Numerical investigation of rotating instability in a single-stage compressor with URANS and IDDES

Rotating instability (RI) is a critical flow phenomenon in axial compressors, characterized by pre-stall disturbances with distinct spectral and propagation features, posing risks such as high-cycle fatigue and broadband noise. This study employs high-fidelity CFD simulations, utilizing both URANS and IDDES methods, to investigate RI mechanisms in a single-stage compressor comprising an inlet guide vane (IGV) and a rotor. The numerical setup includes a 120° sector domain. Simulations are conducted at 70% design speed to capture off-design RI behavior. Both URANS and IDDES results show good agreement with experimental data in compressor performance and static pressure distribution, validating the numerical approach. CFD results reveal that RI manifests as a hump-shaped spectral peak in the 4/15–12/15 blade passing frequency range, with disturbances propagating at about 50% rotor speed. URANS simulations identify a coherent tornado-like vortex structure, which spans from the rotor suction surface to the casing and is featured by a low-pressure region. The vortex crown extends to the casing and maintains in the IGV-rotor gap, propagating circumferentially among adjacent blades and generating the characteristic pressure perturbations associated with RI. The vortex leg extends to the rotor blade suction surface, convecting from the leading edge to the trailing edge. IDDES resolves finer turbulent structures but lacks a clearly defined coherent tornado-like vortex, likely due to insufficient statistical convergence.