Hysteresis effect of propeller jet flows in viscoelastic fluids: Transformation process and turbulence intensity.

• Flow fields of Newtonian and non-Newtonian fluids were studied. • Hysteresis effect in viscoelastic fluids was investigated. • The transformation processes between two flow patterns were visualized. • The semi-radial and axial flow pattern were described as laminar and turbulent flow, respectively. • Reynolds number was incapable to characterize the flow condition in the hysteresis range. This work aimed to investigate the flow pattern transformation process resolved in time and to propose a physical explanation for the hysteresis effect of a propeller jet in a viscoelastic fluid. The propeller jet flow in xanthan gum solution was measured using PIV (Particle Image Velocimetry) and UVP (Ultrasound Velocity Profiler). Based on the distribution of turbulence intensity, the semi-radial and the axial flow patterns generated at the same rotational speed were classified as laminar and turbulent flow, respectively. Therefore, the Reynolds number was considered inappropriate to characterize the flow fields in the hysteresis range, since both laminar and turbulent flow may occur at the same Reynolds number. The distribution of normal stresses derived from the flow induced structure was considered as the determining factor for the flow field formation. [ABSTRACT FROM AUTHOR]