Experimental Study of the Thermal Wake Interference Between Closely Spaced Wires of a X-Type Hot-Wire Probe

Abstract

Summary In constructing an X-type hot-wire probe it has been the policy of a number of experimenters and manufacturers to place the two wires forming the X close to each other to assure that they are both measuring in effectively the same plane. A number of important experiments have been made using such a probe design. Recent experiments at the University of British Columbia and McGill University have shown that an X-wire probe which has two wires almost in the same plane is quite sensitive to movements of the velocity vector out of that plane (defined as pitching motion). This has been attributed to the influence on one wire of the hot wake produced by the other. In this note a Disa X-type probe (type 55A32), with the wires 0·15 mm apart, is tested and found to have a static sensitivity to small angles of pitch, which is very significant for low wire Reynolds numbers (< 5) but becomes small for Reynolds number greater than 10. A modified probe, having the wires one wire length apart, is suggested and when tested was found to have no pitch sensitivity.