Object’s speed and its heating temperature

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Discussion Overview

The discussion centers on the heating temperature of objects, such as asteroids or spacecraft, as they travel at high velocities through Earth's atmosphere. Participants explore the factors influencing heating, including speed, atmospheric density, and object geometry, and seek methods to calculate or estimate the resulting temperatures at various altitudes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Some participants note that calculating heating temperature is complex and specific to the object's geometry and other properties.
  • One participant suggests that a rough estimate could be made by examining drag force, which is influenced by friction and contributes to heating.
  • Another participant mentions the need to find the drag coefficient for the object to proceed with calculations.
  • Participants discuss the use of online calculators and resources for determining drag coefficients and stagnation temperatures.
  • One participant raises a specific scenario involving a long, thin rod at various angles of attack and seeks clarification on the properties of gases relevant to Earth's atmosphere.
  • There is a question regarding the validity of calculated temperatures across different altitudes in the atmosphere.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of calculations based on object geometry and the specific conditions of the atmosphere. There is no consensus on a single method or formula that applies universally across all scenarios discussed.

Contextual Notes

Participants mention limitations regarding the assumptions made about gas properties (calorically perfect vs. imperfect gases) and the specific altitude ranges for which calculations may be valid.

Eagle9
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When some certain object (asteroid, aircraft, spaceship and etc.) moves at great velocities into Earth’s atmosphere it heats. The faster its moves and the denser is the atmosphere the heater this certain object becomes. This is simple is clear. Now, is it possible somehow to predict or calculate this heating temperature? For instance, the object moves at the speed of 975 meter/sec at the altitude of 80 km above the sea level, can we calculate its heating temperature? Are there some formulas in Physics or ready-made charts/diagrams for this purpose? I need this data for the altitude of 0-160 km above the see level…:wink:
 
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No easly calculation: it is specific to the geometry (and other properties) of the object.
 
russ_watters said:
No easly calculation: it is specific to the geometry (and other properties) of the object.

Well, let’s assume that it is long tube with the diameter of 5 meters, now it could be calculated?:wink:
 
You might be able to get a rough estimate by looking at the drag force. The drag is caused by several things, but friction is one, and that is what causes the heating. Force time velocity gives your heating power. So, you need to look up the drag coefficient for the object in question.
 
kcdodd said:
You might be able to get a rough estimate by looking at the drag force. The drag is caused by several things, but friction is one, and that is what causes the heating. Force time velocity gives your heating power. So, you need to look up the drag coefficient for the object in question.

So, if I understood correctly I need to find the drag coefficient? And where is it possible to find it? Are there some ready-made charts?
 
Look for: skin friction coefficient, supersonic drag, slender body

Here is an online calculator for a flat plate(link at bottom of the page):
http://adg.stanford.edu/aa241/drag/skinfriction.html

The drag for given air density, velocity, surface area, friction coefficient is:

D = 0.5 \rho v^{2} S C_{f}

Just to get an idea:
The SR-71 has surface temperatures above 300 degrees celsius at 980m/s(MACH 3.2) and 24km height.

Edit:
You might try to find some surface temperature data from the X-15 program.
 
Last edited by a moderator:
nucleus said:

Ok, thank you very much, I think this is what I wanted :smile:. However, I would like to specify some issues since I am not physicist and sometimes it is a bit difficult for me to understand some problems in this science.
First of all, here is the illustration what I actually wanted to know. Imagine a long and thin rod is rotating in the atmosphere with various angles of attack. I want the result for the situation when this rod has got almost vertical position-70°, 80° or 90°.
http://img576.imageshack.us/i/engd.gif/


Frankly saying I do not know properties of which gas (calorically perfect gas or calorically imperfect gas) should be calculated for the real Earth’s atmosphere. As I know perfect gas does not exist in the nature at all, therefore I need to measure property of imperfect gas, right? I read the information presented in the web-link given by you. If I understood everything correctly I need the Total Temperature calculated in the Java calculator, right? So, as an example, I put the following values: the object moves in the atmosphere at the altitude of 80 000 meters (by the way after the calculation this value for some reason was decreased to 76 200 meters) at the speed of 975 meters/sec. After computations I saw the following result: Total Temperature is equal to 646 Kelvin degrees (for imperfect gas). Is it right? So, this object would be heated to the temperature of 646 degrees?
http://img504.imageshack.us/img504/8301/calculatoru.jpg

I have actually got one more question. For which altitudes this derived result (646 degrees K) is correct? For the whole section of the atmosphere from the seal level to the altitude of let’s say 150 km above the sea level? Or there are some limitations?
 
Last edited by a moderator:
log0 said:
Look for: skin friction coefficient, supersonic drag, slender body

Here is an online calculator for a flat plate(link at bottom of the page):
http://adg.stanford.edu/aa241/drag/skinfriction.html

The drag for given air density, velocity, surface area, friction coefficient is:

D = 0.5 \rho v^{2} S C_{f}

Just to get an idea:
The SR-71 has surface temperatures above 300 degrees celsius at 980m/s(MACH 3.2) and 24km height.

Edit:
You might try to find some surface temperature data from the X-15 program.
Ok, thank you very much, I will take look at it :smile:
 
Last edited by a moderator:

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