Effectiveness of an inlet flow turbulence control device to simulate flight fan noise in an anechoic chamber

Abstract

A hemispherical inlet flow control device was tested on a 50.8-cm (20-in.) diameter fan stage in the NASA-Lewis anechoic chamber. The control device used honeycomb and wire mesh to reduce turbulence intensities entering the fan. Farfield acoustic power level results showed about a 5-dB reduction in blade passing tone noise at 90% design fan speed with the inlet device in place. The device resulted in about a 10-dB reduction in multiple pure tone generation at this fan speed. Hot film cross probes were inserted in the inlet to obtain data for two components of the turbulence at 65% and 90% design fan speed. Without the flow control device the axial intensities were below 1.0% while the transverse intensities were almost twice this value. The inflow control device reduced the circumferential turbulence intensities by a factor of three and also reduced the axial length scale.