Fluid Mechanics Glossary

•  Note: Glossaries only account for terms that do not require a full lesson for adequate explanation. To find a term, search at the homepage.

aerostatics – Pertains to the study of gases at rest. It is part of fluid statics.
capillary – A narrow tube or confined flow channel.
compressibility effects – Significant density changes caused by the flow of a gas.
dilatant – In fluid mechanics means shear thickening. In contrast to pseudoplastic.
continuum approximation – Assuming the substance under question is a continuum.
drag forceForce due to drag. Same as drag. The force a flowing fluid exerts on a body in the flow direction. The magnitude of this force depends, in part, on viscosity.
flow energy – The flow energy is associated with fluid that enters or leaves a control volume. The term is P/ρ, where P is pressure and ρ is density. It can be seen in the Bernoulli equation and also is the Pv term of enthalpy. (v is specific volume and the reciprocal of specific volume is density)
fluid statics – The study of fluids at rest. With regards to fluid statics, there is no relative motion between adjacent fluid layers, and thus there are no shear (tangential) stresses in the fluid trying to deform it. The only stress dealt with in fluid statics is normal stress, which is the pressure, and the variation of pressure is due only to the weight of the fluid. Therefore, the topic of fluid statics has significance only in gravity fields, and the force relations developed naturally involve the gravitational acceleration g. Fluid statics is used to determine the forces acting on floating or submerged bodies and the forces developed by devices like hydraulic presses and car jacks. The design of many engineering systems such as water dams and liquid storage tanks requires the determination of forces acting on the surfaces using fluid statics. The complete description of the resultant hydrostatic force acting on a submerged surface requires the determination of the magnitude, the direction, and the line of action of the force.
homogeneous fluid – A fluid of constant density.
hydrostatic force – a force that relates to the weight of fluid bearing on a submerged surface.
hydrostatics – Pertains to the study of liquids at rest. It is part of fluid statics.
lift forceForce due to lift. Same as lift.
meniscus – The curved free surface of a liquid in a capillary tube. (picture)
pitching moment – The moment about the side force direction.
Pitot tube – A Pitot tube is a small tube with its open end aligned into the flow so as to sense the full impact pressure of the flowing fluid. It measures the stagnation pressure. (picture)
pseudoplastic – Shear-thinning. In contrast to dilatant.
side force – Neither a loss nor a gain.
specific weight – weight per unit volume, denoted by gamma, equals density times the gravitational acceleration, γs = ρg; The units may be in lbf/ft3 or N/m3, for example; Specific weight is very useful in hydrostatic pressure applications.
static hole – Same as static pressure tap below.
static pressure tap – A static pressure tap is simply a small hole drilled into a wall such that the plane of the hole is parallel to the flow direction. The hole itself should be normal to the wall. Burrs should be avoided. It is used for measuring the static pressure. (picture)
yaw – The moment about the lift axis or lift direction. Also known as yawing moment.
yawing moment – Same as yaw, defined just above.