Transient flow in infinitely thin airfoil cascade

The transfer of stationary circumferential inlet distortion through a rotor is analyzed using unsteady thin airfoil cascade theory which can account for the distortion wave length, rotor chord and cascade solidity. The model consists of representing each blade by a moving doublet filament of finite length immersed in a compressible stream containing a velocity distortion. The study is limited to an unloaded, flat plate rotor. This model provides a new physical interpretation for the flow adjustments observed ahead of the rotor and for the generation of sound when an inlet distortion is imposed. The analytical results show the influence of solidity and other rotor design parameters on the distortion transfer. They are found to approach the semi-actuator disk results as the solidity tends to infinity.

Download Full-text

Unsteady Flow Simulation of Leading-Edge Separation in Thin-Airfoil Cascade: A Modification to Turbulence Model

Volume 2B: Turbomachinery ◽

10.1115/gt2015-43849 ◽

2015 ◽

Author(s):

Atsushi Tateishi ◽

Toshinori Watanabe ◽

Takehiro Himeno ◽

Chihiro Inoue

Keyword(s):

Separation Bubble ◽

Large Angle ◽

Turbulence Models ◽

Leading Edge ◽

Turbulence Energy ◽

Angle Of Incidence ◽

Thin Airfoil ◽

Rans Simulations ◽

Airfoil Cascade ◽

Edge Separation

Leading edge separation of thin airfoil cascade in subsonic flow at large angle of incidence was simulated by implicit large eddy simulation (ILES) and Reynolds averaged Navier-Stokes (RANS) simulations with various turbulence models. In the ILES simulations with fine grids, the time-averaged surface pressure qualitatively agreed with the experimental data. The RANS and ILES simulations on the coarse mesh failed to capture a peak of pressure near the leading edge. From spectrum analysis, it was observed that the flow-field was turbulent in the separation bubble. In the failed RANS simulations, the separation bubble was much longer and the turbulence energy near the leading edge was much lower than those in the ILES results. The development of lambda-shaped vortex structures and their sudden weakening near the reattachment point was observed in the unsteady simulations. Two possible modifications to existing turbulence models in RANS simulations were proposed based on the comparison of turbulence energy between the ILES and RANS results. It is shown that these modifications improve the bubble length and Cp distributions of RANS simulations, though further validation and modeling are needed for the application to realistic cases.

Download Full-text