Drag force (external forced convection)

[quessy]

Homework Statement

Air at 20kPa and 20°C flows across 5cm diameter cylinder at velocity of 20m/s. Compute the drag force exerted on the cylinder

Homework Equations

the formula should be use is this, FD = CD*A*den*V^2 / 2
where FD & CD is the drag force and drag coefficient, respectively

The Attempt at a Solution

i already have density & velocity. my questions are:

1.) I am a little confuse (pls don't laugh)..the cylinder is exposed to the flowing air right? or is the air flowing inside the cylinder?

2.) for the area A, based on my references it is the frontal area which is L*D, the length is not given what should i do?

3.) my way in solving for the drag coeff is to solve first for the reynolds number and refer to the figure provided in the book..am i doing it right? is it accurate?

thank you! :)

 

[KataKoniK]

1. Based on the given information, it seems like the air is flowing across the cylinder, which means the cylinder is exposed to the air flow.

2. In this case, since the diameter of the cylinder is given (5cm), you can use the formula for the area of a circle (A = πr^2) to calculate the frontal area. In this case, the radius would be 2.5cm, so the frontal area would be approximately 19.63 cm^2.

3. Yes, calculating the Reynolds number and referring to a figure or table for the drag coefficient is a common method for estimating drag force. However, it is important to note that this method may not be completely accurate, as the actual drag force can be affected by other factors such as surface roughness and turbulence. It is always best to use experimental data or simulations to get a more accurate estimation of drag force.