Chapter 9 Flashcards
Drag
The resultant force in the direction of the upstream velocity.
Lift
The resultant force normal to the upstream velocity.
Lift Coefficient
CL=L/((1/2)ρU2A)
Drag Coefficient
CD=D/((1/2)ρU2A)
Wake Region
Region of recirculating flow immediately behind a moving or stationary solid body, caused by the flow of surrounding fluid around the body.
Region of disturbed flow (usually turbulent) downstream of a solid body moving through a fluid, caused by the flow of the fluid around the body.
Wake Region
Boundary Layer
The layer of fluid in the immediate vicinity of a bounding surface where the effects of viscosity are significant.
Laminar Boundary Layer
A laminar boundary layer is one where the flow takes place in layers, i.e., each layer slides past the adjacent layers.
Turbulent Boundary Layer
There is an intense agitation. A turbulent boundary layer is marked by mixing across several layers of it.
boundary layer thickness
The boundary layer thickness, δ, is the distance across a boundary layer from the wall to a point where the flow velocity has essentially reached the ‘free stream’ velocity.
transition
is where the laminar B.L. is going to a turbulent B.L. and occurs at a critical value of the Reynolds number, Rexcr on the order of 2x105 to 3x106 which is dependant on the roughness of the surface and the amount of turbulence in the upstream flow.
free-stream velocity
The air/fluid far upstream of an aerodynamic body, that is, before the body has a chance to deflect, slow down or compress the air.
favorable pressure gradient
A decrease of pressure in the direction of flow.
adverse pressure gradient
Occurs when the static pressure increases in the direction of the flow.
boundary layer seperation
Flow separation occurs when the boundary layer travels far enough against an adverse pressure gradient that the speed of the boundary layer relative to the object falls almost to zero. The fluid flow becomes detached from the surface of the object, and instead takes the forms of eddies and vortices.
friction drag
Caused by the friction of a fluid against the surface of an object that is moving through it. It is directly proportional to the area of the surface in contact with the fluid and increases with the square of the velocity.
pressure drag
The dominant component in the case of vehicles with regions of separated flow, in which the pressure recovery is fairly ineffective. The friction drag force, which is a tangential force on the aircraft surface, depends substantially on boundary layer configuration and viscosity.
stall
A reduction in the lift coefficient generated by a foil as angle of attackincreases. This occurs when the critical angle of attack of the foil is exceeded.
circulation
Is the line integral around a closed curve of the velocity field.
Magnus Effect

A particular manifestation of Bernoulli’s theorem: fluid pressure decreases at points where the speed of the fluid increases. In the case of a ball spinning through the air, the turning ball drags some of the air around with it.