Prediction of transonic buffet in an axial flow fan using global stability analysis

ifasd2024 Tracking Number 175

Shock oscillation arising due to shock-boundary layer interaction in transonic flow, also known as transonic buffet, gives rise to time varying airloads on fan and compressor blades, which can lead to failure of the concerned component through fatigue. While the transonic buffet phenomenon is well-investigated in fixed wings [1], there is a paucity of literature on it in turbomachinery. Strazisar [2] studied shock structure and shock oscillations of a transonic fan, NASA rotor 67, using laser anemometry data and reported shock structures at various operating points on the fan operating map. Strazisar also reported to have observed shock oscillations with an amplitude of 3–4% of rotor chord at certain operating points but without any information on the shock oscillation frequency or any other attributes of shock oscillation. Recently, Klinner et al. [3] investigated shock-boundary layer interactions in a transonic compressor cascade and presented a more detailed description of shock structures that consisted of a detached bow shock, a lambda passage shock and lip shocks. They also reported that the unsteady airloads arising due to shock oscillation induced flexural vibrations, also known as transonic buffeting, in the blade. More recently, Majhi and Venkatraman [4] simulated transonic buffet in NASA rotor 67 using unsteady Reynolds-averaged Navier-Stokes (URANS) and explained the buffet mechanism at design mass flow with the help of wave propagation analysis of buffet flow. In the present work, we use a global stability framework [5] for transonic flow to predict transonic shock buffet in an axial flow fan, the NASA rotor 67. Global stability analysis of fluid flow involves investigation of the behavior of a steady or mean flow field, also known as base flow, upon introduction of small three-dimensional perturbations in terms of growth or decay of the resulting flow field. In this work, firstly, aerodynamic stability of the flow field is predicted at a few operating points on the fan operating map using global stability analysis, and subsequently the prediction obtained so is compared vis-à-vis the prediction obtained using URANS. References 1. Gao, C., and Zhang, W., 2020, “Transonic aeroelasticity: A new perspective from the fluid mode,” Progress in Aerospace Sciences, Vol. 113, p. 100596. https://doi.org/10.1016/j.paerosci.2019.100596. 2. Strazisar, A. J. 1985. Investigation of flow phenomena in a transonic fan rotor using laser anemometry. ASME Journal of Engineering for Gas Turbines and Power, 107, pp.427-435. https://doi.org/10.1115/1.3239743. 3. Klinner, J., Hergt, A., Grund, S., and Willert, C. E., 2019, “Experimental investigation of shock-induced separation and flow control in a transonic compressor cascade,” Experiments in Fluids, Vol. 60, No. 6, p. 96. https://doi.org/10.1007/s00348-019-2736-z. 4. Majhi, J. R., and Venkatraman, K.,” On the Nature of Transonic Shock Buffet in an Axial-Flow Fan”, 2023,” AIAA Journal, Articles in Advance. https://doi.org/10.2514/1.J063318. 5. Timme, S., “Global Instability of Wing Shock-Buffet Onset, 2020,” Journal of Fluid Mechanics, Vol. 885, p. A37. https://doi.org/10.1017/jfm.2019.1001.