Brief Description

An open-source code "Xcompact3D" is used to run Direct Numerical Simulations (DNS) of a fully developed Turbulent Channel Flow. DNS is necessary to resolve all the scales of turbulence which is vital for studying turbulence cascade. A multi-scale analysis is then used to isolate structures at a given scale. The transport equation for these isolated scales can then be solved to calculate inter-scale kinetic energy flux, enstrophy flux, and enstrophy generation at a small scale due to stretching caused by larger scales. 

This methodology is being used to study the locality of the energy cascade. The spatial inhomogeneity of the energy cascade can also be studied. 

As the method isolates in physical space, individual structures can be identified associated with the energy and enstrophy transfer. 

Brief Description

The experiments are performed in an open-circuit wind tunnel. Single-wire constant temperature hotwire anemometers are used to measure the velocities in the boundary layer. The acquired velocity time series is then analyzed using Fourier and Wavelet transform to perform the time-frequency analysis. We observe two transition scenarios differing in their time-frequency behavior: one with intermittent regions of turbulence in an otherwise non-turbulent flow, which we call "Spotty-transition" and the other, where the transitional flow does not exhibit such intermittent character, which we call "Non-spotty transition". 

For further details refer to the thesis.

Thesis

• Anand A. (2019) Two scenarios for the late stages of transition in a boundary layer subjected to random distributed surface roughness. M.Tech (Res), Indian Institute of Science, Bangalore