Eventos Anais de eventos
ENCIT 2018
Brazilian Congress of Thermal Sciences and Engineering
ANALYSIS OF WAKE VELOCITIES AND PRESSURE FLUCTUATIONS IN A BISTABLE FLOW USING HILBERT-HUANG TRANSFORM AND WAVELETS
Submission Author:
Ana Ost , RS , Brazil
Co-Authors:
Ana Ost, Roberta Fatima Neumeister, Sergio Viçosa Möller
Presenter: Ana Ost
doi://10.26678/ABCM.ENCIT2018.CIT18-0071
Abstract
This paper shows the study about pressure fluctuations and velocity results from the wakes of two cylinders side-by-side in a bistable flow. The experimental measurements were conducted in an aerodynamic channel with a pair of 25mm cylinders located in the test section, with a pitch to diameter p/D of 1.26. The tested Reynolds Number is 25.7x103, based on diameter and free stream velocity. The pressure fluctuations were measured using condenser microphones positioned in the upper channel wall and the velocity signals were acquired using hot wire anemometry. In order to perform the analysis of the acquired data, Hilbert-Huang transform is used, as well as continuous wavelet transforms, and PDF (Probability Density Function). The results show the presence of the bistable flow in the raw signal, the PDF shows the changes in the wake modes with the deviation in the pressures occurrences. The continuous wavelet present high energy under 150 Hz and can be associated to the cylinders vortex shedding. Comparing the techniques is observed that Wavelet transform better represents the bistable signals, showing the phenomena and the main frequency ranges. Hilbert-Huang transform shows all the instantaneous frequency modulations present in the signal, the EEMD represents the important oscillations of the flow, and the bistable phenomenon is identified. The Hilbert spectra show the locations of those oscillations on time and amplitude, but the bistable phenomenon is not visible in the spectra.
Keywords
Pressure fluctuations, Turbulence, Hilbert-Huang transform, Wavelet Transform, PDF
