant field levels are applied to wind-tunnel data for a wide range of aircraft noise sources. To establish the validity of the correction method, two research aircraft - one propeller-driven (YOV-10A) and one turbojet-powered (XV-5B) - were flown in free field and then tested in the wind tunnel. Corrected noise spectra from the two environments agree closely.

Atencio, A., Jr.↗

NASA NTRS2014

A New Global Regression Analysis Method for the Prediction of Wind Tunnel Model Weight Corrections

A new global regression analysis method is discussed that predicts wind tunnel model weight corrections for strain-gage balance loads during a wind tunnel test. The method determines corrections by combining "wind-on" model attitude measurements with least squares estimates of the model weight and center of gravity coordinates that are obtained from "wind-off" data points. The method treats the least squares fit of the model weight separate from the fit of the center of gravity coordinates. Therefore, it performs two fits of "wind- off" data points and uses the least squares estimator of the model weight as an input for the fit of the center of gravity coordinates. Explicit equations for the least squares estimators of the weight and center of gravity coordinates are derived that simplify the implementation of the method in the data system software of a wind tunnel. In addition, recommendations for sets of "wind-off" data points are made that take typical model support system constraints into account. Explicit equations of the confidence intervals on the model weight and center of gravity coordinates and two different error analyses of the model weight prediction are also discussed in the appendices of the paper.

strain-gage balance↗

NASA NTRSDate not supplied

Modal Test and Analysis Correlation of Wind Tunnel Blades for the National Transonic Facility

NASA has a significant maintenance challenge with the aging wind tunnel infrastructure across the agency . Wind tunnel blades, such as the ones in the National Transonic Facility at NASA Langley Research Center, have been subjected to damage from impacts and fatigue. Accurate analytical models of these blades are necessary to either recertify replacement blades to be built or for redesign of these blades. In this paper an upgraded finite element model of these wind tunnel blades with the capability of representing damage is presented. An eigenvalue analysis of the structural model is performed, and the boundary conditions are adjusted to simulate the natural frequencies obtained by experimental testing of a set of twenty five blades in 1992. Additional numerical studies of the effect of delamination damage on the natural frequencies of the blade are conducted using the tuned finite element model.

wind tunnel↗

NASA NTRSDate not supplied

Modal Test and Analysis Correlation of Wind Tunnel Blades for the National Transonic Facility

wind tunnel↗

NASA NTRS1982

Adaptive-wall wind-tunnel research at Ames Research Center

Adaptive-wall wind-tunnel research is summarized. This research includes small-scale two- and three-dimensional wind-tunnel experiments and numerical experiments with a three-dimensional adaptive-wall simulator. Airflow through the test-section walls is controlled by adjusting the pressures in segmented plenums. Interference free conditions are successfully attained in subsonic and transonic flows. An adaptive wall test section is constructed for the transonic wind tunnel. Wall interference was reduced in the three dimensional experiment at several angles of attack at Mach 0.60. A wing on wall configuration was modeled in the numerical experiments. These flow simulations showed that free air conditions can be approximated by adjusting boundary conditions at only the floor and ceiling of the test section. No sidewall control was necessary.

Schairer, E. T.↗

NASA NTRS1973

Aeroacoustic research in wind tunnels: A status report

The increasing attention given to aerodynamically generated noise brings into focus the need for quality experimental research in this area. To meet this need several specialized anechoic wind tunnels have been constructed. In many cases, however, budgetary constraints and the like make it desirable to use conventional wind tunnels for this work. Three basic problems are inherent in conventional facilities: (1) high background noise, (2) strong frequency dependent reverberation effects, and (3) unique instrumentation problems. The known acoustic characteristics of several conventional wind tunnels are evaluated and data obtained in a smaller 4- x 5-foot wind tunnel which is convertible from a closed jet to an open jet mode are presented. The data from these tunnels serve as a guideline for proposed modifications to a 7- x 10-foot wind tunnel. Consideration is given to acoustic treatment in several different portions of the wind tunnel.

Bender, J.↗

NASA NTRS1995

Reduction of Background Noise in the NASA Ames 40- by 80-Foot Wind Tunnel

Background noise in both open-jet and closed wind tunnels adversely affects the signal-to-noise ratio of acoustic measurements. To measure the noise of increasingly quieter aircraft models, the background noise will have to be reduced by physical means or through signal processing. In a closed wind tunnel, such as the NASA Ames 40- by 80- Foot Wind Tunnel, the principle background noise sources can be classified as: (1) fan drive noise; (2) microphone self-noise; (3) aerodynamically induced noise from test-dependent hardware such as model struts and junctions; and (4) noise from the test section walls and vane set. This paper describes the steps taken to minimize the influence of each of these background noise sources in the 40 x 80.

Jaeger, Stephen M.↗

NASA NTRS2012

An Overview of the Semi-Span Super-Sonic Transport (S4T) Wind-Tunnel Model Program

A summary of computational and experimental aeroelastic (AE) and aeroservoelastic (ASE) results for the Semi-Span Super-Sonic Transport (S4T) wind-tunnel model is presented. A broad range of analyses and multiple AE and ASE wind-tunnel tests of the S4T wind-tunnel model have been performed in support of the ASE element in the Supersonics Program, part of the NASA Fundamental Aeronautics Program. This paper is intended to be an overview of multiple papers that comprise a special S4T technical session. Along those lines, a brief description of the design and hardware of the S4T wind-tunnel model will be presented. Computational results presented include linear and nonlinear aeroelastic analyses, and rapid aeroelastic analyses using CFD-based reduced-order models (ROMs). A brief survey of some of the experimental results from two open-loop and two closed-loop wind-tunnel tests performed at the NASA Langley Transonic Dynamics Tunnel (TDT) will be presented as well.

Silva, Walter A.↗

NASA NTRS1976

The cryogenic transonic wind tunnel for high Reynolds number research

Based on theoretical studies and experience with a low speed cryogenic tunnel and with the transonic cryogenic tunnel, the cryogenic wind tunnel concept has been shown to offer many advantages with respect to the attainment of full scale Reynolds number at reasonable levels of dynamic pressure in a ground based facility. The unique modes of operation available in a pressurized cryogenic tunnel make possible for the first time the separation of Mach number, Reynolds number, and aeroelastic effects.

Kilgore, R. A.↗