Swirling Boundary Layer in Conical Diffuser
Experiments by Clausen et al.
Swirling boundary layer developing in a conical diffuser. The conical diffuser is placed 100 mm
downstream of a rotating swirl generator of diameter D=260 mm and discharges into the atmosphere at
X=510 mm. It has a 20o included angle and an area ratio of 2.84.
The swirling flow is created by a rotating cylinder including a honeycomb screen at its
inlet. At its outlet, the inlet swirl is close to solid-body rotation. Along the diffuser,
the swirl is of sufficient magnitude to prevent boundary layer separation but just
insufficient to cause recirculation in the core flow. The axial pressure gradient and the
curvature of the streamlines have been found to be the dominant perturbations imposed to
the swirling boundary layer as it exits the cylindrical part and enters the conical
diffuser. The swirl is responsible for severe radial gradients near the wall for most of
the turbulence quantities.
- Air with a kinematic viscosity:
= 1.5 × 10-5 m2/s.
- Average axial velocity at inlet (x = -25 mm): Uo = 11.6 m/s.
- Reynolds number: UoD/ = 202,000.
- Atmospheric pressure at outlet.
The following measurements are provided at station -25, located at x = -25
mm, 75 mm downstream of the swirl generator and 25 mm upstream of the
diffuser entrance. The swirl is close to solid-body rotation with a nearly uniform axial
velocity in the core region outside the boundary layers. The swirl number is
Wmax/Uo = 0.59 where Wmax is the maximal circumferential velocity.
The wall shear stress is /Uo2 = 0.00282
in the x direction and /Uo2 = 0.00190
in the z direction. The wall streamline angle is = tan-1(W/U)y=0 = 34o.
- First order moments from wall to centreline (files
- Second order moments for y ranging from 4 to 20 mm (files
- Reynolds stresses:
- Turbulent kinetic energy: k/Uo2 (deduced)
The following measurements are available at 7 stations along the diffuser:
x = 025, 060, 100, 175, 250, 330, 405 mm ($$$ in the file names)
- Velocity measurements: Profiles perpendicularly to diffuser wall of:
- First order moments from wall to centreline (files u$$$.dat and w$$$.dat)
- Second order moments for y ranging from 4 to 20 mm (files usq$.dat, vsq.dat,
wsq.dat, uv$.dat, uw$.dat and vw$.dat)
- Reynolds stresses:
- Turbulent kinetic energy:
- Distribution along the diffuser of:
- Distribution of the wall shear stress:
/Uo2 (files Mm$$$.dat)
- Pressure measurements (file cp.dat):
The following measurements are available along the diffuser:
- Distribution of the static pressure coefficient: Cp
Instructions for calculations
The calculations should be performed for the whole diffuser (not only for the boundary
The calculation of the duct flow should be started at station x=-25 mm using the
experimental values provided as inlet conditions.
The diffuser discharges to the atmosphere at X=510 mm. Zero gradients may be
assumed for the flow variables.
Presentation of results:
The following results should be plotted and compared with the data.
At x= 025, 060, 100, 175, 250, 330, 405 mm:
- normalized mean velocity, Reynolds stress and k profiles against y (perpendicular to diffuser
Along the diffuser wall:
- /Uo2 and
Previous Numerical Studies
Description of experiments
- CLAUSEN, P.D., KOH, S.G. & WOOD, D.H. (1993). Measurements of a swirling turbulent
boundary layer developing in a conical diffuser. Experimental Thermal and Fluid
Science, Vol. 6, pp. 39-48
- CLAUSEN, P.D. & WOOD, D.H. (1989). The correction of X-Probe Results for transverse
contamination. Journal of Fluids Engineering, Vol. 111, pp. 227
Previous numerical studies
- ARMFIELD, S.W., CHO, N.H. & FLETCHER , C.A.J. (1990). Prediction of turbulence
quantities for swirling flow in conical diffusers. AIAA, Vol. 28, No. 3, p. 453
- CHO, N.H. & FLETCHER , C.A.J. (1991). Computation of turbulent conical diffuser
flows using a non-orthogonal grid system. Computers and Fluids, Vol. 19, p. 347