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Fluid Mechanics Test 3
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Fluid Mechanics Test 3
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  • Question 1/15
    1 / -0.33

    Reynolds number is the ratio of the inertia force to the:
    Solutions

  • Question 2/15
    1 / -0.33

    The total drag on a plate held normal to the flow is equal to ______
    Solutions

    Drag is defined as forceful pull experienced by the flat plate while the fluid flows over it.

    Pressure drag comes from the eddying motions that are set up in the fluid by the passage of the body. This drag is associated with the formation of a wake in the flow.

    Frictional drag comes from friction between the fluid and the surfaces over which it is flowing.

    For the plate held normal to flow, fluid flows across and there’s huge wake formation occurring behind the plate. As the fluid is not flowing anywhere tangentially to the plate, there is negligible or no viscous drag experienced. So, the total drag on a plate held normal to the flow is equal to pressure drag only.

    Figure A: Plate held parallel to the flow ⇒ Only viscous drag takes place

    Figure B:  Plate held normal to the flow ⇒ Only pressure drag takes place
  • Question 3/15
    1 / -0.33

    The term  is known as
    Solutions

    Energy per unit weight of water is used in Bernoulli’s equation to defined energy head at a section.

    Bernoulli’s equation is given as

    Kinetic energy for the fluid flow is given by 

    Kinetic energy per unit weight for the fluid flow is given by 

    Pressure energy for the fluid flow is given by 

    Pressure energy per unit weight for the fluid flow is given by
  • Question 4/15
    1 / -0.33

    Continuity equation deals with the law of conservation of ________
    Solutions

    Continuity Equation is based on the principle of conservation of mass. For a fluid flowing through a pipe at all the cross-section, the quantity of fluid per second is constant.

    The continuity equation is given as 

    Bernoulli’s Equation is based on the principle of conservation of mass. For an ideal fluid flowing through a pipe at all the cross-section, the total energy would be constant.

    Conservation of momentum states that the net force acting on the fluid mass is equal to the change in momentum of flow per unit time in that direction.
  • Question 5/15
    1 / -0.33

    The correct relationship among displacement thickness ‘d’, momentum thickness ‘m’ and energy thickness 'e' is
    Solutions

    Displacement thickness,

    Momentum thickness,

    Energy thickness,

    δ > δE > δθ 
  • Question 6/15
    1 / -0.33

    The figure shows curves for velocity distribution across a section for different Reynold’s Number. The curve A corresponds to the Reynold number ___

    Solutions

    Laminar flow through a circular pipe follows parabolic velocity distribution.

    For the flow through a circular pipe,

    Laminar flow – Reynold’s Number is less than 2000

    Turbulent Flow – Reynold’s Number is greater than 4000

    Transition Flow – Reynold’s Number is between 2000 to 4000

    Curve A given the figure is of logarithmic pattern and thus Reynold’s number should be more than 4000 i.e. 5000 for the given question.
  • Question 7/15
    1 / -0.33

    The velocity distribution across a section of two fixed parallel plates having viscous flow is given by
    Solutions

    The velocity distribution across a section of two fixed parallel plates is parabolically given by

    Where  pressure gradient along the length of the plate

    y = point of consideration from lower fixed plate

    t = distance between the two fixed parallel plates

  • Question 8/15
    1 / -0.33

    The total head of a liquid particle in motion is equal to
    Solutions

    Pressure head: Head measured due to the pressure experienced/exerted by fluid at the given section.

    Kinetic head: Head measured equivalent to the kinetic energy of the fluid in the section.

    Potential head: Head attained by the fluid due to its presence at some altitude with reference to the fixed bottom.

    Total Head = Pressure Head + Kinetic Head + Potential Head

  • Question 9/15
    1 / -0.33

    For the laminar flow through a circular pipe
    Solutions

    For the laminar flow through a circular pipe, velocity distribution is parabolic.

    Velocity profile is given by,  

    Maximum velocity is at the center line of the pipe i.e. r = 0

    Maximum velocity, 

    Average velocity, 

    Therefore 
  • Question 10/15
    1 / -0.33

    Continuity equation for a compressible fluid is:
    Solutions

    A controlled mass or closed system is characterized by a fixed quantity of mass of a given identity, while in an open system or control volume mass may change continuously due to the flow of mass across the system boundary.

    The continuity equation is the equation of conservation of mass in a fluid flow. 

    According to the law of conservation of mass:

    Rate of flow in section 1 - 1 = Rate of flow at section 2 - 2

    This equation is applicable to the compressible as well as incompressible fluid and is called a continuity equation.

    If the fluid is incompressible, then ρ1 = ρ2; and continuity equation reduces to A1V1 = A2V2

  • Question 11/15
    1 / -0.33

    Which type of forces dominates a fluid flow with a very high Reynolds Number (Re ≈ 10000)?
    Solutions
    • The Reynolds number is the ratio of inertial forces to viscous forces and is a convenient parameter for predicting if a flow condition will be laminar or turbulent
    • It can be interpreted that when the viscous forces are dominant (slow flow, low Re) they are sufficient enough to keep all the fluid particles in line, then the flow is laminar
    • When the inertial forces dominate over the viscous forces (when the fluid is flowing faster and Re is larger) then the flow is turbulent
  • Question 12/15
    1 / -0.33

    For pipes, turbulent flow occurs when Reynolds number is-
    Solutions

    Type of flow

    Reynolds Number

    Laminar

    Less than 2000

    Transition

    2000-4000

    Turbulent

    Greater than 4000

  • Question 13/15
    1 / -0.33

    The local acceleration in the direction of x is given by
    Solutions

    Total acceleration in any direction is given by

    Where,  is convective acceleration and  is local acceleration

    u = velocity in the given direction

    x = direction of consideration

    t = time of consideration

    Convective acceleration is defined as the rate of change of velocity due to the change in the position of fluid particles in a fluid flow.

    Local acceleration is defined as the rate of increase of velocity with respect to time at a given point in a flow field.
  • Question 14/15
    1 / -0.33

    The coefficient of velocity is determined experimentally by using the relation ____
    Solutions

    Coefficient of velocity is experimentally determined with the tank with an orifice in the side.

    Coefficient of velocity is given by 

    where, H = Constant head maintained above the center line of the orifice, y = Vertical fall in the level over the distance ‘x’ traveled from the entrance, x = Horizontal distance the fluid has traveled

    Note:

    Horizontal Distance: x = V × t

    Vertical Distance: y

    Theoretical velocity:

  • Question 15/15
    1 / -0.33

    If a thin plate is held normal to the flow, the viscous drag on it is ______

    Solutions

    Viscous force is experienced if the fluid flows along the surface of the plate.

    When a plate is held normal to the flow, the water hits the plate perpendicular and wake formation takes place behind the plate which leads to the pressure drag.

    Since the flow does not take place along the plate, viscous drag on the plate is zero.

    Figure A: Plate held parallel to the flow ⇒ Only viscous drag takes place

    Figure B:  Plate held normal to the flow ⇒ Only pressure drag takes place
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