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Note for Fluid Mechanics - FM By Engineering Dude

  • Fluid Mechanics - FM
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  • Veer Surendra Sai University Of Technology VSSUT -
  • Mechanical Engineering
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Fundamentals of Fluid Mechanics SUB: Fundamentals of Fluid Mechanics Subject Code:BME 307 5th Semester,BTech Prepared by Aurovinda Mohanty Asst. Prof. Mechanical Engg. Dept VSSUT Burla 1

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Fundamentals of Fluid Mechanics Disclaimer This document does not claim any originality and cannot be used as a substitute for prescribed textbooks. The information presented here is merely a collection by the committee members for their respective teaching assignments. Various sources as mentioned at the reference of the document as well as freely available material from internet were consulted for preparing this document. The ownership of the information lies with the respective authors or institutions. Further, this document is not intended to be used for commercial purpose and the committee members are not accountable for any issues, legal or otherwise, arising out of use of this document. The committee members make no representations or warranties with respect to the accuracy or completeness of the contents of this document and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. 2

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Fundamentals of Fluid Mechanics SCOPE OF FLUID MECHANICS Knowledge and understanding of the basic principles and concepts of fluid mechanics are essential to analyze any system in which a fluid is the working medium. The design of almost all means transportation requires application of fluid Mechanics. Air craft for subsonic and supersonic flight, ground effect machines, hovercraft, vertical takeoff and landing requiring minimum runway length, surface ships, submarines and automobiles requires the knowledge of fluid mechanics. In recent years automobile industries have given more importance to aerodynamic design. The collapse of the Tacoma Narrows Bridge in 1940 is evidence of the possible consequences of neglecting the basic principles fluid mechanics. The design of all types of fluid machinery including pumps, fans, blowers, compressors and turbines clearly require knowledge of basic principles fluid mechanics. Other applications include design of lubricating systems, heating and ventilating of private homes, large office buildings, shopping malls and design of pipeline systems. The list of applications of principles of fluid mechanics may include many more. The main point is that the fluid mechanics subject is not studied for pure academic interest but requires considerable academic interest. 3

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Fundamentals of Fluid Mechanics CHAPTER -1 Definition of a fluid:Fluid mechanics deals with the behaviour of fluids at rest and in motion. It is logical to begin with a definition of fluid. Fluid is a substance that deforms continuously under the application of shear (tangential) stress no matter how small the stress may be. Alternatively, we may define a fluid as a substance that cannot sustain a shear stress when at rest. A solid deforms when a shear stress is applied , but its deformation doesn’t continue to increase with time. Fig 1.1(a) shows and 1.1(b) shows the deformation the deformation of solid and fluid under the action of constant shear force. The deformation in case of solid doesn’t increase with time i.e  t1   t 2 .......   tn . From solid mechanics we know that the deformation is directly proportional to applied shear stress ( τ = F/A ),provided the elastic limit of the material is not exceeded. To repeat the experiment with a fluid between the plates , lets us use a dye marker to outline a fluid element. When the shear force ‘F’ , is applied to the upper plate , the deformation of the fluid element continues to increase as long as the force is applied , i.e  t 2   t1 . Fluid as a continuum :Fluids are composed of molecules. However, in most engineering applications we are interested in average or macroscopic effect of many molecules. It is the macroscopic effect that we ordinarily perceive and measure. We thus treat a fluid as infinitely divisible substance , i.e continuum and do not concern ourselves with the behaviour of individual molecules. The concept of continuum is the basis of classical fluid mechanics .The continuum assumption is valid under normal conditions .However it breaks down whenever the mean free path of the molecules becomes the same order of magnitude as the smallest significant characteristic dimension of the problem .In the problems such as rarefied gas flow (as 4

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