I had to look it up (Fluid Dynamics was not my cup of tea in college, and I've not worked with it since):

You do have to be careful about applying any one equation without knowing certain things having to do with laminar and turbulent flow (see http://en.wikipedia.org/wiki/Reynolds_number and http://en.wikipedia.org/wiki/Drag_equation).

From: http://en.wikipedia.org/wiki/Drag_(physics):

The drag equation calculates the force experienced by an object moving through a fluid at relatively large velocity (i.e. high Reynolds number, Re > ~1000), also called quadratic drag. The equation is attributed to Lord Rayleigh, who originally used L2 in place of A (L being some length). The force on a moving object due to a fluid is:

where:

is the force of drag,

is the density of the fluid,[3]

is the speed of the object relative to the fluid,

is the drag coefficient (a dimensionless parameter, e.g. 0.25 to 0.45 for a car)

is the reference area,

. . .

The power required to overcome the aerodynamic drag is given by:

Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power.

. . .

The equation for viscous resistance or linear drag is appropriate for objects or particles moving through a fluid at relatively slow speeds where there is no turbulence (i.e. low Reynolds number, Re < 1). Note that purely laminar flow only exists up to Re = 0.1 under this definition. In this case, the force of drag is approximately proportional to velocity, but opposite in direction. The equation for viscous resistance is:

where:

is a constant that depends on the properties of the fluid and the dimensions of the object, and

is the velocity of the object

You do have to be careful about applying any one equation without knowing certain things having to do with laminar and turbulent flow (see http://en.wikipedia.org/wiki/Reynolds_number and http://en.wikipedia.org/wiki/Drag_equation).

From: http://en.wikipedia.org/wiki/Drag_(physics):

The drag equation calculates the force experienced by an object moving through a fluid at relatively large velocity (i.e. high Reynolds number, Re > ~1000), also called quadratic drag. The equation is attributed to Lord Rayleigh, who originally used L2 in place of A (L being some length). The force on a moving object due to a fluid is:

where:

is the force of drag,

is the density of the fluid,[3]

is the speed of the object relative to the fluid,

is the drag coefficient (a dimensionless parameter, e.g. 0.25 to 0.45 for a car)

is the reference area,

. . .

The power required to overcome the aerodynamic drag is given by:

Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power.

. . .

The equation for viscous resistance or linear drag is appropriate for objects or particles moving through a fluid at relatively slow speeds where there is no turbulence (i.e. low Reynolds number, Re < 1). Note that purely laminar flow only exists up to Re = 0.1 under this definition. In this case, the force of drag is approximately proportional to velocity, but opposite in direction. The equation for viscous resistance is:

where:

is a constant that depends on the properties of the fluid and the dimensions of the object, and

is the velocity of the object

**Did anybody's eyes not gloss over when reading that - especially if you started digging deeper into the Reynolds number?**Now you know why I wasn't too excited about fluid dynamics. (no. 573)

'98 Concorde LXi - Candy Apple Red | Black chrome ring gages | Black Diamond headlights | Clear turns

'99 Concorde LX - Candy Apple Red | 16" Mille Miglia Cello Wheels | Raybestos PHP cryo-treated rotors | LHS electroluminescent gages

'98 Concorde LXi - Candy Apple Red | Black chrome ring gages | Black Diamond headlights | Clear turns

'99 Concorde LX - Candy Apple Red | 16" Mille Miglia Cello Wheels | Raybestos PHP cryo-treated rotors | LHS electroluminescent gages