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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.

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Methods of diagnosing aerodynamic characteristics are constantly developing in order to conduct the precise and energy efficient wind tunnel testing of transport vehicles in the prototype design early stages. This is of a special importance when facing the time/cost consumption problems of detection of the transition zone over the simplified design of the high-speed train. Herein the applied thermodynamics found a very significant role in the field of experimental aerodynamics. With the intention of detecting the boundary-layer transition zone the following measurements were applied: the infrared thermography, flow visualization, and drag force measurements. In addition, the CFD was applied to predict the flow behaviour and transition zone, solving PDE consisting of the Reynolds-averaged Navier-Stokes equations, energy equation, and the equation of state for an ideal gas employing density-based solver. The thermal imaging defined the transition zone by simple application, and fast recognition, while the transition bounds were defined in the analysis. The flow visualization confirmed thermography results and the method itself as favourable, especially in the most expensive early phases of redesigning for aerodynamically optimized and energy efficient solutions. The numerical method was confirmed by the experiments, resulting in acceptable differences in the definition of the transition zone. For a better understanding of the phenomenon, the overlapped implementation of the presented methods focused on forced convection showed as the best solution. Based on the experiences of this research, development of the additional equipment and adjustments will be introduced in the future experiments.