The standard κ-ϵ equations and other turbulence models are evaluated with respect to their applicability in swirling, recirculating flows. The turbulence models are formulated on the basis of two separate viewpoints. The first perspective assumes that an isotropic eddy viscosity and the modified Boussinesq hypothesis adequately describe the stress distributions, and that the source of predictive error is a consequence of the modeled terms in the κ-ϵ equations. Both stabilizing and destabilizing Richardson number corrections are incorporated to investigate this line of reasoning. A second viewpoint proposes that the eddy viscosity approach is inherently inadequate and that a redistribution of the stress magnitudes is necessary. Investigation of higher-order closure is pursued on the level of an algebraic stress closure. Various turbulence model predictions are compared with experimental data from a variety of isothermal, confined studies. Supportive swirl comparisons are also performed for a laminar flow case, as well as reacting flow cases. Parallel predictions or contributions from other sources are also consulted where appropriate. Predictive accuracy was found to be a partial function of inlet boundary conditions and numerical diffusion. Despite prediction sensitivity to inlet conditions and numerics, the data comparisons delineate the relative advantages and disadvantages of the various modifications. Possible research avenues in the area of computational modeling of strongly swirling, recirculating flows are reviewed and discussed.

Bubbles, Drops, and Particles

Vortex breakdown: a review

Hydrodynamic and hydromagnetic stability

The inviscid stability of swirling flows with mean velocity profiles similar to that obtained by Batchelor (1964) for a trailing vortex from an aircraft is studied with respect to infinitesimal non-axisymmetric disturbances. The flow is characterized by a swirl parameter q involving the ratio of the magnitude of the maximum swirl velocity to that of the maximum axial velocity. It is found that, as the swirl is continuously increased from zero, the disturbances die out quickly for a small value of q if n = 1 (n is the azimuthal wavenumber of the Fourier disturbance of type exp{i(αx + nϕ − αct)}); but for negative values of n, the amplification rate increases and then decreases, falling to negative values at q slightly greater than 1·5 for n = −1. The maximum amplification rate increases for increasingly negative n up to n = −6 (the highest mode investigated), and corresponds to q ≃ 0·85. The applicability of these results to attempts at destabilizing vortices is briefly discussed.

The stability of a trailing line vortex. Part 1. Inviscid theory

An approximate analysis of atmospheric effects on wake vortex motion and decay is presented. The effects of density stratification, turbulence, and Reynolds number are combined in a single model so that the relative importance of different parameters can be determined. Predicted wake motion is shown to be in good agreement with limited data from both ground facility and flight test measurements taken under low turbulence conditions. Wake decay was found to depend strongly on both density stratification and turbulence. For typical levels of turbulence, wake decay was found to result from the 'Crow instability' except under strongly stratified conditions.

An approximate model of vortex decay in the atmosphere

Combined forced and free-convection over thin needles

The problem of laminar combined forced and free‐convection heat transfer from a thin needle in a uniform external stream is considered. The series and local similarity solutions have been discussed.

Combined Forced and Free‐Convection Heat Transfer from Vertical Thin Needles in a Uniform Stream

Forced Heat Transfer over Thin Needles

Stability of a rotating axisymmetric jet surrounded by a potential vortex to infinitesimal disturbances in the inviscid incompressible fluid approximation is considered. The jet and the vortex may have different densities. The dispersion relation for angular frequency covers a wide range of configurations. A rotating or nonrotating jet in a medium at rest is unstable for all density ratios. A vortex enclosing a stagnant core is stable for axisymmetric disturbances for all densities. A vortex with a rotating core without axial velocity is unstable if the jet fluid density is greater than the vortex fluid density. The jet vortex system is destabilized by the slightest amount of axial velocity; increasing jet fluid density has a destabilizing effect. A vortex around a rotating or nonrotating jet of any density suppresses some of the large scale instabilities. In general, axial velocity of the jet, its rotation, and increase in its density have a destabilizing effect. The surface tension between the two fluids has a stabilizing effect for small scale disturbances.

Stability of Coaxial Rotating Jet and Vortex of Different Densities

A similarity solution is obtained for the problem of free‐convection heat transfer over a thin vertical needle with uniform heat flux at the surface. A few errors in previous papers on “isothermal” needles have been modified.

Jai Prakash Narain

Papers

Combined forced and free-convection over thin needles

Combined Forced and Free‐Convection Heat Transfer from Vertical Thin Needles in a Uniform Stream

Forced Heat Transfer over Thin Needles

Stability of Coaxial Rotating Jet and Vortex of Different Densities

Laminar Free Convection from Vertical Thin Needles