The paper by W. R. Dean and J. M. Hurst discusses the motion of fluid in a curved pipe, focusing on the primary and secondary motions. The primary motion along the pipe's axis is accompanied by a secondary motion in the cross-sectional plane, which reduces the flow rate and shifts the region of maximum primary motion outward. The authors simplify the governing equations by assuming a uniform secondary stream and derive approximate solutions for both circular and rectangular cross-sections. They show that the pressure distribution is of the form \( P = -CR\phi + g(\omega, z) \), where \( C \) is a constant related to the pressure gradient. The secondary motion is represented by a stream function \( \psi \), and the total flow rate is affected by the curvature of the pipe. For a circular cross-section, the flow rate is reduced by a factor that depends on the curvature parameter \( k \). For a rectangular cross-section, the reduction is more pronounced. The paper also presents experimental results from C. M. White, showing the relationship between non-dimensional factors and the flow rate in curved and straight pipes. The authors conclude that the ratio of the velocity components at the center of the pipe, \( U/V \), decreases with increasing curvature, suggesting that the secondary motion becomes more significant as the pipe becomes more curved.The paper by W. R. Dean and J. M. Hurst discusses the motion of fluid in a curved pipe, focusing on the primary and secondary motions. The primary motion along the pipe's axis is accompanied by a secondary motion in the cross-sectional plane, which reduces the flow rate and shifts the region of maximum primary motion outward. The authors simplify the governing equations by assuming a uniform secondary stream and derive approximate solutions for both circular and rectangular cross-sections. They show that the pressure distribution is of the form \( P = -CR\phi + g(\omega, z) \), where \( C \) is a constant related to the pressure gradient. The secondary motion is represented by a stream function \( \psi \), and the total flow rate is affected by the curvature of the pipe. For a circular cross-section, the flow rate is reduced by a factor that depends on the curvature parameter \( k \). For a rectangular cross-section, the reduction is more pronounced. The paper also presents experimental results from C. M. White, showing the relationship between non-dimensional factors and the flow rate in curved and straight pipes. The authors conclude that the ratio of the velocity components at the center of the pipe, \( U/V \), decreases with increasing curvature, suggesting that the secondary motion becomes more significant as the pipe becomes more curved.