Effects of Low Reynolds Number on Wake‐Generated Unsteady Flow of an Axial‐Flow Turbine Rotor

The unsteady flow field downstream of axial-flow turbinerotors at low Reynolds numbers was investigated experimentallyusing hot-wire probes. Reynolds number, based on rotor exitvelocity and rotor chord length Reout,RT, wasvaried from 3.2×104 to 12.8×104 at intervals of1.0×104 by changing the flow velocity of the windtunnel. The time-averaged and time-dependent distributions ofvelocity and turbulence intensity were analyzed to determine theeffect of Reynolds number. The reduction of Reynolds number had amarked influence on the turbine flow field. The regions of highturbulence intensity due to the wake and the secondary vorticeswere increased dramatically with the decreasing Reynolds number. Theperiodic fluctuation of the flow due to rotor-stator interactionalso increased with the decreasing Reynolds number. Theenergy-dissipation thickness of the rotor midspan wake at the lowReynolds number Reout,RT=3.2×104 was 1.5times larger than that at the high Reynolds number Reout,RT=12.8×104. The curve of the −0.2 power of theReynolds number agreed with the measured energy-dissipationthickness at higher Reynolds numbers. However, the curve of the−0.4 power law fitted more closely than the curve of the −0.2power law at lower Reynolds numbers below 6.4×104