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.
A six-component wind tunnel balance of a robust, unconventional design was produced using semiconductor strain gages on a compression-type axial-force element. The balance was designed primarily for supersonic tests of high-drag models in short-duration wind tunnels. It was first used in a short crash program to test a design of a high-drag training kineticenergy projectile. Obtained data were useful for the development of the projectile, but a lack of reliable references to validate the performance of the balance was felt, especially in view of the different opinions on the usability of semiconductor strain gages for wind tunnel balances. This issue was dealt with when the balance was used in wind tunnel tests of a HB-2 hypervelocity-ballistic standard model at Mach numbers 1.5 to 4, in a campaign of tuning the supersonic performance of the T-38 wind tunnel in VTI. Test results were compared with the reference data and with results from an earlier test of the same model where a conventional-design balance was used. The evaluation of the balance was focused on the measurement of the axial-force coefficient. It was concluded that the balance was very convenient for the intended type of wind tunnel tests, but not for general use.
AGARD-B is a widely-used configuration of a standard wind tunnel model. Beside its originally intended application for correlation of data from supersonic wind tunnel facilities, it was tested in a wide range of Mach numbers and, more recently, used for assessment of wall interference effects, validation of computational fluid dynamics codes and validation of new model production technologies. The researchers and wind tunnel test engineers would, naturally, like to know the "true" aerodynamic characteristics of this model, for comparison with their own work. Obviously, such data do not exist, but an estimate can be made of the dispersion of test results from various sources and of the probable "mean" values of the aerodynamic coefficients. To this end, comparable transonic test results for the AGARD-B model at Mach numbers 0.77, Mach 1.0 and Mach 1.17 from six wind tunnels were analyzed and average values and dispersions of the aerodynamic coefficients were computed.
Published results for standard wind tunnel models at non-standard test conditions are quite rare and/or may not be available. It has been found that those results are a useful aid in preparations for a number of wind tunnel tests in the Military Technical Institute (VTI) in Belgrade. Test campaigns of standard models at non-standard conditions are performed to serve as an internal database for future wind tunnel tests in such environments. Those tests, that partially overlap the referenced Mach number and/or angle of attack ranges, are conducted in different VTI’s test facilities; different model sizes and support stings were used. The standard models used in static measurements in VTI, ranging from simple missile shapes and re-entry bodies to complicated airplanes, are briefly described and sample non-standard test results are given. The correlation of the test results among models and facilities has been done with references in the available ranges, and, after confirming a good agreement, it is assumed that the results are also valid in the extended ranges of conditions. These results may be useful for researchers in other wind tunnel facilities and for those who handle CFD tools.
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