EURAMET Project no. F1565 - Insertion depth effect and blockage effect for vane and cup anemometers

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00177016%3A_____%2F26%3AN0000008" target="_blank" >RIV/00177016:_____/26:N0000008 - isvavai.cz</a>

Result on the web

<a href="https://www.euramet.org/technical-committees/tc-f/projects" target="_blank" >https://www.euramet.org/technical-committees/tc-f/projects</a>

DOI - Digital Object Identifier

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Result language

angličtina

Original language name

EURAMET Project no. F1565 - Insertion depth effect and blockage effect for vane and cup anemometers

Original language description

In this study we investigate two types of installation effects which influence calibration results of anemometers in wind tunnels and which can lead to significantly different measurement errors obtained in wind tunnels of different type or size. The first of the effects, so called insertion depth effect, affects anemometers consisting of a straight mounting rod with an air speed sensor at the tip of the rod (e.g., most common types of thermal, vane or cup anemometers). When these types of anemometers are gradually inserted deeper into the wind tunnel test section their air speed indication may vary by several percent even if the velocity field in the wind tunnel is homogeneous.The evolving flow pattern influences a sensor at the tip of the mounting rod leading to observed variations of the air speed indication of up to about 10 %. This makes comparability of anemometer calibrations problematic because different insertion depths are usually used in wind tunnels with different dimensions and typical calibration uncertainties are an order of magnitude smaller than the variations caused by the insertion depth effect. The goal of this study is to find out how the insertion depth effect depends on type (open/closed) and size of a wind tunnel test section and whether consistent calibration results can be obtained when anemometers are installed with the same insertion depth in different wind tunnels. Four vane anemometers with propeller diameters from 16 mm to 107 mm were tested in 9 wind tunnels with test section diameters from 17.5 cm to 100 cm including both open and closed types of the test section. Air speed range from 0.5 m/s to 20 m/s was investigated. On top of that, several types of cup and vane anemometers were tested in the largest wind tunnel at 8 m/s in test section bounded or unbounded by a wall. In each wind tunnel a dependence of a measurement error of the anemometers on their insertion depth was measured, the resulting curves were compared and conclusions on systematic deviations between calibrations using the same insertion depth in different wind tunnels were drawn. The second of the effects is the blockage effect. When a large size cup or vane anemometer is calibrated in a wind tunnel the velocity field surrounding the anemometer for given velocity indication of the instrument depends on geometry (size and shape) of the test section and on conditions at the test section boundary (open or closed). A reference anemometer, e.g. LDA, is then placed to certain position usually upstream the meter under test and a measurement error is obtained which is sensitive to both – selection of the wind tunnel and selection of the position for the reference anemometer. As ideal calibration we may consider a calibration in an infinite unbounded asymptotically homogeneous flow with a reference air speed measured far upstream of the meter under test. A question then is what is the deviation of the measurement error obtained in a real wind tunnel from the ideal conditions, how this measurement error depends on position of the reference anemometer and if the deviation from the ideal conditions can be mitigated by a suitable selection of the reference position. In order to address these questions, air velocity fields upstream three anemometers were measured: cup anemometer with propeller diameter of 18 cm, vane anemometer with propeller diameter of 10.7 cm surrounded by a solid frame and vane anemometer with propeller diameter of 20 cm without any frame. The velocity fields were measured for two nominal velocities 5 m/s and 20 m/s (or 12 m/s in case of the smaller vane anemometer) in 4 wind tunnels – 3 of them with open circular test section with diameters 25.5 cm, 32 cm and 45 cm and one of them with closed square test section 54 cm x 54 cm. For the open test sections, the corresponding blockage ratios cover values below, close to and above the recommended maximum of 10 % and for the closed test section the corresponding blockage ratios are below or close to the recommended maximum of 5 %. All the velocity fields were measured using an LDA system placed on a positioning device. On top of that, all the anemometers were calibrated in a large wind tunnel with square cross section 100 cm x 100 cm which we consider as an approximate realization of the ideal conditions. Based on the measured velocity fields in different wind tunnels we discuss the sensitivity of the calibration results to the position of the reference LDA and we investigate the optimal LDA positioning which leads to minimal difference between the measurement error obtained in a “small size” wind tunnel and in the “large size” wind tunnel approximating the ideal conditions.

Czech name

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Czech description

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Type

V_souhrn - Summary research report

CEP classification

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OECD FORD branch

20302 - Applied mechanics

Project

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Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2026

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Number of pages

71

Place of publication

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Publisher/client name

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Version

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