Modelling of turbulent rotor-blade flow and ground effect
Rotor blade flows occur in numerous physical systems from helicopters to fans, and from propellers to food mixers. Many previous studies have concentrated on the laminar flow generated by a set of rotors but in many practical cases the flow is turbulent, a setting in which previous research appears to be mainly experimental or purely numerical. The thesis examines turbulent rotor flow as its prime feature, before moving on to the impact of the ground and side structures on the flow. Whilst there exists a wide variety of rotor blade flows in industry, the present research is motivated by the application to helicopters. Using asymptotic analysis and computational methods the thesis first examines the turbulent boundary layer on a flat plate with a moving surface and, second, a rotating disc. Analytical and numerical predictions are then derived and compared with previous results. Asymmetry about the axis of rotation is introduced next and the problem of a rotating cut-disc is studied as an approximation to a set of rotors. A numerical solution is obtained and is supported by analytical results. Blade inclination and thickness are then incorporated into the three-dimensional case, with asymmetric blade shape being analyzed as if in two dimensions only. The influence of ground effect is examined firstly through the use of an image potential in the two-dimensional asymmetric blade shape problem and secondly in the axisymmetric case of flow between a stationary and a rotating disc. A numerical solution is determined and compared with existing research, whilst an analytical solution is produced for large radii. The flow between a stationary disc and a rotating cut disc is then briefly discussed before, finally, the possible extension of this thesis to the problem of turbulent jets is examined.