Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Thrust calculation is incorrect when core or bypass are choked #95

Open
ngomezve opened this issue Oct 25, 2024 · 0 comments
Open

Thrust calculation is incorrect when core or bypass are choked #95

ngomezve opened this issue Oct 25, 2024 · 0 comments

Comments

@ngomezve
Copy link
Contributor

ngomezve commented Oct 25, 2024

In tfsize(), the core mass flow rate is calculated using
$$\dot{m}_c = \frac{F_e-F_i}{(1-f_o+f_f)u_6 - u_0 + BPR(u_8-u_0)+f_0 u_9}$$,
where the far-wake speeds $u_6$ and $u_8$ are calculated by isentropically expanding the nozzle flow to ambient pressure. If the nozzles are only convergent, this equation is incorrect if either stream is choked.

The thrust equation for a turbofan engine with a convergent nozzle is, using the TASOPT station notation,
$$F_e = F_i+ \dot{m}_c\left[(1-f_o+f_f) u_5- u_0+BPR(u_7 - u_0) + f_0 u_9\right] + A_5(p_5-p_0)+A_7(p_7-p_0)$$,
where stations 5 and 7 are the core and fan nozzle throats.

If the nozzle is not choked and the flow expands to atmospheric pressure, the TASOPT calculation is correct as the pressure terms will drop to 0. Otherwise, they have to be included. The calculation in TASOPT would be equivalent to a variable-area convergent-divergent nozzle whose pressure is always matched.

https://github.com/MIT-LAE/TASOPT.jl/blob/36196792dfac68bc83ac1f821eaa8a3142db0e1e/src/engine/tfsize.jl#L629C13-L630C76

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
None yet
Projects
None yet
Development

No branches or pull requests

1 participant