The airflow development in the pipe, in the entrance region of the wind tunnel located in the Lithuanian Energy Institute, the laboratory of Heat Equipment Research and Testing is investigated to analyze the conditions for the reproduction of air velocity values. The analysis is performed to reveal undeveloped flow conditions where the calibration of the devices is usually made, the entrance region of the pipes, or free stream from the nozzles. In this study, different flow regimes have been investigated using different air velocity measurement methods. Experimental and numerical results clearly show the features of the developing flow. They both demonstrate the stable core of the velocity profile up to 5 D in the pipe and ≤1 D from the entrance into the free stream in the testing chamber. Ultrasonic anemometer (UA) installed in the aerodynamic test facility shows reliable and highly comparable results with another non-intrusive device – laser Doppler velocimeter (LDA) in a range of velocities from 0.05 m/s up to 30 m/s. UA integrated into the wind tunnel is not found to be used for metrological issues for air velocity. Due to the fast response, they both enabled to analyze fluctuations in the flow. Local vortices identified in the flow have influenced the low-frequency fluctuations and the scatter of measurement results. Moreover, high-frequency fluctuations found in the flow originated from the flow turbulence and might be due to the electronic or acoustic noise. The stabilization of the entrance region in the pipe influences the mean value of air velocity, the transversal distribution of velocity and the development of axial velocity in different test sections of the pipe in a wind tunnel. Along with the recirculation zones in cavities of ultrasonic transducers, these factors are essential that make an impact on the reproduction of air velocity value.

在立陶宛能源研究所的风洞入口区域，热设备研究和测试实验室，研究了管道中的气流发展情况，以分析再现空气速度值的条件。进行分析以揭示通常在进行设备校准的未开发的流量条件，管道的入口区域或来自喷嘴的自由流。在这项研究中，已使用不同的空气速度测量方法研究了不同的流态。实验和数值结果清楚地表明了显影流的特征。它们都显示出管道中高达5 D的速度剖面的稳定核心，并且从进入测试腔室的自由流的入口开始≤1D。空气动力学测试设备中安装的超声波风速计（UA）与另一种非侵入性设备–激光多普勒测速仪（LDA）的速度范围从0.05 m / s至30 m / s，显示出可靠且高度可比的结果。尚未发现集成到风洞中的UA用于风速的计量问题。由于响应速度快，它们都能够分析流量波动。流动中识别出的局部涡旋影响了低频波动和测量结果的分散。而且，在流体中发现的高频波动是由流体湍流引起的，并且可能是由于电子或声学噪声引起的。管道入口区域的稳定性会影响空气流速的平均值，风洞中管道不同测试段的速度横向分布和轴向速度的发展。这些因素以及超声换能器腔体中的回流区一起，对于影响空气速度值的再现至关重要。