Railways Technical Ability Fluid Mechanics and Machinery Question Bank Fluid Mechanics

  • question_answer The velocity distribution in laminar boundary layer is given by the relation \[u/{{u}_{x}}=y/\delta .\] What is the displacement thickness for the boundary layer?

    A) \[\delta \]                                  

    B) \[\delta /2\]

    C) \[\delta /3\]                                

    D) \[\delta /4\]

    Correct Answer: C

    Solution :

    \[\delta *=\int\limits_{0}^{\delta }{\left( 1-\frac{u}{{{U}_{\infty }}} \right)}\,\,dy\] \[=\int\limits_{0}^{\delta }{\left( 1-\frac{y}{{{2}'}} \right)}\,\,dy=\left| y-\frac{{{y}^{2}}}{{{2}'}} \right|=\delta -\frac{\delta }{2}=\frac{\delta }{2}\]

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