cases:case023

# 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 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.

Cases Without Turbulence-Generating Grid
Location Mean velocity & Reynolds stresses Triple moments
$x=-56$ cm fn1.dat fn2.dat
$x=35.5$ cm ($15^o$ station) cn151.dat cn152.dat
$x=71$ cm ($30^o$ station) cn301.dat cn302.dat
$x=106.5$ cm ($45^o$ station) cn451.dat cn452.dat
$x=142$ cm ($60^o$ station) cn601.dat cn602.dat
 Cases With Turbulence-Generating Grids Location Mean velocity & Reynolds stresses Triple moments $x=-56$ cm fg191.dat Grid placed at $x=-177$ cm $x=-56$ cm fg101.dat Grid placed at $x=-120$ cm $x=35.5$ cm ($15^o$ station) cg151.dat cg152.dat Grid placed at $x=-127$ cm $x=71$ cm ($30^o$ station) cg301.dat cg302.dat Grid placed at $x=-92$ cm $x=106.5$ cm ($45^o$ station) cg451.dat cg452.dat Grid placed at $x=-56$ cm $x=142$ cm ($60^o$ station) cg601.dat cg602.dat Grid placed at $x=-32$ cm
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:

case023 (dbcase, confined_flow)
case023
titleBoundary Layer in a Concave Bend
authorJohnson
year1990
typeEXP
flow_tag2d, curvature