The stability of a trailing-line vortex in compressible flow

We consider the inviscid stability of the Batchelor (1964) vortex in a compressible flow. The problem is tackled numerically and also asymptotically, in the limit of large (aximuthal and streamwise) wavenumbers, together with large Mach numbers. The nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumbers. At very high wavenumbers and Mach numbers, the mode which is present in the incompressible case ceases to be unstable, while new 'center mode' forms, whose stability characteristics, are determined primarily by conditions close to the vortex axis. We find that generally the flow becomes less unstable as the Mach number increases, and that the regime of instability appears generally confined to disturbances in a direction counter to the direction of the rotation of the swirl of the vortex. Throughout the paper, comparison is made between our numerical results and results obtained from the various asymptotic theories

Self-administration of methohexital, midazolam and ethanol: effects on the pituitary–adrenal axis in rhesus monkeys

There is disagreement in the literature with respect to how drugs of abuse affect the functioning of the hypothalamic–pituitary–adrenal (HPA) axis, and whether these changes in endocrine function may be related to the rewarding effects of these drugs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46363/1/213_2004_Article_1986.pd

The effects of viscosity on the stability of a trailing-line vortex in compressible flow

Jillian A. K. Stott ; Peter W. Duc

The effect of buoyancy on upper branch Tollmien-Schlichting waves

We investigate the effect of buoyancy on the upper-branch linear stability characteristics of an accelerating boundary-layer flow. The presence of a large thermal buoyancy force significantly alters the stability structure. As the factor G (which is related to the Grashof number of the flow, and defined in Section 2) becomes large and positive, the flow structure becomes two layered and disturbances are governed by the Taylor-Goldstein equation. The resulting inviscid modes are unstable for a large component of the wavenumber spectrum, with the result that buoyancy is strongly destabilizing. Restabilization is encountered at sufficiently large wavenumbers. For G large and negative the flow structure is again two layered Disturbances to the basic flow are now governed by the steady Taylor—Goldstein equation in the majority of the boundary layer, coupled with a viscous wall layer. The resulting eigenvalue problem is identical to that found for the corresponding case of lower-branch Tollmien—Schlichting waves, thus suggesting that the neutral curve eventually becomes closed in this limit.Eunice W. Mureithi, James P. Denier and Jillian A. K. Stot