Experimental investigation of the velocity time-traces of the turbulent flow in a rectangular channel with a lateral slot

Abstract

In the present work it is performed an experimental evaluation of turbulent, incompressible air flow at the steady state in compound channel. The purpose is to evaluate the influence of the geometrical parameters over the fluid dynamic behavior of the turbulent flow such as the generation of coherent structures and Strouhal numbers. In order to perform this investigation it is employed the classic approach Power Spectral Density Function (PSD) and Time–Frequency tools for spectral analysis of velocity fluctuations. Hot wire probe was employed to measure time-series velocities. Test sections were formed by two parallel plates attached on a side wall of an aerodynamic channel, forming a slot with width D and depth P. In this paper twelve test sections were investigated covering the P/D- ratio ranging from 3.33 up to 11.00. For every test sections the Reynolds number is considered constant, ReDh=7.98×104. The main results showed that the dynamic characteristics of the turbulent flow in these structures are not dependent only on the P/D-ratio, but also the test section’s length along with the gap width. Periodic patterns in the time-series of velocity fluctuations, that suggests the presence of large scale structures, could be seen as the channel becomes longer and the Strouhal number tends to those previously noticed in the literature. The spectrogram of Continuous Wavelet Transform (CWT) revealed that different frequencies are excited as the time passes causing the broadness of the main frequency peak in PSD. Furthermore, the scattering of the higher energetic coefficients from CWT seems to increase as the width of the slot increases, showing that the large vortices formation might present some degree of unsteadiness