4 Fundamental Thoughts

4 Fundamental Thoughts - "A Flowing Gas"...

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“A Flowing Gas” Continuum Mechanics Continuum Mechanics Fluid Mechanics Fluid Mechanics Solid Mechanics Solid Mechanics Aerodynamics Aerodynamics Hydrodynamics Hydrodynamics • Aerodynamics is a special subset of Fluid Mechanics, which in turn is a subset of Continuum Mechanics • Aerodynamics is a special subset of Fluid Mechanics, which in turn is a subset of Continuum Mechanics
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Four Aerodynamic Quantities • Pressure Force per unit area: N/m 2 , lb/in 2 , lb/ft 2 •Den s i ty Mass per unit volume: kg/m 3 , slug/ft 3 • Temperature Measure of average kinetic energy •Ve loc i ty A vector quantity: ft/s, m/s, mi/hr, km/hr • Pressure Force per unit area: N/m 2 , lb/in 2 , lb/ft 2 •Den s i ty Mass per unit volume:
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Pressure • “Pressure is the normal force per unit area exerted on a surface due to the time rate of change of momentum of the gas molecules impacting on that surface.” • The concept of “force” arises from Newton’s 2 nd Law: F = m a or F = d(mv)/dt or F = m dv/dt mv is the momentum or linear momentum • Pressure varies from point to point p = lim dF/dA as dA 0 • Pressure depends on position and time: p = p(x,y,z,t) where t- dependence unsteady flow p = p(x,y,z) where no t- dependence steady flow • “Pressure is the normal force per unit area exerted on a surface due to the time rate of change of momentum of the gas molecules impacting on that surface.” • The concept of “force” arises from Newton’s 2 nd Law: F = m a or F = d(mv)/dt or F = m dv/dt mv is the momentum or linear momentum • Pressure varies from point to point p = lim dF/dA as dA 0 • Pressure depends on position and time: p = p(x,y,z,t) where t- dependence unsteady flow p = p(x,y,z) where no t- dependence steady flow dF dA gas B
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Density •“The densityof a substance (including a gas) is the mass of that substance per unit volume.” • The concept of density obviously combines the concepts of mass and volume • Density varies from point to point ρ = lim (dm/dv) as dv
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4 Fundamental Thoughts - "A Flowing Gas"...

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