Aeroengines/Fluid Mechanics - Steady Flow

JRS192

Homework Statement

See Fig.2.4a, let the gases flowing through the nozzle control volume be perfect with Cp = 1.004kJ/kg.K

Determine V9 if T5 = 1000K, T9 = 670K and V5 = 120ms^-1.

Homework Equations

I've detailed the equations in the attached pdf for clarity.

The Attempt at a Solution

See attached pdf. The question paper has the answer as 822.8m/s, but I'm consistently getting 120m/s. Where am I going wrong?

Thank you

Attachments

• Fig2.4a.png
47.3 KB · Views: 437
• doc00586420150126151206.pdf
329.4 KB · Views: 159

Staff Emeritus
Homework Helper
You've confused the universal gravitational constant G for the acceleration due to gravity on earth, gc.
It's not clear why you don't understand the distinction between these two constants.

JRS192
Hi SteamKing,

Thanks for that. I did some research and everything directed me to that figure, even to the point of using gc...

Staff Emeritus
Homework Helper
Hi SteamKing,

Thanks for that. I did some research and everything directed me to that figure, even to the point of using gc...

I doubt that. You have misinterpreted something in what you read.

The universal gravitational constant G (which is invariably capitalized) is typically used to find the force of gravitational attraction between two masses, as described by the formula

F = Gm1m2/r2

G is used more often in physics type calculations. G also has some rather unusual units: G = 6.67*10-11 m3/kg-s2

The acceleration due to gravity on earth, gc, which is invariably lower case, is typically commonly found in engineering type calculations, more so than G.

JRS192
Thank you for your help.