Conditional symmetries and Riemann invariants for inhomogeneous hydrodynamic-type systems

TL;DR

This paper introduces a novel method combining conditional symmetries and Riemann invariants to solve complex inhomogeneous hydrodynamic PDEs, providing new solutions and insights into fluid dynamics under external forces.

Contribution

It develops a systematic approach for constructing rank-2 and rank-3 solutions using Riemann invariants and symmetry methods, applicable to inhomogeneous hydrodynamic systems.

Findings

Derived necessary and sufficient conditions for solutions in terms of Riemann invariants.

Reduced the solution construction to trace conditions on wave vectors.

Obtained several new rank-2 solutions with physical interpretations.

Abstract

A new approach to the solution of quasilinear nonelliptic first-order systems of inhomogeneous PDEs in many dimensions is presented. It is based on a version of the conditional symmetry and Riemann invariant methods. We discuss in detail the necessary and sufficient conditions for the existence of rank-2 and rank-3 solutions expressible in terms of Riemann invariants. We perform the analysis using the Cayley-Hamilton theorem for a certain algebraic system associated with the initial system. The problem of finding such solutions has been reduced to expanding a set of trace conditions on wave vectors and their profiles which are expressible in terms of Riemann invariants. A couple of theorems useful for the construction of such solutions are given. These theoretical considerations are illustrated by the example of inhomogeneous equations of fluid dynamics which describe motion of an ideal fluid subjected to gravitational and Coriolis forces. Several new rank-2 solutions are obtained. Some physical interpretation of these results is given.