Convegni ATI - Accesso riservato soci CTI

Autore: M. Elfert

Collana: CA - 49 - Perugia 1994

Note:
The buoyancy and rotation influence on the development of a pressure-driven air flow in a circular-sectioned coolant channel is presented in this paper. The channel is rotating about an axis perpendicular to its own centerline with an eccentric orientation, thus, representing a typical configuration in turbine blade cooling design. Modem concepts for blade cooling consist of a multipass channel system tuming the flow direction along a serpentine. In this experimental analysis, the two basic cases of radially inward and outward directed flow have been investigated, without the additional complexity of a 180 deg turn. The flow field of the duct is investigated by means of experiments and numerical calculations to demonstrate rotation effects under both isothermal and heated flow conditions. Coriolis forces generate two counterrotating vortices in the flow and change the distributions of flow velocity as well as turbulence intensity. In the presence of density variations across the channel induced by thermal fluxes, buoyancy forces arise significantly influencing the velocity wall gradients and the turbulence levels. Flow visualizations by the oil flow visualization technique and a newly developed online CCD-camera monitoring of the secondary flow structure during the test run were conducted within the rotating channel. Nonintrusive flow measurements were performed with an advanced Laser-2-Focus velocimeter (L2F). A finite element flow analysis code is adapted to this flow situation solving the threedimensional Reynolds averaged Navier-Stokes equations. The experimental data help to understand the Coriolis and buoyancy force affected flow phenomena and provide test data for the validation of numerical flow predictions.