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Reynolds number,turbulence and entropy

 
 
Reply Fri 29 Aug, 2014 04:08 pm
Are you believe that when fluid flows,firstly fluid forms layers and then flows like assumed by newton on the viscosity concept?.Molecules of fluid have also certain tendency to go randomness even during laminar flow due presence of entropy of fluid.Am i right or not?As Reynolds number increases, fluid flow change from laminar to turbulent but we found that temperature and heat content of the fluid is pratically same.So entropy of the fluid is same even during laminar or turbulent flow.So how turbulence and randomness of the molecules is originated in fluid in increasing Reynolds number as no significant change in heat content and entropy.This may lead the concept of entropy as hypothetical.

So i assumed that randomness appear on the molecules as on increasing Reynolds number is apperent in nature.If randomness is really originated,then for the validity of entropy concept,heat content of the system ie fluid must be increases which can increase the temperature of fluid by significant amount but it was not significantly observe in nature.So why.Any one have ideas,please you can share?
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Type: Question • Score: 0 • Views: 1,313 • Replies: 3
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farmerman
 
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Reply Fri 29 Aug, 2014 07:47 pm
@krishna basnet,
what about"D'arcy Fields"?
krishna basnet
 
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Reply Wed 1 Oct, 2014 04:33 am
@farmerman,
You means field direction.
Simply considered that fluid is flowing on the cylindrical pipe of poiseuillies apparatus.
georgeob1
 
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Reply Wed 1 Oct, 2014 06:16 pm
@krishna basnet,
The scale of turbulent vorticity and eddies is much larger than the scale of molecular motion on which the measure of entropy is based (S =K Ln W, where S is entropy; K is the Boltzman constant; and W is the probability of the macrostate (Temperature , Pressure ,density, entropy) of the fluid in question. That means there is no connection between the flow condition (laminar vs turbulent) and the entropy of the fluid or gas.

The problem of fluid turbulence is the last unsolved problem in Newtonian mechanics, and because of the strong nonlinearity of the Navier Stokes equations governing the motion of viscous fluids, it is likely to remain so.

Despite the intractability of turbulent flows, great progress has been made in designing aircraft (and golf balls) that operate at high enough Reynolds numbers for turbulence to occur. That is because some aspects of the gross characteristics of turbulent flows are quite invariant despite the chaos that occurs on smaller scales. That's why empirically derived fudge factors developed in the 1930s for, for example, the behavior of turbulent boundary layers close to the wings of airfoils are in reliable use today for the design of airfoils on modern aircraft.

The dimples on golf balls are designed expressly to create a turbulent boundary layer for the airflow past the ball. This increases the frictional component of drag, drawing energy from the distant flow into the boundary layer near the surface of the ball. The result is the boundary layer remains attached to the ball longer and the turbulent wake behind the ball is, as a direct result, of a smaller diameter and involves less total energy. In short a small addition to the frictional drag leads to a much larger reduction in profile or total drag - and the golf ball travels farther.
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