Academia.edu no longer supports Internet Explorer.
To browse Academia.edu and the wider internet faster and more securely, please take a few seconds to upgrade your browser.
1999, Journal of Aircraft
AI
This research presents a unified measurement approach using temperature sensitive paint (TSP) and model deformation measurement systems in wind tunnel tests. The techniques were integrated to allow for simultaneous measurements of aerodynamic transition and model deformation, specifically analyzing a trapezoidal semispan wing at various angles of attack and conditions. The findings indicate that these systems can operate together effectively, highlighting the potential for enhanced productivity in aerodynamic testing.
(NFAC) 40 foot by 80 foot wind tunnel at NASA Ames Research Center in the summer of 2011. The development of two measurement techniques is discussed in this work, both with the objective of making measurements on AMELIA for CFD validation. First, the work on the application of the Fringe-Imaging Skin Friction (FISF) technique to AMELIA is discussed. The FISF technique measures the skin friction magnitude and direction by applying oil droplets on a surface, exposing them to flow, measuring their thickness, and correlating their thickness to the local skin friction. The technique has the unique ability to obtain global skin friction measurements. A two foot, nickel plated, blended wing section test article has been manufactured specifically for FISF. The model is illuminated with mercury vapor lamps and imaged with a Canon 50D with a 546 nm bandpass filter. Various tests are applied to the wing in order to further characterize uncertainties related with the FISF technique. Human repeatability has uncertainties of ±2.3% of fringe spacing and ±2.0° in skin friction vector direction, while image post processing yields ±25% variation in skin friction coefficient. A method for measuring photogrammetry uncertainty is developed. The effect of filter variation and test repeatability was found to be negligible. A validation against a Preston tube was found to have 1.8% accuracy. Second, the validation of a micro flow measurement device is investigated. Anemometers have always had limited capability in making near wall measurements, driving the design of new devices capable of measurements with increased wall proximity. Utilizing a thermocouple boundary layer rake, wall measurements within 0.0025 inches of the surface have been made. A Cross Correlation Rake (CCR) has the advantage of not requiring calibration but obtaining the same proximity and resolution as the thermocouple boundary layer rake. The flow device utilizes time of flight measurements computed via cross correlation to calculate wall velocity profiles. The CCR was designed to be applied to AMELIA to measure flow velocities above a flap in a transonic flow regime. The validation of the CCR was unsuccessful. Due to the fragile construction of the CCR, only one data point at 0.10589 inches from the surface was available for validation. The subsonic wind tunnel's variable frequency drive generated noise which could not be filtered or shielded, requiring the use of a flow bench for validation testing. Since velocity measurements could not be made in the flow bench, a v comparison of a fast and slow velocity was made. The CCR was not able to detect the difference between the two flow velocities. Currently, the CCR cannot be applied on AMELIA due to the unsuccessfully validation of the device.
AIAA Journal, 2000
In image-based measurements, quantitative image data must be mapped to three-dimensional object space. Analytical photogrammetric methods, which may be used to accomplish this task, are discussed from the viewpoint of experimental uid dynamicists. The direct linear transformation (DLT) for camera calibration, used in pressuresensitive paint, is summarized. An optimization method for camera calibration is developed that can be used to determine the camera calibration parameters, including those describing lens distortion, from a single image. Combined with the DLT method, this method allows a rapid and comprehensive in situ camera calibration and, therefore, is particularly useful for quantitative ow visualization and other measurements such as model attitude and deformation in production wind tunnels. Also included is a brief description of typical photogrammetric applications to temperature-and pressure-sensitive paint measurements and model deformation measurements in wind tunnels.
FME Transactions, 2006
Optical methods in wind tunnel flow visualization This paper reports the application of optical methods: shadow, schlieren and holographic interferometry in wind tunnel flow visualization. Some examples obtained in the MTI wind tunnels are presented. The comparative advantages of holographic method in regard to shadow and schlieren method for quantitative flow field test are analyzed.
Scientific Technical Review, 2007
An attempt is made to describe and review the most widely used methods for flow visualization. The first part described the basis and applications of different visualization methods for subsonic and supersonic flow in wind and water tunnels. This part concentrates on optical methods (shadow, schlieren and interferometry) and their application in compressibe flow visualization. Almost all presented photos have been made in the laboratories of the VTI.
and Acoustic Microphone Array has been conducted at the NASA Langley Research Center. The fundamental purposes of conducting the test were to (a) identify and solve compatibility issues among the techniques that would inhibit their simultaneous application in a wind tunnel, and (b) demonstrate that simultaneous use of advanced instrumentation techniques is feasible for increasing tunnel efficiency and identifying control surface actuation / aerodynamic reaction phenomena. This paper provides summary descriptions of each measurement technique used during the Unified Instrumentation Test, their implementation for testing in a unified fashion, and example results identifying areas of instrument compatibility and incompatibility. Conclusions are drawn regarding the conditions under which the measurement techniques can be operated simultaneously on a non-interference basis. Finally,
We present in this paper a novel approach dedicated to the measurement of velocity in fluid experimental flows. Such information, which is fundamental for specialists, is usually computed by correlation methods on a special kind of images (named PIV). We present here a motion estimation technique which is based on an optical-flow extension. Results are presented on an experimental flow and are compared to those computed with standard methods of the fluid mechanics community.
Journal of Aircraft, 2009
In this paper, wind-tunnel measurements are presented for the airflow fluctuation detection using pressure optical sensors. Twenty-one wind-tunnel test runs for various Mach numbers, angles of attack, and Reynolds numbers were performed in the 6 9 ft 2 wind tunnel at the Institute for Aerospace Research at the National Research Council Canada. A rectangular finite aspect ratio half-wing, having a NACA 4415 cross section, was considered with its upper surface instrumented with pressure taps, pressure optical sensors, and one Kulite transducer. The Mach number was varied from 0.1 to 0.3 and the angle of attack range was within 3 to 3 deg. Unsteady pressure signals were recorded and a thorough comparison, in terms of unsteady and mean pressure coefficients, was performed between the measurements from the three sets of pressure transducers. Temperature corrections were considered in the pressure measurements by optical sensors. Comparisons were also performed against theoretical predictions using the XFoil computational fluid dynamics code, and mean errors smaller than 10% were noticed between the measured and the predicted data.
38th Aerospace Sciences Meeting and Exhibit, 2000
The objective of this paper is to compare the current state-of-the-art of the following three optical techniques under study by NASA for measuring model deformation in wind tunnels: (1) video photogrammetry, (2) projection moiré interferometry, and (3) the commercially available Optotrak ΤΜ system. An objective comparison of these three techniques should enable the selection of the best technique for a particular test undertaken at various NASA facilities. As might be expected, no one technique is best for all applications. The techniques are also not necessarily mutually exclusive and in some cases can be complementary to one another.
FME Transactions, 2018
The requirements for the accuracy of measurements in a wind tunnel test become more and more severe while the complexity of the test increases. In an environment of reduced time available for wind tunnel test and increasing test costs, it is important that the accurate calibrations and verifications of all components of the measurement chain in a wind tunnel facility are established, maintained and statistically controlled through prolonged periods of time. The paper presents the efforts undertaken to establish and maintain a system of control of the quality of measurements in the T-35 4.4 m × 3.2 m low-speed wind tunnel of the Military Technical Institute in Belgrade. The assurance of the quality of measurement in this facility is based on ensuring the quality of three main constituents: the calibration of the test section of the wind tunnel, the calibration of the instrumentation used, and the periodic tests of the standard wind tunnel models. Sample results from relevant wind tunnel calibration tests are presented and compared with the results from other facilities. The tests confirmed a good overall quality of the facility, and that the achieved quality level has to be maintained, periodically checked and systematically documented.
Progress in Aerospace Sciences, 2008
For decades, wind tunnel testing has been conducted in test section environments that have not been adequately or consistently documented. Since wind tunnel flow quality can adversely affect test results, accurate and consistent flow quality measurements are required, along with an understanding of the sources, characteristics, and management of flow turbulence. This paper will review turbulence measurement techniques and data obtained in subsonic, transonic, and supersonic test facilities as they relate to the determination and assessment of wind tunnel flow quality. The principles and practical application of instrumentation used in the measurement and characterization of wind tunnel turbulence will be described. Techniques used for the identification of the sources of wind tunnel disturbances, and the performance of turbulence suppression devices will be outlined. These test techniques will be illustrated with extensive measurements obtained in a number of test facilities. The measurements will provide comprehensive turbulence data that are vital to the assessment and management of flow quality. Procedures designed to assess the potential influence of adverse flow quality on wind tunnel model test performance will also be discussed.
The report that follows gives a step by step procedure of the calibration and the flow quality analysis of the L. A. Comp Subsonic Closed-Circuit Wind Tunnel currently in operation at the University of Oklahoma. The calibration was done by studying the relationship between dynamic pressure across a Pitot static probe and the pressure difference across the contraction of the wind tunnel. The relationship between the free stream velocity and the pressure drop across the contraction was also studied. Using this data the wind tunnel was then set at a particular pressure difference across the contraction and the dynamic pressure across a Pitot probe and hence free stream velocity at different points in a cross-section of the test section was analyzed for consistency. The experiment showed that the dynamic pressure and free stream velocity was consistent at points that were close to the center of the cross section. The dynamic pressure and free stream velocity was outside the acceptable range of uncertainty when measured at the walls of the test section.
Measurement Science and Technology, 2017
Within recent years, methods based on the use of liquid-crystal (LC) coatings which change their optical properties when being exposed to external disturbances have gained widespread acceptance for panoramic visualization of surface temperature and friction fields. A thin layer of an LC on the surface under study introduces no additional disturbances into the boundary layer, and the optical response of the LC to already existing distortions of the temperature or shear-stress field allows the researcher to employ the LC for measuring them. The above fields are very sensitive to various changes of the boundary-layer structure. Therefore, the panoramic observation of temperature and friction distributions over the streamlined surface permits easy visualization of transition regions from laminar to turbulent flow, as well as flow separation and flow reattachment regions, and makes it possible to study the effect of shock waves on the boundary layer. The present paper is devoted to optical phenomena in thermotropic liquid crystals and their application for the surface flow visualization. The main properties of liquid crystals (structure, texture, viscoelastic and optical characteristics) that are of interest for wind tunnel testing are discussed. The visualization studies on several models in different wind tunnels are presented. Method of liquid crystal thermography is also described.
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.