Contents

# Fluid mechanics interview questions and answers

## Q: What is fluid mechanics?

A: Fluid mechanics is the study of fluids, which includes liquids, gases, and plasmas. It deals with the behavior of fluids when they are in motion or at rest, and the forces and energy associated with the motion of fluids.

## Q: What are the types of fluids?

A: There are three types of fluids: liquids, gases, and plasmas.

## Q: What is the difference between a liquid and a gas?

A: Liquids have a definite volume but no definite shape, while gases have neither a definite volume nor a definite shape.

## Q: What is viscosity?

A: Viscosity is a fluid property that describes the resistance of a fluid to flow. It is a measure of the internal friction within the fluid.

## Q: What is the difference between laminar and turbulent flow?

A: Laminar flow is a smooth, orderly flow pattern in which the fluid flows in layers, while turbulent flow is characterized by irregular, chaotic flow patterns.

## Q: What is Bernoulliโs equation?

A: Bernoulliโs equation is a fundamental equation in fluid mechanics that relates the pressure, velocity, and elevation of a fluid in a steady flow.

## Q: What is a boundary layer?

A: A boundary layer is the thin layer of fluid that is adjacent to a solid surface in a fluid flow. It is characterized by a gradual transition from zero velocity at the surface to the free stream velocity.

## Q: What is a lift force?

A: A lift force is a force that is generated by a fluid flow around an object. It is perpendicular to the direction of the flow and is responsible for the upward force on an airfoil that allows it to generate lift.

## Q: What is a drag force?

A: A drag force is a force that is generated by a fluid flow around an object. It is parallel to the direction of the flow and is responsible for the resistance to motion of the object through the fluid.

## Q: What is the difference between a centrifugal pump and a positive displacement pump?

A: A centrifugal pump is a dynamic pump that works by imparting momentum to the fluid and converting it to pressure, while a positive displacement pump works by trapping a fixed amount of fluid and forcing it through the pump.

## Q: What is cavitation?

A: Cavitation is the formation of vapor bubbles in a fluid when the pressure drops below the vapor pressure of the fluid. It can cause damage to pumps and other fluid-handling equipment.

## Q: What is the difference between laminar and turbulent boundary layers?

A: A laminar boundary layer is a thin layer of fluid that is adjacent to a solid surface in which the fluid flows in smooth, parallel layers, while a turbulent boundary layer is characterized by irregular, chaotic flow patterns.

## Q: What is the Coanda effect?

A: The Coanda effect is a phenomenon in fluid mechanics in which a fluid jet or stream follows a curved surface rather than continuing in a straight line.

A: Steady flow is a flow pattern in which the fluid properties (such as velocity and pressure) do not change with time, while unsteady flow is characterized by changes in these properties over time.

## Q: What is a hydraulic jump?

A: A hydraulic jump is a phenomenon that occurs when a fast-moving fluid abruptly slows down and increases in height. This can occur when a high-velocity fluid flows into a pool or a basin.

## Q: What is the difference between a closed and open system in fluid mechanics?

A: In fluid mechanics, a closed system is one in which no mass can enter or leave the system, while an open system allows for the inflow and outflow of mass.

## Q: What is the difference between compressible and incompressible fluids?

A: Compressible fluids are fluids that can be compressed or expanded under pressure, while incompressible fluids are fluids that cannot be compressed or expanded under pressure.

## Q: What is a pump curve?

A: A pump curve is a graphical representation of a pumpโs performance characteristics, showing how its flow rate and pressure vary under different operating conditions.

## Q: What is a diffuser?

A: A diffuser is a component of a fluid system that is used to slow down the fluid flow and increase its pressure. It is often used in conjunction with a pump or a compressor.

## Q: What is the difference between a laminar and turbulent pipe flow?

A: Laminar pipe flow is a smooth, orderly flow pattern in which the fluid flows in layers, while turbulent pipe flow is characterized by irregular, chaotic flow patterns.

## Q: What is the difference between a nozzle and a diffuser?

A: A nozzle is a component of a fluid system that is used to increase the velocity of the fluid flow and decrease its pressure, while a diffuser is used to slow down the fluid flow and increase its pressure.

## Q: What is a boundary layer separation?

A: Boundary layer separation is a phenomenon in fluid mechanics in which the boundary layer detaches from a solid surface, creating a wake behind the object. This can result in increased drag and reduced lift.

## Q: What is a hydraulic gradient?

A: A hydraulic gradient is the slope of the water table or piezometric surface in an aquifer. It represents the rate of change of hydraulic head with distance along the flow path.

## Q: What is a vorticity?

A: Vorticity is a measure of the rotation of fluid particles in a fluid flow. It is related to the curl of the velocity field and can be used to predict the formation of vortices in a flow.

## Q: What is a pitot tube?

A: A pitot tube is a device that is used to measure the velocity of a fluid flow. It works by measuring the difference in pressure between a stagnation point and a point in the fluid flow.

## Q: What is a fluidized bed?

A: A fluidized bed is a system in which a solid material is suspended and agitated in a fluid flow. This can be used for various purposes, such as mixing, drying, and chemical reactions.

## Q: What is the difference between a centrifugal and positive displacement pump?

A: A centrifugal pump uses an impeller to create a flow by increasing the kinetic energy of the fluid, while a positive displacement pump uses a mechanical mechanism to trap and move a fixed amount of fluid.

## Q: What is a Reynolds number?

A: The Reynolds number is a dimensionless quantity used in fluid mechanics to predict whether a fluid flow will be laminar or turbulent. It is defined as the ratio of inertial forces to viscous forces.

## Q: What is the Bernoulliโs principle?

A: Bernoulliโs principle is a fundamental principle in fluid mechanics that states that as the velocity of a fluid increases, its pressure decreases, and vice versa.

## Q: What is a cavitation?

A: Cavitation is a phenomenon that occurs when the pressure of a fluid drops below its vapor pressure, causing bubbles to form and then rapidly collapse. This can cause damage to pumps, propellers, and other equipment.

## Q: What is a pressure head?

A: Pressure head is the vertical distance that a fluid can be lifted by a pump, measured in units of length.

## Q: What is the difference between a jet engine and a rocket engine?

A: A jet engine uses the atmospheric air for combustion, while a rocket engine carries its own oxidizer, fuel, and ignition source.

## Q: What is a drag coefficient?

A: The drag coefficient is a dimensionless quantity that is used to quantify the resistance of an object to fluid flow. It depends on the shape of the object, its size, and the fluid properties.

## Q: What is the continuity equation?

A: The continuity equation is a fundamental equation in fluid mechanics that states that the mass flow rate of a fluid through any given cross-sectional area must remain constant, assuming no mass is added or removed.

## Q: What is a laminar boundary layer?

A: A laminar boundary layer is a thin layer of fluid that forms along a solid surface in a smooth, ordered manner. It is characterized by a gradual increase in velocity from the surface to the outer flow.

## Q: What is a hydraulic system?

A: A hydraulic system is a system that uses a fluid to transmit power or force from one point to another. It typically consists of a pump, a reservoir, and a network of pipes or hoses.

## Q: What is a subsonic flow?

A: A subsonic flow is a fluid flow in which the fluid velocity is less than the speed of sound. In such flows, the compressibility of the fluid can usually be neglected.

## Q: What is the difference between laminar and turbulent boundary layer?

A: A laminar boundary layer is smooth and ordered, while a turbulent boundary layer is characterized by chaotic flow patterns and mixing of fluid. The transition from laminar to turbulent boundary layer depends on Reynolds number.

A: Steady-state flows are those in which the fluid properties, such as velocity and pressure, remain constant with respect to time at any given point in the flow field, while unsteady-state flows are those in which the fluid properties vary with time.

## Q: What is a fluid force?

A: A fluid force is the force exerted on an object by a fluid in motion. This force can be divided into drag force, lift force, and buoyancy force.

## Q: What is a stagnation point?

A: A stagnation point is a point in a fluid flow where the velocity of the fluid is zero. At this point, the pressure of the fluid is at its maximum value.

## Q: What is a shock wave?

A: A shock wave is a type of wave that is generated when a fluid flow exceeds the speed of sound. It is characterized by a sudden, drastic change in pressure and density.

## Q: What is a streamline?

A: A streamline is a line that represents the direction of fluid flow at a given point in a fluid flow field. It is perpendicular to the fluid velocity vector.

## Q: What is the Mach number?

A: The Mach number is a dimensionless quantity that is used to characterize the speed of an object relative to the speed of sound in the surrounding medium.

## Q: What is a hydraulic accumulator?

A: A hydraulic accumulator is a device that is used to store hydraulic energy in the form of pressurized fluid. It can be used to supplement the flow from a hydraulic pump and to maintain system pressure during peak demand.

## Q: What is a lift coefficient?

A: The lift coefficient is a dimensionless quantity that is used to quantify the ability of an object to generate lift when moving through a fluid. It depends on the shape of the object and the angle of attack.

## Q: What is a wind tunnel?

A: A wind tunnel is a device that is used to study the behavior of fluid flows around objects at different speeds and angles. It consists of a test section, a fan, and a measuring system.

## Q: What is a manometer?

A: A manometer is a device that is used to measure the pressure of a fluid. It typically consists of a U-shaped tube filled with a fluid, such as mercury or water, and a scale to measure the height difference between the two legs of the tube.

## Q: What is a fluid viscosity?

A: Fluid viscosity is a measure of a fluidโs resistance to flow. It is related to the internal friction between fluid molecules and depends on temperature and pressure.

## Q: What is a swirl flow?

A: A swirl flow is a fluid flow that contains a rotational component around a central axis. It can be used to improve mixing and heat transfer in fluid systems.

## Q: What is a Venturi meter?

A: A Venturi meter is a device used to measure the flow rate of a fluid in a pipe. It consists of a narrow section, called a throat, and two wider sections, called the inlet and outlet.

## Q: What is a hydraulic jump?

A: A hydraulic jump is a phenomenon that occurs when a high-velocity fluid flow meets a low-velocity fluid flow. It results in a sudden increase in the fluid depth and a decrease in velocity.

## Q: What is a cavitation?

A: Cavitation is a phenomenon that occurs when the pressure of a fluid drops below its vapor pressure, causing bubbles to form in the fluid. It can cause damage to machinery and reduce efficiency in fluid systems.

## Q: What is a fluid head?

A: Fluid head is the energy per unit weight of a fluid due to its pressure and elevation. It is often used in hydraulic and fluid systems to describe the energy of the fluid.

## Q: What is laminar flow?

A: Laminar flow is a type of fluid flow in which the fluid moves in parallel layers with no turbulence. It occurs at low velocities and is characterized by a smooth and orderly flow pattern.

## Q: What is turbulent flow?

A: Turbulent flow is a type of fluid flow in which the fluid moves in a chaotic and irregular pattern. It occurs at high velocities and is characterized by fluctuations in velocity and pressure.

## Q: What is a pressure head?

A: Pressure head is the energy per unit weight of a fluid due to its pressure. It is often used in hydraulic and fluid systems to describe the pressure of the fluid.

## Q: What is a siphon?

A: A siphon is a device used to transfer fluid from a higher level to a lower level by means of a tube. It works by using the difference in pressure between the two levels to create a flow of fluid through the tube.

## Q: What is a water hammer?

A: A water hammer is a pressure surge that occurs in a fluid system when a fluid flow is suddenly stopped or redirected. It can cause damage to pipes and equipment and can be prevented with the use of surge suppression devices.

## Q: What is the Navier-Stokes equation?

A: The Navier-Stokes equation is a set of partial differential equations that describe the motion of a fluid. It takes into account the forces acting on the fluid, including pressure, viscosity, and external forces.

## Q: What is the Euler equation?

A: The Euler equation is a simplified version of the Navier-Stokes equation that neglects the effects of viscosity. It is used to study the motion of ideal fluids, such as air.

## Q: What is a boundary layer?

A: A boundary layer is a thin layer of fluid that forms at the surface of a solid object in contact with a fluid. It is characterized by a gradual increase in velocity from zero at the surface to the free stream velocity away from the surface.

## Q: What is drag?

A: Drag is a force that opposes the motion of an object through a fluid. It is caused by the interaction between the fluid and the object and is dependent on the shape and size of the object and the properties of the fluid.

## Q: What is lift?

A: Lift is a force that acts perpendicular to the direction of motion of an object through a fluid. It is caused by the difference in pressure above and below the object and is dependent on the shape and angle of attack of the object.

## Q: What is a boundary condition?

A: A boundary condition is a set of conditions that must be specified at the boundaries of a fluid system to determine the behavior of the fluid. Examples include specifying the velocity or pressure at the boundary.

## Q: What is a shock wave?

A: A shock wave is a high-pressure wave that travels through a fluid faster than the speed of sound. It is caused by a sudden change in flow conditions and is characterized by a steep increase in pressure and temperature.

## Q: What is a compressible flow?

A: A compressible flow is a type of fluid flow in which the density of the fluid changes due to changes in pressure and temperature. It is typically observed at high velocities and is important in the design of aircraft and rockets.