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Published May 2004 | public
Journal Article Open

The response of hot wires in high Reynolds-number turbulent pipe flow


Issues concerning the accuracy of hot-wire measurements in turbulent pipe flow are addressed for pipe Reynolds numbers up to 6 × 106 and hot-wire Reynolds numbers up to Rew ap 250. These include the optimization of spatial and temporal resolution and the associated feature of signal-to-noise ratio. Very high wire Reynolds numbers enable the use of wires with reduced length-to-diameter ratios compared to those typical of atmospheric conditions owing to increased wire Nusselt numbers. Simulation of the steady-state heat balance for the wire and the unetched portion of wire are used to assess static end-conduction effects: they are used to calculate wire Biot numbers, \sqrt{c_0}l , and fractional end-conduction losses, σ, which confirm the 'conduction-only' theory described by Corrsin. They show that, at Rew ap 250, the wire length-to-diameter ratio can be reduced to about 50, while keeping \sqrt{c_0}l\gt3 and σ < 7% in common with accepted limits at Rew ap 3. It is shown that these limits depend additionally on the choice of wire material and the length of unetched wire. The dynamic effects of end-cooling are also assessed using the conduction-only theory.

Additional Information

© 2006 IOP Publishing Limited Received 2 October 2003; Published 26 March 2004; Print publication: Issue 5 (May 2004) The support of ONR under grant nos N00014-98-1-0525, N00014-99-1-0340 and N00014-03-1-0320 is gratefully acknowledged. JFM is indebted to the Engineering and Physical Sciences Research Council (grants GR/M64536/01 and GR/R48193/01), the Royal Academy of Engineering (England), and the Leverhulme Trust (grant F/07058/H) for financial support.


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