Dijana Damljanović

T-38 Wind-Tunnel Data Quality Assurance Based on Testing of a Standard Model

The tests of the standard models serve to confirm the overall accuracy and repeatability of measurements in every single wind-tunnel facility and to confirm confidence in results obtained. The intention of the authors in this paper is to present, with exemplary test results, a methodology for certification and verification of the overall reliability of the T-38 Military Technical Institute’s trisonic wind tunnel on the basis of check standard testing together with a small number of repeat-run sets prior to the customer’s tests. Wind-tunnel data uncertainty is considered in the form of repeatability of a few presumably identical tests of a standard model. Test data are also correlated with those from other wind-tunnel facilities.

Evaluation of a force balance with semiconductor strain gages in wind tunnel tests of the HB-2 standard model

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 kinetic-energy 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.

An Evaluation of the Overall T-38 Wind Tunnel Data Quality in Testing of a Calibration Model

Tests of standard models serve to confirm the overall accuracy and repeatability of measurements in a wind tunnel facility and to confirm confidence in results obtained. The intention of the authors in this paper is to certify and to verify the overall reliability of the VTI’s trisonic wind tunnel. The methodology is based on the check standard testing. Wind tunnel data uncertainty is considered in the form of repeatability of a few supposedly identical tests of a standard model. Test data are also validated based on comparisons with those from other wind tunnel facilities.

Tail Flare vs Fins in the Design of a Subcaliber Projectile

A typical aerodynamic configuration of a subcaliber projectile is composed of a slender body with a small cross-sectional area and fins at the rear part of the projectile. Projectile fins require high-precision manufacturing because their shape and size are designed to achieve high normal-force coefficients and a satisfactory static-stability margin. The influence of aerodynamic asymmetry to the projectile flight is minimized by the projectile rotation. An alternative aerodynamic configuration can be obtained by replacing fins with a tail flare. In this paper, the criteria for designing a tail flare replacing the fins were the maximum effective range and the maximum height of the trajectory. Computational fluid dynamics was used for calculating the aerodynamic coefficients of both a finned projectile and a projectile with a tail flare, with and without holes. The computation accuracy was verified by comparing the calculated aerodynamic coefficients with wind-tunnel measurements. The justification of the r...

Observations on some transonic wind tunnel test results of a standard model with a T-tail

As a part of a periodic health monitoring of the wind tunnel structure, instrumentation and flow quality, a series of tests of an AGARD-C calibration model was performed in the 1.5 m T-38 trisonic wind tunnel of the Military Technical Institute (VTI) in Belgrade. The tests comprised measurements of the forces and moments in the transonic Mach number range with the purpose of comparing the model’s obtained aerodynamic characteristics with those from other wind tunnel laboratories, in accordance with an adopted procedure for standard models testing. Inter-facility correlations were based on test results of physically the same model in the 5ft trisonic wind tunnel of the National Research Council (later operated as National Aeronautical Establishment) of Canada, in the 1.2 m trisonic wind tunnel of the Romanian National Institute for Scientific and Technical Creation and in the T-38 wind tunnel during the commissioning period. Analysis of correlated test results confirmed a good flow quality in the T-38 test section, good condition of wind tunnel structure and instrumentation, and the correctness of the data reduction algorithm. Small differences were observed in the pitching moment coefficient data obtained in the ‘normal’ and ‘inverted’ model configurations, and it has preliminary been concluded that the effect may have been caused by a slight asymmetry of flow in the rear part of the wind tunnel test section, the AGARD-C model being known for the high sensitivity of the pitching moment to local conditions.

Selection criteria of optimal conditions for supersonic tests in a blowdown wind tunnel

A natural desire of a wind tunnel test engineer is to plan and perform a test that will resemble the actual flight conditions as closely as possible. Geometric similarity and identical flight and wind tunnel Mach numbers are the primary requirements and they can be achieved without much problems, but the reduced size of the model and the limits of the operating envelope of the wind tunnel prevent the achievement of desired similarity with respect to the Reynolds number, which is generally much lower in a wind tunnel than in flight. Pressurized blowdown wind tunnels, like the T-38 in the Military Technical Institute (Vojnotehnički institut), Belgrade, were designed to reduce this discrepancy and achieve high Reynolds numbers by raising the stagnation pressure of the test-section flow. It is shown, however, that not the Reynolds number but instead the constraints related to model size, load range of available instrumentation, available run time, high aerodynamic loads, etc., are often decisive in the selection of the conditions for a high-speed wind tunnel test.