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

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 section was fixed to 106 m−1, resulting in Reynolds numbers Reδ2, based on the streamwise momentum thickness and the local freestream velocity, between 3.9 and 11 × 103. The particular feature of the experiment is the succession of two opposite changes of core flow direction which causes a sign change of the spanwise pressure gradient accompanied by a reversal of the spanwise 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 insight into the development of the mean and fluctuating flow field in three-dimensional pressure-driven boundary layers, in particular of the turbulence structure of the near-wall and the cross-over region.Mean velocities, Reynolds stresses and all triple correlations were measured with a newly developed miniature triple-hot-wire probe and a near-wall hot-wire probe which could be rotated and traversed through the test plate. Skin friction measurements were mostly performed with a wall hot-wire probe. The data from single normal wires extend over wall distances of y+ [gsim ] 3 (in wall units), while the triple-wire probe covers the range y+ [gsim ] 30. The data show the behaviour of the mean flow angle near the wall to vary all the way to the wall. Then, to interpret the response of the turbulence to the pressure field, the relevant terms in the Reynolds stress transport equations are evaluated. Finally, an attempt is made to assess the departure of the Reynolds stress profiles from local equilibrium near the wall.

Large-Reynolds-number asymptotics of the streamwise normal stress in zero-pressure-gradient turbulent boundary layers

“…Hence, an outer maximum of uu + higher than the inner maximum at y + ≈ 15 could only arise from .7); --, composite expansions (4.9); · · · · · · , logarithmic slope of −1.26 proposed by Marusic et al (2013). Data with fits: (pink) p , Bruns et al (1993) a significant depletion of vv + and ww + , for which we see no clear evidence. This is not to say that we exclude some redistribution between components.…”

Self-consistent high-Reynolds-number asymptotics for zero-pressure-gradient turbulent boundary layers

“…Therefore, we have made the quality assessment of more than a dozen ZPG TBL data sets known in the literature the subject of a separate publication. 11 Nevertheless, data of Karlsson, 12 Smith, 13 Hites, 1 Bruns,14,15 DeGraff and Eaton, 3 Carlier and Stanislas, 7 and Nickels et al 9 have been included in some figures. ͑For a justification of this data selection, see Ref.…”

Experimental investigation of Reynolds stress complex eddy viscosity model for coherent structure dynamics

“…The phase information of turbulent fields therefore should be included in the eddy viscosity model. This proposal has been confirmed by the numerical simulations of Wu [2], Luo [5,8] and experimental measurements of Falco [4], Bruns [9], Wang [10], Li [11] and Guo [12]. However, the theoretical model of CS still needs to be further investigated to gain more detailed information in the different regions of the whole TBL.…”