ME 406 Fluid Mechanics - mod 1

Fluid Mechanics

Physical science that studies fluids at rest or in motion and their engineering applications.

Fluid Statics

Branch of fluid mechanics that deals with fluids at rest.

Fluid Dynamics

Branch of fluid mechanics concerned with fluids in motion.

Hydrodynamics

Study of liquid flow or low-velocity gas flow where the gas behaves as incompressible.

Hydraulics

Application of fluid mechanics to engineering devices involving liquids, such as pipes, pumps, turbines, nozzles, and flowmeters.

Ideal Fluid

Hypothetical fluid with zero viscosity, incompressibility, uniform velocity distribution, and no turbulence or friction.

Real Fluid

Actual fluid that exhibits viscosity, compressibility, non-uniform velocity distribution, friction, and possible turbulence.

Newtonian Fluid

Real fluid whose shear stress is directly proportional to shear rate; examples include water, air, steam, and simple liquids.

Non-Newtonian Fluid

Fluid whose shear stress–shear rate relationship deviates from Newton’s law, including pseudoplastic, dilatant, and Bingham fluids.

Pseudoplastic Fluid

Shear-thinning non-Newtonian fluid whose viscosity decreases with applied stress; e.g., blood or cornstarch suspension.

Dilatant Fluid

Shear-thickening non-Newtonian fluid whose viscosity increases with applied stress; e.g., quicksand, bullet-proof vest slurry.

Bingham Fluid

Viscous fluid possessing a yield strength that must be exceeded before it flows; e.g., lava.

Mass Density (ρ)

Mass per unit volume of a fluid; units: kg/m³ (SI), slug/ft³ (English), g/cm³ (metric).

Specific Volume (Vs)

Volume occupied by a unit mass of fluid; inverse of density (Vs = 1/ρ).

Specific Weight (γ)

Weight per unit volume of a fluid; γ = ρg.

Specific Gravity (SG)

Dimensionless ratio of a fluid’s density to a reference density (water for liquids, air for gases).

Viscosity (Dynamic Viscosity, μ)

Measure of a fluid’s resistance to shear; shear stress τ = μ (dV/dy); units: Pa·s, lb·s/ft², poise (0.1 Pa·s).

Kinematic Viscosity (ν)

Ratio of dynamic viscosity to density (ν = μ/ρ); units: m²/s, stoke (10⁻⁴ m²/s).

Shear Stress (τ)

Tangential force per unit area acting within a fluid due to viscosity.

Shear Rate (dV/dy)

Velocity gradient perpendicular to flow direction that produces shear in a fluid.

Surface Tension (σ)

Cohesive ‘skin’ on a liquid surface caused by intermolecular forces; responsible for droplet shape and capillary action.

Cohesion

Attraction between like fluid molecules that keeps them attached to each other.

Adhesion

Attraction between fluid molecules and a solid boundary, allowing wetting of surfaces.

Capillarity (Capillary Action)

Rise or fall of a liquid in a small-bore tube due to surface tension and balance of adhesion and cohesion.

Contact Angle (θ)

Angle between liquid surface and tube wall indicating wetting; θ

Compressibility (β)

Fractional change in fluid volume per unit pressure change at constant temperature.

Bulk Modulus of Elasticity (EB)

Measure of a fluid’s resistance to compression; EB = Δp · (V/ΔV).

Sonic Velocity (Pressure-Wave Celerity)

Speed at which a pressure disturbance propagates through a fluid.

Ideal Gas Law

Equation of state for ideal gases, pV = mRT, relating pressure, volume, temperature, and gas constant.

Adiabatic Exponent (k)

Ratio of specific heats (cp/cv) used in isentropic relationships for ideal gases.

Vapor Pressure

Equilibrium pressure exerted by vapor molecules above a liquid at a given temperature.

Volatile Liquid

Liquid possessing significant vapor pressure at normal temperatures, boiling easily.

Poise

CGS unit of dynamic viscosity; 1 poise = 0.1 Pa·s.

Stoke

CGS unit of kinematic viscosity; 1 stoke = 10⁻⁴ m²/s.

Capillary Rise/Depression

Height a liquid rises or falls in a capillary tube, h = (4σ cos θ)/(γd) for complete wetting (θ=0°).