Conventional measuring probes in the wall layer of turbulent subsonic ducted flows

This piece of work is concerned with the application of two conventional measuring probes, pressure probe and hot wire, in the wall layer of subsonic ducted, pipe and channel, flows for velocity measurements. Careful measurements have been carried out and analysed accordingly for Reynolds number range of 2.8×10⁵≤Rem≤4.5×10⁵ and 4×10⁴≤Rem≤2.3×10⁵ for the pipe and the channel, respectively. Pressure probes of outer diameters (d ₀ ⁺ = d ₀·u_τ/v) 20-120 wall units and hot wire, having wire length (l+= l u_τ/v) of 50-250 for the current Reynolds range, have been utilized to carry out the present measurements. When the pressure probe was applied in the wall layer, the wall proximity and the shear gradient played major roles of its incorrect velocity readings, however, this effect was far from being influencing the hot-wire velocity measured in the overlap region. When the pressure probe results compared to those obtained by the hot wire, the pressure probe's data showed hump in the normalized mean velocity profiles around the wall distances y⁺≤300 and y⁺≤150 for the pipe and the channel, respectively. Available corrections are adopted and applied to the pressure probe data measured, yielding results that are comparable to those of the hot wire and this was also demonstrated by comparing the present results corrected to the so-called the logarithmic velocity profile.