Fundamental Definitions Flashcards
Define total pressure
Static pressure + dynamic pressure = p + 1/2rhoV^2
Define static pressure
The pressure exerted by a fluid at rest. This is the only force on a static fluid because there will be no shearing stresses.
Define dynamic pressure
½rho V^2. It is the kinetic energy per unit volume of a fluid.
Define viscosity
It is the shear stresses which are caused by colliding particles exchanging momentum.
Describe viscosity and what causes it qualitatively.
Viscosity causes friction between fluid particles and boundary walls. It introduces a resistance to motion. Qualitatively, viscosity is the resistance to motion of a fluid.
What causes the no-slip condition?
Viscosity since it causes a resistance to motion.
Define total drag.
Pressure drag + frictional drag.
Define pressure drag.
Form drag + induced drag.
Define parasitic drag.
Frictional drag + form drag.
Define centre of pressure.
The point at which the resultant force due to the pressure distribution acts.
How does CoP vary with AoA?
As AoA increases, the CoP moves forward, and vice versa.
Define Bernoulli’s equation.
p + pdyn (+rhogh) = constant along a streamline
Define Bernoulli’s equation for a real flow.
p1 +pdyn1 = p2 + pdyn2 + deltaploss
What causes pressure loss along a streamline?
Any work on the flow causes losses due to viscous effects.
Define total pressure coefficient.
(static gauge pressure + dynamic pressure) / freestream dynamic pressure = energy at a point / energy in freestream (since pfreestream = 0)
Define pressure coefficient.
(static pressure - freestream static pressure) / freestream dynamic pressure
What causes CpT to vary?
Without the total pressure drop, CpT always = 1. So CpT is actually just a function of total pressure drop! In other words, CpT is just a function of how much energy is lost to friction etc., which explains why we lost CpT when accelerating flow: because of the shear forces etc. that the flow experiences.
