# Fluid Dynamics Topics

**Acoustic Streaming**- Unidirectional flow currents in a fluid that are due to the presence of sound waves.
**Aerodynamic Drag**- Resistance of a vehicle body to motion through the air. A smooth surface has less drag than a rough one.
**Atmospheric Boundary Layer**- The atmospheric layer adjacent to the surface of the Earth that is affected by friction against the surface boundary.
**Back Pressure**- Pressure exerted backward; in a field of fluid flow, a pressure exerted contrary to the pressure producing the main flow.
**Bernoulli′s Principle**- The pressure in a fluid decreases as its velocity increases.
**Boost Pressure**- The increase above atmospheric pressure produced inside the intake manifold by a forced-induction system such as a turbocharger or supercharger.
**Boundary Layer**- The portion of a fluid flowing past a body that is in the immediate vicinity of the body.
**Brookfield Viscosity**- Apparent viscosity determined by Brookfield viscometer.
**Centre of Pressure**- The point at which the aerodynamic forces on a body appear to act, and at which there is no aerodynamic movement.
**Clogging**- The restriction of a flow path due to the accumulation of material along the flow path boundaries.
**Computational Fluid Dynamics**- A tool for predicting the aerodynamics and fluid dynamics of air around flight vehicles by solving a set of mathematical equations with a computer.
**Condensation Shock Wave**- A sheet of discontinuity associated with a sudden condensation and fog formation in a field of flow.
**darcy**- A CGS unit of permeability.
**Differential Pressure Indicator**- An indicator which signals the difference in pressure between two points, typically between the upstream and downstream sides of a filter, valve or expansion element.
**Drag**- Resistance of a vehicle body to motion through the air. A smooth surface has less drag than a rough one.
**Drag Coefficient**- A dimensionless value that allows the comparison of shape and orientation of different bodies.
**Dribbling**- Slow seeping of liquid from a control valve after it has been closed.
**Dynamic Pressure**- The pressure of a fluid resulting from its motion when brought to rest on a surface.
**Dynamic viscosity**- That molecular property of a fluid which enables it to support tangential stresses for a finite time and thus to resist deformation.
**Fluid Dynamics Books**- Lists all Fluid Dynamics Books in the Encyclopaedia
**Fluid Dynamics Calculations**- Lists all Fluid Dynamics Calculations in the Encyclopaedia
**Fluid Dynamics Conversions**- Lists all Fluid Dynamics Conversions in the Encyclopaedia
**Fluid Dynamics Weblinks**- Lists all Fluid Dynamics Weblinks in the Encyclopaedia
**Fluid Pump**- A device for moving fluids.
**Hydrostatic Pressure**- The pressure at any point in a liquid at rest; equal to the depth of the liquid multiplied by its density.
**Impact Pressure**- Another name for Dynamic Pressure.
**Inertial Impaction**- The process whereby a particle moving in a gas stream strikes slowly moving or stationary obstacles or targets directly in its path.
**Inviscid**- Not viscous, not clinging or sticky, frictionless.
**Inviscid Fluid**- A perfect fluid.
**Kinematic Viscosity**- The dynamic viscosity of a fluid divided by the fluid density.
**Mass Median Particle Diameter**- The particle diameter at which half the particulate mass is composed of particles larger than this diameter and half the mass is composed of particles smaller than this diameter.
**Molecular Slip**- The existence of a finite net gas velocity at the surface of very small particles resulting in a lower drag force.
**Navier Stokes Codes**- Computer software that contains the mathematical equations of motion for a viscous fluid.
**Negative Pressure**- A relative pressure that is below atmospheric pressure.
**Pascal Second**- The SI unit of dynamic viscosity, equal to 10 poise.
**Perfect Fluid**- A fluid chiefly characterized by lack of viscosity and, usually, by incompressibility.
**Pressure**- Defined as the force exerted per unit area.
**Pressure Coefficient**- A dimensionless value which acts as a means of indicating the local pressure at some point of interest around a body, and which is independent of velocity.
**Pressure Drop**- A measure of the resistance the gas stream encounters as it flows through an air control device or other piece of equipment.
**Pressure Head**- Pressure head is one of the main characteristics of a pump.
**Pressure Relief Valve**- A type of valve used to control or limit the pressure in a system or vessel.
**Pressure Zone**- As sound waves strike a solid surface, the particle velocity is zero at the surface and the pressure is high, thus creating a high-pressure layer near the surface.
**Profile Drag**- This is drag from the three-dimensional shape of the aircraft or vehicle.
**Reynolds Stresses**- The transfer of momentum due to turbulent fluctuations of a viscous, incompressible, homogeneous fluid in turbulent motion.
**Richardson Number**- A nondimensional number arising in the study of shearing flows of a stratified fluid.
**Saybolt Universal Seconds**- Another name for Saybolt Universal Viscosity.
**Saybolt Universal Viscosity**- The time in seconds required for 60 cubic centimeters of a fluid to flow through the orifice of the Standard Saybolt Universal Viscometer at a given temperature under specified conditions.
**Service Drag**- This is drag from air ducted to cooling components.
**Stagnation Pressure**- Another name for Dynamic Pressure.
**Static Pressure**- A measure of the resistance of airflow through a system.
**Supercritical Fluid**- A fluid state that occurs when the pressure and temperature exceed the substance′s critical pressure and critical temperature.
**Total Pressure**- Another name for Dynamic Pressure.
**Turbulence**- Describes fluid motion disturbed from its average behaviour by random fluctuations over a range of temporal and spatial scales.
**Turbulent Boundary Layer**- Within this layer the Reynolds stresses are much larger than the viscous stresses.
**Vehicle Aerodynamic Drag**- Resistance of a vehicle body to motion through the air.
**Velocity Pressure**- The difference between dynamic pressure and static pressure.
**Viscosity**- A measure of the internal friction within a fluid.
**Viscosity Grade**- Any of a number of systems which characterize lubricants according to viscosity for particular applications.
**Viscosity Index**- An arbitrary measure for the change of kinematic viscosity with temperature.
**Viscosity Index Improvers**- Additives that increase the viscosity of the fluid throughout its useful temperature range.
**Viscosity Modifier**- Lubricant additive, usually a high molecular weight polymer, that reduces the tendency of an oil′s viscosity to change with temperature.
**Viscous**- Possessing viscosity. Frequently used to imply high viscosity.
**Viscous Flow**- The flow of fluid through a duct under conditions such that the mean free path is very small in comparison with the smallest dimension of a transverse section of the duct.
**Viscous Fluid**- A fluid whose molecular viscosity is sufficiently large to make the viscous forces a significant part of the total force field in the fluid.
**Viscous Force**- The force per unit volume or per unit mass arising from the action of tangential stresses in a moving viscous fluid.
**Weight Flow Rate**- Mass flow rate multiplied by gravity.

**Subjects: ** Mechanical Engineering Physics