Sufficient condition for finite-time singularity and tendency towards self-similarity in a high-symmetry flow

A highly symmetric Euler flow, first proposed by Kida (1985), and recently simulated by Boratav and Pelz (1994) is considered. It is found that the fourth order spatial derivative of the pressure (p_xxxx) at the origin is most probably positive. It is demonstrated that if p_xxxxgrows fast enough, there must be a finite-time singularity (FTS). For a random energy spectrum E(k) ∝ k^-v, a FTS can occur if the spectral index v < 3. Furthermore, a positive p_xxxx has the dynamical consequence of reducing the third derivative of the velocity u_xxx at the origin. Since the expectation value of U_xxx is zero for a random distribution of energy, an ever decreasing u_xxx means that the Kida flow has an intrinsic tendency to deviate from a random state. By assuming that U_xxx reaches the minimum value for a given spectral profile, the velocity and pressure are found to have locally self-similar forms similar in shape to what are found in numerical simulations. Such a quasi self-similar solution relaxes the requirement for FTS to v < 6. A special self-similar solution that satisfies Kelvin's circulation theorem and exhibits a FTS is found for v = 2.