Browsing by Author "Vahdati, Mehdi"
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Item Open Access Investigations of the unsteady aerodynamic characteristics for intakes at crosswind(American Society of Mechanical Engineers, 2022-10-28) Piovesan, Tommaso; Wenqiang, Zhang; Vahdati, Mehdi; Zachos, Pavlos K.The ground vortex generated in front of an intake operating near the ground and subjected to crosswind is investigated using CFD and compared to the experiments. The flow field of a scale-model intake is numerically simulated with both steady and unsteady approach, with the aim of predicting ground vortex effects and to characterize the vortex unsteady behaviour. The experimental results showed that for an intake near the ground under crosswind the ground vortex that forms under the intake and the in-duct separation, when present, exhibit unsteady behaviour that becomes stronger as the crosswind velocity is increased. The simulations indicate that a steady-state approach only partially reproduces the time-averaged ground vortex characteristics and in-duct distortion losses, while an unsteady approach shows a lower level of unsteadiness compared to the experimental observations. The consequences of the unsteady flow in the intake on the fan aerodynamic and aeroelastic stability are finally discussed to reinforce that these can result in significant non-synchronous vibration (NSV) and loss of stall margin which cannot be adequately assessed if no unsteady component of the inlet distortions is taken into account.Item Open Access Three-dimensional low-order surge model for high-speed axial compressors(Global Power & Propulsion Society, 2020-12-18) Righi, Mauro; Pachidis, Vassilios; Könözsy, László Z.; Zhao, Fanzhou; Vahdati, MehdiSurge in modern aero-engines can lead to violent disruption of the flow, damage to the blade structures and eventually engine shutdown. Knowledge of unsteady performance and loading during surge is crucial for compressor design, however, the understanding and prediction capability for this phenomenon is still very limited. While useful for the investigation of specific cases, costly experimental tests and high-fidelity CFD simulations cannot be used routinely in the design process of compressor systems. There is therefore an interest in developing a low-order model which can predict compressor performance during surge with sufficient accuracy at significantly reduced computational cost. This paper describes the validation of an unsteady 3D through-flow code developed at Cranfield University for the low-order modelling of surge in axial compressors. The geometry investigated is an 8-stage rig representative of a modern aero-engine IP compressor. Two deep surge events are modelled at part speed and full speed respectively. The results are compared against high-fidelity, full annulus, URANS simulations conducted at Imperial College. Comparison of massflow, pressure and temperature time histories shows a close match between the low-order and the higher-fidelity methods. The low-order model is shown capable of predicting many transient flow features which were observed in the high-fidelity simulations, while reducing the computational cost by up to two orders of magnitude