Find the thrust from the engine

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SUMMARY

The forum discussion focuses on designing a static thrust stand for testing a jet engine, specifically calculating the thrust produced under given inlet and outlet conditions. The inlet area is 1 m2 with a velocity of 250 m/s and a gage static pressure of -22.5 kPa, while the outlet conditions include an exhaust gas velocity of 444 m/s, a gage static pressure of 0 kPa, and a temperature of 268 K. The calculated thrust force is 402.5 kN, derived using the equation F = P2A2 based on total pressure values of 15.78 kPa and 120.75 kPa at the inlet and outlet, respectively. The discussion raises questions about the assumptions made and the applicability of Bernoulli's equation in this context.

PREREQUISITES
  • Understanding of fluid dynamics principles, particularly Bernoulli's equation
  • Knowledge of static and dynamic pressure concepts
  • Familiarity with thrust calculation methods in jet propulsion
  • Basic grasp of thermodynamics, specifically gas behavior under varying pressures and temperatures
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  • Study the application of Bernoulli's equation in jet propulsion systems
  • Learn about the principles of mass flow rate in fluid mechanics
  • Explore the relationship between thrust and momentum change in jet engines
  • Investigate advanced thrust measurement techniques for jet engines
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Aerospace engineers, mechanical engineers, students in fluid dynamics, and professionals involved in jet engine testing and design will benefit from this discussion.

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Homework Statement


A static thrust stand is to be designed for testing a jet engine. The inlet conditions for the test are an inlet area of 1 {m2}, inlet velocity of 250 {m/s}, and gage static pressure of -22.5 {kPa}. The expected conditions at the 0.3 {m2} outlet are an exhaust gas velocity of 444 {m/s}, gage static pressure of 0 {kPa} and temperature of 268 {K}. Find the thrust the engine produces. Assume constant mass flow rate through the engine (i.e. mass of fuel in negligible) and that the gauge pressure is atmospheric pressure

Homework Equations

The Attempt at a Solution


First I calculated the total pressure entering and exiting the turbine:
(ρv2/2)+P+ρgh=Ptotal

The first term being dynamic pressure, the second being static pressure, and the third being hydrostatic pressure. I assumed hydrostatic pressure was negligible since I was given no information about the height.

Ptotal,1=15.78 kPa
Ptotal,2=120.75 kPa

Then I used F=P2A2
And found the force to be 402.5 kN

Does what I did make sense? I'm not really sure if this is the proper way to find the force of the thrust.
 
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Bernoulli's equation is based on conservation of energy. I would guess the engine is adding quite a bit.
What is the mass flow rate?
What is the rate of change of momentum of the air flowing through?
 

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