An experimental investigation of a three-dimensional turbulent boundary layer in an 'S'-shaped duct

Citation
Jm. Bruns et al., An experimental investigation of a three-dimensional turbulent boundary layer in an 'S'-shaped duct, J FLUID MEC, 393, 1999, pp. 175-213
Citations number
55
Categorie Soggetti
Physics,"Mechanical Engineering
Journal title
JOURNAL OF FLUID MECHANICS
ISSN journal
00221120 → ACNP
Volume
393
Year of publication
1999
Pages
175 - 213
Database
ISI
SICI code
0022-1120(19990825)393:<175:AEIOAT>2.0.ZU;2-H
Abstract
This paper describes the evolution of an incompressible turbulent boundary layer on the flat wall of an 'S'-shaped wind tunnel test section under the influence of changing streamwise and spanwise pressure gradients. The unit Reynolds number based on the mean velocity at the entrance of the test sect ion was fixed to 10(6) m(-1), resulting in Reynolds numbers Res,, based on the streamwise momentum thickness and the local freestream velocity, betwee n 3.9 and 11 x 10(3). The particular feature of the experiment is the succe ssion of two opposite changes of core flow direction which causes a sign ch ange of the spanwise pressure gradient accompanied by a reversal of the spa nwise velocity component near the wall, i.e. by the formation of so-called cross-over velocity profiles. The aim of the study is to provide new insigh t into the development of the mean and fluctuating flow field in three-dime nsional pressure-driven boundary layers, in particular of the turbulence st ructure of the near-wall and the cross-over region. Mean velocities, Reynolds stresses and all triple correlations were measure d with a newly developed miniature triple-hot-wire probe and a near-wall ho t-wire probe which could be rotated and traversed through the test plate. S kin friction measurements were mostly performed with a wall hot-wire probe. The data from single normal wires extend over wall distances of y+ greater than or similar to 3 (in wall units), while the triple-wire probe covers t he range y(+) greater than or similar to 30. The data show the behaviour of the mean flow angle near the wall to vary ail the way to the wall. Then, t o interpret the response of the turbulence to the pressure field, the relev ant terms in the Reynolds stress transport equations are evaluated. Finally , an attempt is made to assess the departure of the Reynolds stress profile s from local equilibrium near the wall.