Fluid Mechanics - Drag coefficient and Pressure coefficient

In summary, the speaker is working on a lab about pressure variation normal to streamlines. They have data points for Cp vs Theta and now need to calculate Cd using an integral they found online. However, they have found out that their calculated value for Cd should be higher and are asking for assistance in determining if there is another relationship between Cp and Cd.
  • #1
hammacks
1
0
Hey guys,
I'm working on a lab here about pressure variation normal to streamlines. For the last experiment, there is airflow around a cylinder with a static pressure tap. The pressure tap records Cp (divides by dynamic pressure) and angle of rotation.

I have data points for Cp vs Theta (10° increments) that looks great, just like it should. Now I need to calculate Cd. After looking on the web a lot I found something that said

Cd=.5*INT(Cp*cos(x) dx, 0, 360(or 2pi))

I have computed this integral as an area under the curve both in Excel as Riemmen Sums and with a fit line on my calculator. Both ways I get answers around 30. I thought I was fine...

Now I have a lab due tomorrow and found out Cd should be more like 1.1 or so. Any ideas? Is there another relationship between Cp and Cd?
 
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  • #2
The expression for drag coefficient looks good. What are your (theta, Cp) values?

--
Chusslove Illich (Часлав Илић)
 

1. What is the drag coefficient in fluid mechanics?

The drag coefficient is a dimensionless quantity that represents the amount of drag or resistance an object experiences when moving through a fluid, such as air or water. It is dependent on factors such as the shape, size, and speed of the object, as well as the properties of the fluid.

2. How is the drag coefficient calculated?

The drag coefficient can be calculated using the formula Cd = Fd / (0.5 * ρ * V^2 * A), where Cd is the drag coefficient, Fd is the drag force, ρ is the density of the fluid, V is the velocity of the object, and A is the reference area of the object.

3. What is the relationship between the drag coefficient and the pressure coefficient?

The pressure coefficient, Cp, is a measure of the pressure distribution around an object in a fluid. There is a direct relationship between the drag coefficient and the pressure coefficient, as the distribution of pressure on an object affects the amount of drag it experiences. A lower drag coefficient usually corresponds to a lower pressure coefficient and vice versa.

4. How does the drag coefficient affect the motion of an object?

The drag coefficient plays a significant role in determining the motion of an object in a fluid. A higher drag coefficient means there is more drag acting on the object, which can slow it down or even cause it to come to a stop. On the other hand, a lower drag coefficient means less drag, allowing the object to move more easily through the fluid.

5. What factors can affect the drag coefficient?

The drag coefficient can be influenced by several factors, including the shape and size of the object, the speed at which it is moving, and the properties of the fluid, such as density and viscosity. Other factors such as surface roughness and the presence of obstacles can also affect the drag coefficient.

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