Research On Equivalent Method Of Airworthiness Noise Take-Off Test

With the increasingly serious aircraft noise problem brought about by the continuous increase in air traffic,more and more stringent airworthiness noise standards had also been introduced.The new model aircraft will face more severe noise airworthiness certification when airworthiness is obtained.Facing the challenge of stricter noise airworthiness certification procedures,equivalent flight test procedures that can reduce noise airworthiness certification costs and shorten the noise airworthiness certification period are one of the important measures for the airworthiness certification of new models of aircraft.In this paper,the engine jet noise,which contributes the most to the aircraft noise during the aircraft’s full-thrust takeoff process,was used as the research object.A hybrid numerical algorithm combining CFD and CAA was used to study flow characteristics and noise characteristics of static engine jets.On the basis of calculating the static noise,combined with the reference trajectory of the aircraft airworthiness noise takeoff test,through the correction of sound propagation,the jet noise radiation characteristics in the take-off flight state were obtained.This method is used to initially establish a technical system suitable for equivalent procedures for aircraft noise airworthiness certification,and provide a calculation method for designing equivalent procedures for take-off tests for new models of aircraft before airworthiness certification.The main work of this paper is as follows:(1)Research on the theory and method of numerical calculation of jet flow field and sound field.Three turbulence calculation models of direct numerical simulation,Reynolds time average,and large eddy simulation,and two aerodynamic noise calculation models of Lighthill acoustic analog and Mohring acoustic analog were introduced.Through the jet flow experiment of NASA’s SMC002 nozzle,the reliability of the calculation of the large eddy simulation flow field was verified,and the reliability of the Lighthill acoustic analog and the Mohring acoustic analog were compared and analyzed.The Mohring acoustic analog is more suitable for high subsonic jets.Calculation of noise.(2)Research on the correction method of jet noise in flight.Analyze the basic requirements of aircraft noise airworthiness certification,and establish the calculation model of the airworthiness noise takeoff test reference trajectory based on the ANP database.The noise Doppler effect correction model,the atmospheric absorption attenuation model and the principle of acoustic superposition were studied.(3)Analysis of the flow field characteristics and static acoustic characteristics of the simplified scale model of the CFM56-7B engine nozzle.The basic structure of the flow field and the evolution process of the vortex were analyzed,combined with the characteristics of the sound field,the principle of jet noise and the spectral characteristics and directivity of the jet noise are analyzed.On this basis,the airworthiness noise takeoff test of the B737-800 was calculated.Baseline trajectory,got the noise result of the flight state,construct its cut-in flight procedure.