The steady, incompressible, isothermal, developing flow in a square-section curved duct with smooth walls has been investigated. The 40 x 40mm duct had a radius ratio of 2.3 with long upstream and downstream straight ducts attached. Measurements of the longitudinal and radial components of mean velocity, and corresponding components of the Reynolds-stress tensor, were obtained with a laser-Doppler anemometer at a Reynolds number of 4 x lo4 and in various cross-stream planes. The secondary mean velocities, driven mainly by the pressure field, attain values up to 28 yo of the bulk velocity and are largely responsible for the convection of Reynolds stmsses in the cross-stream plane. Production of turbulent kinetic energy predominates close to the outer-radius wall and regions with negative contributions to the production exist. Thus, at a bend angle of 90' and near the inner-radius wall, uszcraU,/& is positive and represents a negative contribution to the generation of turbulent kinetic energy.In spite of the complex mean flow and Reynolds stress distributions, the crossstream flow is controlled mainly by the centrifugal force, radial pressure gradient imbalance. As a consequence, calculated mean velocity results obtained from the solution of elliptic differential equations in finite difference form and incorporating a two-equation turbulence model are not strongly dependent on the model; numerical errors are of greater importance.

A numerical study of heat transfer in 90 deg, constant cross section curved duct, steady, laminar, flow is presented. The work is aimed primarily at characterizing the effects on heat transfer of duct geometry and entrance conditions of velocity and temperature by considering, especially, the role of secondary motions during the developing period of the flow. Calculations are based on fully elliptic forms of the transport equations governing the flow. They are of engineering value and are limited in accuracy only by the degree of computational mesh refinement. A comparison with calculations based on parabolic equations shows how the latter can lead to erroneous results for strongly curved flows. Buoyant effects are excluded from the present study so that, strictly, the results apply to heat transfer flows in the absence of gravitational forces such as arise in spacecraft.