# Developing Flow in a Curved Rectangular Duct

## Description

• Developing turbulent flow in a 90 deg. curved duct of rectangular cross-section.
• Duct with two straight and one curved sections.
• Rectangular cross-section of the duct with a width of H = 20.3 cm and a height of 6H.
• Inner radius of curvature of the bend: Ri = 3×H.
• Straight upstream section with a length of 7.5H = 1.52 m.
• Straight downstream section with a length of 25.5H = 5.18 m.

### Flow Characteristics

The initially 2D boundary layers developing on the vertical lateral walls are subjected to strong streamwise curvatures and associated pressure gradients along the bend. On the other hand, the pressure-driven secondary motion in the corner regions eventually leads to the formation of a longitudinal vortex on the convex wall. The duct aspect ratio is such that these two features of the flow develop more or less independently, without interaction.

### Flow Parameters

• Air with a kinematic viscosity: =1.45 × 10-5 m2/s.
• Freestream velocity at station U1 (x = -4.5H): Uo = 16 m/s.
• Reynolds number: UoH/ = 224,000.

### Inflow Conditions

At station U1 (x = -4.5H), the velocity is uniform in the core flow, outside the boundary layers, within a deviation less than 1%. On the vertical lateral walls, the boundary layers are of flat-plate type with a momentum thickness Reynolds number of 1650, a boundary layer thickness of = 0.08H and a friction coefficient of Cf = 0.0038. The 2D wind-tunnel contraction located 3H upstream of U1 introduces a secondary motion in the boundary layers on top and bottom flat walls but its magnitude reaches only 5% of the freestream velocity. The following measurements are then provided for a slightly three-dimensional duct flow but are sufficiently detailed to be used as inlet conditions.

• Velocity vectors: (files mu1@@@.dat) V/Uo, W/Uo
• Contour maps of: (files mu1@@@.dat)
• First order moment U/Uo
• Second order moments
• Reynolds stresses: /Uo2, /Uo2, /Uo2, /Uo2, /Uo2
• Turbulent kinetic energy: k/Uo2(deduced)
• Wall friction coefficient,Cf, distribution on each wall (files su1in.dat, su1out.dat and su1up.dat).