The flow structure and the periodical oscillation in the right-angle branch have been experimentally studied in laminar steady flow using laser Doppler velocimeter. The side branch bifurcates at right angle from the trunk, and both upstream and downstream corners at the entrance of the side branch are square edge. The axial and the transverse velocity components have been primarily measured for the trunk 12.2 mm in radius and the side branch 6 mm in radius. In addition, the velocity oscillation has been measured for several radii of side branch, 4, 5, 7, 9 mm. The wall shear stress at the upstream corner takes very large magnitude. The change of wall shear stress around the upstream corner is comparable to that around the flow divider, the downstream corner. Furthermore, it has been clarified that the periodical oscillation of velocity is induced in the side branch and the Strouhal number based on the variables in the side branch is constant in terms of the Reynolds number. Therefore, this periodical oscillation in the side branch is a characteristic flow phenomenon in the right-angle branch.
