Flutter in a simplified blade cascade: Limits of the quasi-steady approximation

0573425 - ÚT 2024 RIV GB eng J - Journal Article
Šidlof, P. - Šimurda, David - Lepičovský, Jan - Štěpán, M. - Vomáčko, V.
Flutter in a simplified blade cascade: Limits of the quasi-steady approximation.
Journal of Fluids and Structures. Roč. 120, July (2023), č. článku 103913. ISSN 0889-9746. E-ISSN 1095-8622
R&D Projects: GA ČR(CZ) GA20-11537S
Institutional support: RVO:61388998
Keywords : flutter * aeroelasticity * blade cascade * transonic flow * quasi-steady approximation
OECD category: Applied mechanics
Impact factor: 3.6, year: 2022
Method of publishing: Limited access
https://www.sciencedirect.com/science/article/pii/S0889974623000816

Flow-induced vibration in turbomachinery represents a major and persistent concern, especially in modern turbine and compressor designs with long and slender blades operating in transonic flow conditions. There is a wide range of computational and experimental methods for blade flutter prediction and analysis. In certain situations, the quasi-steady approximation can be utilized, considering the unsteady flow as a sequence of steady flow fields for each position of the oscillation cycle. The study is focused on experimental investigation of the limits of applicability of the quasisteady approximation in the case of a simplified linear five-blade cascade with the middle blade undergoing high-frequency torsional oscillation due to kinematic excitation. A measurement campaign of more than 100 wind tunnel runs was carried out for flow velocities ranging from high subsonic to transonic regimes (M = 0, 0.529, 0.777 and 1.018), frequency ratios 0 - 0.75 and reduced frequencies k = 0 – 0.41. A comparison of quasi-steady and time-resolved blade surface pressure measurements is reported, and the degree of unsteadiness of the airflow is quantified. For low reduced frequencies the stationary distributions match almost perfectly the time-resolved profiles. The degree of unsteadiness remains below 2% up to k = 0.1 for the subsonic and supercritical flow regimes. For reduced frequencies above 0.2, the global degree of unsteadiness increases quickly up to 10%, with local differences between the stationary and time-resolved pressure profiles up to 40%. In the case of transonic flow regime, the flow unsteadiness is generally higher and further complicated by intermittency — stochastic transition from supersonic to subsonic flow in the aft part of the blade.
Permanent Link: https://hdl.handle.net/11104/0344917