Turbulent flow and heat transfer in channels with shark skin surfaces: Entropy generation and its physical significance

Abstract In order to understand the mechanisms by which drag is reduced and heat transfer is affected when a wall is covered by a shark skin like texture the local entropy generation rate was determined and compared to that for a flow over smooth walls. Based on direct numerical simulations (DNSs) details of the turbulence close to the wall could be analyzed and lead to the conclusion that basically certain turbulent structures are lifted off the wall and get rearranged, a mechanism we call lift off and alignment (LOA). The distribution of (time mean) entropy generation rates supports this interpretation, showing a reduction next to the wall and an increase further away, however, such that the overall effect leads to a drag reduction. By solving the thermal energy equation it is shown that also heat transfer is reduced thus increasing the thermal body protection.

[1]  B. Bhushan,et al.  Shark-skin surfaces for fluid-drag reduction in turbulent flow: a review , 2010, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[2]  Heinz Herwig,et al.  A new approach to understanding and modelling the influence of wall roughness on friction factors for pipe and channel flows , 2008, Journal of Fluid Mechanics.

[3]  George Em Karniadakis,et al.  A direct numerical simulation of laminar and turbulent flow over riblet-mounted surfaces , 1993, Journal of Fluid Mechanics.

[4]  Bharat Bhushan,et al.  Biomimetic structures for fluid drag reduction in laminar and turbulent flows , 2010, Journal of physics. Condensed matter : an Institute of Physics journal.

[5]  S. Menon,et al.  Coherent Structures in a Turbulent Mixing Layer: A Comparison Between Direct Numerical Simulations and Experiments , 1987 .

[6]  V. Kolár,et al.  Vortex identification: New requirements and limitations , 2007 .

[7]  Ming Xiong,et al.  Investigation of turbulence effects on forced convection in a composite porous/fluid duct: Constant wall flux and constant wall temperature cases , 2003 .

[8]  Jinhee Jeong,et al.  On the identification of a vortex , 1995, Journal of Fluid Mechanics.

[9]  D. W. Bechert,et al.  Experiments on drag-reducing surfaces and their optimization with an adjustable geometry , 1997, Journal of Fluid Mechanics.

[10]  M. J. Moran,et al.  Fundamentals of Engineering Thermodynamics , 2014 .

[11]  S. Lee,et al.  Flow field analysis of a turbulent boundary layer over a riblet surface , 2001 .

[12]  Wolfram Hage,et al.  Experiments with three-dimensional riblets as an idealized model of shark skin , 2000 .

[13]  Enrico Nobile,et al.  Direct numerical simulation of heat transfer over riblets , 2003 .

[14]  Javier Jiménez,et al.  Drag reduction by riblets , 2011, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[15]  Heinz Herwig,et al.  The Role of Entropy Generation in Momentum and Heat Transfer , 2012 .

[16]  Lawrence Sirovich,et al.  Direct numerical simulation of turbulent flow over a modeled riblet covered surface , 1995, Journal of Fluid Mechanics.

[17]  H. Herwig,et al.  From single obstacles to wall roughness: some fundamental investigations based on DNS results for turbulent channel flow , 2013 .

[18]  Ming Xiong,et al.  Development of an engineering approach to computations of turbulent flows in composite porous/fluid domains , 2003 .

[19]  P. Motta,et al.  Bristled shark skin: a microgeometry for boundary layer control? , 2008, Bioinspiration & biomimetics.

[20]  R. Adrian,et al.  On the relationships between local vortex identification schemes , 2005, Journal of Fluid Mechanics.

[21]  Parviz Moin,et al.  Direct numerical simulation of turbulent flow over riblets , 1993, Journal of Fluid Mechanics.

[22]  N. D. Cardwell,et al.  Developing and fully developed turbulent flow in ribbed channels , 2011 .

[23]  Kwing-So Choi,et al.  Turbulence management using riblets for heat and momentum transfer , 1997 .

[24]  Andrey V. Kuznetsov,et al.  Forced convection in a composite parallel plate channel: modeling the effect of interface roughness and turbulence utilizing a k-ε model , 2005 .