## Motion of uniformly advancing piston.(English)Zbl 07453767

Summary: We study, in a unified manner the motion of a uniformly advancing piston in the planar $$(m=0)$$, cylindrically symmetric $$(m=1)$$ and spherically symmetric $$(m=2)$$ isentropic flow governed by Euler’s equations. In the three dimensional space the piston is replaced by an expanding cylinder or a sphere which produces a motion in the medium outside. Under the hypothesis of self symmetry pair of ordinary differential equations is derived from Euler’s equations of fluid flow. Based on the analysis of critical solutions of this system of ordinary differential equations, unified treatment of motion of uniformly advancing piston is given with different geometries viz. planar, cylindrically symmetric and spherically symmetric flow configuration. In case of nonplanar flows, solutions in the neighbourhood of nontransitional critical points approach these critical points in finite time. Transitional solutions exist in nonplanar cases which doesn’t correspond to the motion of a piston. In the planar case, it is found that solutions take infinite time to reach critical line.

### MSC:

 35Q31 Euler equations 35L65 Hyperbolic conservation laws 35J70 Degenerate elliptic equations 35R35 Free boundary problems for PDEs 35J65 Nonlinear boundary value problems for linear elliptic equations
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### References:

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