16:00   Rotary aeroelasticity 2 Chair: Jurij Sodja 16:00 30 mins Nonlinear aeroelastic analysis of large wind turbine blades Yang Meng, Changchuan Xie Abstract: The large wind turbine blades, while enhancing the efficiency of wind energy capture, inevitably lead to more complex nonlinear aeroelastic problems. This work aims to establish a nonlinear aeroelastic model for wind turbine blades by coupling strain-based beam with rotational effects and finite-state inflow theory with Prandtl tip loss correction. Numerical studies were conducted on a real blade model and compared with measured data. 16:30 30 mins A Strongly Coupled Frequency Domain FSI Solver for Turbomachinery Blade Vibration Analysis Johann Gross, Christian Berthold, Christian Frey, Malte Krack Abstract: The efficiency requirements of modern turbomachinery lead to light and flexible blades that promote potentially damaging vibrations. Specifically, turbine blade vibrations and their interactions with the surrounding flow can be significantly nonlinear. In order to reliably predict the nonlinear behavior and achieve endurable blade design, strongly coupled FSI solvers are essential. In this work, we present the first nonlinear Frequency Domain Fluid-Structure Interaction solver for blade vibration analysis. The solver is based on the Harmonic Balance method applied to fluid and structure domains. We utilize the cyclic symmetry of the problem to reduce the multi-physics computational domain to only one sector, which is validated with full annulus simulations in the time domain. Based on a realistic aeroelastic model of a bladed disk with interlocked shrouds we demonstrate the computational performance of the solver. We perform flutter simulations, where the initial exponential amplitude growth is bounded by dry friction between shrouds. Amplitude-dependent change of the aeroelastic vibration shape and frequency are accounted for, which in contrast to conventional methods enables accurate limit cycle prediction and even detection of the nonlinear instability phenomenon, i.e. a situation, where the initially stable equilibrium becomes unstable due to a sufficiently strong perturbation (e.g. impact or forced excitation). Further, we propose two variants of numerical path continuation framework for the solver. The first variant is a straight forward coupling along the sequential computation of dynamic equilibrium points. The second variant relies on an already available or easily computed prediction of the solution curve, e.g. by initially considering the aerodynamic influence in a linearized manner. Subsequently, a fully coupled refinement is performed on each of the relevant solution points in parallel. Both variants are applied to a forced response computation of the same model, the advantages of each variant are assessed. We are convinced that the proposed method unlocks the potential towards the necessary increase of endurable turbine blade design. 17:00 30 mins Prediction of transonic buffet in an axial flow fan using global stability analysis Jyoti Majhi, Kartik Venkatraman Abstract: 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.

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