The present paper describes the results of a theoretical study aimed at relating noise signatures obtained in a freejet facility for simulation of forward flight effects on jet noise with the noise signatures recorded in true flight. An important feature of the paper is extensive theory-data comparison. The transformation is carried out by extracting the "basic directivity" of the noise after correcting for refraction, turbulent scattering, and absorption effects and then employing a suitable multipole source decomposition to evaluate the proper dynamic effect. Detailed directivity comparisons are presented for three primary jet velocities and two flight velocities for the three nozzle types as described in Part I of this paper. It is concluded that the validity of the freejet technique and associated transformation procedure has been satisfactorily demonstrated.
A study was conducted to identify and evaluate several inflight simulation techniques. These include closedcircuit wind tunnels, freejets, rocket sleds, and high-speed trains. The most promising technique was selected for demonstration and validation. The pertinent results from the evaluation phase and the rationale which led to the selection of the freejet simulation technique are discussed, including advantages and disadvantages. Acoustic results from the Learjet and NASA-Lewis F106 aircraft flyovers and the French Aerotrain tests, taken with a baseline, 8-lobe, and 104-tube nozzle, were used to formulate a data base for verification of the inflight simulation technique. The freejet scale model test results are discussed and compared to the full-scale flight tests which included the Learjet, F106, and Berlin Aerotrain.
NomenclatureA 8 = exhaust nozzle area, in. 2 EGA = extra ground attenuation r = source-to-observer distance, ft T T8 = exhaust gas total temperature, °R Vj -Jet velocity, isentropic fully expanded, fps V 0 -freestream velocity, fps 0/ = acoustic angle referenced to the nozzle inlet PISA -ambient density, Ibm/ft 3 PJ = fully expanded jet density, Ibm/ft 3 co = density ratio exponent
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.