Fluid Mechanics MCQs Aeronautical Engineering

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The “continuity equation” in fluid mechanics states that: a) Mass flow rate is constant along a streamline b) The sum of the pressures in a fluid system is constant c) The density of a fluid remains constant d) The volume flow rate is constant in a closed system Answer: a) Mass flow rate is constant along a streamline Bernoulli’s equation is based on the principle of: a) Conservation of mass b) Conservation of momentum c) Conservation of energy d) Conservation of volume Answer: c) Conservation of energy In an incompressible fluid flow, the velocity field satisfies: a) Continuity equation b) Euler’s equation c) Navier-Stokes equation d) Bernoulli’s equation Answer: a) Continuity equation The “Reynolds number” is used to predict: a) The type of flow (laminar or turbulent) b) The velocity distribution in a pipe c) The pressure drop in a pipe d) The temperature distribution in a fluid Answer: a) The type of flow (laminar or turbulent) The “Navier-Stokes equations” describe: a) The motion of viscous fluid flow b) The energy conservation in fluid flow c) The pressure distribution in an ideal fluid d) The relationship between velocity and pressure in a fluid Answer: a) The motion of viscous fluid flow The “Bernoulli’s equation” assumes that the fluid is: a) Compressible and non-viscous b) Incompressible and non-viscous c) Compressible and viscous d) Incompressible and viscous Answer: b) Incompressible and non-viscous The “viscosity” of a fluid is a measure of: a) Its resistance to shear stress b) Its density c) Its compressibility d) Its temperature Answer: a) Its resistance to shear stress The “boundary layer” in fluid flow is characterized by: a) A transition from laminar to turbulent flow b) A region of rapid velocity change near a solid surface c) The formation of vortices behind a body d) The steady-state condition of a flow Answer: b) A region of rapid velocity change near a solid surface The “drag coefficient” (Cd) depends on: a) The shape and surface roughness of the object b) The density of the fluid only c) The velocity of the fluid only d) The temperature of the fluid only Answer: a) The shape and surface roughness of the object The “potential flow theory” assumes that: a) The flow is compressible and viscous b) The flow is incompressible and inviscid c) The flow is compressible and inviscid d) The flow is incompressible and viscous Answer: b) The flow is incompressible and inviscid The “Stokes’ law” applies to: a) The drag force on a sphere in a viscous fluid b) The lift force on an airfoil c) The pressure drop in a pipe d) The flow rate through an orifice Answer: a) The drag force on a sphere in a viscous fluid The “Bernoulli’s principle” can be applied along: a) A streamline b) A boundary layer c) A path of maximum velocity d) An equipotential surface Answer: a) A streamline The “momentum equation” in fluid mechanics is derived from: a) Newton’s second law b) Bernoulli’s equation c) The first law of thermodynamics d) The conservation of mass Answer: a) Newton’s second law The “laminar flow” occurs when: a) The Reynolds number is below a critical value b) The flow is turbulent c) The fluid is highly compressible d) The velocity is high Answer: a) The Reynolds number is below a critical value The “turbulent boundary layer” is characterized by: a) Irregular and chaotic flow patterns b) Smooth and regular flow patterns c) Steady and predictable velocity profiles d) Minimal velocity fluctuations Answer: a) Irregular and chaotic flow patterns The “velocity potential function” is used to describe: a) Incompressible and irrotational flow b) Compressible and turbulent flow c) Viscous flow near a boundary d) The heat transfer in a fluid Answer: a) Incompressible and irrotational flow The “pressure drop” across a pipe due to friction is calculated using: a) Darcy-Weisbach equation b) Bernoulli’s equation c) Continuity equation d) Newton’s law Answer: a) Darcy-Weisbach equation The “boundary layer thickness” increases with: a) Increasing distance from the leading edge of an airfoil b) Increasing Reynolds number c) Decreasing flow velocity d) Decreasing fluid viscosity Answer: a) Increasing distance from the leading edge of an airfoil The “velocity distribution” in laminar flow through a circular pipe is: a) Parabolic b) Linear c) Uniform d) Exponential Answer: a) Parabolic The “conservation of mass” in fluid flow is expressed by: a) Continuity equation b) Bernoulli’s equation c) Navier-Stokes equation d) Euler’s equation Answer: a) Continuity equation The “Prandtl number” is a dimensionless number representing: a) The ratio of momentum diffusivity to thermal diffusivity b) The ratio of kinetic energy to potential energy c) The ratio of pressure drop to velocity d) The ratio of inertial forces to viscous forces Answer: a) The ratio of momentum diffusivity to thermal diffusivity The “drag force” experienced by a body in a fluid depends on: a) The fluid’s density, velocity, and the body’s shape b) The body’s mass and velocity c) The temperature of the fluid only d) The body’s elasticity Answer: a) The fluid’s density, velocity, and the body’s shape The “dynamic viscosity” is measured in units of: a) Pascal-seconds (Pa·s) b) Newton-meters (N·m) c) Joules per kilogram (J/kg) d) Meters per second (m/s) Answer: a) Pascal-seconds (Pa·s) The “total pressure” in a fluid flow is: a) The sum of static pressure and dynamic pressure b) The difference between static pressure and dynamic pressure c) The absolute pressure minus atmospheric pressure d) The average of static and dynamic pressure Answer: a) The sum of static pressure and dynamic pressure The “specific energy” of a fluid flow is the sum of: a) Kinetic energy, potential energy, and flow work b) Kinetic energy and potential energy c) Pressure energy and internal energy d) Kinetic energy and pressure energy Answer: a) Kinetic energy, potential energy, and flow work The “Euler’s equation” for fluid flow is based on: a) The conservation of momentum b) The conservation of energy c) The conservation of mass d) The conservation of volume Answer: a) The conservation of momentum In “compressible flow,” the density of the fluid: a) Varies significantly b) Remains constant c) Is always zero d) Depends on the temperature only Answer: a) Varies significantly The “Froude number” is used to characterize: a) The ratio of inertial forces to gravitational forces b) The ratio of viscous forces to inertial forces c) The ratio of dynamic pressure to static pressure d) The ratio of pressure forces to inertial forces Answer: a) The ratio of inertial forces to gravitational forces The “compressibility factor” (Z) for a gas is used to correct for: a) Deviations from ideal gas behavior b) The effect of temperature on pressure c) The effect of velocity on density d) The effect of surface tension Answer: a) Deviations from ideal gas behavior The “hydraulic diameter” for a non-circular duct is defined as: a) 4 ⋅ Flow Area Wetted Perimeter Wetted Perimeter 4⋅Flow Area ​ b) Flow Area × Wetted Perimeter Flow Area×Wetted Perimeter c) Wetted Perimeter Flow Area Flow Area Wetted Perimeter ​ d) Flow Area / Wetted Perimeter Flow Area/Wetted Perimeter Answer: a) 4 ⋅ Flow Area Wetted Perimeter Wetted Perimeter 4⋅Flow Area ​ The “Mach number” in fluid mechanics is defined as: a) The ratio of the flow velocity to the speed of sound in the fluid b) The ratio of dynamic pressure to static pressure c) The ratio of inertial forces to viscous forces d) The ratio of flow area to wetted perimeter Answer: a) The ratio of the flow velocity to the speed of sound in the fluid The “flow separation” in a boundary layer typically leads to: a) Increased drag and formation of wake b) Decreased drag and smoother flow c) Increased lift and decreased pressure d) Decreased lift and increased pressure Answer: a) Increased drag and formation of wake In “laminar flow” through a pipe, the shear stress is: a) Proportional to the velocity gradient b) Inversely proportional to the velocity c) Constant across the pipe cross-section d) Zero Answer: a) Proportional to the velocity gradient The “vorticity” in fluid mechanics is a measure of: a) The local rotation of fluid particles b) The local velocity of fluid particles c) The local density of fluid d) The local pressure in the fluid Answer: a) The local rotation of fluid particles In “turbulent flow,” the “eddy viscosity” is used to: a) Model the effects of turbulence on the flow b) Measure the density of the fluid c) Calculate the static pressure d) Determine the velocity profile Answer: a) Model the effects of turbulence on the flow The “pressure recovery” in a diffuser is due to: a) The conversion of kinetic energy into pressure energy b) The increase in velocity of the flow c) The decrease in the density of the fluid d) The increase in temperature of the fluid Answer: a) The conversion of kinetic energy into pressure energy The “siphon” operates based on: a) The difference in gravitational potential energy b) The principle of conservation of mass c) The increase in flow velocity d) The decrease in fluid density Answer: a) The difference in gravitational potential energy The “Bernoulli effect” is observed when: a) The fluid velocity increases, resulting in a decrease in pressure b) The fluid velocity decreases, resulting in an increase in pressure c) The fluid density increases, resulting in a decrease in velocity d) The fluid viscosity decreases, resulting in an increase in drag Answer: a) The fluid velocity increases, resulting in a decrease in pressure The “stream function” is used to describe: a) Incompressible flow in two dimensions b) Compressible flow in three dimensions c) Viscous flow in one dimension d) The temperature distribution in a fluid Answer: a) Incompressible flow in two dimensions The “incompressible flow” assumption implies that: a) The fluid density remains constant b) The fluid velocity is constant c) The fluid pressure is constant d) The fluid temperature is constant Answer: a) The fluid density remains constant The “dimensionless quantity” used to characterize flow around an object is: a) Reynolds number b) Mach number c) Froude number d) Prandtl number Answer: a) Reynolds number The “continuity equation” in fluid dynamics expresses: a) The conservation of mass in a flow field b) The conservation of energy in a flow field c) The conservation of momentum in a flow field d) The conservation of volume in a flow field Answer: a) The conservation of mass in a flow field

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