exit-flow velocity survey of two single-tangential-inlet vaneless turbine volutes

for two existing single tangential inlet volutes, time-averaged radial and tangential velocity and static pressure measurements of exit flow have been obtained on a cylindrical cut plane through the radial-inflow section using a three-port yawmeter in air. the reynolds numbers based on inlet pipe mean conditions, around 10⁵, are well into the fully-turbulent regime and on the order of comparable water turbines.

a comprehensive map of time-averaged exit flow of both volutes is presented. the integrated values of gross angular momentum flux change and total pressure loss coefficient are tabulated. circumferential variation of flowrate and swirl strength highlight unexpected differences in outlet flow between the two volute designs. results are presented alongside corresponding numerical results from the commercial package fluent (fluent, inc., lebanon, nh, usa) using reynolds stress, k–ω, and inviscid flow models.

in both volutes, measured gross exit angular momentum flux was more than 1.7 times what the zero-torque assumption would predict when blindly applied to the volute as a whole. this discrepancy is attributed to significant turning near the volute’s inlet region leading to an updated view of what an appropriate control volume is when applying the zero-torque assumption. additionally, variation of both radial and tangential velocity in both the circumferential and axial directions on the order of 15% of the mean value reveal that volute swirl characterization by a single measurement would have a significant associated uncertainty.