DEVELOPMENT OF ACOUSTICALLY LINED EJECTOR TECHNOLOGY FOR MULTITUBE JET NOISE SUPPRESSOR NOZZLES BY MODEL AND ENGINE TESTS OVER A WIDE RANGE OF JET PRESSURE RATIOS AND TEMPERATURES

摘要

An experimental program comprising model nozzle and full-scale engine tests was undertaken to acquire parametric data for acoustically lined ejectors applied to primary jet noise suppression. Ejector lining design technology and acoustical scaling of lined ejector configurations were the major objectives. Ground static tests were run with a J-75 turbojet engine fitted with a 37-tube, area ratio 3.3 suppressor nozzle and two lengths of ejector shroud (L/D = 1 and 2). Seven ejector lining con¬figurations were tested over the engine pressure ratio range of 1.40 to 2.40 with corresponding jet velocities between 305 and 610 m/sec. One-fourth scale model nozzles were tested over a pressure ratio range of 1.40 to 4.0 with jet total temperatures between ambient and 1088 K. Scaling of multi¬element nozzle ejector configurations was also studied using a single element of the nozzle array with identical ejector lengths and lining materials. Acoustic far field and near field data together with nozzle thrust performance and jet aerodynamic flow profiles are presented in this report. The parametric variation of lining sound power insertion loss and tuning frequency is presented as a function of lining material and nozzle flow conditions. The directivity of far field acoustic radiation is found to be a critical factor in lining evaluation, as is noise generated downstream of the ejector exit plane. Geometric scaling of configurations is demonstrated, and the importance of flow simi¬larity between scaled configurations is emphasized. Comparisons made between measured lining performance and the predicted performance based upon existing lined duct analysis procedures indi¬cate good agreement in the lining core depth and tuning frequency relationship. However, measured attenuations are generally less than the predicted values by up to 3 dB. The bare 37-tube nozzle suffers a 2 to 3% thrust penalty relative to the conical nozzle, although static thrust augmentation is obtained with the ejector configurations. At a pressure ratio of 2.40, the 37-tube nozzle suppresses the overall sound power by 8 dB relative to the equivalent conical nozzle. With the L/D = 2 lined ejector this suppression increases to 15 dB. Calculated sideline perceived noise levels at 649 m (2128 ft) indicate a peak sideline PNL reduction of 10 PNdB with the 37-tube nozzle and 15 PNdB with the 37-tube nozzle and L/D = 2 lined ejector. Model-scale data indicate additional reductions of 2 to 3 PNdB for these configurations at a jet velocity of 800 m/sec. This velocity is above the oper¬ating range of the J-75 engine.