HOT-WIRE MEASUREMENTS IN TURBULENT TRANSONIC-FLOWS

In transonic flows, problems arise in hot-wire anemometry at moderate Reynolds number Rd(t), and at low and moderate overheat of the wire a(w). However, these operating parameters are necessary if velocity and temperature fluctuations are to be measured by the technique of fluctuation diagrams. A measurement method adapted to this range (7<Rd(t)<38 and a(w)<0.45) is proposed. The sensitivities of the hot wire to the mass flux, Mach number and total temperature are defined and determined by calibration. The results are verified in known turbulent flows: an equilibrium boundary layer and a free shear flow containing large transonic zones. The present method gives results in agreement with classical results. In contrast, neglecting the sensitivity to the Mach number, as is usual with supersonic flows, would lead to unrealistically low levels of turbulence. A simplified method, already used for supersonic flows, in which the hot wire is operated at a single overheat, is proposed and validated for the transonic range.