Analysis of Atmospheric Flow Over a Surface Protrusion Using the Turbulence Kinetic Energy Equation With Reference to Aeronautical Operating Systems

摘要

Flow over surface obstructions can produce significantly large wind shears such that adverse flying conditions can occur for aeronautical systems (helicopters, STOL vehicles, etc.). Atmospheric flow fields resulting from a semi-elliptical surface obstruction in an otherwise horizontally homogeneous statistically stationary flow are modelled with the boundary-layer/Boussinesq-approximation of the governing equation of fluid mechanics. The turbulence kinetic energy equation is used to deter-mine the dissipative effects of turbulent shear on the mean flow. Mean flow results are compared with those of a previous paper where the same problem was attacked using a Prandtl mixing length hypothesis. The diffusion and convection of turbulence kinetic energy not accounted for in the Prandtl mixing length concept cause departures of the mean wind profiles from those previously computed primarily in the regions of strong pressure gradients.nIso-lines of turbulence kinetic energy and turbulence intensity are plotted in the plane of the flow and highlight regions of high turbulence intensity in the stagnation zone and sharp gradients in intensity along the transition from adverse to favourable pressure gradient.nDiscussion of the effects of the disturbed wind field on CTOL and STOL air¬craft flight path and obstruction clearance standards is given. The results indicate that closer inspection of these presently recommended standards as influenced by wind over irregular terrains is required.