Different flow regimes and test facility constructions impact on a stable low air velocity value reproduction AGNƠ BERTAŠIENƠ, VYTAUTAS JANUŠAS Heat equipment research and testing laboratory Lithuanian Energy Institute Breslaujos sr. 3, Kaunas LITHUANIA agne@mail.lei.lt , http://www.lei.lt Abstract: Air velocity value standard was under research to investigate velocity range limits in order to expand it with proper uncertainty in international context. Influencing factors to measurement instruments readings and aerodynamic facility with different channel construction were revealed. Flow regime transition with the leading factors is discussed. Key-Words: transitional flow, LDA, profile, turbulence intensity, ejector 1 Introduction Air (gas) flow velocity measurements are encountered in many fields of practical interest. They occupy an important place in industry, environmental, safety and research. However, many problems are faced with the air velocity measuring instruments (MI) use in various different environments and conditions, which need to be analyzed in detail and the findings, should be presented to consumers. This is particularly important in order to measure the low velocity especially in flow regime transition. The need to measure the increasingly lower rates with the smallest possible uncertainty is increasing at an international level. Micro fluids in recent years have become one of the major research areas, which include engineering, chemistry, physics, micro and bio-technology, medicine, etc. Industry representatives, consumers and researchers have already showed an interest in micro-application and implementation opportunities. Micro fluids are particularly relevant to the health and protection field, which has recently developed and preferably is supported by the European Union Funds. An estimation are being done of indoor air movement, emissions that are harmless to man and the available equipment, as far as possible at the lowest energy consumption and environmental pollution, the optimization of technological processes are being done as well. However micro flow’s research requires an appropriate equipment, and detailed information about the environment and other influencing factors effects. Namely, for these reasons, the air velocity MI study is focused on the low velocities (0.05 - 1.0 m/s) in this paper and their reproduction seeking to reduce the uncertainty in the current design facility and in the use of different methods. Lithuanian state air velocity unit standard [1] opportunities, limits, medium impact research, analysis of the different air velocity values MI correlation with standard reproducible values [2], the exploration of new areas of research, assessing the reliability of MI, by expanding different measurement sections applications and improving unit measurement characteristics have been done with regard to reasons mentioned above. A number of tasks have arisen during experiments. The first one, to use an additional means influencing the flow structure such as artificial low velocity flow turbulence increase with grids, which the large scale flow instabilities transform into a stable of small scale vortices. The second one, to use different type of equipment which forces the flow to move, in this case the ejector is used instead of fan, installed at the measuring channel outlet, in order to remove the fan caused flow pulsation, or to avoid the fan working at a small roundabout way. 2 Flow rate accuracy and influencing factors It is competently known that air velocity measurements in the channels using various kinds of MI for fully developed turbulent flow or for flow in entrance region of measurement channel (MC) is not complicated because velocity values are high enough and stable. The situation is converse for air Proceedings of the 7th IASME/WSEAS International Conference on FLUID MECHANICS and AERODYNAMICS ISSN: 1790-5095 163 ISBN: 978-960-474-106-9