The development of steady, turbulent flow in a 90 degrees section of a curv
ed square duct was studied at a Reynolds number of 4 x 10(4) by hot-wire an
emometer. The curved duct has a cross-section measuring 80 x 80 mm and a cu
rvature radius ratio of 4 and is connected with a long, straight duct at it
s both ends. The longitudinal and lateral components of mean and fluctuatin
g velocities, and the Reynolds stresses were measured by the method of rota
ting a probe with an inclined hot-wire. The velocity fields of the primary
and secondary flows, and the Reynolds stress distributions in the cross-sec
tion were illustrated in the form of contour map. The development of the pr
imary flow was found to be connected with a strong pressure gradient near t
he outer and inner wall and a secondary flow induced in the cross-section o
f the bend by a pressure difference between the outer and inner wall and a
centrifugal force acting on the fluid; the fluid is accelerated near the in
ner wall and decelerated near the outer wall between the bend angle phi con
gruent to 0 degrees and phi congruent to 30 degrees, but an increase and de
crease of the fluid velocity are reversed between phi congruent to 30 degre
es and phi congruent to 90 degrees. The fluctuating velocity correlations,
i.e. the Reynolds stresses follow a complicated progress according to the c
omplex development of the primary flow. The results obtained can be availab
le to verify various types of turbulence models and to develop new models.