EMD Adaptive Filtering and Time-Frquency Analysis for Low Turbulence Intensity

Abstract

Turbulence intensity is an important flow field parameter in wind tunnel, but variation interference noise cause the measurement of low turbulence intensity much trouble, so that lots of methods were used to process turbulence intensity signal. For purpose of improving measurement precision, an EMD(Empirical Mode Decomposition) adaptive filter is designed and HHT(Hilbert-Huang Transform) time-frquency analysis is used initially for low turbulence intensity. Experiment is carried out in three kinds of wind tunnel, includes a low turbulence wind tunnel, a general low speed wind tunnel and an open jet wind tunnel. The turbulence intensity signal is acquired with hot wire anemometry, the EMD method is compared with traditional methods, includes BPF(Band Pass Filter), ENC(Electronic Noise Correction), HPIA(High Pass Inertia Attenuation Filter). Using the EMD filter, the flow field turbulence intensity in the low turbulence wind tunnel test section is measured and found to be less than 0.05% at speed of 30m/s~100 m/s. Using HHT, the low frequency flow fluctuation signal is found in the open jet wind tunnel. To conclude, method of EMD adaptive filter can be used to control the interference of noise in hot wire signal, which is a practical method for low turbulence intensity digital signal process.