ABSTRACT
The secondary flow moves from the inner bend (closer to the center of curvature of the bend) to the outer bend (farther from the center of curvature of the bend) along the plane of the bend, and it returns to the inner bend through the top and bottom surfaces of the bend. As a result of the secondary flow, the maxima of the velocity profile is shifted toward the outer bend. Schematic representation of the axial velocity contours and secondary flow streamlines are shown in Fig. 80. The secondary flow superimposed upon the axial flow results in a flow of helical nature in the top and bottom halves of the bend separately. These secondary flow cells are called "Dean cells," after W. R . Dean who first predicted these secondary motions in his theoretical analysis [ 181, 182]. The flow is completely three dimensional within the bend. The general nature of the flow as described here does not depend on whether the geometry of the cross section of the bend is circular or otherwise.
