The paper describes a pneumatic method for determining the velocity in spatial flow. Its main advantage is simplicity, reliability, and stability during long-term operation. Three, four, five and seven-channel sensors are used. The main drawback of the known methods of studying spatial flows is that the methods of measurement, data processing and calibration of multi-channel sensors are complex and do not always provide an unambiguous result. Errors occur because the calibration curves are not closed, are obtained in different quarters of the coordinates, and are described by different ratios that do not coincide at their boundaries. The uncertainty in the choice of a particular ratio and the possibility of obtaining a discontinuity of functions at the boundaries leads to significant errors in determining the angles of flow. It is described a new calibration method that eliminates the above disadvantages. The difference from the known calibration methods is that the calibration dependencies are obtained by replacing the deviation of the sensor in one of the planes, with the rotation of the sensor relative to the axis in the angle range from 0° to 360°. As a result of calibration closed curves are obtained that connect the flow angles and the velocity. The use of the proposed algorithm for calibration and data processing makes it possible to increase the accuracy of determining the speed and its direction and expand the measurement range to the area of small flow angles. The latter is achieved due to the fact that when determining the velocity and angles of flow on the sensor, calibration dependencies are used in the form of closed curves. It is also described the proposed and implemented three-channel speed sensor, (sensor diameter 2.4 mm, measuring tube diameter 1.2 mm), which eliminates a number of disadvantages inherent in multi-channel sensors. In particular, the disadvantages of five and six-channel sensors include the inability to manufacture small-diameter sensors with an accurate location of the channels around the circle through 90°, which leads to asymmetry of the calibration curves and a decrease in the accuracy of three-dimensional velocity measurements. The method of calibration and measurement of the velocity vector using a three-channel speed sensor is presented. An example of the performed velocity vector measurements in 11 cells of the model assembly (seven — rod model-1:10 magnification) with twisted fuel rod simulators at the numbers Re = 3500 and 30000 is presented.
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