# Shared Flashcard Set

## Details

Fluid Mechanics
Exam 1 Fluid Mechanics
60
Engineering
Pre-School
02/22/2010

Term
 internal flow
Definition
 flows that are completely bounded by solid surfaces. i.e. in pipes or ducts
Term
 external flow
Definition
 flow of unbounded fluid over a surface. such as flow over a plate
Term
 open channel flow
Definition
 flow of liquids with a free surface above. i.e. flow in a river or ditch
Term
 what causes no-slip condition?
Definition
 the viscosity of the fluid
Term
Definition
 flow process in which there is no change with time inside the system or at the system boundaries
Term
 normal stress within a fluid
Definition
 pressure
Term
 definition of a fluid
Definition
 distinction between a solid and a fluid is made on the basis of the substance's ability to resist an applied shear stress that tends to change its shape. A fluid deforms continuously under a shear stress, no matter how small
Term
 what different forms of energy constitute total energy?
Definition
 kenetic, potential, and internal
Term
 What is viscosity?What causes viscosity in liquids and in gases?
Definition
 Viscosity is a measure of a fluid's resistance to deformation. Viscosity in fluids is caused by cohesive forces between molecules. In gases, it's caused by the collision of molecules.
Term
 How does the dynamic viscosity of fluids vary with Temp?Of gases?
Definition
 in liquids it decreases with temperature. in gases it increases with temp
Term
 what is surface tension?
Definition
 the magnitude of the pulling force at the surface of a liquid per unit length
Term
 incompressible flow
Definition
 a fluid flow during which the density of the fluid remains nearly constant
Term
 incompressible fluid
Definition
 a fluid whose density is practically independent of pressure (such as a liquid).
Term
 must the flow of a compressible fluid be treated as compressible?
Definition
 no, the flow of a compressible fluid (such as air) is not necessarily compressible since the density of a compressible fluid may still remain constant during flow
Term
 Pascal's Law
Definition
 the pressure applied to a confined fluid increases the pressure throughout by that same amount
Term
 what is a boundary layer?
Definition
 when a fluid stream encounters a solid surface, the fluid velocity assumes a value of zero at the surface. The velocity then varies from zero at the surface to the free-stream value at a sufficient distance from the surface. The boundary layer is the region of flow in which the velocity gradients are significant
Term
 what causes a boundary layer to develop?
Definition
 the no-slip condition
Term
 Continuum
Definition
 a continuous, homogeneous, matter with no holes. the continuum idealization allows us to treat properties as point functions and to assume that the properties vary continually in space with no jump discontinuities.
Term
 When can a real gas be treated as ideal?
Definition
 At a high temperature or low pressure relative to its critical temperature and pressure
Term
 Microscopic energy
Definition
 the forms of energy related to the molecular structure of a system and the degree of their molecular activity.
Term
 Internal Energy
Definition
 the sum of all microscopic forms of energy. Denoted by U or u
Term
 Macroscopic Energy
Definition
 related to motion and the influence of some external effects such as gravity, magnetism, electricity, and surface tension
Term
 Viscosity
Definition
 a measure of the "resistance to deformation of a fluid due to the internal frictional force that develops between different layers of fluids as they are forced to move relative to each other
Term
 What is the cause of Viscosity?
Definition
 Viscosity is caused by the cohesive forces between the molecules in liquids, and by the molecular collisions in gases. Liquids have higher dynamic viscosities than gases.
Term
 What are Newtonian fluids?
Definition
 The fluids whose shear stress is proportional to the velocity gradient are called Newtonian fluids. (most common fluids such as water, air, gasoline, and oil are Newtonian fluids)
Term
 Dynamic Viscosity of Liquids
Definition
 decreases with temperature
Term
 Dynamic viscosity of gases
Definition
 increases with temperature
Term
 kinematic viscosity of liquids
Definition
 is practically independent of pressure
Term
 kinematic viscosity of gases
Definition
 is inversely proportional to density and thus pressure (because the density of a gas is proportional to its pressure)
Term
 what causes surface tension?
Definition
 the attractive forces between the molecules. (the surface tension is also surface energy since it represents the stretching work that needs to be done to increase the surface area of the liquid by a unit amount)
Term
 What is the capillary effect?
Definition
 the rise or fall of a liquid in a small-diameter tube inserted into the liquid. The capillary effect is proportional to the cosine of the contact angle, which is the angle that the tangent to the liquid surface makes with the solid surface at the point of contact.
Term
 What causes the capillary effect
Definition
 the net effect of the cohesive forces (the forces between like molecules) and adhesive forces (the forces between dislike molecules)
Term
 Is the Capillary Rise greater in small- or large- diameter tubes?
Definition
 Capillary Rise is greater in small-diameter tubes because they are inversely proportional to the diameter of the tube
Term
 What is Pascal's Law?
Definition
 the pressure applied to a confined fluid increases the pressure throughout by the same amount
Term
 Stable Body
Definition
 Center of gravity, G, is directly below center of buoyancy B
Term
 neutrally stable
Definition
 G (center of gravity) and B (center of buoyancy) are coincident
Term
 unstable
Definition
 G (Center of Gravity) is directly above B (Center of buoyancy)
Term
 barometer
Definition
 device used to measure atmospheric pressure (aka barometric pressure)
Term
 Does the length or cross-sectional area of the tube have an effect on the height of the fluid column of a barometer?
Definition
 No
Term
 local acceleration
Definition
Term
 local acceleration
Definition
Term
Definition
 (v dot grad)v. can be nonzero even for steady flows. accounts for a fluid particle moving to a new location in the flow where the velocity field is different
Term
 streamline
Definition
 a curve that is everywhere tangent to the instantaneous local velocity vector. can be derived mathematically
Term
 pathline
Definition
 an actual path traveled by an individual fluid particle over some time period
Term
 streakline
Definition
 the locus of fluid particles passed sequentially through a prescribed point in the flow
Term
 timeline
Definition
 a set of adjacent fluid particles that were marked at the same instant in time
Term
 What is the Lagrangian description of fluid motion?
Definition
 In the Lagrangian description of fluid motion, individual fluid particles (fluid elements composed of a fixed, identifiable mass of fluid) are followed. Similar to that of studying billiard balls and other solid objects in physics.
Term
 Is the Lagrangian method of fluid flow analysis more similar to a study of a system or a control volume?
Definition
 Lagrangian method is more similar to system analysis. We follow a particular chunk of fluid as it moves in a flow
Term
 Define the Eulerian description of fluid motion
Definition
 In the Eulerian description, we are concerned with field variables such as velocity, pressure, temperature, etc., as functions of space and time within a control volume.
Term
 How is the Eulerian description different from the Lagrangian?
Definition
 In contrast to the Lagrangian method, fluid flows into and out of the Eulerian control volume, and we do not keep track of the motion of particular identifiable fluid particles. (This method is not as natural as the Lagrangian because the fundamental conservation laws apply to moving particles not fields)
Term
 What is the static pressure, P?
Definition
 the actual pressure of the fluid
Term
 What is the dynamic pressure, rhoV^2/2
Definition
 The pressure rise when the fluid in motion is brought to a stop
Term
 What is the hydrostatic pressure rho*g*z
Definition
 not pressure in a real sense since its value depends on the reference level selected, and it accounts for the effects of fluid weight on pressure
Term
 What is the stagnation pressure? What kind of device measures it?
Definition
 The stagnation pressure is the sum of the static and dynamics pressures and can be measured by a pitot tube whose inlet is normal to flow.
Term
 What is the pressure head P/rho*g?
Definition
 the height of a fluid column that produces the static pressure P
Term
 What is the velocity head, V^2/2g?
Definition
 The elevation needed for a fluid to reach the velocity V during frictionless free fall.
Term
 What is the elevation head z?
Definition
 The height of a fluid relative to a reference level.
Term
 What is the hydraulic grade line (HGL)?
Definition
 The sum of the static pressure and elevation heads. P/rho*g +z
Term
 What is the energy grade line (EGL)?
Definition
 the line that represents the total head of the fluid, P/rho*g + V^2/2*g + z
Term
 How is the location of the HGL determined for open-channel flow?
Definition
 For open-channel flow, the hydraulic grade line coincides with the free surface of the liquid.
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