Analysis of the Characteristics, Physical Concepts and Entropy Generation in aTurbulent Channel Flow Using Vortex Blob Method

In this paper, using vortex blob method (VBM), turbulent flow in a channel is studied and physicalconcepts of turbulence are obtained and discussed. At first, time-averaged velocities, u and v , andthen their fluctuations are calculated. To clarify turbulence structures, velocity fluctuations u and vare plotted. It is observed that turbulence structures occupy different positions and move withconvection velocity. To verify the second law of thermodynamics, averaged vorticity and itsfluctuations as well as averaged entropy and its fluctuations are calculated. Contours of thesefluctuations (,s) show that their positions coincide with the positions of turbulence structures andboth positions move with the same velocity. Correlation coefficient of velocity fluctuations betweentwo points, and temporal correlation coefficient at a point, which have significant role in understandingphysics of turbulence, are calculated and plotted. Having obtained these coefficients, time and spatialmicro-scales and then turbulence energy dissipation rate (  ) are obtained. Also, spatial-temporalcorrelation coefficients is calculated and then for turbulence structures microscale of time (memory),micro-scale of spatial (size) and convection velocity of structures are found. These scales estimate theirlife and size. Having obtained dual correlation coefficients, spectral studies of the velocity fluctuations,u and v , are performed, which include both frequency amplitude (related to temporal correlationcoefficient) and wave number (related to special correlation coefficient). In fact, spectral study offluctuations is Fourier transform (Cosine) of these fluctuations. Finally, dropping rate of this transformis compared with available data in turbulence literature. In this research, for the first time, theturbulence structures are visualized and presented by employing the vector of velocity fluctuations,vorticity and entropy generation fluctuations.