Reverse thrust operations of a model scale Contra-Rotating Open Rotor design were numerically modelled to produce individual rotor thrust and torque results comparable to experimental measurements. The aims of this research were to develop an understanding of the performance and aerodynamics of open rotors during thrust reversal operations and to establish whether numerical modelling with a CFD code can be used as a prediction tool given the highly complex flowfield. A methodology was developed from single rotor simulations initially before building a 3D‘frozen rotor’ steady-state approach to model contra-rotating blade rows in reverse thrust settings. Two different blade pitch combinations were investigated (β1,2 =+30°,- 10° and β1,2 =-10°,-20°). Thrust and torque results compared well to the experimental data and the effects of varying operating parameters, such as rpm and Mach number, were reproduced and in good agreement with the observed experimental behaviour. The main flow feature seen in all the reverse thrust cases modelled, both single rotor and CROR, is a large area of recirculation immediately downstream of the negative pitch rotor(s).This is a result of a large relative pressure drop region generated by the suction surfaces of the negative pitch blades. An initial 3D unsteady sliding-mesh calculation was performed for one CROR reverse thrust case. The thrust and torque values were in poor agreement with experimental values and the disadvantages relating to time costs and required computational resources for this technique were illustrated. However, the results did yield a nominal unsteady variation of thrust and torque due to rotor phase position. Overall the work shows that it may be possible to develop a CROR reverse thrust prediction tool of beneficial quality using CFD models. The research also shows that the frozen rotor approach can be adopted without undermining the fidelity of the results.

Renewed interest in open rotor aeroengines, due to their fuel efficiency, has driven renewed interest in all aspects of the noise they generate. Noise due to the ingestion of distorted atmospheric turbulence, known as Unsteady Distortion Noise (UDN), is likely to be higher for open rotors than for conventional turbofan engines since the rotors are fully exposed to oncoming turbulence and lack ducting to attenuate the radiated sound. However, UDN has received less attention to date, particularly in wind-tunnel and flight testing programmes. In this thesis a new prediction scheme for UDN is described, which allows inclusion of many key features of real open rotors which have not previously been investigated theoretically. Detailed features of the mean flow induced by the rotor, the form of atmospheric turbulence, asymmetries due to installation features, and the effect of rotor incidence are all considered. Parameter studies are conducted in each of these cases to investigate their effect upon UDN in typical static testing and flight conditions. A thorough review of the technological issues of most relevance and previous theoretical work on all types of turbulence-blade interaction noise is first undertaken. The prediction scheme is then developed for the case in which the mean flow into the rotor is axisymmetric. This shows excellent qualitative agreement with previous findings, with increased streamtube contraction resulting in a more tonal noise spectrum. The theoretical framework involves using Rapid Distortion Theory to calculate the distortion of an isotropic turbulence field (such as given by the von Karman spectrum) by the mean flow induced by the rotor (such as given by actuator disk theory), leading to an expression for the velocity incident upon the leading edge of the rotor blades. Strip theory is then used to calculate the pressure jumps across the blades, input as the forcing term in the far-field wave equation. Models are derived for open rotor-induced flow which account for the variation of blade circulation with radius, and the presence of the rotor hub and rear blade row. An investigation of appropriate turbulence models and realistic turbulence parameters is also undertaken. A key finding is that the heights of the tonal peaks are determined by the overall magnitude of the induced streamtube contraction (dependent on the total thrust generated) whereas the precise form of distortion (affected by the detailed components of the mean flow and the form of atmospheric turbulence present) alters the resulting broadband level. The prediction scheme is formulated in such a way as to facilitate extension to the asymmetric case, which is also fully derived. The model is applied in the first instance to the case of two adjacent rotors and then to the case of a single rotor at incidence. Under flight conditions, when distortion is reduced but UDN can still contribute a significant broadband component to overall noise levels, asymmetry is found to increase broadband levels around 1 Blade Passing Frequency but reduce levels elsewhere.