High-resolution numerical studies of stable boundary layer flows in a closed basin: Evolution of steady and oscillatory flows in an axisymmetric Arizona Meteor Crater

摘要

We describe high-resolution numerical simulations of flow within and over an axisymmetric approximation of the Arizona Meteor Crater under stable boundary layer conditions. Motivations included guidance of and comparisons with observations during the Meteor Crater Experiment (METCRAX) performed in October 2006. Modeling objectives were to assess the dynamical processes accounting for cold pool breakup. Various initial stable boundary layer (SBL) flows were considered on the basis of observed SBL flows and responses. Forcing conditions include impulsive SBL startups, constant SBL accelerations, and oscillatory SBL flows. Dominant responses include Kelvin- Helmholtz shear instability at the top of the crater cold pool, gravity waves arising from the crater geometry, and seiches within the crater cold pool. Shear instability at the cold pool top exhibits a range of behaviors in response to different initial conditions, including vortex shedding from the inflow crater lip, vortex pairing, strong mixing and erosion of the cold pool stratification, and secondary vortex formation at the top of the mixing layer. Gravity wave responses depend on the flow speed, are strongly three-dimensional and time dependent, and impact flow structure within and above the crater. Seiches arise from transient or oscillatory forcing and exhibit complex responses and spatial structures, including upward phase progression, multiple periods and vertical structures, and sloshing that ejects cold pool air into the external SBL. We conclude that both sloshing of cold pool air and mixing accompanying shear instability represent efficient dynamical mechanisms by which cold pool stratification can be eroded in response to external SBL motions.