Further Tests of a Non-Resonant Configuration

An open jet wind tunnel can produce resonant acoustic conditions, some so large as to endanger the physical structure itself. A previous paper suggested a configuration for a collector with an inlet sloped at 45 degrees that eliminates these resonant conditions. The present paper expands on those earlier observations by presenting acoustic results for more collector configurations and also presents pressure distributions for test sections with lengths up to 8 nozzle diameters. Collector configurations with less slope are shown to be just as effective for conventional test sections (L/Dn∼3) as the earlier work. Collectors with steep slopes can avoid resonance even for very long test sections. Acoustic resonance is shown to correlate with test section pressure distribution and the area of constant pressure in the test section is maintained with the sloped collector. Test results show that long test sections with constant pressure and without resonance are possible.