Numerical Study of Flow over a Rotating Cone under Axial and Non-Axial Inflow

Master thesis (2020)

Authors

S.K. Mukhopadhyay Aerospace Engineering

Contributors

A. Gangoli Rao Flight Performance and Propulsion - Aerospace Engineering (mentor)
S.S. Tambe Flight Performance and Propulsion - Aerospace Engineering (graduation committee member)
I. Langella Flight Performance and Propulsion - Aerospace Engineering (graduation committee member)
A.C. Viré Wind Energy - Aerospace Engineering (coach)
Faculty
Aerospace Engineering, Aerospace Engineering
Copyright: © 2020 S.K. Mukhopadhyay
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Published Date

27-10-2020

Language

English

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Faculty

Aerospace Engineering

Abstract

Although significant strides have been made with regards to increasing the fuel economy of commercial passenger aircraft, the reduction of the environmental footprint remains of the utmost importance. The flow development over an aero-engine spinner will affect the velocity distribution over the fan of the engine and this affects the estimation of the losses generated in the fan and consequently the performance of the engine itself. Previous experimental studies have shown the existence of spiral vortices formed due to boundary layer instabilities over a rotating cone under axial and non-axial inflow. To study the effects of hub-corner separation in detail, it is first important to check the efficacy of existing commercial numerical simulation tools in the prediction of this boundary layer transition development of flow over a rotating nose-cone.
The objective of the thesis was thus to simulate using URANS and LES, the formation of the counter-rotating vortices over a rotating cone. To this end. ANSYS DesignModeler and ICEM CFD were used to generate a meshed computational domain and ANSYS CFX was used as the solver.
With axis-symmetric cones considered as an idealised geometry for the spinner of an aircraft engine, a 15° half-angle cone with a diameter of 47 mm was chosen. The tip of this cone was blunted by a factor of 1/100th of the cone-diameter. The domain diameter was set to 10 times the cone diameter to reduce the impact of the flow over the side walls. Two structured hexahedral meshes were generated.
The BSL EARSM was chosen for the URANS simulation and the WALE Model for the LES run. To check if the simulations were able to capture the vortices, the footprint left behind by them were visualised using the non-dimensionalised instantaneous wall shear values. 
The magnitude of the inlet flow velocity given was 2.46 m/s. A 2° incidence is given to the flow for the non-axial case. The effect of mesh refinement was studied for the axial case using both meshes and the finer mesh was used for the non-axial case. The axial case was studied using both the URANS and LES runs, while the non-axial case was studied using only the LES run.
The variation of local Reynolds number (defined using boundary layer edge velocity) with local rotation ratio (defined using local radius, boundary layer edge velocity, and rotation velocity of the cone) was also studied and compared with available experimental data. The wall parallel velocity profiles over the length of the cone were also studied. Using the contours of the wall parallel velocity, the momentum mixing in the boundary layer due to the vortices was visualised and compared with the results from the experiments.
To characterise the spatial development of the spiral vortices, a critical point was defined using the wall friction coefficient. This critical point was then compared to the one obtained through the experiments. The number of counter-rotating vortices formed over the length of the cone was also checked and the trend between the simulations and experiments were compared.