TENSOSENSITIVITY OF THE HOT-WIRE PROBE

© A.Yu. Pak

Institute of Theoretical and Applied Mechanics SB RAS,

630090 Novosibirsk, Russia

The principle of operation of a hot-wire anemometer is based on measurement of changes in the electrical resistance of some thin sensitive element. These changes, however, may be related not just to fluctuations of flow parameters, but also to probe deformations, mechanical vibrations, electromagnetic fields, etc. The false electric signals caused by various external factors may seriously distort measurement results. It is therefore of extreme importance to apply all possible measures to reduce the sensitivity of a hot-wire probe to such factors, vibrations for in- stance, that affect the probe resistance and bring about false signals. There are quite a number of methods that may be used for transforming vibrations into a reference electrical signal that bears no relation to fluctuations of flow quantities and therefore may be subsequently use to apply corrections for the vibrations. The strain gage effect is probably the most substantial source of falsesignals. The forces influencing a hot-wire probe were analyzed in [1-3], and estimations of the strains arising in a hot wire were given in these publications.

The contribution due to false electric signals may depend on the probe-overheating factor and on the manner in which the electric power is supplied to the probe, i.e., on the anemometer type. In a constant current anemometer, it is possible to measure and separate out the noise owing to the electric circuit of the anemometer; it is not the case with hot-wire anemometers of other types. To separate out the strain-induced component from the total signal is a very difficult task since this component arises alongside with the useful signal and directly at the hot wire. Therefore, in order to develop a way for diminishing the detrimental component owing to the strain gage effect or have a possibility to apply a proper correction for it, it is necessary to analyze the influence of different flow quantities, hot-wire probe properties and specific features of different types of hot-wire anemometers on probe tensosensitivity.

The equation relating the electric power supplied to a hot-wire probe to the thermal energy removed from it by the flow may be generally written as This equation was analyzed in [4] when deriving relations for the probe sensitivity coefficients to flow parameters. To analyze the possibility of origination of a false signal owing to the strain gage effect, we assume the wire length, as well as all flow quantities, to be variable parameters. Unlike [4], we shall consider a general case in which no restrictions are imposed on the type of the anemometer used with the hot-wire probe.

P.S. СПАСИБО, ЧТО ПОСЕТИЛИ МОЮ СТРАНИЧКУ, УДАЧНОГО ВАМ ДНЯ!!!