Evaluation of X-probe response to wire separation for wall turbulence measurements

Abstract

Inevitable errors in X-probe measurement are investigated in simulated Gaussian velocity fields generated on a digital computer. Two types of X arrangement are studied: one is a conventional X-probe comprised of two inclined hot wires, and the other consists of inclined and normal hot wires (modified X-probe). The computer simulation results under typical wall-turbulence conditions indicate that the most significant factor producing measurement errors, in both high and low intensity turbulence, is the difference between the instantaneous velocities sensed by the two wires, associated with wire separation. In particular, the measurement accuracy of the modified X-probe depends greatly on the effect of wire separation, and at worst, data obtained with such a probe result in fallacious information. To confirm the error analysis, turbulent quantities in a pipe flow were measured using these X-probes. The experimental results are consistent with the results of the error analysis. Also, based on the present analysis, simple formulae have been developed to estimate inherent errors in X-probe measurements.

Spatial averaging effects on the streamwise and wall-normal velocity measurements in a wall-bounded turbulence using a cross-wire probe

“…For example, the wire separation effects have been studied in isolation both experimentally (Browne et al, 1988;Strohl & Comte-Bellot, 1973) and numerically (Suzuki & Kasagi, 1992). While Tagawa et al (1992) investigated the effects of the wire inclination angle numerically. Here, we present extensive numerical studies using a direct numerical simulation (DNS) database where multiple parameters related to the dimension and relative position of the sensors are systematically considered, and their effect on the measured turbulent stresses and energy spectra are investigated.…”

Spatio-temporal turbulent structures of thermal boundary layer subjected to non-equilibrium adverse pressure gradient

“…Reynolds number based on momentum thickness, Table 1 Flow parameters (U0 ¼ 10:8 m=s, He ¼ 10 K) point was found to be located 0.6 mm from the wall, from examining the reliability of the data (Tagawa et al, 1992). An array of five identical three-wire probes, each composed of an X-type hot wire and a fine cold-wire, is aligned in the wall-normal direction for simultaneous measurement, as shown in Fig.…”

“…Also, the bias error, which is ascribed to the spatial separation of the two wires of an X-probe, was removed in accordance with the procedure indicated by Tagawa et al (1992).…”

Effects of adverse pressure gradient on heat transfer mechanism in thermal boundary layer

“…The spatial resolution of the threewire probe in the wall-normal direction is about 0.3 mm. The first measurement point is located at 0.6 mm from the wall, after examining reliability of the data (Tagawa et al, 1992;Nagano and Tsuji, 1994). Fig.…”