Aerodynamics

Boudary layer flows

Experimental investigations on turbulent flat plate boundary layer, superstructures and their control

Large organized vortex clusters forming Large and Very Large Scale Motions (LSMs and VLSMs) that dominate in nature and technology can cause extreme fluctuations. They affect the global transport of mass, heat and momentum. Nevertheless, a solid definition of their nature and vivid understanding of their evolution and impact on turbulent flow properties are still insufficient. At the same time controlling of these superstructures and their dynamics is very important for many technical applications such as for reducing the drag of ships and airplanes, Motuz 2014. Hence, better understanding of the physics of the flow structure is needed. For instance, Smits et al. 2011 indicated that with regard to the coherent motions, the very-large-scale motions or superstructures exist at all Reynolds numbers, but they become increasingly important with Reynolds number in terms of their energy content and their interaction with the smaller scales near the wall.

The overall objective of this proposal will focus on clarification of the nature of the LSMs and the VLSMs, describing and identifying them in qualitative and quantitative manner. In addition, new methods for the near-wall turbulent flow-control, for instance, utilizing the micro-blowing distributed air will be investigated. The effect of the micro-blowing on the vortex structures near the wall and on the formation of both the LSMs and VLSMs is to be studied.

The present work aims at experimental investigations of turbulent flow over a flat plate in near-wall region where the viscous effects are of importance, in particular, at high Reynolds numbers. In addition, the impact of the shear micro-flow on the development of the large scale turbulent structures and control of the wall layer using the micro-blowing method is to be carried out. To this end, experiments will be performed at Reynolds numbers of 1x103 ≤ Re ≤ 4x106, measuring turbulent flow properties using Hot Wire Anemometry (HWA), Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV) methods.

Literature

Motuz, V. Gleichmäßiges Mikro-Ausblasen zur Beeinflussung einer turbulenten Grenzschicht, Ph.D. Thesis, BTU, 2014, Link.
Smits, A. J., McKeon, B.J., Marusic I., High–Reynolds Number Wall Turbulence, Ann. Rev. Fluid Mech. 2011. 43:353–75.

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