Development of a Hot-Wire Probe with Two Parallel Wires Placed Closely Together

Abstract

We manufactured a new hot-wire probe with two parallel wires placed closely together for measuring a transitional boundary-layer flow. The main feature of this new probe is that it is much smaller than a conventional multi-sensor probe, such as an X-type probe. Thus, the new probe can be regarded as a sensor similar in configuration to a single normal probe and is expected to provide high spatial resolution for fluctuating velocities in a transitional boundary layer. The measurement principle is very simple, as the streamwise and the normalwise velocity components are simultaneously obtained from the sums and the differences of the linearized outputs of two hot-wire circuits with the aid of the look-up-matrix method. It was found that the complicated relations between the hot-wire-circuit outputs and the flow angle can be simplified by limiting the flow angle to within θ = ±30 deg. The new hot-wire probe was used to measure the velocity profiles in a low Reynolds number turbulent boundary layer. The results revealed that the probe is a useful tool for measuring velocities in a transitional boundary layer having a thickness of only several mm.