Simulation For Nose Cones In High-speed Flow Field And Study Of Its Acoustic Characteristics

Nose cone is an equipment that mounted with the forebody of microphones to protect the diaphram of microphones. With the increase of the flow speed the aerosynamic noise on the surface of nose cones will be bigger and bigger. The sound pressure level of aerodynamic noise will limit the required flow speed of aeroacoustic experiment and affect the conventional acoustic experiment. So it is necessary to study the aerodynamic noise of nose cones in high speed air flow field. And the reduction of aerodynamic noise of nose cones has become one of the keys for the acoustics wind tunnel experiment. In this paper,we study the aerodynamic noise of nose cones in high speed air flow field from two aspects of simulation and acoustics wind tunnel esperiments. Main work of this article is shown below.(1) The numerical calculation of aerodynamic noise for nose cones in high speed air flow field. We build different nose cone models, and numerical calculate the flow field on the surface of nose cones with the Ansys software. Then take the flow field calculation results as the initial value, numerical calculate the sound field of aerodynamic noise on the nose cone surface with the Virtual.Lab acoustics software. The aerodynamic noise of different nose cone models at different air flow speed are analysed. From the numerical compute results we find that the aerodynamic noise of nose cone is broadband noise, and there is no dominant frequency. The energy of the aerodynamic noise is mainly concentrated in the low frequency area, and with the increase of frequency the sound pressure level falls. In the low frequency area, the sound pressure level falls rapidly. Through the compare results of the noise sound pressure level(SPL) of different models we found that the aerodynamic noise of the nose cone that with a ellipsoid head is lower than the one with a hemispherical head, and the ellipsoid nose cone has lower flow-induced SPL than those two commercial nose cone models at relative high air flow velocities at most frequencies.(2) Measurement and calibration of Microphone Parameters at high sound pressure level. This paper presents a method for measuring a few microphone parameters based on the high-pressure calibration system. Firstly, the high pressure calibration apparatus and method are given. And then the linearity uncertainty, the distortion and the dynamic range limit of microphones at high sound pressure levels (SPL) are measured. Finally, the measurement results are compared with the manufacturer parameters, and the experimental results are consistent with manufacturer data. Because of the fact that the distortion of the high sound pressure generator is very little, the high sound pressure calibration system can calibrate the linearity deviation of microphones with the uncertainty less than0.20dB. (3) The measurement experiment for the aerodynamic noise of nose cones in acoustic wind tunnel. Design and process different nose cone models, and measure their dynamic noise in wind tunnel. Compare the measurement result with the simulation result. The comparison result shows that the numerical calculation results and measurement results on the trend and scale have a good consistency and the feasibility of the numerical simulation model is verified. And explore factors that influencing the acoustic characteristics of nose cones by the method of experiment.