半空間蒸発流に対する擬定常解の存在とその構成について

In dimensionally degenerate source flow problems in an infinite space such as half-space evaporation flows or source flows, the steady state solutions which satisfy the specified conditions at the boundary surface and at infinity do not exist. This is a well known fact. So far, the common understanding of this phenomenon of solution non-existent would be that the flow field of such kind never attains the steady state because the shock wave, which is produced at the same time with the onset of the evaporation process or source flow at the surface of the boundary, still remains and keeps propagating in an infinitely far field even after an elapse of infinitely large times. Of course, the transient or unsteady solution, in a strict sense, should surely exist. However, with the consideration of only the existence of shosk wave at infinity, the transient solution after an elapse of infinitely large times, which is called here the pseudo-steady state solution, can not be properly constructed. The present study reveals that, in addition to the shock wave, the contact region (contact surface in Euler terms, i.e., inviscid flows) also plays an important role in the formation of the flow field at all times. The contact region and the shock wave initially produced at the same time with the onset of the flow keep moving and propagating indefinitely in time and space, persisting forever at infinity. With the persistently existing contact region following the shock wave properly taken into account at infinity, one can construct a set of solutions, which might be considered to be the one for its virtually steady state. This is what the present study is concerned with.