Boundary Layer in a Concave Bend

Developing boundary layer submitted to destabilizing concave curvature at \(Re_{\theta} = 1450\) without longitudinal pressure gradient (\(S = \partial p/\partial x \approx 0\)).

The test facility is a free surface water channel, shown schematically in figure 1, consisting of an asymmetric 4:1 contraction, a 4.88 m long straight development section with dimensions 25 cm (width) by 1.25m (span), a 90 degree constant radius curved wall (\(R = -136\) cm), and a straight recovery section. The channel walls are contoured to minimize pressure gradient in the straight development section and along the concave test surface. The boundary layer is tripped 1 m downstream of the nozzle exit using a 0.476 cm square rod. Spanwise surveys show good spanwise uniformity; specifically, the roll cells which appear in the curved section are not fixed in space, but are randomly distributed in space and time.

Fig. 1: Experimental arrangement

LDV measurements of all three velocity-component were made down to \(y^+ \approx 5\); \(u'\) and \(w'\) are at even smaller \(y^+\) at a number of streamwise locations, as indicated in figure 2.

One set of measurements were taken with no grid-generated turbulence present (without the grid shown in figure 2). For the other sets, a square, biplanar, square bar grid (mesh spacing \(M = 6.35\) cm; ratio of mesh spacing to bar width \(M/w = 4\)) was placed at various locations upstream of the curved wall and used to generate nearly axisymmetric turbulence. In most cases the free-stream turbulence levels were nominally \(u'/U_{pw} = 0.05\).

Fig. 2: Flow geometry and measurement locations

Velocities measured using LDV.

For most cases profiles are available at a number of streamwise locations around the bend for

• Mean velocity
• Reynolds stresses
• Triple moments, skewness, flatness

Sample plots of selected quantities are available.

The data can be downloaded as compressed archives from the links below, or as individual files.

• blcb-allfiles.zip
• blcb-allfiles.tar.gz

The file readme.txt contains a description of the files and data formats.

xdata.dat contains a summary of the channel width as a function of streamwise distance, and values of wall skin friction at measurement locations.

1. Barlow, R.S., Johnston, J.P. (1988). Structure of a turbulent boundary layer on a concave surface. J. Fluid Mech., Vol. 191, pp. 137-176.
2. Johnson, P.L. (1990). PhD thesis, Stanford University.
3. Johnson, P.L., Johnston, J.P. (1989). The effects of grid-generated turbulence on a flat and concave turbulent boundary layer. Report MD-53, Thermosciences Division, Dept. of Mech. Eng., Stanford University.

Indexed data: