Forward/rearward engine gas loads

[Flight_Idle]

Although not an engine tradesman myself, I have long been curious about the forward rearward gas loads on an engine with reheat.

Most online explanations just mention the change of momemtum resulting in forward thrust, without giving detailed explanations on the resultant areas of gas loads throughout the engine.

I have seen diagrams of a typical old axial flow engine like the RR Avon, with large forward gas loads in the compressor & combustion chamber areas, & lesser rearward gas loads in the turbine area, with the addition of a further rearward gas load in the exit nozzle (Closed position) area.

But the bit that puzzles me is.... When reheat is selected, all you are doing if relieving the rearward gas load in the nozzle area, thus contributing to the total forward thrust, but if the nozzle sticks in the open position without reheat, you get less than normal dry thrust.

Yet I have not been able to find an explanation of the new gas loads (In the unusual non reheat, nozzle open situation)

So, we have relieved a rearward gas load (By having the nozzle stuck open) but we are getting less thrust. So we must have a situation where we have reduced the forward gas loads somehere in the engine. Any idea where?

I have read that the engine should be 'Unaware' if the reheat is active or not. There are some good diagrams of gas loads in the Rolls Royce book, but they do not illustrate the loads in the 'Nozzle open, reheat off scenario'

I hope that makes sense.

Regards, Flight Idle.