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Much confusion about jet noise has come about as a direct result of inadequate facilities and insufficient knowledge and control of test conditions, in many cases giving rise to completely erroneous conclusions. The facility described here has been carefully designed, accounting for the shortcomings of other facilities and being guided by the stringent demands of ongoing jet noise research at Lockheed. The design goal was the capability of testing model jets up to 2000°F at pressure ratios as high as 8, in a free-field environment anechoic at all frequencies above 200 Hz. A comprehensive series of flow visualization and temperature mapping experiments in a one-sixth scale-model anechoic room was conducted. The results dictated the design of the exhaust collector/muffler to provide entrainment and room cooling air in the quantities demanded by the jet operating conditions. In order to optimize the choice of material and anechoic wedge design to achieve the 200-Hz requirement, a special impedance tube was used extensively in performance evaluations. Some features of the facility are (1) an exhaust collector providing air in quantities dictated by the particular jet operating condition with no special forced-air injection or fan installation and (2) a “cherry-picker” crane used to gain access to instrumentation, etc., for maintenance, calibration, and setup, thus eliminating the need for access platforms, etc. The crane is stowed by remote control under an anechoic cover during all test operations. The superior performance of the room is described by intensity/distance plots obtained from a fixed loudspeaker source and moving microphone installation.

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The facility described in this paper comprises two essentially identical installations, very carefully designed, for the measurement of both the acoustic and the flow fields associated with coannular jet configurations. Both primary and secondary flows may be operated at temperatures up to 1500°F at pressure ratios as high as eight. The nozzle designs were carefully selected to provide the basis for systematic investigations. Acoustic measurements are made in the anechoic chamber in a free-field environment anechoic above 200 Hz, while corresponding flow measurements are made in the turbulent flow facility using a four-channel laser velocimeter (LV) system. A brief description of the anechoic chamber is given with a more detailed discussion of the turbulence facility, the laser velocimeter, and the modifications incorporated to include coannular configurations. Details of the performance tests of the complete facility are discussed. These include (i) exhaust muffler/collector attenuation measurements, (ii) inverse square law tests to determine the anechoic quality of the room, (iii) a systematic study to establish the lack of any significant internal (or upstream) noise levels for cold as well as hot operation, (iv) checks on the performance of the various inner and outer nozzles, and (v) qualification tests of the laser velocimeter as the primary flow measurement device.