Flow development in curved rectangular ducts with continuously varying curvature

A combined experimental and numerical study was conducted to better understand the 3-dimensional flow development in 120° curved rectangular ducts with continuously varying curvature (Cr) that are commonly used for blade profile design of solid-liquid two-phase centrifugal pumps. Three different types of curvature (double circular line, spiral line and involute line) and three different aspect ratios (Ar = 0.4, 1 and 2.3) were studied to analyze the development of axial velocity in the horizontal mid-plane (z = 0) and secondary flow patterns at various cross-sections along the ducts. The inlet flow satisfied fully developed turbulent condition, with Reynolds number ranged from Reb = 2.4 × 104 to 1.4 × 105. The flow fields were measured using Particle Image Velocimetry (PIV) and numerical simulations were performed by solving the Reynolds Averaged Navier-Stokes (RANS) equations. The results reveal complex changes in the flow pattern with respect to both the flow and geometric parameters (Re, Cr and Ar) in terms of onset, development and disappearance of different types of Dean vortex. Comparison with the literature confirms that the flow development in these ducts with continuously varying curvature is quite different from that in conventional curved ducts with constant curvature.