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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.

Acoustical and mechanical design features of NASA Lewis Research Center’s engine fan noise facility are described. Acoustic evaluation of the 1420-m (50,000-ft) chamber, which is lined with an array of stepped wedges, is described. Results from the evaluation in terms of cut-off frequency and non-anechoic areas near the walls are detailed. Fan models with 0.51-m (20-in.) diameters are electrically driven to 20,600 rpm in either the inlet mode (drawing air from the chamber) or exhaust mode (discharging air into the chamber) to facilitate study of both fore and aft fan noise. Inlet noise characteristics of the first fan tested, the JT8D Refan, are discussed and compared to full-scale levels. Turbulence properties of the inlet flow and acoustic results are compared with and without a turbulence reducing screen over the fan inlet.