Pressure distribution on the surface of Rushton turbine blades - Experimental measurement and prediction by CFD

The distribution of pressure over the leading and trailing faces of blades on a Rushton turbine was investigated using both experimental and computati onal methods. Pressures on mechanical impeller blades are of interest for s everal reasons, including calculation of power input to the tank, assessmen t of the mechanical design of the impeller, and predicting the gas entrainm ent rate for impellers in gas-liquid systems. Experimental measurements of pressure on the surfaces of the impeller blades in a rotating Rushton turbi ne have been made using a hollow blade fitted with pressure tappings and co nnected to an external pressure cell. Pressures on the trailing face show a pattern indicative of roll vortex formation and detachment. Pressures are used to calculate the power number, which compares fairly well with power a ccording to a torque meter. Fluid flow in the laboratory tank was simulated using computational fluid dynamics (CFD), using a Multiple Frames of Refer ence method to account for impeller motion. Since the region of interest re presents a small fraction of total tank volume, a second simulation was car ried out in which better grid resolution was obtained by restricting the co mputational domain to a zone surrounding a single impeller blade. Pressures on the impeller blades are predicted by the CFD simulations and both metho ds show reasonable agreement compared with the experimental: measurements, with some improvement using the second method. The CFD results were also us ed to calculate power, and both CFD methods show good agreement with measur ements from a torque meter. The study shows that CFD can provide a very use ful tool for the analysis of impeller blade design and process issues relat ed to pressure in the impeller region.