System for acquisition and processing of pressure data around body in airflow D. Mežnarić, K. Krajček Nikolić, D. Franjković Faculty of Transport and Traffic Sciences / Department of Aeronautics, Zagreb Hrvatska domagoj.meznaric@gmail.com, kkrajcek@fpz.hr, dfranjkovic@fpz.hr The article deals with the system and methods for determination of the pressure distribution around aerodynamically shaped body immersed in airflow and further calculations of aerodynamic characteristics. Measurements are conducted in the subsonic closed-loop wind tunnel AT-1, in Aerodynamics Laboratory of Department of Aeronautics at Faculty of Transport and Traffic Sciences. Pressure distribution around airfoil NACA 2421 is sensed by the system for acquisition of pressure data Intelligent Pressure Scanner 9016, produced by the Pressure Systems Company. Data are digitalized and transferred to the computer through the Ethernet link. Data are processed by NUSS and LabVIEW software. Measurement results are displayed and compared to those obtained from piezometric harp. Results of experiments are commented and recommendations for further research are given. I. INTRODUCTION Wind tunnels are devices or facilities for experimental measurements in aerodynamics and they are used from the early beginning of aviation. The tunnels are used to obtain high-quality experimental data, especially when certain data can’t be obtained by theoretical calculations. In the wind tunnel, a controlled flow of air is produced which is acting on the model - subject of research and physical quantities are felt and measured and physical phenomena arising from the interaction of the body and the air flow are observed and recorded. The measurements were performed in the subsonic wind tunnel AT-1 on the model of wing made of airfoil NACA 2421. The aim of the experiment was the construction of the measuring system from the measuring model through the acquisition of pressure system to the computer with appropriate programs. Intelligent pressure transducer of Pressure Systems company uses electrical resistance elements by which mechanical displacement caused by the pressure is converted into an electrical signal. It consists of two module of code 9016 each containing 16 measurement points, each with input for reference pressure which is equal to the atmospheric pressure of the ambient air. In addition to the two modules, there is pressure calibrator of code 9034. It is used to calibrate the measuring instrument to zero and for the range. The modules convert analog signal to digital and send it through the Ethernet connection to the computer where the signal is further processed. The results are compared with the results of hydrostatic pressure measurements. Two softwares are used for data processing: NUSS and LabView. NUSS is a basic program used to calibrate and adjust the system, and LabView is used to obtain pressure distribution on the upper and lower wing surface and to calculate the lift and the drag force due to the pressure. II. WIND TUNNELS Wind tunnels are complex installations which in its test section simulate flow conditions similar to those around the actual object or model. Wind tunnels are divided in regard to the velocity in the test section (subsonic, transsonic, supersonic) and the shape of the airstream line (open- or closed-circuit). According to their purpose or operating mode, tunnels are divided into: tunnels with a controlled pressure, tunnels with variable density of the working fluid, tunnels for testing prototypes in full size, tunnels for flow visualization, tunnels for testing free flight (the model is not fixed on the sting), tunnels for testing of spiral maneuvers, testing the stability of the flight, testing icing conditions on aircraft or other vehicles, for testing V/STOL aircraft, for testing aerodynamic characteristics of cars and boats, as well as for other uses in civil engineering (wind load on the building), ecology (the spread of pollution by natural air flow, the boundary layer to the surface of the Earth), sports (car racing, sailing, ski jumping, cycling ...) and for many other purposes. Wind tunnel AT-1 (Figure 1.) at the Faculty of Transport and Traffic Sciences is a closed-circuit tunnel with a single return line. The test section has elliptical cross-section and partly open. Other components of the wind tunnel are converging nozzle, corner sections with air routers, honeycomb and screens, diffuser, the electric motor and fan, and the return line. Scheme of the wind tunnel AT-1 is shown in Figure 2. Figure 1. Wind tunnel AT-1