Brij Bhushan, IIT Madras:

10. Experimental Investigations of Turbulence

Turbulence is still the unsolved problem of fluid mechanics. Although quite some information has become available through numerous studies of particular turbulent flows, there is still a lack of understanding how turbulence comes about and what causes its properties. Deductions of information from the Navier-Stokes equations are possible but usually result in unknown terms that need to be modeled. Such modeling is tremendously supported by results of detailed experimental studies of turbulent flows. It is pointed out that experiential fluid mechanics has to concentrate on experiments carried out in turbulent flows to yield the information needed to advance turbulence models. In the lecture, various measurement techniques and their application in measuring turbulent flows will be highlighted. Processing of turbulence data is an important lecture which provides an introduction into this technique and explains how it can be used to study mean flow properties, as well as averaged turbulence properties. Particular attention is given to the measurement of the second moments of turbulent fluctuations. Measurements in grid generated turbulence are summarized and it is pointed out that the resultant measurements yield information that present days turbulence models cannot capture. The need for more detailed studies of turbulence is stressed and flows are given that are worthwhile to be investigated experimentally to provide a sound basis for developing improved turbulence models.

Tutors: Prof. F. Durst

Presentation (PDF, new Window)