New method of obtaining dissipation

To understand turbulence from a physical as well as a practical point of view it is imperative to know how the turbulent energy is created, transported and finally dissipated. The above physical processes are described by the turbulent kinetic energy equation. Two terms, namely the pressure diffusion and the dissipation, cannot yet be measured in a strict sense. The former has not been successfully measured by any means but the latter can be measured by invoking local isotropy for most of the fine scales of dissipating eddies.This research deals with the study of dissipation from an experimental point of view. Different experimental results have been reviewed and compared. First of all, methods are tested and compared in two well-known flows, boundary layer and fully developed pipe flow. A new method of obtaining dissipation that has proven to be most successful is the one where the dissipations calculated from the integration of the spectra from different lengths of the hot wire are extrapolated to zero length. High intensity of turbulence up to 60% is present in a large portion of the wall layer of a diffuser. The correction for dissipation due to high intensity of turbulence, introduced by Lumley (1965) and followed by Champagne (1978) in specific form, has been adopted to correct the dissipation in diffuser flow. The corrected dissipation compares quite well with the dissipation obtained from the kinetic energy equation as a closing term.