Journal of Fluid Mechanics

Effects of imperfect spatial resolution on measurements of wall-bounded turbulentbx shear flows

Arne V.  Johansson a1 and P. Henrik  Alfredsson a1
a1 Department of Mechanics, The Royal Institute of Technology, S-100 44 Stockholm, Sweden

Article author query
johansson av   [Google Scholar] 
alfredsson ph   [Google Scholar] 


The effects of imperfect spatial resolution on hot-film and hot-wire measurements of wall-bounded turbulent shear flows were studied. Two hot-film probes of different length were used for measurements of fully developed turbulent channel flow in a water tunnel. In the near-wall region significant effects of spanwise spatial averaging due to finite probe size were found for a probe 32 viscous units long. The maximum turbulence intensity attained a 10% lower value than that for a probe about half as long, and the zero-crossing of the skewness factor was shifted away from the wall. This could be attributed to spatial averaging of narrow low-speed regions. Results for different Reynolds numbers, but with the same sensor length in viscous units, showed that Reynolds-number effects are small, and that much of the reported discrepancies for turbulence measurements in the near-wall region can be ascribed to effects of imperfect spatial resolution. Also the number of events detected with the variable-interval time-averaging (VITA) technique was found to depend strongly on the sensor length, especially for events with short duration.

(Published Online April 20 2006)
(Received September 13 1982)
(Revised July 5 1983)