Confused with static pressure and total pressure and Bernoulli's eq

In summary, the conversation is about calculating the pressure at a point on an airplane's wing. The equation p1+1/2(rou)(v1)^2=p2+1/2(rou)(v2)^2 is used, with p1 representing the static pressure at a standard altitude of 3km and p2 representing the total pressure at the point on the wing with a velocity of 70m/s. The confusion lies in understanding static, dynamic, and total pressure. The table given in the solution refers to the static pressure at the standard altitude of 3km. Dynamic pressure is the pressure exerted by a fluid in motion, while total pressure is the sum of static and dynamic pressure.
  • #1
degredationz
6
0
hi all, am a confused-being after trying to solve this really simple question..
somewhere somehow my concepts are just not right ):

Consider an airplane flying with a velocity of 60m/s at a standard altitude of 3km. At a point on the wing, the airflow velocity is 70m/s. Calculate the pressure at this point.

By using p1+1/2(rou)(v1)^2=p2+1/2(rou)(v2)^2 and the standard atmospheric pressure table, the given solution is
7.0121 X 10^4 + 1/2(9.0926X10^(-1))(60^2)/2 = P2 + 9.0926X10^(-1)(70^2)/2
I do not understand why P1 = 7.0121 x 10^4 N (given in the table), where P1 should be the pressure at the point of the flow where velocity is 60m/s.
What is the pressure given in the table referred to as?
I am confused with static/dynamic and total pressure!

Would any kind soul please help?
Thanks a lot in advance!
 
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  • #3


Hi there, it seems like you're having trouble understanding the concept of pressure in relation to airflow. Let me try to break it down for you.

First, let's define some terms. Static pressure is the pressure exerted by a fluid (in this case, air) on a solid surface when it is at rest. Dynamic pressure is the pressure exerted by a fluid on a solid surface when it is in motion. Total pressure is the sum of static and dynamic pressure.

In this scenario, the point on the wing is experiencing a velocity of 70m/s, which means that the air is in motion. This is known as dynamic pressure. The table is giving you the value of static pressure at the standard altitude of 3km, which is 7.0121 x 10^4 N. This means that at rest, the air at this altitude exerts a pressure of 7.0121 x 10^4 N on a solid surface.

Now, let's use the equation you mentioned: p1+1/2(rou)(v1)^2=p2+1/2(rou)(v2)^2. This equation is used to calculate total pressure at two different points in a fluid flow.

In this case, we are looking at the total pressure at the point on the wing where the airflow velocity is 70m/s. So, p2 is the total pressure at this point, which we are trying to find. And p1 is the total pressure at the standard altitude of 3km, which we already know is 7.0121 x 10^4 N from the table.

The equation is essentially saying that the total pressure at one point (p1) plus the dynamic pressure (1/2(rou)(v1)^2) is equal to the total pressure at another point (p2) plus the dynamic pressure at that point (1/2(rou)(v2)^2). By rearranging the equation, we can solve for p2, which is the total pressure at the point on the wing where the airflow velocity is 70m/s.

I hope this helps to clarify things for you. Let me know if you have any other questions or if anything is still unclear. Good luck!
 

What is the difference between static pressure and total pressure?

Static pressure is the pressure exerted by a fluid at rest, while total pressure is the sum of both static pressure and dynamic pressure (pressure due to the fluid's motion).

How is Bernoulli's equation related to static pressure and total pressure?

Bernoulli's equation describes the relationship between the pressure, velocity, and height of a fluid in a continuous and non-viscous flow. It takes into account both static pressure and total pressure.

What is the significance of static pressure and total pressure in fluid dynamics?

Static pressure and total pressure are important parameters in fluid dynamics as they help determine the behavior of fluids in motion. They are used to calculate factors such as flow rate, velocity, and energy conservation in a fluid system.

Can static pressure be greater than total pressure?

No, static pressure cannot be greater than total pressure. This is because total pressure includes both static and dynamic pressure, and the sum of these two pressures cannot exceed the total pressure.

How are static pressure and total pressure measured in a fluid system?

Static pressure is typically measured using a pressure gauge or manometer, while total pressure is measured using a Pitot tube. A Pitot tube measures the total pressure by subtracting the static pressure from the total pressure at a specific point in the fluid flow.

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