CONE-AND-PLATE APPARATUS - A COMPACT SYSTEM FOR STUDYING WELL-CHARACTERIZED TURBULENT-FLOW FIELDS

We have investigated the turbulent flow field inside a cone-and-plate Couette flow apparatus (CPA). The CPA presents a compact, easily varie d and easily measured flow system with well-characterized turbulent an d laminar flow fields and a good full turbulent spectrum. The CPA can also produce the same time-average stress for both laminar and turbule nt regimes, The apparatus consisted of a shallow 2-degrees cone of 0.7 5 m radius rotating above a flat plate in air. A high-resolution X-wir e probe was used to measure the turbulent and time-mean flow propertie s. A single parameter R = (r2 omega alpha2)/(12nu), which is a measure of the centrifugal forces acting on the moving fluid, governs the deg ree of secondary flow and turbulence in the device. In the fully turbu lent region, R > 4, the mean velocity profile has steep gradients near each surface and is nearly uniform in the central core; and the norma lized azimuthal velocity closely follows the ubiquitous law of the wal l near the plate. The turbulence intensity exhibits two peaks at the e dges of the core flow, and the frequency spectrum of velocity fluctuat ions near the plate resembles that found in isotropic turbulence. This study also suggests that the rotational symmetry with the stationary bottom plate is a much more convenient experimental geometry than a ci rcular Couette flow.