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UBC Theses and Dissertations

An experimental study of interference effects between closely spaced wires of an X-type hot-wire probe Jerome, Frederick Ernest


The Disa type 55A32 X-wire probe has been widely used in turbulence measurements. However, the author was unable to obtain agreement between turbulence measurements made simultaneously with this type of X-wire probe and an ultrasonic anemometer at the same position in the atmospheric boundary layer over the ocean. The nature of the disagreement between the two instruments suggested that there existed an unexpected response of the wires to the cross stream wind component normal to the plane of the X-array. Wind tunnel experiments confirmed this response and attributed most of it to thermal coupling between the two wires of the array via their hot wakes. The prongs and/or probe body were also shown to be contributors to the anomalous responses of the X-wires. Similar experiments carried out with a Thermo-Systems model 1241-20 X-probe (with a sensor length to sensor separation ratio of 5/8 compared with 0.2 or less for the Disa 55A32 X-wire probe) demonstrated that the interference effects were absent (or, at least, insignificant). As a consequence of these findings, the Disa Electronik A/s company of Herlev, Denmark, modified their 55A32, 55A38 and 55A39 lines of X-wire probes to make the length/separation ratio close to unity.

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