Final Exam Flashcards
What does dimensionally homogenous mean?
units on left hand side equal units on right hand side
Out of the following parameters, which are the hardest to vary? V, D, rho, mu (lec slides)
rho is hard to vary w/ ot changing mu and vice versa
What the the 3 necessary similarity conditions between a model and a prototype?
1) Geometric Similarity: the model needs to have the same shape as the prototype (just scaled)
2) Kinematic Similarity: thw velocity/acc. at a certain point in the model flow must be proportional to the corresponding point in the prototype flow
3) Dynamic Similarity: the forces acting in the model flow must be scaled by a constant factor to corresponding forces in the prototype flow
When are similitude pi term not equal?
in distorted models (for ex. if a suitable fluid cannot be found for the model)
What are the two components of external flow around objects?
Drag: force parallel to velocity
Lift: forces perp. to velocity
What are the two forces that describe the interaction between the fluid and body?
1) wall shear stress due to viscous forces
2) normal shear stress due to pressure perp. to the body
What do the drag and lift magnitude depend on?
1) Shape of the object (streamline vs bluff)
2) Orientation of the object (angle of attack)
Define frontal area and planform area.
frontal area: area as seen by somebody looking at the object in the direction of approaching flow
planform area: area as sees by somebody looking at the object from above in a direction normal to the body
What is CL dependent on?
1) Pressure forces
2) Geometry of object
3) Roughness
4) Angle of attack
5) Reynolds number
What does the flow separation location depend on?
1) Reynold’s #
2) Geometry
3) Surface Roughness
4) amount of turbulence
What causes flow separation?
high velocity and sharp edges
The larger the wake region is the _______?
the higher the pressure drag is
What is a wake region?
zone of turbulence and low pressure
Define Vortices:
the formation and shedding of circular fluid structures in the wake region
Define Vortex Shedding:
the periodic generation of vortices downstream
What is conudction?
heat transfer through a solid or a stationary fluid.
energy passed by molecular interaction
What is convection?
heat transfer from surface to fluid
conduction + advection = convection
What does the convection heat transfer coefficient depend on?
fluid prop., geometry, flow regime
What is radiation?
heat transfer in the form of electromagnetic waves, travels through a vacuum
What is a black body?
emission of max. radiation (emissivity = 1), ideal emitter
if epsilon < 1, then surface is a non-ideal emitter
What are the three types of convection?
Free Convection: set up by buoyancy due to difference in density
Forced Convection: due to external means (fan, wind)
Mixed Convection: due both buoyancy forces and forced flow
What is qmax^’’?
maximum heat flux rate / radiation heat energy emitted from a unit area in one second
What does emissivity depend on?
surface finish and material
