Prediction of diesel engine cooling fan noise

This effort focuses on measuring and predicting the discrete-frequency and broadband noise radiated by a diesel engine cooling fan. In such engine cooling systems, where space is very limited, it would be very difficult if not impossible to measure the fan inflow velocity field using the conventional, stationary hot-wire method. Instead, the fan inflow was measured with a twocomponent x-type hot-film probe attached very close to the leading edge of a rotating blade. The fan's radiated noise was measured without contamination from the engine noise by driving the fan with an electric motor. The spatially non-uniform mean velocity field was used in axial-flow fan noise theory to predict the discrete-frequency noise at the blade-pass frequency and harmonics. The influences due to an upstream finger guard were also investigated. The spacetime correlations of the inflow velocity fluctuations were utilized in stochastic lifting surface theory to calculate the unsteady blade lift and resulting broadband fan noise. The radiated sound power spectra that were measured for the fan are shown to be in excellent agreement with those predicted.