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

Abstract

The unsteady flow field downstream of axial-flow turbine rotors at low Reynolds numbers was investigated experimentally using hot-wire probes. Reynolds number, based on rotor exit velocity and rotor chord length Re out,RT , was varied from 3.2 × 10 4 to 12.8 × 10 4 at intervals of 1.6 × 10 4 by changing the flow velocity of the wind tunnel. The time-averaged and time-dependent distributions of velocity and turbulence intensity were analyzed to determine the effect of Reynolds number. The reduction of Reynolds number had a marked influence on the turbine flow field. The regions of high turbulence intensity due to the wake and the secondary vortices were increased dramatically with the decreasing Reynolds number. The periodic fluctuation of the flow due to rotor-stator interaction also increased with the decreasing Reynolds number. The energy-dissipation thickness of the rotor midspan wake at the low Reynolds number Re out,RT = 3.2 × 10 4 was 1.5 times larger than that at the high Reynolds number Re out,RT = 12.8 × 10 4 . The curve of the −0.2 power of the Reynolds number agreed with the measured energy-dissipation thickness at higher Reynolds numbers. However, the curve of the −0.4 power law fitted more closely than the curve of the −0.2 power law at lower Reynolds numbers below 6.4 × 10 4 .

Effects of Low Reynolds Number on Loss Characteristics in Transonic Axial Compressor

“…After wind tunnel tests on a turbine cascade with tip clearance, Matsunuma 5) analyzed the relationship between tip leakage flow, Reynolds number and turbulence intensity, reporting that the Reynolds number and free-stream turbulence intensity don't affect tip clearance loss although they change the distribution of the internal flow. Using experiments on total pressure loss change caused by low Reynolds numbers from 32,000 to 128,000 in a small one-stage axial turbine, Matsunuma and Tsutsui 6) showed that the region with high turbulence intensity due to the wake and the flow fluctuation due to the stator-rotor interaction increase with decreasing Reynolds number.…”

Effects of Low Reynolds Numbers on Performance of a One-Stage Axial Compressor

“…At low Reynolds numbers, the distribution of high turbulence intensity behind a compressor rotor is different from the distribution behind a turbine rotor reported by Matsunuma and Tsutsui. 7) In their experimental data using an axial turbine, the turbulence intensity behind the rotor increases significantly as the Reynolds number decreases.…”

“…This phenomenon was also observed in the turbine nozzle flow reported by Matsunuma and Tsutsui. 7) Figure 17 shows circumferentially area-averaged turbulence kinetic energy to measure flow unsteadiness for two different Reynolds numbers. Behind the rotors, as the Reynolds number decreases, the turbulence kinetic energy also decreases significantly because of weaker tip leakage flow and shock waves.…”

“…Matsunuma 6) reported with his wind tunnel test data that Reynolds number and inlet turbulence intensity affect the internal flow in an axial turbine cascade, but have nothing to do with loss caused by the tip leakage flow. Matsunuma and Tsutsui 7) analyzed the total pressure loss variation induced by low Reynolds numbers from 32,000 to 128,000 in a one-stage axial turbine and found that a low Reynolds number causes high turbulence intensity in the wake region and increases the flow fluctuation between the stator and the rotor.…”

Effects of Low Reynolds Number on Performance in a Centrifugal Compressor

“…Van Treuren et al 5) ran wind turbine tests at different Reynolds numbers from 25,000 to 50,000 and found that large separation is generated near the trailing-edge of a turbine cascade and causes large total pressure loss. Matsunuma and Tsutsui 6) found, in their experiments, that a decreasing Reynolds number causes high turbulence intensity in the wake and large flow fluctuations between stators and rotors. In the paper that followed, Matsunuma 7) found that total pressure loss varies according to the ¹0.35 power of the Reynolds number, but the tip leakage loss is not affected by the Reynolds number.…”