Two-dimensional jet flow into an unequal pressure field through a convergent nozzle with straight walls is analized here. Although the analysis is carried out with the object of getting fundamental data to the performance of annular jet type GEM, the existence of the ground is neglected here, because of tremendous difficulty in calculus, which arises by taking the ground into account from the outset. It is also assumed, for mathematical simplicity, that the convergent angle of the nozzle is a moderate one, so that there is neither positive pressure gradient along the nozzle walls, nor inflexion point along the free stream lines, and that the nozzle wall ends are situated on the same equi-potential line of flow.
The calculation is pursued by expansion of power function, making use of the relation γ(the nozzle convergent angle)<<π. As the results, geometric patterns of flow, volumetric flow and power are obtained.
The results obtained here, are of ideal character, especially so in neglecting the existence of the ground. Nevertheless, they will serve as criterions for the actual effect of jet in annular jet type GEM, and the procedure of approximation developed here may be extended to the cases in which above assumptions are not set up, and further to the cases in which the ground exists.