Influence of inlet pressure distortion on a convertible engine fan

An experimental and computational study of the flowfield of a fan with uniform and distorted inlet flow is presented. The research facility is a full-scale integrated engine with a constant-speed turbofan. The blade-incidence angles of the fan-rotor can be changed during the operation. Thrust variation is thus achieved by altering the incidence of the fan-rotor blades in the same manner as a variable-pitch propeller. The flowfield of the fan with a uniform inlet flow was first studied by a quasui-three-dimensional approach based on a radial-equilibrium method. The radial-equilibrium solutions are within 1.5-10% of experimental measurements. The results indicated the stable operating range of the fan as a function of the rotor-blade-incidence angles. Then, the results obtained with the uniform inlet flow were used as a reference basis for the study of the distorted inlet flow. The small-perturbation method was very useful to design the distortion screens and to study the propagation characteristic of the distortion. The results revealed that the fan attenuation capacity is augmented when the fan load increases. The distribution of the periodic and random velocity fluctuations at the rotor inlet and outlet was obtained by hot-film probes by using an ensemble-averaging technique. This technique proved to be a useful tool for the assessment of distorted flow characteristics.