Acoustic Measurements of Exhaust Nozzles Using a Shock Tube

Abstract

Acoustic measurements of exhaust nozzles using a shock tube driven by compression air were conducted to validate the methodology and accuracy. The original method was proposed by Kirk( J. Propul. Power, Vol. 17, No. 4, 2001, pp. 928-935) to reduce the cost of acoustic tests of exhaust nozzles and improve the test efficiency. They showed a feasibility of the technique. However, we thought again the necessity to meet the tailoring condition of a shock tube at the nozzle temperature to simulate take-off condition. Validation tests up to temperature ratio of 1.7 using ASME standard nozzle were conducted and the uncertainty analysis was performed. It was found that the acoustic data agreed with the data obtained by a conventional facility within 1.3 dB for overall SPL even if the shock tube was operated under over-tailored conditions. The uncertainty analysis showed that the data was available with uncertainty of ±0.5-0.7 dB or less for 1/3 octave band SPL and a key component of the uncertainty was jet condition. Acoustic measurement of nozzles using a shock tube driven by air will provide good productivity under those uncertainties.