# Why do we take into consideration holes for pressure thrust in jet engine calculations?

In many sources related to jet engine thrust calculations such as https://www.jet-x.org/a8.html , pressure thrust of a module such as combustion chamber, nozzle or compressor, is calculated by front and rear cross sectional area of them (including holes at their center) and flow pressure at front and rear of them.

If they were a complete solid disc without any hole, I could understand this calculation.

However, for turbine in an example, it has a hole at rear and front, so either pressure at rear can't act on the hole at rear or pressure at front can't on the hole at front. In my opinion, these holes should be taken out of cross sectional area term.

Why do we think as if fluid pressure is able to act on the whole cross sectional area including holes at the center whereas they can't physically?

• Can you be more specific? The linked source is very long. Which portion do you think is wrong? And what do you think the correct answer should be? E.g. In section x they use use area Y m^2 but you think it should be area Z Jun 7 at 16:46
• A diagram might help understand your question. Jun 7 at 20:59
• Specifically, where do you see the page state the cross-sectional area includes the “holes” (which are in fact opposite of holes, because it's the body with the shaft)? I only see them say “nozzle cross-sectional area” and that is just the area of the nozzle itself (which has annular shape). Jun 7 at 21:34